HARVARD UNIVERSITY

Library of the Museum of Comparative Zoology

Hie WIson Bulletin

PUBLISHED BY THE WILSON ORNITHOLOGICAL SOCIETY

VOLUME 90 1978 QUARTERLY

REVIEW editor: ROBERT RAIKOW

COLOR PLATE EDITOR: WILLIAM A. LUNK

EDITORIAL ASSISTANTS: BETTE J. SCIIARDIEN

C. DWIGHT COOLEY PATRICIA ILAMEY MARTHA B. HAYS GARY L. MILLER RENNE R. LOHOEFENER

I’n sidrnt — Douglas A. .Iam«-s, I )rparliiu‘nt (»f Zoology, I niversity of Arkansas, Fayetteville, Arkansas 72703.

First Vi«»*-l*resi(l«‘nl (ieorge A. Hall. Department of Chemistry, West Virginia Univer- sity. M(»rganl«»wn, \\ Csl \ irginia 20.300.

.'^eeornl Vice-President — Ahhot .S. (iaunt, Department of Zoology, Ohio I^tate University, (adumhus, Ohio 43210,

Kditor — .l«‘roim* A. Jackson, Department of Hiol(»gieal .Sciences, P.O. Drawer Z. Mississippi .Statj* University, Mississippi .State, Mississippi .39702. (.See Ornithological News, p. 1.3«).

.S«-eretarv — Curtis .S. Adkisson, Department of Biology. Virginia Polytechnic Institute and .State University, Blackshurg. \ irginia 24001.

Treasurer — Krnest K. Hoover, 1044 Webster St., N.W., Grand Rapids, Michigan 49504.

Fleeted (aumcil Memhers — James K. Karr (term exjjires 1979); Clait E. Braun (term expires 1980); Sidney A. (iauthreaux. Jr. (term expires 1981).

I)\TKS OF ISSUE OF VOLUME 90

OF I'llK W ILSON BULLETIN

\o. 1—19 April 1978 NO. 2 — 16 August 1978 NO. :3 — 21 Novemher 1978 NO. 1 1.5 FERRUARY 1979

CONTENTS OF VOLUME 90

NUMBER 1

owTH AND SURVIVAL OF YOUNG FLORIDA SCRUB JAYS Glen E. If oolfenden

RTICAL DISTRIBUTION OF BIRDS IN A LOUISIANA BOTTOMLAND HARDWOOD FOREST

James G. Dickson and Robert E. Noble

rRICULTURAL IMPACT OF A WINTER POPULATION OF BLACKBIRDS AND STARLINGS

Richard A. Dolbeer, Paul P. Woronecki, Allen R. Stickley, Jr., and Stephen B. White

;eeding behavior of the Louisiana heron James A. Rodgers, Jr.

ATUS AND numerical FLUCTUATIONS OF SOME NORTH AMERICAN WADERS ALONG THE

SURINAM COAST ^rie L. Spaans

;eding of nestling and fledgling eastern bluebirds Benedict C. Pinkowski

FFERENTIAL USE OF FRESH WATER ENVIRONMENTS BY WINTERING WATERFOWL OF COASTAL

xexas Donald H. White and Douglas James

■PRODUCTIVE SUCCESS AND FORAGING BEHAVIOR OF THE OSPREY AT SEAHORSE KEY, I'LORIDA

Robert C. Szaro

SNERAL NOTES

CHANGING AVIAN COMMUNITY STRUCTURE DURING EARLY POST-FIRE SUCCESSION IN THE

SIERRA NEVADA Garl E. Bock, Martin Raphael, and Jane H. Bock

NOTES ON THE DISTRIBUTION OF BIRDS IN SONORA, MEXICO

Stephen M. Russell and Donald W . Lamm

EGG CARRYING BY WOOD DUCK

Robert W. Strader, Richard Di Giulio, and Robert B. Hamilton

EVIDENCE OF BROOD ADOPTION BY RUFFED GROUSE Stephen J. MaXSOn

MARSH HAWKS FOLLOW' HUNTING RED FOX LeRoy ff . Bandy and Barbara Bandy

PREDATION ECOLOGY OF COEXISTING GREAT HORNED AND BARN OWLS Seri G. Rudolph

HOST RECORDS FOR THE STRIPED CUCKOO FROM COSTA RICA

Lloyd F. Kiff and Andrew ff illiams

ANT-FOLLOWING BIRDS IN SOUTH AMERICAN SUBTROPICAL FORESTS

Michael Gochfeld and Guy Tudor

FISHING BEHAVIOR OF BLACK AND TURKEY VULTURES

Jerome A. Jackson, Irvine D. Prather, Richard N. Conner, and Sheila Parness Gaby A NEW HYBRID WARBLER COMBINATION Richard C. Banks and James Baird

RNITIIOLOGICAL LITERATURE

RNITHOLOGICAL NEWS

EQUESTS FOR ASSISTANCE

NUMBER 2

REVISION OF THE MEXICAN PICULUS (PICIDAE) COMPLEX Luis F. Baptista

ISTRIBUTION, DENSITY, AND PRODUCTIVITY OF ACCIPITER HAWKS BREEDING IN OREGON

Richard T. Reynolds and Howard M. Wight

OCIAL AND FORAGING BEHAVIOR OF WARBLERS WINTERING IN PUERTO RICAN COASTAL SCRUB

William I*ost

DE RESIDUES AND EGGSHELL THINNING IN LOGGERHEAD SHRIKES

William L. Anderson and Ronald E. Duzan

1

19

31

45

60

84

99

112

119

123

131

132

133

134

138

139

141

143

145

157

118

159

182

197

215

n<^^. s|-K( IKS I SKI) in IlIKDS IN I «)(,(. KD \M) I NLoGOKI) MIXKD-CO.MI KHOL S FORKSTS

Kathleen E. Franzreb 221 ;

1)01 III riiHMoDKDNKSS IN I’l RiM.K MARTINS IN TKXAS Charles R. Brown 239 t

H)oi) OF NvsTi.iNi; iTRi’i.K MARiiNs Helene Walsh 248.

RKl’Kom ( TloN AND NKST SITK SKI.F.CTION RY RKD-WINGKI) RLACKRIRDS IN NORTH LOUISIANA

Bryan T. Brown and John W. Goertz 261 TIIK RUFors-coLLARKi) SPARROW AS A HOST OF TiiK SHINY cowRiRD Rosendo M. Fmga 271

(.KNKHAI. NOTKS

SKXL’AL SIMILARITY OF RKD-IIKADKI) WOODPFCKKRS AND POSSIRLE EXPLANATIONS BASED

ON FALL TERRITORIAL REH AMOR — - Lawrence Kilham 285

NOTES ON THE COURTSHIP REHAVIOR OF RROW N-C APPEI) ROSY FINCHES

Paul Hendricks 285

EFFECTS OF NEST REMOA AL ON STARLING POPULATIONS

// W' Heusmann and Robert Bellville 287

UNUSUAL INCUBATION REHAMOR IN RORAVHiTE George A. Hurst 290

A CATTLE EGRET-DEER MUTUALISM Marc R. Halley and Wayne D. Lord 291

A TEST OF SIGNIFICANCE FOR MAYFIELD’s METHOD OF CALCULATING NEST SUCCESS

Douglas D. Dow 291

MIRROR IM AGE AERSI S CONSPECIFIC STIMULATION IN ADULT MATE ZEBRA FINCHES

Michael J. Ryan 295

PROTOCAU.irilORA INFESTATION IN GREAT HORNED OWLS Robert T. Bohm 297

TERRITORIAL DEFENSE OF A NECTAR SOURCE BY A PALM AVARBLER

Joseph M. Wunderle, Jr. 297

RING-RILLED (H LL PAIR AATTH 2 NESTS William E. Southern 299

CLUTCH SIZE AND NEST PLACEMENT OF THE PIED-BILLED GREBE IN MANITOBA

Spencer G. Sealy 301

NEST PLACEMENT IN SAGE THRASHERS Terrell D. G. Rich 303

GREAT BLACK-RACKED GULLS BREEDING IN SALT MARSH IN NEAV JERSEY

Joanna Burger

president’s PA(.E . ...

ORNITIHH.«)GICAL NEAAS

H).NSKRA ATION ( OMMITTEE REPORT

«)RNITHOLOGICAL UTERMURE

304

306

308

309 322

NUMBER 3

Al TI M.N BIRD CASI AI.IH.S AT A NORTHAVEST FLORIDA TA TOAVER: 1973-1975

Robert L. Crawford 335^

WHITE PELICAN PRODUCTION AND SURVIVAL OF YOUNG AT CHASE LAKE NATIONAL WILDLIFE

REFUGE, NORTH DAKOTA Robert F. Johnsoji, Jr. and Norman F. Sloan 346

EGG VOLUME AS A PREDICTOR OF HATCHLING WEIGHT IN THE BROWN-HEADED COWBIRD

I al Nolan Jr. and Charles F. Thompson 353

BEHAVIOR AND SEX ROLES OF NESTING ANHINGAS AT SAN BLAS, MEXICO

Joanna Burger, Lynne M. Miller, and D. Caldwell Hahn 359

POST-FLEDGING BEHAVIOR OF PURPLE MARTINS Charles R. Brown 376

NESTING ECOLOGY OF THE PLAIN CHACHALACA IN SOUTH TEXAS

Wayne R. Marion and Raymond J. Fleetwood 386

SPATIAL RELATIONSHIPS IN PERCHING BARN AND CLIFF SWALLOWS Anne E. HuttOn 396

POPULATIONS OF BAY-BREASTED AND CAPE MAY WARBLERS DURING AN OUTBREAK

OF THE SPRUCE BUDWORM Douglass H. Morse 404

AGE AND FORAGING ABILITY RELATIONSHIPS OF OLIVACEOUS CORMORANTS

Michael L. Morrison, R. Douglas Slack, and Edwin Shanley, Jr. 414

ANALYSIS OF ROOSTING COUNTS AS AN INDEX TO WOOD DUCK POPULATION SIZE

Delbert E. Parr and M. Douglas Scott 423

GENERAL NOTES

BLACK SKIMMER ABUNDANCE ON THE LOUISIANA-MISSISSIPPI-ALABAM A COAST

John W . Portnoy 438

KiLLDEER BREEDING DENSITIES Terrence R. Mace 442

BROWN PELICAN RESTOCKING EFFORTS IN LOUISIANA

Stephen A. Nesbitt, Lovett E. Williams, Jr., lAtrry McNease, and Ted Joanen 443

NOTES ON 2 SPECIES OF BIRDS PREVIOUSLY UNREPORTED FROM PERU

Dan A. Tallman, Theodore A. Parker, III, Gary D. Lester, and R. A. Hughes 445

RESPONSES OF BIRDS TO A SNOWSTORM IN THE ANDES OF SOUTHERN PERU

John P. O’Neill and Theodore A. Parker, HI 446

CANNIBALISM BY AN ADULT GREAT HORNED OWL

J. B. Millard, T. H. Craig, and O. D. Markham 449

CACHING BEHAVIOR OF SCREECH OWLS IN INDIANA James B. Cope and John C. Barber 450

ATTACKS ON RED-HEADED WOODPECKERS BY FLYCATCHERS Roland R. Roth 450

AN ANALYSIS OF GILA WOODPECKER VOCALIZATIONS Gene L. Brenowitz 451

AN AGGRESSIVE ENCOUNTER BETWEEN A PINTAIL WITH A BROOD AND A FRANKLIN GULL

George Hochbaum and Garth Ball 455

CANADA GOOSE-GREAT BLUE HERON-GREAT HORNED OWL NESTING ASSOCIATIONS

Richard L. Knight and Albert H . Erickson 455

GIANT CANADA GOOSE INCUBATES EGGLESS NEST Conrad A. Fjetland 456

NESTING SUCCESS AND NEST SITE SELECTION OF RED-WINGED BLACKBIRDS

IN A FRESHWATER SWAMP Brent Ortego and Robert B. Hamilton 457

EXTREME NESTING DATES FOR THE MOURNING DOVE IN CENTRAL ILLINOIS L. Barrie Hunt 458

A VOLUMETRIC ANALYSIS OF SHARP-TAILED GROUSE SPERM IN RELATION TO DANCING

GROUND SIZE AND ORGANIZATION Wayne M. Nitchuk and Roger M. Evans 460

PRESIDENTS PAGE 463

FIFTY YEARS OF THE WILSON ORNITHOLOGICAL SOCIETY Maurice BrOoks 464

oH M I H« »l ( il.K M IIIKHMIHK

CiiNslin I|n\ \M» HV-I \\\> <»K TIIK WIl.SON ( )H MTHOI.OCilCAI. SOCIKTY

OKMrimi.ni.M M. >K\\S -

NIIMFIKR 4

MS M\II KMION UK iiix'fkk's - (ieoffie M. Sultan and David F. Parmelee

IIIKII I.IKK. \T CM’K (KU/IKK, KUSS ISLAND

David G. Ainley, Robert C. Wood, and William J. L. Sladen

.s|/K, KU<ID TM'K. XND KuK ACTING SI TKS UF RKD-WI NGKD BLACKBIRDS — Stephen W. Wllson

WINTKK TKRKITURIAL WD KuK ACiINfi BKII AVIOB OF RP:D-HEADED WOODPECKERS IN FLORIDA

Debra Moskovits

TVKSAL col. OR OF AMERICAN COOTS IN RELATION TO AGE Richard D. Cruwford

NFSTINI, BKIIAAloR AND AFFINITIES OF MONK PARAKEETS OF SOUTHERN BUENOS AIRES

PROAINCE, ar(;entina Philip S. Humphrey and Roger Tory Peterson

M<*RPII0L0(.Y OF THE LARYNX OF CORVVS B RACHY RHY \CHOS (PASSERIFORMES: CORVIDAe)

Walter J. Bock

IIAIUTAT I SE BA A ELLOW-RI M PED WARBLERS AT THE NORTHERN EXTREMITIES OF THEIR

WINTER RAN(,E Kenneth J. Wllz and Vincent Giampa

HABITAT SHIFT AND ROADSIDE MORTALITY OF SCARLP:T TANAGERS DURING A COLD WET NEW EN(.LANi) SPRING David C. Zumeta and Richard T. Holmes

loMMI NITA KCoLoGA OF THE HELMINTH PARASITE:S OF THE BROWN PELICAN

Stephen R. Humphrey. Gharles H. Courtney, and Donald J. Forrester

NEST-SiTE SELECTION OF AVILLETS IN A NEW JERSEY SALT MARSH

Joanna Burger and Joseph Shisler

UR(. ANUCIILORINE RESIDUES AND EGGSHELL THINNING IN WOOD STORKS AND ANHINGAS

Harry M. Ohlendorj. Erwin E. Klaas and T. Earl Kaiser II Aim AT SELECIION BA BREEDING RED-AVINGED BLACKBIRDS Peter H. AlberS

GENERAL NuIE>

ANUIIIER COLONA OF HIE (,l ADELOl PE HOUSE AAREN J on C. BarloW

PEMH.IDE LEAELS AND SHELL THICKNESS OF COMMON LOON EGGS IN NEAV HAMPSHIRE

Scott A. Sutcliffe

DE»LINE.s IN ENA IRON MEN ! AL POLLUT ANTS IN OLIVACEOUS CORMORANT EGGS FROM TEXAS.

1970 1977 Michael L. Morrison, R. Douglas Slack, and Edwin Shanley, Jr.

1IRKEA AILIIRE E<.(. SHELL TIIINNINT, IN CALIFORNIA. FLORIDA. AND TEXAS

Sanford R. W ilbur

AN EXPERIMENIAI. ANAI.AsIS OF HIE INTERRELATIONSHIP BETAVEEN NEST DENSITY AND

pREDAiioN IN OLD-MELD HABITATS Bradley 4/. Gottfried

CANADA GOOSE TAKES OVER MALLARD NEST . Thomas N. Mather

NoIM on MiOD HABITS OF THE PLAIN CHACHALACA FROM THE LOAVER RIO GRANDE VALLEY Zdn D. (.hristensen. Danny B. Pence, and Gretchen Scott

468

474

478

479

492

511

521

536

544

553

566

575

587

599

608

619

635

637

641

642

643

646

647

HERRING GULLS STEALING PREY FROM PARASITIC J AEGERS R. 1. G. Morrison

THE USE OF FEEDING AREAS OUTSIDE OF THE TERRITORITY OF BREEDING BLACK

OYSTERCATCHERS E. B. Hartwick

SCREECH OWL PREDATION ON A COMMON FLICKER NEST Mary C. Landin

RED BOBWHiTES IN OKLAHOMA Jack D. Tyler

ASYNCHRONY OF HATCHING IN RED-WINGED BLACKBIRDS AND SURVIVAL OF LATE AND EARLY

HATCHING BIRDS Charles Strehl

WEATHER RELATED MORTALITY OF BLACKBIRDS AND STARLINGS IN A KENTUCKY ROOSTING

CONGREGATION Baul A. Stewart

AN OBSERVATION OF POLYGYNY IN THE COMMON YELLOWTHROAT

George I . N. Rowell and //. Lee Jones

ORNITHOLOGICAL LITERATURE

president’s page

editorial: changing of the guard

ORNITHOL(JGICAL NEWS :

SERIAL PUBLICATIONS CURRENTLY RECEIVED BY THE JOSSELYN VAN TYNE MEMORIAL LIBRARY INDEX

649

650

652

652

653

655

656

658

669

586

670

673

679

The Wilson Bulletin

PUBLISHED BY THE WILSON ORNITHOLOGICAL SOCIETY VOL. 90, NO. 1 MARCH 197J^

Library

MAYS 1973

harvard

JThivbcr®'^^

The Wilson Ornithological Society Founded December 3, 1888

Named after ALEXANDER WILSON, the first American Ornithologist.

President— Douglas A. James, Department of Zoology, University of Arkansas, Fayetteville, Arkansas 72703.

First Vice-President — George A. Hall, Department of Chemistry, West Virginia Univer- sity, Morgantown, W’. Va. 26506.

Second Vice-President — Abbot S. Gaunt, Department of Zoology, Ohio State University, Columbus, Ohio 43210.

Editor — Jerome A. Jackson, Department of Zoology, P.O. Drawer Z, Mississippi State Uni- versity, Mississippi State, Mississippi 39762. (See Ornithological News, p. 158).

Secretary — James Tate, Jr., P.O. Box 2043, Denver, Colorado 80201.

Treasurer — Ernest E. Hoover, 1044 Webster St., N.W., Grand Rapids, Michigan 49504.

Elected Council Members — Sidney A. Gauthreaux, Jr. (term expires 1978) ; James R. Karr (term expires 1979) ; Clait E. Braun (term expires 1980).

Membership dues per calendar year are: Active, 110.00; Sustaining, $15.00;

Life memberships, $200 (payable in four installments).

The Wilson Bulletin is sent to all members not in arrears for dues.

The Josselyn Van Tyne Memorial Library The Josselyn Van Tyne Memorial Library of the Wilson Ornithological Society, housed in the University of Michigan Museum of Zoology, was established in concurrence with the University of Michigan in 1930. Until 1947 the Library was maintained entirely by gifts and bequests of books, reprints, and ornithological magazines from members and friends of the Society. Now two members have generously established a fund for the purchase of new books; members and friends are invited to maintain the fund by regular contribution, thus making available to all Society members the more important new books on ornithology and related subjects. The fund will be administered by the Library Committee, which will be happy to receive suggestions on the choice of new books to be added to the Library. William A. Lunk, University Museums, University of Michi- gan, is Chairman of the Committee. The Library currently receives 104 periodicals as gifts and in exchange for The Wilson Bulletin. With the usual exception of rare books, any item in the Library may be borrowed by members of the Society and will be sent prepaid (by the University of Michigan) to any address in the United States, its possessions, or Canada. Return postage is paid by the borrower. Inquiries and requests by borrowers, as well as gifts of books, pamphlets, reprints, and magazines, should be addressed to “The Josselyn Van Tyne Memorial Library, University of Michigan Museum of Zoology, Ann Arbor, Michigan.” Contributions to the New Book Fund should be sent to the Treasurer (small sums in stamps are acceptable). A complete index of the Library’s holdings was printed in the September 1952 issue of The Wilson Bulletin and newly acquired books are listed periodically.

The Wilson Bulletin

The official organ of the Wilson Ornithological Society, published quarterly, in March, June, September, and December. The subscription price, both in the United States and elsewhere, is $15.00 per year. Single copies, SLOO. Subscriptions, changes of address and claims for undelivered copies should be sent to the Treasurer. Most back issues of the Bulletin are available and may be ordered from the Treasurer. Special prices will be quoted for quantity orders.

All articles and communications for publications, books and publications for reviews should be addressed to the Editor. Exchanges should be addressed to The Josselyn Van Tyne Memorial Library, Museum of Zoology, Ann .\rbor, Michigan. Known office of publication : Department of Zoology, Mississippi State University,

Mississippi State, Mississippi 37962.

Second class postage paid at Mississippi State, Mississippi and at additional mailing office.

Allen Press, Inc., Lawrence, Kansas 66044

Growth stages of Florida Scrub Jays. Top left; a pipped egg and two young, age day 0. Top right: three young, age day 5, in cooling stance with necks stretched over nest rim. Bottom left: usual banding age, day 11, when primaries are breaking from their sheaths. Bottom right: a recent fledgling, age day 18.

THE WILSON BULLETIN

A QUARTERLY MAZAGINE OF ORNITHOLOGY Published by the Wilson Ornithological Society

VoL. 90, No. 1 March 1978 Pages 1-158

GROWTH AND SURVIVAL OF YOUNG FLORIDA SCRUB JAYS

Glen E. Woolfenden

Few studies of growth in passerines pertain to jays (Corvidae: Garrulinae), and fewer still to group breeders. As a possible contribution to both topics, I measured growth rates of young Florida Scrub Jays {Aphelocoma c. coeru- lescens) raised by breeding groups of varying sizes. A notable exception to the paucity of information on corvid growth is the recent work on Pinon Jays [Gyninorhinus cyanocephalus) , a highly social, colonial breeder that nests early in a north temperate climate (Bateman and Baida 1973). Certain comparisons are made with this species.

Florida Scrub Jays almost invariably remain in their natal territory for more than a year; therefore it was possible to obtain numerous post-fledging measurements and to monitor survival of known-age jays. The growth measure used in the analyses of survival is weight.

Florida Scrub Jays breed either as unassisted monogamous pairs or in groups consisting of a pair and several helpers. Brood size varies from 1 to 5; usually it is 3 or 4, and the number of feeders has varied from 2 to 8. Pairs with helpers fledge more young than do the unassisted pairs (Woolfenden 1975).

Preceding the weight data are brief descriptions of general development and the linear growth of certain extremities (see also frontispiece). This in- formation should be useful for aging nestlings whose hatching dates are un- known.

MATERIALS AND METHODS

The data on growth and survival were obtained at the Archbold Biological Station in Highlands County, Florida, where a marked population of Florida Scrub Jays has been under observation since 1969. Individual jays were measured daily or, in a few cases, every other day throughout the nestling stage in 1973 when 47 nests were found, which represented virtually all nesting attempts by 28 pairs, 25 of which produced young. The approximately 136 eggs laid yielded 73 nestlings and 41 fledglings (1.5 per pair), almost

1

2

I IIK W ILSON lUILLKTiN • VoL 90, No. I, March 1978

all of which were measured in the course of this study. The productivity data show that 197d was a near-average breeding year ( Woolfenden 1973). Some measurements of nestlings and fledglings also were taken in 1974 and 1975; however, except where other- wise stated, my various analyses of growth incorporate only the 1973 measurements.

Most of the marked birds lived in open habitat, namely sparse oak scrub (Woolfenden 1969 census no. 52, 1973 >, and some jjarer.t and helper jays scolded loudly at human intruders. Thus nest visits by investigators were brief, lasting only a few minutes, in an attempt not to alter normal nest predation. When measuring, we removed all young from the nest simultaneously and moved several im'ters away; this reduced the intensity of scolding by the older jays. In addition, most nest visits were made in early afternoon (12:30 15:30) when diurnal j)redators seemed less active, and so that several hours of sunlight remained for the odors we left to dissipate before nocturnal predators became active. These i)rocedures precluded obtaining detailed notes on morphological and behavioral ontogeny.

Day 0 designates the day of hatching. Fledgling and yearling are defined as before (Woolfenden 1973): fledgling is applied to a jay from the instant it leaves the nest until it is 1 year old. A yearling is a jay in its second year of existence.

The ratio between the number of jays supplying food and the number of nestlings being fed is termed the feeder index. It has ranged from 0.4 to 3.0. Nestlings wdth a 0.4 feeder index were members of a brood of 5 fed by a pair with no helpers; the 3.0 feeder index represents a lone nestling fed by a ])air with 1 helper.

Five measurements were taken to the nearest 0.5 mm on each young jay: length of beak, tarsus, primary 7, and longest central rectrix (hereinafter referred to as a deck), and w'eight. The beak was measured from the anterior end of the nostril to the tip, the tarsus in a standard fashion as the diagonal from the joint with the tibiotarsus behind to the joint with the middle toe in front. The primary and the longest deck w'ere measured from the place of attachment with the skin to the tip of the papilla or feather. Falconers use the term deck for a central rectrix and it is used here not only for brevity but also to emphasize a function of the central rectrices of shielding the lateral rectrices from abrasive wear. In Florida Scrub Jays the decks often become extremely ragged prior to replacement. Weights w'ere taken with Pesola spring balances which were checked regularly for accuracy.

The expressions significant and highly significant are used only in the statistical sense to signify probability at the 5% and 1% levels, respectively.

Asynchronous hatching confounds the problem of measuring growth during brief once- a-day visits to nests, and in the Florida Scrub Jay hatching of eggs from the same clutch sometimes spans more than 1 day. In 1973 eggs from 9 of 25 nests probably had a time span for hatching of between 1 and 2 days. For 4 of these 9 nests, a time span between 1 and 2 days was known, and for 1 additional nest a span of 2-4 days occurred between tbe hatching cf the first egg and last egg. The nestlings were not marked until over 1 week old, and 1 assumed the smaller young in such nests were the younger. In certain instances individual peculiarities allowed identification of these individuals.

Variation in time of fledging is another problem that vexes those who study growth of young birds. If undisturbed, young Florida Scrub Jays remain in the nest several days past earliest possible fledging age. In 1973, when nestlings were handled daily or every other day, almost all fledged when 15 cr 16 days old, and only 1 healthy nestling remained through day 17. In 1975, when young jays were handled only on day 11, and thereafter nests were checked from convenient distances, most young fledged when 17 or 18 days old, and a few remained through days 19 to 21. Enticing their young from the nest does not seem to be an important part cf Florida Scrub Jay bebavior, and perhaps many nests

Woolfenden • FLORIDA SCRUB JAYS

3

are vacated between days 14 and 19 because of exogenous disturbances. Earliest fledging has occurred between days 12 and 14 (1 brood), the latest on day 20 or 21 (2 broods). These generalizations are based on observations at approximately 120 successful nests.

GENERAL DEVELOPMENT

At hatching Scrub Jays are naked, as typifies jaybirds, and the skin is reddish-pink, nearly identical in color to the skin of a person’s hand when flushed with blood. The viscera, especially the liver, show clearly through the thin and weakly pigmented skin. The beak and legs are pale yellow. Through day 1 they get darker pink, then during days 3^ yellowish pink. On day 2 they match the color of one’s palm when it is drained of blood, and on day 3 they have the color of jaundiced human skin. During day 3 the skin becomes purple-black, usually on the back first, and the young match in color heavily bruised human skin. Darkening progresses through days 4-6 until the young are dark gray-black over most of the body, and especially dorsally. The beak becomes shiny black, the podothecae dull black.

Parting of the eyelids in nestling Scrub Jays is gradual and variable. For a few individuals the process begins as early as day 2, for some the eyes are still closed on day 9. For the majority the eyes open during days 4 through 7. Often in the same individual one eye begins opening before the other.

GROWTH

Tables 1 and 2 and Fig. 1 summarize data on growth of nestlings; they are based only on young hatched in 1973. Table 3 presents information on fledglings, for which birds hatched both in 1973 and 1974 were used. In order to provide a smooth transition in the growth data from nestlings to fledglings, the 0.5-month-old young in Table 3 are the same 20 15-day-old young in Tables 1 and 2.

Feathers. — Papillae of several tracts on the dorsum protrude prominently from the skin about day 4. Primary 7 is at least 1 mm long by day 7 ; the longest deck is at least 2 mm long by day 13 ( Table 1). Feathers of the femoral and posterior dorsal tracts and secondary coverts of the alar tract usually break from their sheaths about day 9, with the earliest on record day 7. Primary 7 erupts between days 10 and 13, usually on day 11, and the decks erupt between days 11 and 15, usually on day 14. Jhis rate and pat- tern of feathering means that young Florida Scrub Jays are only sparsely feathered until hut a few days before they fledge.

The longer 7th primaries of adult-plumaged jays (age in months 24+) versus 6-12-month-old birds (Table 3) are new feathers, the original primaries having been replaced during the complete second prehasic molt. The juvenal

4

THK W ILSO.N lUlLLF/riN • VoL 90, No. J, March 1978

I’kimaky

Table 1

7 AND Dkck Lkngtiis (mm) of Nksti.inc Flokida Sckuh Jays

A«t* in clays

Seventh primary

Longest deck

N

X

S.I).

Range

X

X

S.D.

Range

0

49

_

_

_

49

-

-

-

1

56

-

-

-

56

-

-

-

2

51

-

-

-

51

-

-

-

3

59

-

-

-

59

-

-

-

4

57

0.01

0.07

0-0.5

50

-

-

-

5

33

0.45

0.52

0 1.5

49

-

-

-

f)

34

1.49

0.92

0 4

44

-

-

-

7

40

3.09

1.64

1-7

45

-

-

-

8

43

5.84

1.83

4-10

46

-

-

-

9

36

9.33

2.28

5.5-15

41

0.02

0.16

0-1

10

38

12.96

2.55

8-18

39

0.33

0.57

0-2

11

32

16..59

2.41

13-22

31

0.94

1.36

0-4

12

33

21.06

2.59

17-28

32

2.77

1.59

0-5

13

26

25.38

2.42

22-31

25

5.28

1.77

2.5-9

14

26

30.85

2.87

26-37

24

8.25

2.27

5-13

15

20

34.05

1.79

32-38

20

10.90

3.09

7-15

16

8

39.13

3.64

36-46

8

15.25

3.99

9-20

decks exist only a short time after attaining full length before they are replaced during an incomplete first prehasic molt. The longer decks of adult-plumaged jays versus 6-12-month-old birds are new feathers, the decks of the first basic plumage having been replaced during the complete second prehasic molt.

Beak and foot. — The beak of Florida Scrub Jays is little more than half full size at fledging (Table 2), and continues to grow for almost 2 months after hatching (Table 3j. As the measurement taken includes both the integu- mentary rhinotheca and the premaxillary bones, the increase in length shown between ages 3-4 months and 6-12 months may merely reflect changes in the rhinotheca. Feeding independence is a slow, gradual process in Florida Scrub jays, which is not fully attained for about 3 months after fledging. Perhaps this behavior reflects the slow growth of the feeding organ.

Fhe tarsometatarsus grow s rapidly ( J'ahle 2 I and attains 94% adult length at fledging (Table 3j. Within a few days post fledging Florida Scrul) Jays escape predators by scurrying off beneath the brush. The rapid development of the leg probably accommodates this behavior. The measurements sum- marized in Table 3 suggest continued slow growth of the tarsometatarsus for many months or even a year post fledging, which, if real, probably reflects lengthening of the bone and not changes in the integument.

1 did not measure wings of live nestlings: however, 4 specimens, age 10

Uooljenden • FLORIDA SCRUB JAYS

Beak

Table 2

AND Tarsus Lengths (mm) of Nestling Florida Scrub Jays

Age in days

Beak

Tarsus

N

X

S.D.

Range

N

X

S.D.

Range

0

49

3.00

0.10

2.5-3.5

51

8.81

0.35

8-9.5

1

55

3.20

0.32

3-4

51

9.66

0.63

8.5-11

2

52

3.59

0.33

3-4

54

10.97

0.90

9.5-13

3

58

3.93

0.36

3-4.5

56

12.73

1.06

10.5-16

4

51

4.38

0.38

4-5

53

14.78

1.35

13-19

5

48

4.81

0.35

4-5.5

46

16.71

1.18

14.5-19.5

6

44

5.22

0.44

4..5-6

47

19.33

1.54

17-23

7

45

5.73

0.43

5-7

42

21.67

1.62

19-25

8

42

6.23

0.44

5.5-7

42

23.89

1.36

2L.5-26.5

9

37

6.55

0.47

6-7.5

37

26.69

1.74

23.5-29.5

10

39

7.02

0.51

6-8

38

28.32

1.63

26-31

11

31

7.37

0.48

6.5-8

31

30.34

1.62

28-34

12

33

7.91

0.42

7-9

34

31.80

1.39

29-35

13

26

8.15

0.56

7-9

26

33.44

1.62

30-37

14

26

8.60

0.53

7-9

26

34.85

1.08

32-36.5

15

20

8.85

0.56

8-10

20

35.48

0.91

34-37.5

16

8

9.69

0.37

9-10

8

36.38

1.22

34-38

days, have carpometacarpi that average 71% adult length. Tarsometatarsi at age 10 days average a similar 74% adult length. Young Scrub Jays cannot fly for many days after leaving the nest, but this may be caused by factors other than retarded growth of wing bones, such as slow development of muscles and feathers.

Table 3

Age and Mean Measurements (mm) of Florida Scrub Jays

Age in months

X

Beak from nostril

Tarsus

Primary' no. 7

Deck

0.5

20

"'*8.9 ± 0.56^

**35.5 ± 0.91

**34.1 ± 1.79

**10.9 ± 3.09

0.5-1

16

**9.8 ± 0.52

36.6 ± 1.21

**42.1 ± 5.60

**20.2 ± 7.92

1-2

9-13

15.3 ± 0.56

36.7 ± 1.32

**82.2 ± 1.77

*124.6 ± 6.37

3-4

27-30

**15.5 ±0.86

36.7 ± 1.34

84.8 ± 2.20

129.4 ± 4.93''

6-12

10-11

17.0 ± 1.15

37.0 ± 1.52

**83.7 ± 2.72"’

**128.9 ± 5.58"

24+

36-56

17.5 ± 0.95

37.7 ± 1.36

87.5 ± 2.86'’

134.9 ± 5.56"

S = means followed by 1 standard deviation.

Asterisks mark each mean that is significantly different from the mean immediately beneath it (f- test ) .

\V = \vear may have caused reduced length from previous age class.

D = different feathers from tho.se measured for previous age category.

M = molt of juvenal decks begins at about age 3 months.

6

TllH W 1 1, SON lUil.LKTIN • VoL 90, Nu. I, March 1978

U cig/it. — 'I'lie firouth measurement analyzed in ptreatest detail is weight. As a base for comparisons the weight of adult-plumaged jays is described first. An adult-plumaged Florida Scrub Jay weighs 79.2 g (s.d. = 4.86j. d'he ()0 weights chosen for this determination are of 5 live jays of each sex for 6 bimonthly periods ( Dec.-jan., etc.). All individuals chosen were at least 2 years old and appeared to he in good health. The sample range (65.6-92.0 g) encomi^asses the 283 live weights available for Florida Scrub jays 2 years old and older. Variation in weight with sex in Scrub jays was shown by l^itelka ( 1951 I for various of the western races, hut he had only 3 weights for the Florida race. 3 he 30 males 1 used to deter- mine “adult” weight averaged 81.7 g (s.d. = 4.09, range 74.1-92.0), the females 76.7 g (s.d. = 4.25, range 65.6-141.5). The weight difference between sexes is highly significant ( t = 4.67). Seasonal variation in weight of adult- plumaged jays, sexes combined, is graphed at bimonthly intervals (Fig. 2 ) ; no significant differences among the 6 samples were found.

Bent ( 1916) describes the color, shape, and size of Florida Scrub Jay eggs, hut gives no weights. The mean size of 26 eggs laid in my study tract in 1973 and 1975 (27.5 X 20.5 mm ) is similar to that for Bent’s sample of 46 eggs taken from various localities in Florida prior to 1946 (27.5 X 20.3 mm). I he weights of 32 fresh eggs, all measured within 1 day after laying in 1973, averaged 5.81 g ( s.d. = 0.66, range 4.1-7. 1) ; the weights of 27 eggs in the process of hatching (not necessarily the same eggs) averaged 5.03 g (s.d. = 0.55, range 4.3-6.2 ) . For these samples weight loss from the time of laying to the time of hatching averaged 13.3%. Eight eggs weighed when fresh and also during hatching sustained weight losses ranging from 6.8 to 18.9%, with a mean loss of 12.8%, which is similar to the 13.3% registered for the larger hut less controlled sample.

According to Nice (1943:74) fresh eggs weigh 8-12% of the adult female in passerines weighing up to 135 g. Nice deleted from her summary corvids weighing over 135 g, which had lesser percentages (2.5-5%). For Florida Scrub jays, fresh eggs weigh 7.6% of adult females. In the Pihon Jay fresh eggs (x = 6.65) weigh 6.4% of adults (x = 103.3), both sexes included (calculated from Bateman and Baida 1973). Perhaps corvid eggs tend to constitute a smaller percentage of adult weight regardless of size. Four unfed hatchlings averaged 1.19 g (range 3.6— 1.5 ) . The weight of additional unfed hatchlings was estimated by sul)tracting the mean weight of moist empty shells, taken from eggs that failed to hatch, from the mean weight of hatching eggs. Seven fresh empty shells averaged 0.5 g (range 0.4-0.7j, and the hatching eggs averaged 5.03 g, giving an estimated average value of 4.53 g. At 78% the weight of a fresh egg ( 5.81 g), hatchling Florida Scrub jays are within the range listed for certain other passerines: Lanius ludovicianus

Woolfenden • FLORIDA SCRUB JAYS

l

Table 4

Weights of Nestling Florida

Scrub Jays

A'^e in days

\

Weight (g)

Age in days X

Weight (g)

X

S.D.

Range

X

S.D.

Range

0

50

4.82

0.73

3. 5-6.5

9

37

38.22

4.67

28.4-49.0

1

55

6.83

1.01

5.4-9.2

10

40

41.97

4.86

32.6-55.6

2

55

9.33

1.42

7.3-13.9

11

32

47.26

5.79

36.7-59.0

3

58

12.77

2.55

9.1-23.0

12

33

51.18

4.39

41.5-60.3

4

57

16.03

2.47

12.1-24.6

13

26

55.93

4.87

47.0-64.0

5

45

19.61

2.87

14.3-25.4

14

26

56.55

4.42

49.0-68.0

6

44

23.80

3.46

17.3-31.2

15

20

59.62

4.89

51.0-67.0

7

42

29.03

4.11

21.4-35.2

16

8

59.75

2.25

57.0-64.0

8

46

32.77

4.11

24.4-40.6

73-75% (Miller 1931), Molothrus ater and Quiscalus quiscula 73% I Wether- bee and Wetherbee 1961) and Agelaius phoemceus 79% ( Holcomb and Twiest 1968). The 95% figure obtained for Piiion Jays is suspect as pointed out by the authors. Hatchling Florida Scrub Jays weigh 6% of an adult’s weight, which also is within the range for certain other passerines at 6-8% (Nice 1943) including the Pihon Jay (Bateman and Baida 1973).

The weight data for nestlings obtained in 1973 are summarized in Table 4 and graphed in Fig. 1. The day 0 weights used were taken almost entirely from nestlings that had received food before weighing. These compilations obscure the considerable variation that exists in the number of helpers and nestlings that a given pair may have. These important variables are discussed below.

Ricklefs (1968) found that growth for 2 corvid species was best described by the logistic equation:

2 -|- 0~K(t\V — to)

where W is the weight of the bird in grams at the age t„ ( in days ) , A is the asymptote of weight (g) approached by nestlings, e is the base of natural logarithms, K is a constant proportional to the specific rate of growth, and to is the age in days at the point of inflection on the growth curve. The procedures outlined by Ricklefs (1967) were used by Bateman and Baida (1973) and in this study with similar results. For the Florida Scrub Jay, A is 60.0 (78.9 for the Pihon Jay). The age at which half of A is attained (to) is 8.2 days (7.6 for the Pihon Jay). The overall growth rate index (K) for the Florida Scrub Jay (0.335) is similar to that for the Pihon Jay (0.328)

1 IIK WILSON HliLLKTIN • Vol. <)0, Nu. I, March I97H

Fig. 1. Weights of nestling Florida Seruh Jays. In the diagram the single vertical line represents the range of observations, the cross line the mean, the open column 1 standard deviation, and the figure atop each vertical line the sample size. Below each mean, starting with day 1, are 2 points which represent the weights of 2 starving siblings.

ami the magitie Pica pica (0.332), but larger than that for the crow Corvus brachyrhynchos (0.172), a large, slow growing passerine.

An inverse measure of the overall rate of nestling growth (K) is the time retiuired to grow from 10% to 90% (tio-.Ki) of the asymptote ( Ricklefs 1968 1 . Based on Bicklefs’ regression etiualion of ti(»-<M» on body size, the crow grows more slowly than expected ( observed = 25.5 days, expected = 21.5 days), the magpie more rapidly (observed = 13.3, expected = 17.7), the Pinon Jay essentially as expected (observed = 13.4, expected = 13.3), and the Scrub Jay slightly slower ( observed = 13.1, expected^ 12.3).

Woolfenden • FLORIDA SCRUB JAYS

9

Fig. 2. Annual fluctuation in weights of “adult” and fledgling Florida Scrub Jays. The lines connect the bimonthly means for “adults” (upper) and fledglings (lower). The vertical bars represent 95% confidence levels. The figures denote the bimonthly sample sizes for adults (above the lines) and fledglings (below the lines). Fledglings were weighed from day of departure from the nest (left side April-May sample) through 1 year.

The ratio between the asymptote and adult weight describes develoimient at fledging. The Florida Scrub Jay at 0.76 is similar to the Pihon Jay at 0.79 (Bateman and Baida 1973), and below the values obtained for 42 of 56 other passerines ( Ricklefs 1968, Table 2, R value). Low values correlate with adult foraging and fledgling escape tactics, namely moving about on the ground in search of food and eluding predators by running. An additional factor may be the location of the nest, with early fledging of species whose

10

rilK W IKSOiN HULLK'riN • VoL 90, No. I, March 1978

Wkk.iits \M) tiik

J'amle 5

Fkkdkij Indkx ioh Nks

TI.INC

; Flohida

.ScKUH Jays

.\«c in (

cler index 0.5- 1.4 Weight (g)

Feeder index 1.. 5-3.0 Weight (g)

lays N

X

S.D.

N

X

S.D.

0

39

4.74

0.66

11

5.09

0.91

1

47

6.78

0.98

8

7.13

1.21

2

45

9.34

1.48

10

9.34

1.18

49

12.62

2.67

9

13.63

1.62

4

47

15.72

2.43

*

10

17.51

2.21

5

36

18.90

2.84

*

9

21.39

2.59

6

35

23.16

3.15

*

9

26.32

3.62

7

35

28..58

3.96

7

31.30

4.42

8

39

32.24

3.90

*

7

35.70

4.33

9

31

37.51

4.43

*

6

41.90

4.47

10

34

41.02

4.31

**

6

47.35

4.51

11

26

45.98

5.21

**

6

52.83

5.16

12

27

50.24

4.15

**

6

55.42

2.76

U

13

54.60

4.66

**

6

60.35

2.31

14

13

55. 1 5

3.62

**

6

61.20

3.72

15

14

58.29

4.78

6

62.72

3.88

* and ** indicate significant differences at the .05 and .01% level, respectively.

nests are more accessible to predators. Scrub Jays do not achieve adult weight for many months post fledging (Fig. 2).

Weights of fledgling and adult-plumaged jays are plotted at bimonthly intervals for 1 year (Fig. 2). The fledgling weights include only those of jays up through 1 year of age from the 1973 and 1974 year classes. The sex of many of these fledglings was unknown, however at age 1 year the sex ratio of Florida Scrub Jays seems to he equal (W’oolfenden 1975), and there- fore all available weights were used.

Covariance analyses (a = 0.05 I of the data graphed in Fig. 2 reveal the following relationships. Weights of “adults” from May through August- Seiftemher are statistically indistinguishable from the weights of “adults” taken from Octoher-Xovemher through the following April-May; thus all “adults” are treated as 1 unit in the comparisons with fledglings. The weights of fledglings taken from time of fledging in May through August-Septemher are neither coincident nor parallel with the weights of fledglings taken from Octoher-Xovemher through the following April-May, and the same is true of their relationship to the weights of all “adults.” The weights of fledglings taken from Octoher-Xovemher through the following .\pril-May also are non-coincidenl fp < 0.05 1 with the weights of all “adults,” hut they are

Wooljenden • FLORIDA SCRUB JAYS

11

Table 6

Weights and the Feeder Index for 130 Day 11 Nestling Florida Scrub Jays

Year

Feeder index

N

X

Weight (g)

S.D. Range

1973

0.5-1. 4

26

**45.98

5.21

36.7-55.0

1.5-3.0

6

52.83

5.16

47.1-59.0

1974

0.4-1.4

11

*38.95

7.13

29.6-49.2

1.5-2.7

5

48.10

5.05

40.6-54.5

1975

0.5-1.4

68

*43.49

7.44

24.6-56.2

1. 5-2.0

14

48.32

5.22

39.4- .58.4

Asterisks ( * ) mark each mean that is significantly different from the mean immediately beneath it ( f-test ) .

parallel. These analyses support the conclusion that after gaining rapidly from fledging until August-September, the young jays level off at a weight below that of “adults.” Inspection of the bimonthly samples (Fig. 2) reveals that between October-November and the following April-May, fluctuations in the weights of “adults” and fledglings tend to he parallel. The only bi- monthly change that is significant is for fledglings between December-January and February-March ( t = 2.36 ) ; however the concomitant gains and losses by the 2 age-classes suggest that the changes may be real.

In 1973 significant differences in weight existed between chicks with low (0.5-1.4) and high (1.5-3.01 feeder indexes almost daily from day 4 to day 14. Significant differences apparently occur most years as evidenced by weights of day 11 chicks for 3 consecutive years (Table 6), including 1974 when the feeder index ranged from 0.4 to 2.7 and 1975 when the range was 0.5 to 2.0. Day 11 was chosen for time of weighing because it is late enough in the nestling cycle for differences in weight to have developed, hut early enough that handling the young does not cause early fledging. Day 11 also is a convenient age for banding. Few other weight data useful for comparing years were obtained, and none was analyzed.

MORTALITY FACTORS

Though difficult to measure, starvation of nestlings seems a minor cause of death in Florida Scrub Jays. Based on once-daily or less frequent visits to nests during the 6 years 1970-1975, 33 of 342 nestlings ( 10%) disappeared from broods known to have had a continued existence. Such gradual attrition of broods probably includes almost all nestling starvation, hut also includes deaths caused by genetic defects, diseases ( including parasitism ) , and some

12

rilK WILSON imi.LKTIN • Vol. W, No. 1, March 1978

pr(‘(lali<)M. riiiis starvation apparently kills consideral)ly less than 10% of Florida Send) Jay nesllin^2:s.

As a measure of starvation relative to hrood size, gradual disappearance of young uas measured only from nests without helpers and with l)roods of different sizes. For unassisted j)airs with hroods of 2 (n = 11), 3 (n = 25), and I (n = 15) nestlings, the numher of young lost from continuing l)roods is similar at lo, 21, and 17%, respectively. As the feeder index decreases from 1.0 to 0.5 for these unassisted ])airs with 2 versus 4 nestlings, this independent analysis suggests that food provisioning for nestlings is not a factor critical to rei)roductive success in the Florida Scruh Jay. However, food availability probably has selected for clutch size which averages only 3.4 ( Woolfenden 1073).

During 7 years of watching nests, 2 breeding attempts have produced grossly underweight broods, and both of them fledged. In 1973 an unassisted pair fledged an underweight brood of 2. The young were far below normal weight a few days after hatching and soon appeared weak and sick. Their weights are plotted separately in Fig. 1. Growth of extremities, as well as weight, were retarded. At age 15 days both young were below the minimum recorded for all 4 linear measurements taken on heavier and relatively healthy young (Tables 1 and 2), and measured as follows; primary 7, 24 and 18.5 mm, deck, 3 and 0 mm, beak, 7.5 and 7 mm, and tarsus 32 and 29 mm, and weight 41.5 g and 28.0 g, respectively. These young fledged during days 21 and 20, respectively, and the lighter weight individual in all probability died within a few’ days. The heavier fledgling died at age 99 days, at which time he weighed only 49.6 g. However on day 82 he weighed 73.1 g, which is almost normal for that age (see Fig. 2). A heavy helminth burden may have contributed to its death ( see Kinsella 1974, specimen GEW 4804 ) .

The male (-WWS) of this breeding pair appeared to be a poor provider who seemed to spend an inordinate amount of time perched near his nest. Jhree years earlier, as a semi-independent fledgling in his natal territory human occupants of a nearby cabin provided the jays with a bountiful supply of peanuts. At that time I noted that this bird rarely foraged for animal food as do other young fledglings; possibly he never gained the foraging efficiency or drive necessary for feeding young.

In 1971 a case of bigamy resulted in the fledging of a brood of 2 under- weight and sickly young, both of which died within days of fledging. Details, including weights of the nestlings, are given by W oolfenden (1976).

In both these instances it seems that abnormal behavior of the breeding male resulted in failure to provide sufficient nourisbmenl to young, even though the feeder indexes at 0.5 were not abnormally low. Under normal circum- stances breeding female Scrub Jays spend a large percentage of their time

\f ooljemlen • FLORIDA SCRUB JAYS

13

at the nest (unpubl. data), especially early in the nestling cycle. Perhaps this general tendency prevented these 2 females from leaving their nests to forage and thereby compensate for the inadequacies of their mates. The point of interest here is that even when breeders exhibit abnormal behavior resulting in grossly undernourished nestlings, fledging can occur in the absence of predation.

In his analysis of 6 passerine species, Ricklefs (1969) identified only a few causes for nestling loss other than starvation and predation. Two of these, desertion and weather, are easily identified for Florida Scrub jays and are known to he rare. By elimination, predation accounts for about o()% of all nestling losses in the population, a percentage that is considerably higher than the 66% tallied for the other 6 species. The high rate of nestling predation sustained by Florida Scrub Jays probably selects strongly for a breeding regime that reduces such losses.

SURVIVAL

Previously, survival through the first year of life was compared to adult mortality (Woolfenden 1973), based on a sample of 143 young from 4 year classes ( 1969-1972 ) . Now, with a sample of 269 young from 6 year classes, 1970-1975 (the 1969 sample which is small is deleted to reduce chance of bias), and many weight data, it is possible to examine survival as related to nestling weight, the feeder index, and the presence of helpers.

Table 7 summarizes information on survival to feeding independence, which virtually always is accomplished by August at age three months, for 115 of the 130 young whose weights as nestlings are shown in Table 6. No differences in survival are evident among the various weight groups. Perhaps with very large samples the lightest-weight fledglings could be shown to be faring less well, and the same might be true for the heaviest young. However, neither the Mann-Whitney U-test nor the Wilcoxon 2-sample test demonstrated sig- nificance with the present sample.

The feeder index can be used in an indirect method of comparing weight and survival. As shown in Tables 5 and 6, nestlings from families with a high feeder index (1.5-3.0) weigh more than nestlings from families with a low feeder index (0.4-1.4). Even though weights were obtained for only a small portion of the young jays that have been banded and censused, the feeder index is known for virtually all. Thus the sample of young whose post- fledging survival to independence was monitored more than doubled (115 to 267 j when the feeder index was used as an indication of high or low weight. The number of year classes available for testing also increases, from 3 (1973- 1975) to 6 (1970-1975). The data are arranged in Table 8, and again no cause-and-effect relationship is evident; indeed survival plotted against the

'11 IK WILSON lUILLK'l'IN • Vol. 90, No. I, March 1978

1 I

Lamle 7

l’oST-M.KI)(;iN(; SlIKMVAI. (I

iK 115 Ki.okida

.ScKUij Jays Akhanckd hy

Day 11 Wkight

WViuht (U)

Total

No. of

Percent

on Day 11

llcclKlings

independent yonnK

survivinj'

Sr> 60

6

2

33

.SO .S t

24

13

54

4S 49

42

21

50

40 4t

22

9

41

.35-.S9

10

6

60

.30-34

6

3

50

25 29

5

2

40

feeder index yields a straight, horizontal line. These data support the premise that weight of nestlings has little effect on their later survival. Snow (1958) came to similar conclusions from his study of Blackbirds (Turdus nierula) . A regression analysis between feeder index and weight was not made because recent field work shows that merely counting the number of jays bringing food to a nest is an oversimplification in that amount of food brought varies with age and sex of individual jays ( Stallcup and Woolfenden in press).

Florida Scrub Jay helpers do help, and they do so by increasing the reproductive output of breeders, usually close kin, with whom they affiliate (Woolfenden 19751. This conclusion, based on data from 1969 through 1973, is further supported by similar analyses of unpublished data obtained in 1974

Table 8

Post- FLEDGING Survival

OF 267 Florida Scrub Jays Arranged by

THE I'eeder Index

P'eeder index

Total

fledglings

No. of

inclependent young

Percent

surviving

3.0

1

0

0

2.7

3

0

0

2.5

3

3

100

2.3

2

2

100

2.0

18

11

61

1.7

17

8

47

1.5

14

5

36

1.3

20

12

60

1.0

73

34

47

0.8

37

20

54

0.7

4t

24

55

0.5

35

17

49

W oolienden • FLORIDA SCRUB JAYS

15

Post-fledging Survival

Table 9

OF 269 Florida Scrub Jays from Helpers

Families With

AND Without

Helper status

Total

Feeder index nestlings

Percent

fledglings

Percent

independent

young

No helpers

2.0

6

50

33

1.0

30

57

35

0.7

87

54

55

0.7-2.0

123

54

49

Helpers

2.0

26

58

67

1.0

77

73

50

0.7

43

79

53

0.7-2.0

146

72

53

and 1975. But the help helpers provide the young has little to do with food needed and food supplied (Tables 7-8). To further substantiate this phe- nomenon, I stabilized the weight variable by measuring survival of young jays only in families with the same feeder index, some of which had helpers, some of which did not (Table 9), and the difference between production of fledglings by families with and without helpers is highly significant (X“ = 17.9). Survival of fledglings to feeding independence also is greater for the young from families with helpers although the differences are significant for only 2 of the feeder index categories (2.0 and 1.0), and not for the third (0.7) or for all 3 combined.

As a separate analysis, loss of clutches was measured for pairs without and with helpers with similar results: 34% of 93 nesting attempts by families without helpers were destroyed prior to hatching, but only 23% of 120 by pairs with helpers. The difference is significant (x“ = 5.7). As eggs do not starve, this provides further evidence in opposition to the hypothesis that food provided relative to food needed limits Florida Scrub Jay reproductive success.

A question that remains is: How do helpers help increase reproductive output if it is not by means of providing the food necessary for survival of young? In the preceding section on nestling mortality, predation was iden- tified as the factor responsible for about 80% of all nest losses. Suspected nest predators include Fish Crows [ Corvus ossifragus ) , possibly Blue Jays {Cyanocitta cristata) , certain snakes and mammals, and Scrub Jays them- selves (Woolfenden 1973, 1975). Scrub Jays have an elaborate active nest defense that includes scolding, plumage displays, mobbing, and outright attack, all of which suggest these jays are capable of dissuading certain nest predators. Jhus I suggest the major way that Florida Scrub Jay helpers help is by

16

THE W lESON HUEEETIN • Vol. 90, Nu. I, March 1978

decreasing predation on the nests containing eggs or nestlings, and to some extent on the scattered fledglings, of the breeders with which they affiliate.

CONCLUSIONS

(Growth of nestling Florida Scruh Jays seems typical of passerines their size. Minor developmental features common to both Pinon and Scrub jays, which Bateman and Baida ( 1973) consider adaptive for breeding during cold weather by Pinon Jays, seem adaptive for breeding in a bot sunny climate by Florida Scrub Jays. Ihus dark skin pigmentation and tbe more rapid development of dorsal feathers than those of the venter may help shield nestlings from harmful (luantities of ultraviolet light. At fledging Scrub Jay young are less developed than most passerines studied thus far ( Ricklefs PJ68), and although comparative data are few, post-fledging growth seems retarded, as evidenced by the failure of young to attain adult weight by the end of a year. J be social organization of the population probably allow s for gradual growth, and indeed it may even cause it. If an advantage exists for gradual growth, the security of a defended natal territory may permit it. As an alternative hypothesis, intrafamilial dominance hierarchies relegate fledglings to subordinate positions ( Woolfenden and Fitzpatrick P977), which may suppress their gaining weight. It remains to be established whether or not these hierarchies result in higher survival of birds of particular weights.

Most Florida Scruh Jay nests fail (Woolfenden 1973), hut rarely because of desertion or weather. Starvation accounts for less than 10% of all nestling losses while predation apparently accounts for over 80%. Young fed by relatively more feeders are heavier, hut weight and the feeder index do not affect post-fledging survival. However, survival to fledging is related directly to the existence of helpers (Woolfenden 1975 and Table 9). Pre- liminary observations indicate the amount of help helpers provide varies with sex and age; therefore more refined measures of success relative to number of helpers are omitted intentionally. It is postulated that helpers assist breeders by reducing nest predation. The possibility that group breed- ing results in direct advantages to tbe breeders and the helpers is currently under investigation.

SUMMARY

Growth of young was measured in a marked population of Florida Seruh Jays that has been censused from 19f)9 to the present. Data were gathered mostly in 1973 when samples ranged up to 59 nestlings, whieh were the reproduetive efforts of 28 pairs.

Fresh eggs weigh 5.8 g, 7.()% of adult female weight, and lose about 13% of their weight during incubation. Newly hatehed, unfed young weigh about 4.5 g, about 78% of a fresh egg. Based on growth curve computations, nestling growth is half completed at 8.2 days. Tin* overall growth rate index of 0.335 is similar to that of Pinon Jays, and the young

Wooljenden • FLORIDA SCRUB JAYS

17

grow only slightly slower than expected for their body size. Development at fledging lags behind most passerines thus far measured, as is true also of Pihon Jays. Florida Scrub Jays do not attain “adult"’ weight during the first year. Growth of certain extremities also re(juires many months. Fluctuations in fledgling weights parallel those of “adults” from fall to early spring.

Desertion and weather rarely cause nesting failure, and starvation of nestlings accounts for less than 10% of nestling losses. Predation is the major factor; it accounts for over 80% of all nestling losses.

Breeding pairs with helpers produce more young, especially fledglings, than do unassisted pairs. Nestlings fed by relatively more feeders are heavier, hut survival as fledglings does not correlate with nestling weight or the feeder index. Even nestlings half normal weight at day 11 appear to survive as fledglings as well as do heavier birds. Decreasing predation, especially on nest contents, is proposed as the major way that helpers increase reproduction. Elaborate active nest defense by breeders and helpers supports the suggestion. The sus- pected predators they may sometimes dissuade are certain snakes. Fish Crows, Blue Jays and Scrub Jay cannibals.

ACKNOWLEDGMENTS

As is true for the earlier work, this phase of a long-term life histor> study was completed through the generosity and interest of Richard Archbold, Resident Director, and James N. Layne, Director of Research, of the Archbold Biological Station. Release time from teaching during Spring quarter 1973 was made possible through a Research Council Award of the University of South Florida. Additional support came from the Frank M. Chapman Memorial Fund and the St. Petersburg Audubon Society.

Susan C. White and Stephen A. Bloom provided invaluable advice on mathematical procedures and D. Bruce Barbour, Anthony R. DeGange, John W'. Fitzpatrick, Jerre A. Stallcup and Chet E. Wdnegarner helped with the fieldwork. Ralph W. Schreiber and Susan C. W bite improved the manuscript. I thank all of these persons and institutions for their help. The help of the referees, D. F. Caccamise and R. E. Ricklefs, is gratefully acknowledged.

LITERATURE CITED

Bateman, G. C. and R. P. Balda. 1973. Growth, development, and food habits of young Pihon Jays. Auk 90:39-61.

Bent, A. C. 1946. Life histories of North American jays, crows, and titmice. U.S. Natl. Mus. Bull. 191.

Holcomb, L. C. and G. Twiest. 1968. Red-winged Blackbird nestling growth compared to adult size and differential development of structures. Ohio J. Sci. 68:277-284.

Kinsella, J. M. 1974. Helminth fauna of the Florida Scrub Jay: host and ecological relationships. Proc. Helminthol. Soc. Wash. 41:127-130.

Miller, A. H. 1931. Systematic revision and natural history of the Ameriean shrikes ^L(iniiis). Univ. Calif. Publ. Zool. 38:11-242.

Nice, M. M. 1943. Studies in the life history of the Song Sparrow. 2. The behavior of the Song Sparrow and other passerines. Trans. Linn. Soc. N.Y. No. 4.

PiTELKA, F. A. 1951. Speciation and ecological distribution in American jays of the genus Aphelocoma. Univ. (ialif. Publ. Zool. 50:195-464.

Ricklefs, R. E. 1957. A graphical method of fitting eipiations to growth curves. Ecology 48:978-983.

l‘» 'I'HK W ILSON BllLLE'riN • Vol. 90, No. 1, March 1978

. 1%8. I’attcrns of p;rowtli in birds. Ibis 110:419-451.

. 1969. An analysis of nestirifi mortality in birds. Smitbson. Contrib. to Zool.

No. 9.

.'^Now, 1), \V. 19.58. The l)rcedinfr of tbe Blackbird Tardus rnerula at Oxford. Ibis 100:

1-30.

.Stai.lci I*, J. A. AND O. E. WOoi.FKNDKN. In press. Eamily status and contributions to breedings by Elorida .Scrub Jays. Anim. Behav.

W4:tiikhhkk, I). K. and N. S. Wetiikkuke. 1961. Artificial incul)ation of eggs of various bird species and some attributes of neonates. Bird-Banding 32:141-159.

Wooi.FENDEN, (i. E. 1969. Breeding-bird censuses of five habitats at Archbold Biological Station. Audubon Eield Notes 23:732-738,

. 1973. Nesting and survival in a population of Elorida Scrub Jays. Living Bird

12:2.5-49.

— 1975. Elorida Scrub Jay helpers at the nest. Auk 92:1-15,

— 1976. A case of bigamy in tbe Florida .Scrub Jay. Auk 93:443-450.

AND J, W. Fitzpatrick. 1977. Dominance in the Florida Scrub Jay. Condor 79:

1-12.

DKPT. OF BIOLOGY, UMV. OF SOUTH FLORIDA, TAMPA 33620; RESEARCH ASSOCIATE, ARCHBOLI) BIOLOGICAL STATION, THE AMERICAN MUSEUM OF NATURAL HISTORY. ACCEPTED 13 .JULY 1976.

REQUEST EOR ASSISTANCE

Vulture sightings. — Sightings of and information about Turkey Vultures tagged with blue or orange streamers, each with a white letter and a one or two digit number, would be appreciated. Tbe tags are about 3" X 6" and are fastened to the patagium with a num- bered cattle ear tag. Birds are tagged on either the right or left wing. The tags are on both tbe dorsal and ventral surfaces of tbe wing. Data requested include: tag number, tag on left or right wing, date, time and place of sighting, activity of the bird and its proximity to other birds. I am particularly interested in tagged birds seen mating or in tbe nest. An opportunity to tag nestlings of tagged birds would be invaluable. Please send sighting data to: Bird Banding Laboratory, Office of Migratory Bird Management, Fish and Wildlife Service, Laurel, Ml) 20811 and/or Sheila Parness Gaby, 6832 S. W. 68 St., .S. Miami, FL .33143.

VERTICAL DISTRIBUTION OF BIRDS IN A LOUISIANA BOTTOMLAND HARDWOOD FOREST

James G. Dickson and Robert E. Noble

Resources used by avian species are probably in limited supply in forest ecosystems resulting in interspecific competition, in resource partitioning, and in the segregation of species on habitat gradients ( Koplin and Hoffman 1968, Cody 1974, Schoener 1974 j. Resource partitioning has been accom- plished through various “coexistence mechanisms” (Cody 1974). Schoener ( 1974 ) hypothesized that habitat dimensions are important more often than food-type dimensions which are more important than temporal dimensions in resource partitioning. One of these mechanisms or dimensions is a spatial segregation of birds into vertical strata. Vertical height distribution is one dimension of niche definition. MacArthur and MacArthur (1961) correlated vegetative height diversity and bird species diversity showing how bird com- munities responded to vegetative profiles. Tramer (1969) also noted the response of bird populations to vegetative layering. Cody ( 1968) observed vertical feeding height selectivity in tall vegetation, and Pearson (1971) and Karr ( 1971 ) documented vertical stratification in tropical birds.

How does maturity of an ecosystem affect bird populations and resource use? Odum (1969) predicted an increase in potential niches and interspecific competition resulting from increased biomass stratification with the advance of vegetative succession.

Another question that remains essentially unanswered is what are the sea- sonal patterns of resource partitioning in communities. Bird energy budgets fluctuate seasonally (King 1974) as do behavior patterns. Deciduous forests present seasonally changing vegetative profiles and habitat structures. These seasonal phenomena result in changes in bird spatial distributions.

The objective of our investigation was to ascertain vertical distributions of certain avian species and to analyze the seasonal changes in these distributions in a mature Louisiana bottomland hardwood forest.

STUDY AREA AND METHODS

This investigation was conducted on the Thistlethwaite Wildlife Management Area between Washington and Laheau, St. Landry Parish, Louisiana. The area is an old floodplain of the Mississippi and Red rivers. It is described as a south central Louisiana mature bottomland hardwood forest, and classified as hardwood bottom (Braun 1950:293). Vegetation on the area was measured on variable radii plots. The mature bottomland hardwood forest was fully stocked (28.2 m“ basal area/ ha). Oaks iQuercus spp. ) were dominant overstory vegetation. Cane i Arundinaria gigantea) , palmetto (Sah(d minor), and ironwood iCarpinus caroliniuna) were primary understory species.

19

20

TllK W ILSON 1UILLP:TI.\ • Vol. 90, No. I, March 1978

Wrtical data from 4103 sightings of 26 species of birds were analyzed. Height

data were collected approximately 5 mornings per month from .lanuary 1972 to Fehruarx 1974 while c(‘nsusing birds from a 1.6 km transect. .Sightings were made from sunrise to 4 h after sunrise; therefore, no data on daily patterns in heights were gathered. Vertical strata categories (MacArthur and MacArthur 1961) were: ground-0.6 m, 0.6-7. 6 m,

7.6 m-canopy top ( apj)roximately 2.3.9 m), and above-canopy. These zones probably corre- sponded, as well as any, to the vegetation profile, although no distinct layers of vegeta- tion were observable. No corrections were applied to compensate for differences in sight- ing distances in foliage profile throughout the year, although there were decided seasonal changes. In summer the vegetation appeared to be almost ecjually distributed at differ- ent heights. In winter after the deciduous leaves had fallen, the ground and mid-story vegetation, mainly palmetto and cane (both evergreen), was denser than the mostly leaf- less canopy.

.Ringing birds were omitted in this study. Sightings were not restricted to any particular behavioral category, although most birds were foraging when detected. There may have been some height differences corresponding to different bird behavior, but we did not attempt to distinguish behavior when recording heights. A behavioral division of height classes would have reduced our sample sizes significantly. We do not believe this lump- ing significantly affected results.

Birds were categorized into 1 of the 4 strata at the time of initial sighting with a few' minor exceptions (Table 1). Ground occupants were often first seen in mid-air after having been flushed from the ground. These instances of flushing were regarded as ground sightings.

Height diversities were calculated from the information theory of Shannon (1948). Using this formula, dispersal among classes, or diversity, was calculated, based on equal- ity of distribution of observations among the 3 classes (above-canopy stratum excluded). Height diversity = -^ Pi loge Pi, where Pt rz proportion of observations in the fth cate- gor>-. For the 3 height categories used, 1.099 would represent maximum diversity or e(jual dispersal among all categories, and conversely, a complete distribution in only 1 eategory would have zero diversity.

Birds in the “above-canopy” stratum were divided into 2 groups: those carrying on their “normal” activities at that height and those merely relocating themselves. We in- cluded the above-canopy stratum for Black Vultures and Common Crows (Table 1) be- cause they appeared to regularly use that height while carrying on their “normal” ac- tivities. Those relocating themselves in the “above-canopy” stratum were omitted from further consideration.

Bird vertical stratifications were compared on a seasonal, species, and family basis. The 3 strata comparisons within the forest were used for all species except the Black Vulture and Common Crow. Comparisons were tested by means of the chi square test for independent samples at the .01 level of significance unless otherwise specified. There were 2 degrees of freedom in each chi srjuare test of 3 vertical strata. The basic assump- tion of this test is that all observations w'ere independent of all other observations. We felt that data on Common Crackles and Cedar Waxwings did not meet the basic assumption, due to their occurrence in flocks and to our influence on their vertical dis- tribution. As a result, they were excluded from further consideration. Flocking was ob- served to a lesser degree in other bird groups but not to the extent to invalidate the as- sumption of independence. The criterion for sufficient samples for reliability was taken from .'^iegel (1936). In conq)aring the 3 vertical strata within the forest, no expected

Dickson and Noble • VERTICAL DISTRIBUTION OF BIRDS

21

Vertical Stratal Index of

Table 1

Common Thistlethwaite Birds Based on Occurrence in 3 Strata^

Frequency of

Common name

Scientific name

Index-

Black Vulture

( Coragyps atratus )

3.50

Common Crow

iCorvus brachyrhynchos)

3.04

Red-headed Woodpecker

( Melanerpes erythrocephuhis )

2.80

Blue Jay

{ Cyanocitta cristata)

2.75

Fileated Woodpecker

{ Dryocopus pileatus )

2.74

Carolina Chickadee

iParus carolinensis)

2.67

Red-hellied Woodpecker

y Melanerpes caroliniis)

2.66

Tufted Titmouse

{ Paras bicolor )

2.51

Yellow-bellied Sapsucker

iSph y ra p icus va ri us )

2.39

Yellow-rumped Warbler

(Dendroica coronata)

2.34

Brown-headed Cowbird

( Molothrus ater)

2.30

Hooded Warbler

(Wilsonia citrina)

2.24

Mockingbird

( Mi m us pol ygl ottos)

2.24

Common Flicker

( Col apt es aurctus )

2.23

Ruby-crowned Kinglet

{ Regains calendula)

2.14

White-eyed Vireo

( Vireo griseus)

2.13

American Goldfinch

iSpinus tristis)

2.10

Brown Thrasher

(Toxostoma rufum)

2.08

Carolina Wren

( Thryothorus ludovicianus )

2.01

Cardinal

( Cardinalis cardinalis )

2.00

American Robin

( T Urdus migratorius )

1.94

Kentucky Warbler

(Oporornis jormosus)

1.88

Hermit Thrush

( Catharus guttatus )

1.77

Rusty Blackbird

(Euphagus carolinus)

1.74

Rufous-sided Towhee

( Pi pilo eryth rophthal m us )

1.41

hite-throated Sparrow

iZonotrichia albicollis)

1.27

V 58.88

X 2.26

^Fourth stratum (above canopy) used only for Black Vulture and Common Crow.

“ Index was computed by multiplying number of sightings in each stratum by: 1 for stratum 1

(ground— 0.6 m), 2 for strabim 2 (0.6— 7.6 m), and 3 for stratum 3 (7.6 m— canopy top). The sum of these products for each species was then divided by total sightings, giving relative mean height.

values of less than 1 were tolerable, ami no more than 20% of the expected values could be less than 5. In the few instances of a low value in 1 stratum, strata were comliined for purposes of comparison.

For comparative purposes, the strata were assigned the following values: ground, 1;

mid-story, 2; canopy, 3; and aliove-canopy, 4. Stratal index was calculated by multiply- ing these values in each stratum by tlie frequency in each stratum. The sum of these products divided by total frequency defined stratal index, based on frequency of ob- servations in each of the strata.

22

'I'llK WII.SO.N lU'LLKTI.N • Vol. <)0, No. I, March 1978

Fa RLE 2

VKimcAi. IIkk.iit

DiVKK.sTIY of (ioMMON BiHDS IN .‘3 HeIGIIT

Catkgokiks

.Species

Diversity^

Species

Diversity

Muximum Diversity"

1.099

\ ellow-hellied Sapsucker

.702

Ameriean Kohin

1.075

Red-bellied Woodpecker

.082

(iommon Flicker

1.050

Ruby-crowned Kinglet

.078

Husty 8luekl)inl

1.051

White-throated Sparrow

.0.50

Ameriean (iuldfineli

1.014

(Carolina (diickadee

.0.34

Hrown Tliraslier

1.000

Pileated Woodpecker

.022

Hermit Tlirusli

.980

Kentucky Warbler

.010

(Cardinal

.9.50

Blue Jay

.004

Hrown lu'aded Cowl)ird

.924

Carolina Wren

.571

Moekinghird

.898

Hooded Warl)ler

.551

^ ellow-rumped Warhler

.808

White-eyed Vireo

.534

'I'ufted Titmouse

.801

Red-headed Woodpecker

.513

Kufous-sided Towliee

.792

V 18.832

X .785

1 Computed by infoniiation theory (height diversity = — ^ P^ log^ P^, where Pj = proportion of observations in the /tli height category).

- Equal distribution in all height categories, height diversity = 1.099; distribution in only 1

height category, height diversity = 0.

RESULTS .\M) DISCUSSION

S])ecies and jam Hies. — Black Vultures had the highest mean vertical dis- trihution ( Table 1 I . Over % of the sightings were of soaring birds above the canopy.

Woodpeckers were predominately canopy dwellers, hut different niche breadths in vertical distributions were evident. Of all sightings, 68% were above 7.6 m and less than 3% were found near the ground ( Fig. 1 ). Pileated and Red-hellied woodpeckers were similar in vertical distribution to the ag- gregate of woodpeckers. Distributions of 3 species differed from the 2 above species. Common Flickers were more ground oriented (21% of sightings), and were exceeded in vertical dispersion (diversity index (1)1) = 1.056, Table 2 ) by only one bird. \ ellow-hellied Sapsuckers were primarily mid-story oc- cupants (58%), and secondarily canopy occupants (41% of sightings) during their winter j)resence ( 1)1 = 0.762). Red-headed W oodpeckers were the most canopy dependent Picidae (82%) with the most restrictive vertical height dimension of niche breadth of all birds ( 1)1 = 0.513. Table 2 ).

I'he corvids were located high in the Thistlethw aite woods (Table 1 ). Blue Jays were closely associated uith the canopy level (stratal index = 2.75, 1)1 =

Dickson and Noble • VERTICAL DISTRIBUTION OF BIRDS

23

0.604). They were even more strongly canopy oriented than were the Picidae (^“ — 12.6, P < .01). Common Crows were located even higher; 40% above the tree tops.

The similarly distributed ( P > .01 ) Tufted Titmouse and Carolina Chick- adee were common canopy occupants. Fifty-four % of the Tufted Titmice and 67% of the Carolina Chickadees were observed in the canopy. They were less frequently observed in the mid-story ( 43% titmice, 33% chickadees ) . The Paridae, along with the Picidae, were the least frequent ground level oc- cupants ( titmice 3% ; chickadees, none ) .

We sighted 83% of the Carolina Wrens in the mid-story. The chi scjuare value for the comparison of wrens to the aggregate of all birds ( which was also most numerous in mid-story sightings) was 128.6 I P < .01 ) . Supporting this idea of mid-story association is the low height diversity of .571.

The Mimidae, Northern Mockingbirds and Brown Thrashers, were a ver- tically diverse group ( D1 = 0.898, Northern Mockingbirds; DI = 1.006, Brown Thrashers), tending toward the mid-story level. Over 50% of the sightings of each were in this level.

The turdidae exhibited an unusual pattern of height distributions. Al- though we assumed that intrusion into the woods had no influence on bird heights, we may have had some effect on the heights at which Hermit Thrushes and American Robins were observed. Half of the Hermit Thrush sightings were in the mid-story and over % on the ground ( Fig. 1 ) . Perhaps a small portion of the mid-story sightings were of birds that flew there from the ground after being flushed. The robin was the most uniformly distributed bird in the 3 strata ( DI = 1.075) : ground (41%), canopy (35%), and mid- story ( 24%) .

Ruby-crowned Kinglets were common mid-story winter residents. Of 73 sight tallies, 76% were within the 0.6-7.6 m level. The ground stratum was of little importance ( 5% ) and the canopy stratum was of medium importance (19%). Their dispersal among the 3 strata was 0.678, near the mean of all species (0.785).

White-eyed Vireos were the only breeding vireo commonly seen. These birds were closely associated with the mid-story. This is shown by the pro- portion of mid-story sightings (82%) and the low height diversity (0.534, second lowest of all birds). Although there were insufficient sightings of Red-eyed and Yellow-throated vireos ( V . olivaceus and V. flavifrons) for valid conclusions, the few that were sighted, and those heard, showed a canopy preference.

Yellow-rumped Warblers, 1 of 2 common winter warblers, were located mainly in mid-story (54%) and canopy (40%). The 2 commonly seen breed- ing season warblers, Kentucky Warbler and Hooded Warbler were selective

21.

TllK WILSON HLILLKTIN • Vol. 90, No. I, March 1978

SPECIES AND NO. OF SIGHTINGS Black Vulture* (22)

Common Flicker (43)

Pileoted Woodpecker (51)

Red- bellied Woodpecker (99) Red-heoded Woodpecker (373) Yellow-bellied Sopsucker (176) All Woodpeckers (802)

Blue Joy (184)

Common Crow (52)

Carolina Chickadee (55)

Tufted Titmouse (137)

Carolina Wren (148)

Mockingbird (33)

Brown Thrasher (154)

American Robin (229)

Hermit Thrush (30)

Ruby- crowned Kinglet (73) White-eyed Vireo (45)

Yellow - rumped Warbler (82) Kentucky Warbler (24)

Hooded Warbler (17)

Rusty Blackbird (39)

Brown -headed Cowbird (33) Cardinal (390)

American Goldfinch (21)

Rufous -sided Towhee (82) White - throated Sparrow ( II 36) All Birds (4103)

PER CENT OF SIGHTINGS

*Above Conopy Stratum considered for Black Vultures and Common Crows only

I I 0-0.6m. I j 0.6- 7.6m. 7. 6m. - Canopy Top Above Canopy

FlC. 1. Vertical height distrihutions of common birds.

Dickson and Noble • VERTICAL DISTRIBUTION OF BIRDS

25

in their forest profile use. Over 75% of sightings of Kentucky and Hooded warblers were in the 0.6-7. 6 m stratum and the height diversity of each was less than the mean of all birds by more than 25%. They appeared to differ in use of the ground stratum (4 of 24 sightings — Kentucky Warblers, 0 of 17 sightings- — Hooded Warblers), although there were insufficient data for a valid statistical test.

Brown-headed Cowbirds were mainly a mid-story, and secondarily a canopy occupant (DI = 0.924). Rusty Blackbirds were diversely distributed ( DI = 1.051, 34% higher than the mean for all birds); they were found on the ground, mid-story, and canopy in decreasing order of occurrence.

The seed-eating fringillids, as expected, tended to be close to the ground. The 2 species (White-throated Sparrow and Rufous-sided Towhee) found most frequently near the ground were in this family. Over 75% of the White- throated Sparrows and 62% of the Rufous-sided Towhees were detected within 0.6 m of the ground. Conversely, only 3% of the sparrows and 4% of the towhees were detected in the tree canopies. The Northern Cardinal and the less common American Goldfinch differed ( P < .01 ) from other fringillids. Both were mainly located in mid-story (60%, cardinal; 52%, goldfinch), and both showed high dispersal within the 3 strata ( I)I > 20% higher than the mean of all species ) .

Most individual species were more specialized than the aggregate of all birds. Of the different species investigated, only Brown-headed Cowbirds, American Goldfinches, Hermit Thrushes, and Northern Mockingbirds did not differ significantly ( P > .05 ) in height distribution from sightings of all birds. These species were commonly found in all strata and as a result, ex- hibited a greater than average height diversity.

Vertical resource partitioning. — Different vertical resource use strategies were evident in birds in this mature ecosystem. Some species were specialists in using 1 of the 3 strata; some used 2 strata exclusively, or nearly so; some were found in all strata, but preferred 1 or 2 strata; and some species used all strata almost equally. Specialist species ( i.e., those with lowest DI and >78% of sightings in 1 stratum ) in the 7.6 m-canopy top stratum were Pileated Woodpecker, Red-headed Woodpecker, and Blue Jay. Carolina Wrens, White-eyed Vireos, and Kentucky Warblers were mid-story associated species, and no species were predominantly ground dwellers.

Other species concentrated their activities in 2 strata I >94% of sightings ) . Those found predominantly in the mid-story/canopy were: Red-bellied Wood- pecker, Yellow-bellied Sapsucker, Carolina Chickadee, Tufted Titmouse, Ruby-crowned Kinglet, and Hooded Warbler. White-throated Sparrows and Rufous-sided Towhees were the ground/mid-story dwellers.

Northern Mockingbird, Brown Thrasher, Hermit Thrush, Yellow-rumped

26

TllK WILSON IUJLLP:TIN • Vol. 90, No. 1, March 1978

\\ arl)ler, Brow ii-lieaded ("owhird, and .Northern Cardinal were l)asically gen- eralists in vertical selectivity, hut showed slight jireferences for 1 or 2 strata.

(a)ininon Flicker. American Kohin, American Goldfinch, and Rusty Black- bird were generalists in vertical distribution, displaying optimum height dis- persal among the 3 strata, and maximum niche breadth.

riie aggregate heights of all birds revealed a fairly uniform use of the 3 strata I Fig. 2). Each stratum was of approximate e(iual value as an avian resource unit. Ibis substantiated the height units selected, and pointed out the scaling differential of birds in vertical distribution (Cody 1974:70). Although the canopy stratum represented 71% of the total forest height, only 33% of bird sighings were within this stratum. Conversely, the 0-0.6 m ground stratum represented 2% of the total height and contained 31% of the birds. Plant detritus, particularly mast, accumulated on the ground and this provided direct and indirect food sources for the ground foraging birds. Additionally, the solid substrate probably rendered the ground more acces- sible to foraging birds.

d'he mid-story contained proportionately more birds than the canopy, but fewer than the ground stratum. The continuous cover of evergreen cane and palmetto of the mid-story, may have influenced vertical distribution. Flying birds also appeared to prefer this height.

Seasonal vertical distribution. — Seasonal shifts in vertical distribution were evident in Thistlethwaite birds. Due to the seasonal occurrence of some species, and the small number of samples of many others when categorized into seasons, we usually grouped individual species into higher taxa or on a residency status basis.

dTiere was a gradual shift in distribution of birds upward in height through the 3 strata from the winter season through spring to summer and a pro- nounced downward movement from fall to winter. The comparison of win- ter to summer showed decided differences. Spring brought a slight, but non- significant (P>.()5), shift upward in height for the aggregate of all birds, and for permanent residents when considered separately (Fig. 2l. For all birds, ground detections fell from 38 to 36% and canopy detections rose from 29 to 32% from winter to spring. In the permanent resident group, ground detections fell from 27 to 20% and canopy sightings increased from 22 to 27% from winter to spring. Common fringillids ( hite-throated Spar- rows. I^ufous-sided Towhees, and Northern Cardinals), which were, in part, included in the 2 previous groupings, showed a significant ( P < .05 ) shift upward in distribution from winter to spring. Ground detections fell from 70 to 65%, and canopy detections increased from 4 to 7%, as the birds re- sponded to the seasonal spring flourish of primary production of trees and the corresponding shift of available food. Birds were attracted to new vegetation

Dickson and Noble • VERTICAL DISTRIBUTION OF BIRDS

27

ALL BIRDS PERMANENT RESIDENT

NO. OF SIGHTINGS WINTER

I NOV. — 28 FEB.

^ 29 1

3

2298

33|

2

38 1

1

NO. OF SIGHTINGS

]50

258

902

SPRING

1 MAR.

15 MAY

32

32

3

2

1

l27 ■)

|53 i

36]

[20 )

SUMMER

16 MAY— 31 AUG.

C 35|

3

|27 )

j57|

2

^63|

1 8|

1

flo j

413

60 40

FALL

I SEPT— 31 OCT.

]27

20 0 0 20 40

3 — 7.6- Canopy Top 2 - 0.6- 7.6 m.

I - 0 -0.6 m.

60

Fig. 2. Seasonal vertical distribution of Thistlethwaite birds, ex{)ressed as % of siglit- ings in 3 height categories.

growth of the deciduous forest. White-throated Sparrows and Northern Cardinals were commonly observed feeding on new buds and samaras of American elm {Ulmus americana) in March. This winter to spring height distribution shift of the common fringillids was partially responsible for the

TilK W II.SON IUjLLKTI.N • VoL 00, No. J, March 1078

2l\

clumjie in lieifilit (lislrihulioii of other bird fJiroupinf^s in which the fring;illids may liave been included ( ijermanent residents arul all birds).

dhe movement from firound to mid-story, and from mid-story to canopy, was more pronounced from spring to summer. In comparing the spring to summer distributions of all birds combined, a chi s(}uare value of 143.81 ( P < .01 ) was noted. (Ground sightings declined to 8%, mid-story sightings increased to 57%, and canopy sightings increased to 35%. 3 he increase in stratal index of birds substantiated this upward movement. This was par- tially due to a species change between seasons. 3 he departure of White-

throated Sparrows from February to April lessened the lower strata detec- tions. But the permanent residents also exhibited a significant (;^- = 8.98, B < .05) shift upward in response to the vegetation profile change.

A highly significant difference ( P < .01 ) was noted between winter and

summer vertical height distributions for common permanent residents “

26.11) and the aggregate of all birds ( = 178.78 ) . There w as a slight

change in height distribution from winter to spring, and a more pronounced change from spring to summer. 3he winter to summer comparison embodied these 2 lesser seasonal height distribution changes.

I he summer to fall comparison showed no discernible shift in vertical dis- tribution of I histlethw aite birds. Ground detection percentages remained virtually unchanged for all birds and permanent residents. Figure 2 reveals a shift of about 16% of sightings of all birds from mid-story to canopy. We believe this was misleading due to the autumn arrival of numerous Red-headed W oodpeckers. This conspicuous canopy dweller inflated the number of canopy detections. A check of the common permanent residents revealed no notable change in vertical distribution from summer to fall = 0.66, P > .05).

W ith the accumulation of plant detritus, particularly mast, on the ground in fall and early winter, the birds redistributed themselves at lower levels in the i)i ofile. I here w as a highly significant difference ( P < .01 ) between fall and w inter for all birds ( x~ = 156.25 ) and for permanent residents ( x" = 9.81).

Ibis seasonal height distribution change resulted in a corresponding change in height diversity. A Least Sfiuares Analysis of Variance showed a highly significant difference (F = 8.37; d.f. = 2, 3; P<.01) between seasons. Height diversity approached maximum during w inter I 1.092 ) and spring 11.097). During summer and fall diversity was lower (0.890, 0.894), with birds favoring the mid-story and canopy.

SUMMAUY

Vertical liei^ht data from tl03 sightings of 2() species of birds were analyzed in order to better understand height segregations and resource use. Height categories used were:

Dickson and Noble • VERTICAL DISTRIBUTION OF BIRDS

29

ground to 0.6 m, 0.6 m to 7.6 m, and 7.6 m to canopy top (approximately 25.9 m). Bird height distributions were compared J)\ means of the chi square test for 2 independent samples. Height diversities were computed by the information theory. The most ubiquitous species in height dispersion were: American Robin, Common Flicker, Rusty Blackbird, and American Goldfinch. The species most restricted in the forest profile and the zones they inhabited were: Red-headed Woodpecker, Pileated Woodpecker and Blue Jay — canopy; White-eyed Vireo, Kentucky Warbler, and Carolina Wren — mid-story. There was a gradual upward shift in distribution of all birds from winter through spring to the summer breeding season. There was a highly significant winter to summer height distribution change from a nearly e(|ual distrihuton at all levels in winter to a pre- dominantly mid-stor>- and canopy distribution in summer. Corresponding with this was a reduction in height diversty of the aggregate of all birds. These shifts were presumably a response of the birds to the seasonal change in foliage piofile and food supi)ly of a deciduous forest.

ACKNOWLEDGMENTS

The research was supported by the School of Forestry and Wildlife Management and the Agricultural Experiment Station, Louisiana State University, Baton Rouge. We are thankful to R. B. Hamilton, C. R. McLellan, Jr., and P. E. Schilling for valuable as- sistance in the research design and analysis of data, and to M. Raymond for programming the data for computer analysis.

We are grateful to the Louisiana Tech University School of Forestry for clerical as- sistance, and to J. W\ Goertz, R. B. Hamilton, J. A. Jackson, 1). James, and J. R. Karr for valuable suggestions with the manuscript,

LITERATURE CITED

Braun, E, L. 19.50. Deciduous forests of eastern Noith America. Blakiston Co., Phil- adelphia.

Cody, M. L. 1968. On the methods of resource division in grassland bird communities. Am. Nat. 102:107-147.

— . 1974. Competition and the structure of bird communities. Princeton Univ.

Press, Princeton, N.J.

Karr, J. R. 1971. Structure of avian communities in selected Panama and Illinois hab- itats. Ecol. Monogr. 41:207-233,

King, J. R. 1974. Seasonal allocation of time and energy resources in birds. In Avian energetics ( R. A. Paynter, Jr., ed.), Nuttall Ornithol. Club, Cambridge, Mass. Koplin, j. R. and R. S. Hoffman. 1968. Habitat overlap and comjrctitive exclusion in \o\es ( Microt us ) . Am. Midi. Nat. 80:494—507 MacArthur, R. H. and J. W. MacArthlr. 1961. On Irird species diversity. Ecology 42:594-598.

Odum, E. P. 1969. The strategy of ecosystem development. Science 164:262-270. Pearson, 1). L. 1971. Vertical stratification of birds in a tropical dry forest. (Condor 73:46-55.

SciioENER, T. W. 1974. Resource partitioning in (‘cological communities. Science 185: 27-39.

Shannon, C. E. 1948. A mathematical theory of communication. Bell Syst. Tech. J. 27:379-423, 623-656.

M)

THE WILSON BULLETIN • Vol. 90, Nu. 1, March 1978

SiKGKi., S. I9S0. Nonparamctric statistics for the behavioral sciences. McGraw-Hill Co., New ^ ork.

Tkamkk, E. J. 1%9. Bird species diversity: components of !<hannon’s formula. Ecology .SO: 92 7-929.

SCHOOL Of^ F0KP:STRY AM) WILDLIFE MANAGEMENT, LOUISIANA STATE UNIV., BATON KOUGE 7()8().'^ ( IMtESENT ADDRESS .JGD: SOUTHERN FOREST EXPERI- MENT STATION, USDA FOREST SERVICE, NACOGDOCHES, TX 75961). AC- CEPTED 31 MARCH 1976.

REQUESTS EOR ASSISTANCE

International shorehird surveys 1978. — A cooperative International Shorebird Survey scheme has been organized by the Canadian Wildlife Service and the Manomet Bird Observatory since 1974 to obtain information on shorehird migration and to identify and document areas of major importance. This scheme has been highly successful, with much very valuable information on shorehird distribution and migration coming from contribu- tors throughout eastern Canada and the U.S.A., the Caribbean Islands, and Central and South America. Information from the scheme will be valuable in assessing requirements for the future protection and conservation of the birds and their habitat. It is planned to make 1978 the fifth and final year of the project. Any observer who may be able to participate in regular counts of shorehirds during spring and autumn migration periods, as w'ell as during the winter in shorebird wintering areas, is asked to contact one of the undersigned. Occasional counts from observers visiting shorebird areas on an irregular basis would also be most welcome. For areas in Canada: Dr. R. I. G. Morrison, Canadian \^’ildlife Service, 2721 Highway 31, Ottawa, Ontario. Canada KIG 3Z7. For areas in U.S.A., Caribbean Islands. Central and South America: Brian A. Harrington, Manomet Bird Observatory, Manomet, MA 02345.

Shorebird color-marking. — In 1978, the Canadian Wildlife Service will be continuing a large-scale program of banding and color-marking shorebirds in James Bay. During the past 3 years, over 30,000 shorehirds have been captured, resulting in more than 1200 ‘‘bird days” of sightings of dyed birds ranging from eastern Canada to South America. Much valuable information on migration routes and strategies is being obtained and ob- servers are again asked to look out for and report any color-dyed or color-banded shore- birds that they may see. Reports should include details of species (with age if possible), place, date, color-marks and, if possible, notes on the numbers of other shorebirds present. I’or color-dyed birds, please record the color and area of the bird that was dyed. For color hands and standard metal leg hands, please record which leg the bands were on. whether they were above or below the “knee,” the colors involved (yellow or light blue), and the relative position of the hands if more than one was on a leg ( e.g. right lower leg, blue over metal, etc.). All reports will be acknowledged and should be sent to: Dr. R. I. (L Morrison, (Canadian Wildlife Service, 2721 Highway 31. Ottawa, Ontario, (’anada KUi .3Z7.

AGRICULTURAL IMPACT OF A WINTER POPULATION OF BLACKBIRDS AND STARLINGS

Richard A. Dolbeer, Paul P. Woronecki, Allen R. Stickley. Jr., and

Stephen B. White

The major concentration of blackbirds and Starlings (Sturnus vulgaris) in North America occurs in the southeastern United States where an estimated 350 million Red-winged Blackbirds iAgelaius phoeniceus ) . Common Crackles {Quiscalus quiscula). Brown-headed Cowbirds \Molothrus ater), and Star- lings congregate in winter roosts ( Meanley 1971, 1975, 1977 ). An estimated 75-100 major (containing >1 million birds) roosts form in the southeastern states each year.

Increasing attention is being given to many of these roosts because of nuisance problems, reputed health hazards, and agricultural damage asso- ciated with them. Although considerable effort has been directed toward de- veloping methods for reducing roosting populations ( Lefebvre and Seubert 1970), field applications of such methods have met with considerable public opposition ( Graham 1976 ) . L nfortunately, little effort has been directed to ecological studies of the various roosting species during the winter months.

The objectives of this study were: (1) to document food habits, habitat

preferences and use, and general feeding and roosting behavior of the various blackbird species and Starlings using a large winter roost; and (2) to under- take a preliminary survey of the impact that this large roosting population has on agriculture within a 40 km foraging radius of the roost.

STUDY AREA AND METHODS

The study area included a large concentration of blackbirds and Starlings that roosted during the winter of 1975-76 about 7 km east of Milan, Tennessee, on the Milan Army Ammunition Plant site near the Gibson-Carroll county border. The roost, bounded by highway and pastures, was in a 21-year-old, 4.5 ha loblolly pine i Finns taeda) plantation with little understoiy. The birds bad been roosting each winter at various sites on the ammunition plant since at least 1969. The birds foraged primarily in Gibson County. This roost has been a center of controversy since the winter of 1974-75 when the Army attempted to reduce the bird population by spraying the roost with a wetting agent ( Rus- sell 1975) .

Gibson County is a leading agricultural county in western Tennessee (Hobson 1976). In 1975, over 48,000 ba were planted to soybeans; 14,000 ha to cotton; and 11,000 ba to corn. Production of wheat, historically a minor crop in the county, increased from 3200 ha in 1973 to over 8000 ba in 1975. The county bad the largest bog and cattle population in western Tennessee in 1973-75, averaging about 55,000 and 50.000 head, respectively.

Population numbers and species composition. — Between 1 November 1975 and 5 March 1976, 28 estimates of numbers and 18 estimates (at least once weekly) of the species composition of blackbirds and Starlings roosting near Milan were obtained usually by 2

31

32

THE WII.SON BULLETIN • Vol. 90, No. I, March 1978

<)l)S(‘i \(‘is. \\ (* made population (*slimates 1)\ Block-counting (Mcanlcy 1965) birds in all major fliglil lines as they left the roost. 'I'o estimate species composition, we stood under the flight lines of departing birds in the morning or returning birds in the evening. At b'ast 100 randotn binocular sightings were made for each estimate of s{)ecies composi- tion; the first bird that cnter(*d the field of view was identified and recorded.

liird census fur habitat use. — Five automobile routes totaling 80 km were established on secondary roads .5 to .'SO km from the roost, d be routes were in zones where major flight lines from the roost have traditionally occurred and where comj)laints of damage to crops have been most prevalent ( Bussell 1975).

On 24 days between .'SO October and .'S March, bird censuses were conducted on these routes by 2 observers in 1 automobile starting 0.5-1 b after sunrise and ending before 15:30 ( U.'^T ) . The starting route and direction were randomly selected each day; the remaining routes were run in the most exjjeditious order. Routes were driven at 15-45 km/b. The vehicle could be stoi)ped for up to 1 min if necessary to observe a flock of birds through binoculars. Numbers, species, composition, and associated habitat types were recorded for all observed groups of 2 or more Starlings and/or blackbirds.

The 12 habitat tyj)es were: (a) pasture fincludes cemeteries and unimproved pastures

with broomsedge) ; (b) cornfields and corn stubbie; (c) wheat; <d) legumes; )e) soy- bean fields and soybean stubble; (f) feedlots (must include feeding apparatus or closely- fenced livestock); (g) woodlots, forest, or brush; (b) buildings; (i) thoroughly plowed (little evidence of previous crop type); (j) cotton; (k) fallow (weedy fields not in cultivation or pasture previous growing season); and (1) miscellaneous.

We ran 1 to 4 habitat surveys monthly on the census routes from late October to early March to determine the relative proportions of the 12 habitat types. We recorded the habitat type on each side of the road at 0.16 km intervals. Thus, 1000 sample points were recorded for each survey.

Food habits. — ^Between 14 November and 29 Februarv, usually once weekly, we col- lected .50 to 75 birds by shotgun as they settled into the roost at dusk. Each bird was identified, sexed, and weighed before stomach and esophageal contents were placed in a vial containing 5% formalin.

For the analysis of food items, the formalin soluti«)n was drained from each vial and the vial contents were i)laced in a drying oven (40°C) for several hours. Each sample was then placed in a Petri dish containing five 1-mm dots symmetrically placed 2 cm apart in the form of the center and end points of an “X.” The dish was shaken and stopped at random and the food item resting on or nearest each dot was recorded. This procedure was repeated 5 times per sample for a total of 25 recordings per sample. The total for each food item (corn, wheat, sorghum, weed seeds, tree fruits, and insects) was multiplied by 4 to obtain a ])ercentage estimate based on surface area.

This food-hahits analysis is biased toward foods that are difficult to digest fe.g., corn, ceitain we(*d seeds) ; thus, the percentage estimates obtained should be viewed in light of this limitation. In addition, birds were collected only in the evening; thus, any diurnal pattern in food seb*cti\ity was ignored. Nonetheless, we believe this analysis provides a general view of the dominant foods of the various bird species.

If aste corn. — Random areas of har\est«‘d cornfields in Gibson Ca)unty were searched for corn at intervals during the winter to determine the amount of waste corn available to birds. In each field, 2 strips 0.75 m by 55 m were searched. All cobs and pieces of c(/bs bearing kermds were collect«‘d. In addition. 2 randomly-selected areas 0.75 m by 0.75 111 in each strip were searebed for loose kernels. I'liese loose kernels were eollected.

Dolbeer et al. • IMPACT OF BLACKBIRDS

33

Fig. 1. Estimated number of blaekbirds and Starlings using roost near Milan, Ten- nessee, November 1975-early Mareh 1976.

and together with cob samples, removed from the fields. All kernels were removed and weighed to the nearest gram. Kilograms of available corn per ha were then calculated.

Feedlots: bird censuses and observations. — On 9 days between 29 Januar>’ and 2 March 1976, we censused blackbird and Starling populations at 19 to 25 cattle and hog feed- lots within 40 km of the Milan roost in the main area of foraging by the roosting pop- ulation. Censuses were made from 10:00 to 15:00 CST. Each lot was observed for 5-10 min and the number and species composition of blackbirds and Starlings in the lot were estimated. In addition, we made extended oliservations at several lots to study the feed- ing behavior of the various birds species.

RESULTS

Size and species composition of roosting population. — The roost formed in early November and disbanded in early March. The roosting population esti- mates indicated a smooth growth to a peak population of around 11 million blackbirds and Starlings in January and early February and a sudden re- duction in late February (Fig. 1). The species composition remained fairly constant between November and February (Table 1 j with an overall mean

THK WILSON lUILLKTIN • Vol. 90, No. 1, March 1978

'I'ahle 1

Avkkagk Monthly Si’KCiks Composition (%) of Birds at Milan, Tennessee Roost, November 1975 Tiirolgii Early March 1976'

Early

Species

Nov.

Dec.

Jan.

Feb.

March

Mean

(iommon Crackle

70 (2.5)"

75 (5.2)

65 (6.7)

57 (6.3)

47 (0.2)

64

Red-winged

Blaekhird,

20 (0.7)

15 (1.0)

33 (3.5)

34 (.3.7)

4 (<0.1)

27

Brown-headed Cowbird, and Rusty Blackbird .^tarling

10 (0.4)

10 (0.7)

4 (0.4)

9 (1.0)

49 (0.2)

9

^ Red-wiiiKS, cowbirds, and Rusty Blackbirds are lumped together because of our inability' to distinguish during species composition estimates.

-Values in parenthesese are peak monthly population estimates (XlO’’).

of 64% grackles, 27% Red-wings and cowbirds, 9% Starlings, and a trace % of Rusty Blackbirds i Euphagus carolinus). (Red-wings and cowbirds were lumped together because they were difficult to distinguish during the species composition estimates. Based on our general observations, the bird censuses along roadsides, and the species composition of birds collected for food habits, we believe that Red-wings were more numerous than cowbirds. I

Crackle populations peaked in January whereas Red-wing, cowbird, and Starling populations peaked in February (Table 1). Crackle, Red-wing, and cowbird populations decreased rapidly in late February before Starling pop- ulations dispersed.

Daily habitat use. — The number of blackbirds and Starlings seen per census

Table 2

Number of Blackbirds and Starlings Recorded and Species Composition of These Birds on Census Routes, Late Octobp:r 1975 Through Early March 1976, Milan.

Tennessee Area

No. days Species composition of birds observed (%) Avg. birds

census recorded per

Month

nin

Crackles

Red-w ings

Cowbirds

Starlings

Rusty BB

80 km census

Oct.

1

0

23

<1

76

0

1565

Nov.

12

82

8

1

8

0

5430

Dec.

5

54

22

5

19

<1

4537

Jan.

2

20

28

2

50

0

2404

Eel).

3

53

17

13

17

<1

7622

March

1

89

2

6

3

<1

2191

Total

24

62

17

4

16

<1

UolbeeT et al. • IMPACT OF BLACKBIRDS

35

Table 3

Average % of Crackles, Red-wings, Cowbirds, and Starlings Observed by Habitat Type for November 1975 Through February 1976, in Milan, Tennessee Area

Habitat

type

Avg. % of total habitat ( Nov.-Feb. )

Crackles

Red-wings

Cowbirds

Starlings

Pasture

23

4

2

6

31

Corn

4

35

26

11

5

Wheat

5

9

5

<1

5

Soybeans

21

4

36

3

11

Feedlots and legumes

<1

6

3

65

23

Woods

13

36

16

12

11

Buildings and miscellaneous

12

1

3

1

10

Plowed

3

2

6

2

1

Cotton

8

<1

2

0

2

Fallow

11

2

2

0

<1

Iluctuated considerably from day to day, primarily in response to weather conditions ( e.g., during inclement weather more birds were usually seen ) . The species composition of birds seen ( grackles 62%, Red-wings 17%, Starlings 16%, cowbirds 4%, Rusty Blackbirds <l%j was similar to the estimates ob- tained at the roost ( Tables 1 and 2 ) .

The major habitat types along the census routes were pasture (23% ) and soybeans (21%j followed by woods (13%), buildings and miscellaneous ( 12%), and fallow ( 11%) (Table 3). The relative proportions of the various habitat types remained rather stable from November through February.

The various bird species had conspicuous differences in habitat use during the winter months (Table 3). The majority of grackles were seen in corn- fields and woods which made up only 4% and 13% of the habitat, respective- ly. Red-wings were the only species commonly recorded in soybeans; 36% of the Red-wings were seen in soybeans (21% of the habitat). Red-wings also commonly used cornfields. We observed most cowbirds ( 65% ) at feedlots which made up <1% of the habitat. Habitat types most used by Starlings were pasture (31%), feedlots (23%), and woods (11%). They were also the only species commonly seen around buildings and urban areas.

Some major changes in habitat use occurred during the winter (Fig. 2). Starling use of wheatfields declined as the winter progressed. The use of feedlots was rather constant throughout the winter for cowbirds; however, it increased for Red-wings, Starlings, and grackles as winter progressed.

Food habits and body weights. — Corn (averaging 77%) was the dominant food for grackles during each month, November through February (Table 4).

36 TllK WILSON lUJLI.ETIN • Vul. 90, No. 1, March 1978

JQ

A

B

H

•

l_ 10

_ /

Starlings in

Redwings in

OO

■E

Wheat

Feedlots /

CD

\ ^

/

'o 5

.

\

/

”* !

"c

\

\

/

e

\

#

/

O)

\

/

La-

1 1 ♦ ^ n

» — k'' 1 1

U

Nov. Dec. Jan. Feb.

Nov. Dec. Jan. Feb.

C

• /

^ 50

(T3

50

t

/

’.5

Crackles

Starlings '

in •

in

c

Feedlots ,

Feedlots /

oo

TZJ

/ •

/

i

/

CQ

25

! 25

y

'o

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/

O)

n

/

/

/

/

/

0

■Si-.-rr" 1 0

L 1 i L

Nov. Dec. Jan. Feb. Nov. Dec. Jan. Feb.

Fig. 2. Percent of (A) Starlings observed in wheatfields, (B) Red-wings observed at feedlots, (C) Crackles observed at feedlots, and (D) Starlings observed at feedlots during bird censuses, November 1975 through February 1976, Gibson County, Tennessee.

Only in November, when acorns \Quercus spp. ) made up 29% of the food items, was the percentage of corn <75% for grackles. The most common weed seed found was ragweed {Ambrosia sp. I . Grackles, the only species with sufficient numbers collected of both sexes to examine sex-specific food habits, had no apparent sex-specific differences.

Corn ( 38% ) and weed seeds ( 36% ) were the dominant foods for Red-w ings (Table 4l. Weed seeds commonly consumed were Johnson grass {Sorghum halepense ) , cocklehur { Xanthium strumarium ) , chickgrass {Digitaria ischae- mum), dropseed {S])orobolus sp. I , smartweed {Polygonum sp.), and pig- weed { Amaranthus 9>\y.) .

Dolbeer et al. • IMPACT OF BLACKBIRDS

37

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THK WILSON lUILLKTIN • VoL <)0, No. I, March 1978

Iahle 5

Avkhagk Body Wkigiits in (^rams (±1 S.E.) for liLACKRiRDS Collkcted at Milan, Tknnksske Boost, Novkmrkr 1975 Through February 1976

Montli

Male

Grackles

Female

Grackles

Male

Red-wings

November

126.1 ± 1.0

100.0 ±0.9

71.5 ± 0.6

(751*

(54)

(98)

Deeember

126.0 ± 1.7

101.1 ± 0.9

73.6 ± 0.5

(41)

(41)

(68)

Januaiy

132.3 ± 1.0

103.8 ± 1.5

79.0 ± 1.3

(17)

(14)

( 15)

Fel)ruary

126.4 ± 1.0

98.8 ± 1.2

72.8 ± 1.2

(64)

(26)

(24)

* Sample sizes are

in parentheses.

Starlings had the most cosmopolitan diet with plant seeds (29%), wheat seeds or sprouts ( 19%), corn ( 11%), and tree fruits (9%) commonly present (Table 4). Common plant seeds were sumac {Rhus sp.), wild grape iVitis sp. ), and pokeweed [Phytolacca americana) . The tree fruits were predom- inantly hackherry ( Celtis spp. ) . Starlings were the only species in which insects were consistently found.

Corn (54%) and weed seeds (34%) were the dominant foods in the small (15) sample of cowbirds collected (Table 4). Johnson grass, ragweed, and pigweed were the dominant weed seeds.

Monthly average body weights ( November-February ) were determined for male and female grackles and male Red-wings (Table 5). In all cases, weights were highest in January. The average weight (±1 S.E.) for 13 female Red- wings, 56 Starlings, and 9 male and 4 female cowbirds was 48.9 ± 0.4, 86.2 ± 0.9, 52.8 ± 0.6, and 40.0 ± 1.6 g, respectively.

IMPACT ON AGRICULTURE

Winter wheat. — A substantial part of our study was devoted to measuring the damage inflicted by Starlings and blackbirds on winter wheat in Gibson County. This study is the subject of a separate report ( Stickley et al. 1977) and will he only briefly summarized here.

Forty-eight randomly selected wheatfields along the census routes were monitored during the period November through February. Two of the 33 fields planted before 13 November received bird damage ( i.e., pulling up sprouting wheat). All 15 fields planted after 12 November received some damage. Seven of these 15 fields that could he assessed for damage averaged

Dolbeer et uL • IMPACT OF BLACKBIRDS

39

Table 6

Summary of Blackbird and Starling Numbers at Hog and Cattle Feedlots Censused ON 9 Days From 29 January Through 2 March 1976 in Gibson County, Tennessee

Avg. no. Avg. species composition (%)

Type of Avg. no. lots birds in

lot censused/day lot/census Starlings Crackles Covvbirds Red-wings

Hog 14 54.0 (1000)“ 69 15 12 4

Cattle 8 223.0 (3000)“ 17 20 62 1

® Values in parentheses represent maximum number of birds estimated in a lot during a census.

about 11% of their sprouts removed by birds. Frost damage to the 15 late- planted fields averaged 25% of the sprouts destroyed. Overall, the 48 fields suffered an estimated 3.5% sprout removal by birds and 13.5% sprout destruc- tion by frost. Almost no fresh damage was noted after mid-January. A sur- vey of some of these fields in May 1976, shortly before harvest, revealed no significant relationship between amount of bird damage in winter and num- ber of mature heads of grain in May.

Almost all bird damage was done by Starlings (Table 4), a species that made up a minor (9% ) part of the roosting population. Crackles commonly were observed feeding in wheatfields (Table 3) ; but they fed on items such as waste corn and weed seeds.

Corn. — Almost all corn was harvested in Gibson County by the time the roost developed in early November. Thus, the roosting population inflicted almost no damage to standing corn. However, both stomach contents (Table 4) and habitat-use censuses (Table 2) indicated that corn left in fields after harvest was an important food for blackbirds, particularly grackles. Most of this corn should be considered as waste corn, altough in some fenced fields corn was used by livestock during the winter. About 17% of the cornfields along the census routes were fenced.

The estimated waste corn per ha of harvested cornfields declined signifi- cantly ( P < 0.05 ) from an average of 245 kg/ha ( moisture content of 20- 25% ) for 12 fields sampled in November to <10 kg/ha for 20 fields sampled in January and February. Thus, far less corn was available to foraging black- birds late in winter compared with November.

Feedlots. — There were major differences in blackbird and Starling popula- tions in cattle and hog feedlots (Table 6). Cattle lots had an average of 223 birds per census compared to 54 birds for hog lots. Cowbirds, making up 62% of the birds observed, were by far the predominant species at cattle lots, followed by grackles (20%) and Starlings (17%). In hog lots. Starlings, constituting 69% of the birds seen, were by far the predominant species, fob

10

TIIK WILSON lUlLLKTIN • Vol. 90, No. 1, March 1978

lowed hy grackles (15%) and cowhirds (12%). Ked-wings made up <5% of the birds at either cattle or hof>; lots. Although they were not enumerated during feedlot censuses, House Sparrows (Passer dornesticus) were often as numerous as Starlings or blackbirds. Blackbirds and/or Starlings were pres- ent in about 75% of cattle and hog lots during the censuses.

d'he extended observations suggested that during midday, when the feed- lot census was normally run, there was little exchange in the populations of blackbirds and Starlings associated with the feedlots. In the early morning and evening, however, there appeared to be a transfer of birds at feedlots ( i.e., new flocks coming in to feed as other flocks left ) .

d'he actual loss of feed to birds was not measured; however, some behavior- al information on feeding and cjualitative information on feed loss was ob- tained. In hog lots, almost no feed was lost to birds directly from feeders because feeders were covered. Hogs commonly spilled grain out of feeders and this was a source of food for the birds. Starlings, the predominant species at hog lots, were the only birds seen perching on the hogs’ backs. The major concern of hog farmers was the suspected role of the birds in the spread of disease among hog lots.

In cattle lots, the predominant feeding activities of birds were: (1) feed-

ing on corn and other food items in cattle droppings, and (2) feeding in pastures associated with cattle-feeding operations. Cowbirds, grackles. Star- lings, and House Sparrows were observed in feeding troughs (covered feed- ers are not used with cattle). Farmers expressed as much concern over feed contamination from bird droppings as they did over feed consumption by birds. Disease complaints were minor.

DISCUSSION

Niche Differentiation of the Bird Species

Grackles, Red-wings, cowbirds, and Starlings, although using a common roost at night, had strikingly different niches in their daily existence.

Grackles. — Grackles were not only the most numerous species at the roost, constituting about 64% of the birds and peaking at a population of over 6 million in January and early February; but, they also had the greatest body weight per bird. Thus, if we assume a 1:1 sex ratio, grackles, from the view- point of numbers, biomass, and energy consumed, had a greater impact than the other species combined on the ecosystem w ithin the foraging range of the roosting i)opulation.

lood-habits analyses and tbe habitat-use censuses showed that waste corn was of primary importance to grackles. Overall, the negative impact that grackles had on agriculture appeared rather minor. Areas of conflict were:

( 1 ) use of feedlots in late w inter, perhaps as a result of depleted supplies of

Dolbeer et al. • IMPACT OF BLACKBIRDS

41

corn in fields; and (2) competition with livestock feeding in harvested corn- fields. Crackles were the most common species observed in wheatfields; however, our food-habits data and observations indicated they fed on other foods (often corn) and not wheat. Thus, their presence in wheatfields can only be considered as beneficial. Thirty-one percent of the wheatfields had previously been in corn and many had considerable amounts of corn at the soil surface.

Red-wings. — Red-wings were the only species commonly associated with harvested soybean fields (Table 3). A primary food source for Red-wings in these fields appeared to be cocklebur, a common weed in soybeans. Corn was also an important food source for Red-wings; they were often observed with grackles feeding in corn stubble or wheatfields. Red-wings probably had the least impact on agriculture of all roosting species. They, along with grackles, increased their use of feedlots in late winter (Fig. 2), but were still a minor species at feedlots ( Table 6) .

Cowbirds. — Cowbirds were the least common species in the roosting popula- tion (with the exception of Rusty Blackbirds). They also had the lowest body weight per bird and, thus, the lowest total biomass. They were primarily as- sociated with cattle, either in pastures or feedlots. Corn, both from feedlots and harvested fields, was an important food source.

Starlings. — Starlings made up 9% of the roosting population and about 8% of the biomass; they appeared to have the greatest negative impact on agriculture of all species. They inflicted almost all the damage to sprouting wheat and were by far the dominant species associated with hog lots. In addition, they were the only species commonly associated with buildings and urban areas. Starlings also used pastures and grassy areas much more than did the other species.

Of considerable interest also is the fact that many of the Starlings roosting in the mid-southern United States in winter (such as in Cibson Couny) are year-round residents of the region. For example, B. L. Monroe ( pers. comm. ) has estimated that 47% of the Starlings roosting in Kentucky in the winter remain in the state year-round. This contrasts with the vast majority of win- ter-roosting grackles. Red-wings, and cowbirds that are migrants from the northern United States and Canada (Fankhauser 1968, Meanley 1971, Mean- ley and Dolbeer 1977, Dolbeer 1978) .

IMPACT OF BIRDS ON AGRICULTURE

Winter wheat. — The 48 wheatfields surveyed received an estimated 3.5% sprout removal (range 0-34%) by Starlings during the winter and 13.5% sprout destruction ( range 0-50% ) by frost. There was no apparent relation- ship between amount of bird damage in winter and number of mature heads

12

THK WILSON lUiLI.ETIN • VoL 90, No. 1, March 1978

of prain in May. I luis, overall, bird damage to sprouting wheat appeared to he a minor problem in the winter of 1975-76. Most bird damage and all freeze-thavN damage occurred to fields planted after 12 November; therefore, a preliminary management recommendation for areas in western Tennessee, where bird damage is a problem, is that wheat should he planted before early November when possible. ( Of course, additional data are needed to deter- mine year-to-year and geographical variability before final management recommendations are made. I For reasons other than bird damage, the Ten- nessee Agricultural Extension Service recommends that wheat be planted be- fore 1 November (Cobble 1974).

Feedlots. — This study documented that blackbirds and Starlings commonly used feedlots, and that the feeding behavior and species composition of the birds were different for hog and cattle lots. In both types of lots, the pre- dominant species (Starlings or cowbirds) were species that made up a minor part of the bird population at the Milan roost. House Sparrows, which do not roost w ith blackbirds and Starlings and are present year round, were also commonly found at the feedlots.

Additional (juantitative studies are needed to document: (1) the propor-

tion of feed consumed by birds that represents a real loss to the farmer ( Bes- ser et al. 1968, Feare 1975), (2) the loss of feed in cattle lots due to con- tamination by birds, and (3) the role that birds at feedlots play in the spread of diseases. Also, more w ork, both extension and research, needs to be done in the area of feedlot design and in the use of toxicants and mechanical scare devices to reduce bird populations at feedlots (e.g., West 1968, Besser et al. 1967, Wright 1973 ).

Corn. — Standing corn received insignificant damage from the roosting population because almost all was harvested by the time the roost formed in early November. Nevertheless, waste corn was a dominant and perhaps critical food item, particularly for grackles and Red-wings. Further studies should be undertaken on the relationship of roosting populations to corn. The abun- dance of waste corn in fields may be the major factor allowing many of these large roosting populations to exist in their present locations throughout the w inter.

CONCLUSIONS

ddie 1 bird species that composed the roost near Milan, Tennessee, varied considerably in their numhers, biomass, foraging behavior, food habits, and impact on agriculture. Because of this overall diversity and the complexity of the various problems the birds create, simplistic management schemes are likely to fail in solving the conflicts — they may even exacerbate them. For example, much of the nuisance, feedlot problem, and wheat damage in Gibson

Dolbeer et al. • IMPACT OF BLACKBIRDS

43

County was caused by Starlings, a minor species in the roosting population. Attempts to exterminate or greatly reduce the roosting population hy spray- ing with a wetting agent may selectively favor the Starling, a highly adaptable and prolific species that perhaps survives wetting-agent applications and low- temperature stressing better than native blackbird species ( Odum and Pitelka 1939, Lustick and Joseph 1977) .

Long-term relief from the various conflicts most likely will require an in- tegrated management program with a sound ecological basis. The use of bird- control chemicals at feedlots, roost dispersal and roosting habitat manipula- tion techniques, lethal control at certain roosts, changes in certain cultural practices in agriculture, chemical repellents, and public tolerance may all be a part of such an integrated approach. We hope that this preliminary study has contributed information that will help make such a management program a reality.

SUMMARY

Hal)itat preferences and use, food habits, and impact on afirieulture were studietl for 11 million l)lackbirds and Starlings roosting in Gibson County, Tennessee, in the winter of 1975-76. The roost was composed of Common Crackles (64%), Red-winged Black- birds and Brown-beaded Cowljirds (27%), Starlings (9%), and Rusty Blackbirds (<!%)• The various species bad strikingly different niches in their daily existence and impact on agriculture. Waste corn was of primary importance to graekles and Red-wings, which spent most of their time feeding in corn and soybean stubble and woodlots. Red-wings fed commonly on cocklebur seeds in soybean stubble. Cowbirds and Starlings commonly used pastures and feedlots. Starlings did almost all the bird damage to sprouting wheat. Starlings, a minor species in the roost, bad the greatest negative impact on agriculture. Simplistic management schemes are likely to fail in solving bird-man conflicts caused by multi-species roosting populations — they may even exacerbate them. Long-term relief most likely will re(juire an integrated management program with a sound ecological basis.

ACKNOWLEDGMENTS

We thank P. W. Lefebvre, J. C. Rogers, Jr.. B. Meanley, W. C. Royall, Jr., and I). A. Buecker for assistance in the fieldwork. T. McCutcben, Milan Field Station. Univer- sity of Tennessee, generously cooperated with us in many ways. We thank personnel of the Milan Army Ammunition Plant, particularly Colonel Percbutz, W. Oates, and S. Stevenson, for their interest and coo])eration.

LITERATURE CITED

Besser, J. F., W. C. Royall, Jr., and J. W. I)e Crazio. 1967, Baiting Starlings with DRC-1339 at a cattle feedlot. J. Wildl. Manage. 31:48-51.

— , J. W, De (iRAZio, AND J. L. CuARiNo. 1968. Costs of wintering Starlings and

Red-winged Blackbirds at feedlots. J. Wildl. Manage. 32:179-180.

Cobble, R. E. 1974. Growing wheat in Tennessse. Agric. Exten. Serv., Univ. Tenn. Publ. 576 (Rev).

14

THE WILSON BULLETIN • VoL 90, No. 1, March 1978

Doujkkr, IL a. 1978. Movement and migration patterns of Ked-winged Blackbirds: A contimmtal overview. Bird-Banding I In press. 1 Ea.nkii Ai SKK, 1). I’. 1968. A comparison of migration between blackbirds and .Starlings.

Wilson Bull. 80:22.V227.

Ekakk. C. .1. 1975. (iost of Starling damage at an intensive animal husbandry unit.

I’roc. Br. Insecticide and Fungicide Conf. 8:2.53-2.59.

Uhaham, E., .1h. 1976. Blackbirds — A problem that won’t fly away. Audubon 78:118-

125.

Hobson, K. 1976. Tennessee Agricultural Statistics. Annu. Bull. 1976. Tenn. Crop Kej). Serv. Bull. T-13.

Lkfkbvre, \\ W., AM) .1. L. Sei;bp:rt. 1970. Surfactants as blackbird stressing agents.

Proc. Vertebr. Pest Conf., Univ. Calif., Davis 4:156-161.

Lustick, S., and a. Joseph. 1977. Seasonal variation in the effects of wetting on the energetics and survival of Starlings (Sturnus vulgaris). J. Comp. Biochem. & Physiol. 56:173-177.

Meanley. B. 1965. The roosting l)ehavior of the Red-winged Blackbird in the southern United States. Wilson Bull. 77:217-228.

. 1971. Blackbirds and the southern rice crop. U.S. Dept. Int., Bur. Sport Fish.

Wildl. Res. Publ. 100.

. 1975. The blackbird-Starling roost problem. Atl. Nat. 39:107-110.

— . 1977. The 1974-75 winter roost survey for blackbirds and Starlings. Proc.

Bird Control Seminar, Bowling Green State Univ., Bowling Green, Ohio 7:39-40. , AND R. A. Dolbeer. 1977. Source of Common Crackles and Red-winged Black- birds wintering in Tennessee. Migrant 48: fin press.]

Odum, E. P., and F. A. Pitelka. 1939. Storm mortality in a winter Starling roost. Auk 56:451-455.

Russell, H. G. 1975. Blackbird control on two Army installations — Environmental Impact Statement. Office Chief, Eng., Directorate Facilities Eng., Wash., D.C. f A copy has been placed in the Van Tyne Library, Univ. of Mich., Ann Arbor.) Stickley, a. R., Jr., R. A. Dolbeer, and S. B. White. 1977. Starling damage to sprouting winter wheat in Tennessee. Proc. Bird Control Seminar, Bowling Green State Univ., Bowling Green, Ohio 7:30-38.

W EST, R. R. 1968. Reduction of a winter Starling population hy baiting its preroosting areas. J. Wildl. Manage. 32:637-640.

Wright, E. N. 1973. Experiments to control Starling damage at intensive animal hus- bandry units. OEPP EPPO Bull. 9:85-89.

U.S. FISH AM) WILDLIFE SERVICE, OHIO FIELD STATION, DENVER WILDLIFE RE- SEARCH CENTER, C/O PLUM BROOK, TAYLOR AND COLUMBUS ROADS, SAN- DUSKY, OHIO 44870.

(present address, SBW: cooperative wildlife research unit, OHIO STATE UNIVERSITY, COLUMBUS, OHIO 43210 ) . ACCEPTED 31 JULY 1977.

BREEDING BEHAVIOR OE THE LOUISIANA HERON

James A. Rodgers, Jr.

Information on the breeding behavior of the Louisiana Heron ( Hydranassa tricolor ) lacks sufficient detail to permit comparison with other ardeids. Both Bent (1926) and Palmer (1962) summarized the available data from the literature and drew upon previously unpublished information from contribu- tors. Other studies (i.e., Teal 1965, Jenni 1969) deal with the reproductive success or ecology. I have described the displays characteristic of the breed- ing period ( Rodgers 1977 ) . This paper reports on the breeding behavior and nesting ecology of the Louisiana Heron.

STUDY AREA

Most fieldwork was carried out on Grand Island, Barataria Bay, Plaquemines Parish, Louisiana. Except for a few scattered oyster shell beaches, the island is covered by 5-20 cm of water during high tide, hut drains almost completely at low tide except for a few inland pools. Predominant vegetation includes black mangrove (Avicennia nitida) and cordgrass (Spartina alterniflora) .

Observations were made from blinds at 2 sites. Site A was characterized by tall, dense black mangrove averaging 1.5-2 m high with little or no open cordgrass areas. Site B was characterized by numerous small, low-lying clumps scattered throughout an equal area of cordgrass. Herons were designated as to which site they occupied, for example, male A1 or Bl. Most herons and ibises fed in surrounding estuarine regions of Barataria Bay. Hence, Grand Island was used by the Louisiana Heron primarily as a breeding site, though also used for roosting at other times of the year.

PLUMAGE CHANGES

Palmer (1962) described the nuptial molt in preparation for breeding by the Louisiana Heron. The soft-part color depicted in a colorplate (page 367) that accompanies the description retiuires some revision for the Louisiana Heron on the coast of Louisiana.

During the courtship phase of the breeding season, the bill tip was black as indicated, hut the remaining % of the bill, including the orbital skin, was turquoise-cobalt (terminology of Ridgway 1912). Displaying males fre- quently rubbed the bill over the oil gland during preening with the result that the soft part colors became more intense. As noted by Huxley (1922), the turquoise-cobalt color was typically less intense in females. I he entire iris of males was more of a magenta color; in females the inner margin of the iris around the pupil turned to rose. Leg color of both sexes was fleshy maroon.

During the incubation period, the turquoise-cobalt color changed to a mottled yellow in both sexes. The color change occurred first around the

45

1^)

THE WILSON lUlLLETIN • VoL 90, No. 1, March 1978

eye. then alonji; the resl of the hill. The sexes could then no longer he dis- tinguished. riie magenta color of the iris faded, the inner margin around the pupil hecoming almost pink in both males and females. The legs l)ecame grayish-yellow.

TEItKITOllY

Louisiana Herons exhibited no pairing behavior outside the breeding sea- son and behaved as solitary individuals while foraging and roosting in the colony. In February a slow 2-fold increase began in the roost population on Grand Island until the heronry swelled to l)reeding density. Louisiana Herons started to show soft-part breeding color and stayed longer on the island in the morning or returned earlier in the afternoon. Males began spending much time in a certain region of the island that eventually served as their territory. Occasionally a male picked up and manipulated a twig and then dropped it, or tugged on a branch. TTiese actions marked the onset of the breeding season as the males began to set up their territories.

The male set up the territory, often built the foundation of the nest, and undertook the initial defense of the territory from both intruding males and females, as is the case in most North American ardeids ( Meanley 1955, Mey- erriecks I960, Palmer 1962 ). Early male Louisiana Herons staked out large territories with centers far apart; hut, as other males began to enter the breed- ing cycle, the territories gradually became closer and territorial disputes over boundaries became increasingly common. Once a male had selected a site, he preened for long periods. Any disturbance in the vicinity or another Louisiana Heron flying by was viewed intently. Soon after the male had chosen a ter- ritory, he began to grasp and tug at branches around the site. A few low- intensity performances of the Snap-Stretch display I Rodgers 1977 ) sometimes occurred between long preening sessions. The male occasionally went below the nest bush and returned with a twig that he used in the foundation of the nest. No matter how long the male displayed, the nest never got past a loosely arranged foundation stage.

Nests generally did not last until the next season so even the earliest males had to construct new foundations when setting up a terriory. However, they often used the stunted and leafless area amidst the branches where a nest existed the previous season. Abandoned nests were almost always used again by a male later in the season. Nest height ranged between 0.3-1. 3 m above the high water mark. "1 he early males tended to set up a territory in the dense growth of 1.5-2 m tall mangroves, while the later males nested in the lower, more scattered mangroves.

1 he initial territory set up by the male Louisiana Heron ranged in size from 4 to 10 m in diameter. Between preening sessions and ever increasing Snap-

Rodgers • LOUISIANA HERON BEHAVIOR

47

Stretch performances, the male roamed his territory, occasionally stopping to preen or display at a site other than the core display site. Initially all herons were threatened upon their approach to the territory and attacked if they did not leave. Pursuit flights were very frequent during this period of the breed- ing cycle. In general, an intruder was intimidated by the threat display of a resident male and proceeded no further. Once boundaries were established, the territory was recognized and seldom contested; hence aggression between neighboring males decreased with time.

As females were gradually allowed to stay on the territory and an increasing number of new males entered the heronry and began setting up their own ter- ritories, the size of the initially large territory gradually shrank. The terri- tory reached its minimum size just after pair formation. This phenomenon is also characteristic of many other ardeids ( Meanley 1955, Cottrille and Cottrille 1958, Meyerriecks 1960, 1962 ). If the nest of the Louisiana Heron was located in one of the low, isolated bushes, the territory sometimes shrank to include only the bush and its immediate vicinity, a diameter of 2-3 m. If the nest was situated in large, dense mangrove, the territory included all the hushtop area above the nest.

Figure 1 shows the history of one region of site A beginning on 11 March 1973, with special reference to male Al. Male A1 displayed from numerous sites, but concentrated display activities on the core mangrove hush. In the late afternoon of 14 March, male Al paired. From this time on, both male and female participated in the defense of the territory. By 15 June, all nests contained either eggs or young nestlings, with the exception of the aban- doned A6 site. Male A6 allowed a female to come onto his nest, where 1 copulation took place. Afterwards, he drove her from the nest and did not allow her back on. Male A6 never paired.

In the large heronry on Grand Island, territory establishment seemed to be staggered. Because the territory of a given pair shrank and left undefended areas, other males moved in and sometimes began displaying as close as 2 m from an incubating heron. These new males were noticeably tense during this period, exhibiting sleeking and constant head turning as they observed the surrounding heronry. With time, they began to roam the mangrove hush, displaying from any site where they would not be threatened or attacked by neighboring herons. Soon a core display site developed, which was usually the place where the nest foundation was begun.

As the courtship period progressed, male Louisiana Herons performed their Snap-Stretch and Circle Flights (Rodgers 1977) from the nest, hut often could be observed moving to another site and displaying from there. If the nest or core site was located deep down in the mangrove bush, the male oc- casionally moved to the hushtop or out on a limb to display, making him

THE WILSON nULLETIN • Vol. 90, No. 1, March 1978

Fig. 1. The history of territory formation in one region of site A during 1973. During the early morning of 11 March, male A1 was alone and displayed from numerous sites designated hy open circles, but concentrated display activities on the core mangrove bush designated with a solid circle. Later in the day A2 appeared. Territorial boundaries are indicated hy dotted lines and were determined hy mapping display sites and the locations of aggressive clashes.

more conspicuous to Loth roaming females and other territorial males. Ter- ritorial male Louisiana Herons oriented the head and looked in the direction of the acoustic cues produced in the Snap-Stretch. After pair formation, the female joined in the defense of the territory, a pattern typical of many other ardeids ( Meyerriecks 1960, 1962, Blaker 1969j. Later when the nest- lings were 3 weeks and older they too defended the nest from both adult and juvenile ardeids when their parents were away.

Certain points should he brought out in regard to the shrinking effect of the male’s territory. First, a large territory at the early stage of courtship al- lowed more display sites and functioned to make the male more conspicuous to females wandering through the heronry. Second, a larger territory had more area from which the female could observe the displaying male without being driven off immediately (Meyerriecks I960). Third, when the male fi- nally accejited the female and formed a pair bond, a large territory was no longer needed. As a result, more males could come in and occupy newly un- contested areas of the heronry and the high breeding density characteristic of

Rodgers • LOUISIANA HERON BEHAVIOR

49

MALE TWIG SHAKES

\

MALE THREATENS FEMALE

\

MALE ATTACKS FEMALE

MALE AND FEMALE BILL-NIBBLE

FEMALE-NO PAIR BOND FORMED

FEMALE LANDS ON TERRITORY

I

FEMALE ALLOWED TO STAY

\

FEMALE MOVES CLOSER TO CORE

\

FEMALE ASSUMES

MALE PERFORMS SNAP AND STRETCH

\

MALE PERFORMS " CIRCLE FLIGHT

I

FEMALE PERFORMS

WITHDRAWN CROUCH GREETING DISPLAY

t /

FEMALE ALLOWED CLOSER OR ONTO CORE

MALE AND FEMALE PREEN OR

STABLE PAIR BOND FORMED- NESTING BEGINS

Fig. 2. Possible intercations between male and female Louisiana Herons during the courtship period. P"or a full discussion see the text.

this species developed. Fourth, the decrease in the territory size permitted the pair to channel their energy away from territory defense and into reproduc- tion. Fifth, because the initial nest foundation served as the core for display- ing and later as a site for raising the young, the immediate area around the nest was defended most vigorously at all times.

INTERACTIONS WITHIN THE PAIR

Male selection. — There are many possible interactions between males and females during the courtship period (Fig. 2). Females at first landed on the

so

I HE WILSON lUJLI.KTlN • Vul. 90, No. 1, March 1978

edf>;e of the displayiiif? male’s territory. Showing little overt interest in the displaying male or the nest, the females at this time usually did not stop for any great length of time and seemed to he just moving through the colony. If the female moved too far into the territory of the male, he might first ex- hibit Luig Shaking (Rodgers 1977) or immediately drive her away as he would an intruding male. During the early part of the breeding season fe- males generally did not return when driven away by the male. Later the per- sistent female would return repeatedly despite repeated threats and attacks by the male. Male Louisiana Herons during the early phase of courtship per- formed occasional Circle Flights and Snap-Stretches in between long periods of preening or twig manipulation (Fig. 3). The preening exhibited by males during this period was often marked by rapid, forceful, erratic movements. Later, preening movements were more relaxed. With an increase in time, the male performed a greater number of Snap-Stretches I Fig. 3).

At the approach of a female Louisiana Heron, the male generally returned to the core site to perform Snap-Stretch and Circle Flight displays. Once a female became attentive to a displaying male or his nest, she got as close as possible. At first she was thwarted in her attempts to get closer than the edge of the male’s territory. Even though performing Snap-Stretches, the male at this time showed predominantly aggressive behavior. Twig Shaking was com- monly observed as he threatened the female and often drove her off in pur- suit flights. A persistent female was allowed to remain on the edge of the territory, only eliciting mild feather erection in the male. Continual attempts by the female eventually resulted in her getting within a short distance of the nest. During this time, the male repeatedly did Twig Shakes. He threatened the female with Lpright and Forward displays (Rodgers 1977) and oc- casionally drove her back some distance or even off the territory. Often the female remained in view after being chased off by the male and returned onto his territory repeatedly, especially during the late stages of the courtship phase. Meyerriecks (1960) described similar behavior on the part of the female Green Heron { Butorides virescens ) .

The presence of a female initially increased the fre(iuency of Snap-Stretch and Circle Flight displays, which were occasionally performed in rapid suc- cession ( Fig. 3 ) . The maximum number of displays observed during any 1 min ( N = 8328 min ) w as 5 Snap-Stretcbes and 3 isolated Snaps performed by male A1 with a female on the territory.

I he female intently observed the male displaying, preening, and arranging twigs in the nest. Her attention seemed to be directed not only to the male, hut the nest foundation if present. W hen the male performed the Circle Flight, the female watched the entire performance. Females were often observed jumping onto the nest while the male was engaged in the Circle Flight. Upon

Rodgers • LOUISIANA HERON BEHAVIOR

51

I II III IV

1687 min 2672min 2449 min 1520 min

Fig. 3. Shifts in the hehavioral repertoire of male Louisiana Herons, Phases of the courtship period are: L first L2 h of displaying; II, after first h of displaying; HI, behavior with a female present; IV, last Y2 h before copulation. Abbreviations are: A, aggressive behavior (includes the Upright, Forward, and Twig Shake displays); BN, Bill-nibble; CF, Circle Flight; GI). Greeting display; P, preening; S, Snap; SS, Snap- Stretch; TM, twig manipulation.

his return, the male always attacked the female and drove her away. Oc- casionally, as many as 3 females joined the male in the Circle Flight by flying after him and landing nearby when he returned to his nest. The female’s flight did not in any way resemble the initial components of the Circle Flight of the male, but the return flight was similar in posture and calls to the Greet- ing display phase performed liy the male ( see Rodgers 1977 j .

52

THK WILSON IUjLLETIN • Vol. 90, Nu. I, March 1978

1 he female was allowed closer and closer until she was within 1-1.5 m of the nest. She attempted to get even closer and assumed the Withdrawn Crouch (Rodgers 1977). During an encounter with a threatening or attacking male, female Louisiana Herons often i erformed elements of the Greeting display, which aj)peared to function in reducing the aggressiveness of the male (Rod- gers 1977). Often the male stopped his attack and temporarily joined in the performance of the Greeting display. This outcome allowed the female to hold her position or move slightly closer to the nest.

As the female assumed the Withdrawn Crouch, she frequently Bill-nibbled (Rodgers 1977). If she rose from her low-profile posture, she was attacked and driven off. hen the female w as on or near the edge of the nest, the male exhibited a tendency toward a reduction of Snap-Stretch and Circle Flight displaying (Fig. 3). In addition, much preening and Bill-nibbling was done by the female, with a slow increase in the frequency of Bill-nibbling by the male ( Fig. 3) .

Precopulatory period. — This period of courtship from the time the female is first tolerated on the nest to just before the first copulation by the po- tential pair was marked by a sw itch from aggressive to sexual behavior in the male. For long periods both male and female engaged in preening, interrupted by twig manipulation and Bill-nibbling. This appears to be typical of pre- copulatory behavior of most ardeids ( Meanley 1955, Cottrille and Cottrille 1958, Meyerriecks 1960, 1962, Blaker 1969 ) . The male Louisiana Heron still exhibited moderate feather erection, while at the same time Bill-nibbling be- came more frequent. He rarely performed the Snap-Stretch and Circle Flight displays once the female was on the nest I Fig. 3 ). The 2 herons often stood side by side, usually facing in opposite directions for periods up to 40 min. The female then rose out of the Withdrawn Crouch and stood with the male in the center of the nest w ithout being attacked.

Copulation. — Soon after the female succeeded in getting onto the nest, the pair copulated either on (36 of 39 observations) or close to the nest platform or core display site. The male watched the female as she began manipulating tw igs in the nest, and they both often Bill-nibbled. The female leaned forw ard, withdrew the head partially, and s(iuatted. This act probably indicated to the male that she was ready to copulate. I observed no precopulatory display.

1 he male mounted the female from the rear or the side by stepping up onto her back. Flapping his wings to maintain his balance, he sciuatted on her, grasping her shoulders with his toes. He also used leverage of his bill on the shoulder and neck region of the female for additional support. Meanley ( 1955) reported similar use of the bill by the male Little Blue Heron {Florida cacrulea). Copulations ranged in duration from 8 to 11 sec (mean 9.8 sec; N = 23). No feather erection, nor any calls were noticed at any time pieced-

Rodgers • LOUISIANA HERON BEHAVIOR

53

ing, during, or immediately after copulation. Finishing copulation, the male rose and stepped off the back of the female. Copulation seemed to occur ir- regularly during the early phase of pair formation, though I observed copula- tions throughout the egg-laying period.

The length of time a male maintained a territory and engaged in courtship behavior without pairing is not accurately known. One instance recorded was the occupation of a territory by male A6 for only 4 days before abandoning it. Male All maintained a territory for 11 days before pairing.

Although I did not mark adult Louisiana Herons, I believe they practice seasonal monogamy. In 2 years, I observed no evidence of promiscuity once the male and female had paired, nor ‘“rapes” as have been reported for the Little Blue Heron ( Meanley 1955 I .

Postcopulatory period. — Immediately after the first copulation, the pair members engaged in long periods of preening. Bill-nibbling, and manipulating nest twigs. They also spent a lot of time standing side by side, facing in opposite directions. In this position, Huxley (in Bent 1926) has said they “intertwine their necks,” but this is actually an illusion produced by their relative posi- tions. The female soon began rearranging the twigs in the nest with the male looking on. Occasionally, both herons suddenly engaged in short perfor- mances of the Greeting display.

If the female left the nest after the first copulation to preen or find twigs, the male might not allow her back onto the nest. I observed 4 instances ( N = 39 copulations ) in which a male copulated with a female and then attacked her and drove her off or did not allow her return onto the nest after she had left it momentarily. This led to dissolution of the bond in 2 instances when the male repeatedly repulsed the female’s attempts to get back on the nest.

Males under observation did not feed while courting. The presence of wan- dering females and intruding males may be the reason for their abstinence. Only after pair formation, with the presence of its mate to defend the terri- tory, could the male forage without danger of losing his territory. Jenni ( 1969 ) also reported that male Louisiana Herons do not feed during the court- ship period.

^EST BUILDING

I he male was usually the one who went out and found twigs. Male Louisi- ana Herons passed these twigs to the female, who then worked them into the nest. Typically the period from the first copulation to the initiation of stick collecting was short. For example, pair A9 copulated at 11:43 and the male returned with the first twig in 11 min. Most twigs were gathered from on or very near the territory, hut occasionally males brought material from greater distances. Birds would also take twigs from abandoned nests nearby.

When the male returned with a twig in his hill, the pair performed the

rHK WILSON miLLPyriN • VoL <J0, Nu. I, March 1978

rri

(ireelinfi display ( l{o(lj>:ers 10771. I{eachiiif>: out, the female took the twip; in her hill and hotli engaf>:ed in additional head noddirifj; and calling. The fe- male then placed the twig in the nest as the male looked on. I he male often Bill-nihhied while the female v\as inserting the twig. Initially, the male ex- hibited considerable feather erection while passing twigs to his new mate. This feather erection decreased as nest building continued and was limited to the crest and, to a lesser extent, the aigrettes.

I he nest foundation begun by the male during the courtship period con- sisted of large tw igs about 1 cm in rliameter and 30-60 cm long ( N = 27 I . Phis structure sometimes had only 2 or 3 twigs. Twigs brought to the female after pair formation, while occasionally large, usually were about 0.5 cm in diameter and shorter than 30 cm (N = 163). The finishing material con- sisted of small, flexible twigs and Sj)artina grass stems. The completed nest varied in w idth and depth, hut always had a slight depression on the top sur- face that j)re\ented the eggs from rolling out. I could distinguish no differ- ences between the nests of Louisiana Herons and those of Little Blue Herons or Snow y Egrets ( Egretta thula I on Grand Island.

During nest building, one member of the pair was always on or near the territory. This prevented neighboring herons from stealing nest material. After the nest was completed, both sexes occasionally added twigs to the structure for repairs between periods of incubating or brooding. The inter- val between the first copulation and the laying of the first egg for 2 pairs of Louisiana Herons on Grand Island w as 4 and 6 days. Jenni ( 1969 ) recorded l)eriods of 4 and 5 days at Lake Alice, Florida.

INCUBATION STAGE

During the interval before the eggs were laid, the female spent a great amount of time scjuatting down on the nest, rearranging the nest twigs, and placing in new material. On Grand Island, the clutch size averaged 3.0 eggs ( range = 2-5, mode = 3 j . Of the 99 nests examined, 22 contained tw o eggs, 58 three eggs, 18 four eggs, and 1 had five eggs. For Lake Alice, Jenni ( 1969 I recorded the average clutch size for 35 nests as 4.1 eggs (range = 3-9, mode = 4l. deal ( 1965 I reported an average of 3.1 eggs per clutch for 15 nests ( range = 2-4, mode = 3 ) for Sapelo Island, Georgia.

After the clutch was completed, the pair was usually together only during a nest relief. Both sexes incubated. Nest reliefs were irregular and were ac- companied by tbe (/leeting disi)lay and Bill-nibbling. I he returned heron usually preened or manipulated a few twigs in the nest before settling. Its mate often i)reened a short time on the edge of the nest before leaving to col- lect 1 or more twigs which were i)assed in a Greeting display to its mate who inserted them into the nest. Huxley Un Bent 1926) stated the number may be

Rodgers • LOUISIANA HERON BEHAVIOR

DO

as many as 11 twig presentations at 1 nest relief. My data indicate 2-5 pre- sentations (mean 4.2, N = 167) are more common. Because the nests are in good condition structurally, I believe the display functions to reinforce the pair bond in these instances. Sometimes an incubating heron did not imme- diately rise off the nest when its mate returned, but remained sitting on the eggs. The returned heron then engagd in additional Greeting displaying and Bill-nibbling, after which the mate would rise off the nest.

The length of an incubation period varied considerably, from periods of less than 1 h to 1 recorded instance in which the partner did not come hack during the daylight hours ( about 06:00 to 20:30 I . Such long periods between changeovers were rare, and although nest reliefs were irregular, there tended to be 1 during the mid-morning, another during the mid-afternoon, and often 1 during the early evening. Incubation was most continuous in the early morning and early evening periods, when the ambient temperatures were cool- er. During these periods the adult only occasionally rose off the eggs to preen, rearrange nest material, or sunbathe. During the late morning and afternoon, when the temperatures were the warmest, the Louisiana Heron often rose off the eggs. The bird rarely left the eggs unattended; usually it stood on the nest edge while preening or sunbathing. I never saw an incubating bird leave the nest to forage in nearby shallow inland pools. As the heron sat again on the eggs, it first erected the feathers of the lower breast and belly, then dropped the wings slightly, and shifted from side to side as it lowered its body onto the eggs. Mild crest erection also occurred.

Incubating Louisiana Herons were quick to rise and threaten any species of heron intruding on the territory. The area immediately around the nest was defended most vigorously. Disturbances outside the territory usually elicited only the Alert Posture ( Rodgers 1977 ) .

At pipping, the young Louisiana Heron emits high-pitched “pcepmg” sounds. During this time, adults looked at the eggs for long periods of time, sat, then rose again and peered at the eggs while turning the head from side to side. The adult heron later dropped pieces of eggshell out of the nest.

BROODING AND CARE OF THE YOUNG

Because incubation begins with the first egg, hatching is asynchronous. Lntil the nestlings were about 1 week old, the behavior of the adults was the same as during the incubation period, except for feeding the young. Adults brooded most intensively during the cool periods of morning and early eve- ning. Herons commonly sunbathed while sciuatting on the nest or standing over and shading the nestlings.

From age 1 day to about 1 week, nestlings were fed small fish that were regurgitated by the parent onto the floor of the nest. The nestlings picked

56

TIIK W ILSON lUiLLK I’IN • Vol. 90, No. 1, March 1978

up the fish in their hills. Similar hehavior has been reported for the Little Blue Heron ( Meanley 1655), Great Blue Heron, Arden herodias ( Pratt 1970 ), and (5ittle Lfjret Hulbulcus ibis (Weher 1975). Afterwards the adult ate the unconsuined fish. I pon nest relief, the departing parent often fed the nest- lings 1 more time.

W hen the young were 1-2 weeks of age, the hill, legs, and general body strength were well enough developed to allow grasping of the parent’s hill and they obtained a meal directly from the adult. The young were then fed one at a time with the adult leaning forward and extending the mandibles down- ward in such a manner that the dorsal surface of the upper mandible faced the offspring and was grasped. After feeding one nestling, the adult usually moved a short distance from the calling chicks before returning and feeding a second. Ibis i)iocess was usually repeated several times. In such sessions, 1 nestling was often fed twice. Adults stood on the edge of the nest and could easily elude clamoring 1-2-week-old chicks; older young chased the parent around the nest hush. Hence, between feeding bouts the adult flew a short distance away to rest, preen, or sunbathe.

After the nestlings were 3-4 weeks old, the parents were seldom seen with the young except when feeding them. Pratt (1970) reported parent Great Blue Herons stay away after the young are 28 days old; W^eber (^1975) found that 14-21 -day-old Cattle Egret chicks are left by themselves. Perhaps as the young Louisiana Herons got older, almost constant effort on the part of both })arents was recjuired to supply the developing juveniles with an adequate (juantity of fish. Siegfried ( 1972 ) found that Cattle Egret nestling growth curves are steenest (hence high food demands), and chick mortality due to starving is highest at the time when both parents switched from alternate to simultaneous hunting regimes. Also, young Louisiana Herons at this age were old enough to defend themselves. With 4-5-week-old juveniles, the par- ent did not land on its nest hush hut landed 2-5 m away, gave a series of calls and waited for its offspring to come to it. During this time, the parent exhibited moderate feather erection which increased slightly as the young approached to receive food. As food was transferred directly to the juvenile, both the parent and young herons rapidly flapped their wings to maintain an upright position. After feeding its brood, the parent stepped and faced away, then reswallowed any fish that remained in its mouth.

Because parent Louisiana Herons refused to feed many begging juveniles that approached them, I suspect that they were able to recognize their young, (/enerally, the young 3-4 weeks old were the ones that approached nonparents for food. I he older juveniles apparently learned to recognize their parents and probably by the process of habituation ( in the terminology of Thorpe 1963), they learned that they would not get food from hut would he at-

Rodgers • LOUISIANA HERON BEHAVIOR

tacked by a nonparent heron. Skead ( 1966 ) noticed adult-young recognition in the Cattle Egret.

The parents returned at irregular times to feed their young. The number of feedings was usually 4 or 5 per day. When the juveniles were 7-8 weeks old, the parent-young bond had disintegrated and the juvenile herons were on their own. The adult pair bond dissolved at the same time as the parent- young relationship. The parents were no longer observed together at the nest, which by this time had disintegrated and fallen through the mangrove.

Commonly 1 nestling ( less often 2 ) died in the nest. These were generally the youngest and therefore the smallest. Because they were at a physical dis- advantage in competing with older, more aggressive siblings for the limited amount of food, they became emaciated and starved to death. On Grand Is- land during 1973, I recorded a mortality rate from egg laying to the 2-week- old age of 22.5%. Of the 34 nests, 1 contained one nestling, 15 two nestlings, 17 three nestlings, and 1 had four nestlings. Jenni (1969 ) calculated a mor- tality rate of 35.8% for 28 nests for the same nestling period. Teal ( 1965 ) reported a mortality rate of 68% from egg laying until the young were fledged. I attribute most of the nestling mortality on Grand Island to starva- tion of the younger nestlings. I saw no evidence of predation by raccoons \Procyon lotor): Boat-tailed Crackles (Quiscahis major) destroyed some eggs in a small region of the heronry outside my study area. Nestlings oc- casionally died after becoming entangled in mangrove branches during wind storms or while wandering from the nest. A factor that may have contributed to the low mortality rate on Grand Island is that the Barataria Bay estuarine marsh is rich faunistically and provides a good nutrient source throughout the breeding season ( Day et al. 1973 ) .

SUMMARY

Observations on the l)reeding behavior of the Louisiana Heron were made in a large heronry on Grand Island, Barataria Bay, Plaquemines Parish, Louisiana. Male Louisiana Herons with breeding soft-part colors set up large territories initially. The male ap- peared tense at first but soon began performing Snap-Stretch and Circle Flight displays. Soon after establishing a core display site, a male constructed the foundation of the nest there. During the early courtship period the male defended his territory from both intruding males and females. As additional males entered the breeding cycle and females began to move through the heronry, the size of the male’s territory shrank.

At first a male threatened and chased away all females, but a persistent female was soon tolerated on the edge cf the territory. The freciuency of Snap-Stretch and Circle flight displays increased with time and in the presence of the female. With time, she was allowed closer and closer to the nest. Assuming the Withdrawn Crouch, the female was finally allowed onto the nest where copulation took place within a short time. Later the female was allowed to occupy the center of the nest and began final construction.

rilK W ILSON lUILLKTIN • VoL 90, No. I, March 1978

nil

'riic male hroii^lit twifis to tlu- ffinale on the nest as both engaged in tlie (Greeting dis- play and l>ill-nil)l)ling.

dlu* first eggs appeared 4 6 days after the initial copulation. On Cirand Island the average clutch size was 3.0 ( range rr: 2-.3. mode = 3, N=99). Both sexes incubated. When one mate returned, the pair engaged in the (Greeting display before the heron that was relieved fh'w off.

Both sexes fed the young, at fiist r(*gurgitating small fish onto the floor of the nest. Nestlings 2 weeks and older fed by grasping the hill of the parent. Adults brought food to the brood 4-5 times a day. Many of the youngest nestlings died of starvation; chicks of all ages occasionally died in accidents. A mortality rate of 22.4% was recorded for nestlings on Grand Island for the period from egg laying through the second week after hatching. The parent-young bond l)cgan to break down when the juveniles were 6-7 weeks old.

ACKNOWLEDGMENTS

This paper represents part of a thesis submitted in partial fulfillment of the require- ments for the M..*^. degree in the Department of Zoology and Physiology. Louisiana State I'niversity, Baton Rouge, Louisiana. I would like to thank George H. Lowery, Jr. of the Museum of Zoology for providing both assistance and direction during my graduate re- search. I am indebted to the Louisiana WildLife and Fisheries for furnishing me with e(|uipment and use of the Marine Biological Laboratory on Grand Terre. The Louisiana Ornithological Society awarded me a grant that helped defray the cost of research during 1973. Finally, I would like to thank my wife Linda for her assistance throughout the entire investigation.

LITERATURE CITED

Bent, A. C. 1926. Life histories of North American marsh birds. Bull. L.S. Natl. Mus. 135:1-490.

Blaker, I). 1969. Behaviour of the Cattle Egret Ardeola ibis. Ostrich 40:75-129.

C(JTTRiLLE, W. P., AND B. I). CoTTRiLLE. 1958. Great Blue Heron: behavior at the nest.

Misc. Publ. Mus. Zook, Univ. Michigan, no. 102.

Day, J. W., W. G. Smith, P. R. Wagner, and W. C. Stowe. 1973. Community struc- ture and carbon budget of a salt marsh and shallow bay estuarine system in Louisi- ana. Center for Wetlands Resources, Louisiana State University, LSU-SG-72-04. Huxley. J. 1922. Preferential mating in birds with similar coloration in both sexes. Br. Birds 16:99-101.

Jenni, I). A. 1969. A study of the ecology of four species of herons during the breed- ing season at Lake Alice, Alachua County, Florida. Ecol. Monogr. 39:245-270. -Meani.ey, B. 1955. A nesting study of the Little Blue Heron in eastern Arkansas. \\ ilson Bull. 67 :85-99.

Meyerriecks, a. j. 1960. Comparative breeding behavior of four species of North American herons. Publ. Nuttall Ornithol. Club, no. 2.

. 1962. In Handbook of North American birds, Vol. I (R. S. Palmer, ed.). Yale

Univ. Press, New Haven, Conn.

Palmer, R. .S., (ed). 1962. Handbook of North American birds, Vol, 1. Yale Univ.

Press, New Haven, Conn.

Pratt, H. M. 1970. Breeding ecology of (ireat Blue Herons and Common Egrets in central ('alifornia. Condor 72:407-416.

Rodgers • LOUISIANA HERON BEHAVIOR

59

Ridgway, R. 1912. Color standards and color nomenclature. Published by the author, Washington, U.C.

Rodgers, J. A., Jr. 1977. Breeding displays of the Louisiana Heron. W'ilson Bull. 89: 266-285.

Siegfried, W. R. 1972. I'ood reciuirements and growth of Cattle Egrets in South Africa. Living Bird 11:193-206.

Skead, C. J. 1966. A study of the Cattle Egret, Ardeola ibis, Linnaeus. Proc. Second Pan-African Ornithol. Congr., Ostrich Suppl. 6:109-139.

Teal, J. M. 1965. Nesting success of egrets and herons in Georgia. Wilson Bull. 77: 257-263.

Thorpe, W. H. 1963. Learning and instinct in animals. Methuen, London.

Weber, W. J. 1975. Notes on Cattle Egret breeding. Auk 92:111-117.

MUSEUM OF ZOOLOGY, LOUISIANA STATE UNIV., BATON ROUGE 70803. PRESENT ADDRESS: DEPT. OF BIOLOGY, UNIV. OF SOUTH FLORIDA, TAMPA 33620.

ACCEPTED 20 SEPT. 1976.

STATl'S AND NIJMKKICAL FLUCTUATIONS OF SOME NORTH AMFIHCAN WADERS AI.ONG THE SURINAM COAST

A kip: L. Spa ans

'i'hroufihoul the year, the muddy coast of Surinam (South America) forms a favorite haunt for large numbers of North American shorebirds (Haver- sclimidt 1955, 1968). This paper deals with the status, numerical fluctuations, and habitat selection of species that visit the Surinam coast regularly. Data were gathered from April 1970 through May 1973.

STUDY AREA AND METHODS

Study area.- The Surinam coast is situated on the northeastern fringe of South America at about 6° N latitude and between 54° and 57° W longitude (Fig. 1). Geographically, it forms a part of the Guiana coast, the nearly 2000 km of muddy and sandy shore of the Atlantic Ocean between the mouths of the Amazon and Orinoco rivers.

The coast of Surinam consists largely of vast tidal mud flats bordered on the higher paits by forests of black mangrove i Avicennia germinans) . The flats alternate in space and time from an accretion to an erosion coast; the succession of accretion and erosion has a cyclic character. For a relatively small area along the Guyana coast, Diephuis (1966) established that such a cycle takes about 30 years. The rapid succession of accre- tion and erosion has resulted in a rather unstable shoreline. In a few places, the coast is fringed with a narrow sandy beach. In 1971, 66% of Surinam’s 350 km shoreline was in accretion, 24% w^as in erosion, 4% was stationary, while 6% w^as fringed with a sandy beach ( P. A. Teunissen, pers. comm.).

The mud deposited along the Surinam coast originates from the Amazon. This river yearly discharges large amounts of fine sediments into the Atlantic Ocean, which are transported along the Guiana coasts by the Guiana Current. There the silt is deposited as a w^atery sediment, called “sling mud” (l)iej)huis 1966). These depositions result in the development of the tidal flats mentioned above. During exposure, the flats contain much water, and as a result, are very soft. In general, it is impossible for men to walk on them without sinking in. The flats are very rich in tanaids (Tanaidacea, Crustacea) and, during exposure, constitute a very important feeding habitat for North American waders.

Along the erosion parts of the coast, the littoral zone consists mostly of a narrow, firm, and tough hank of clay layers eroding from older deposits. Like the narrow' sandy beaches, these clay hanks are less attractive for waders, having a much lower bird density than the tidal flats.

Landward, the coastal fringe is bordered by a wide zone of shallow lagoons and of brackish herbaceous swamps, broken by several low and narrow, wooded sand or shell ridges lying parallel to the coast. The large complexes of lagoons also form an important feeding habitat for waders. The lagoons are former mangrove forests in which the Aiicennia has died in situ after prolonged inundation by sea water. For many years, the trunks of the dead mangroves are a dominant feature of the lagoons. After some time, the hare mud bottom of the lagoons may he covered by an herbaceous vegetation of halophytes, predominately saltw<»rt iBatis marilima) and sea purslane (Sesuvium portiilacastnim) . .Some lagoons have an extensive underwater vegetation of wigeon grass ^ Ruppia maritima) .

()0

Spaans • WADERS ALONG SURINAM COAST

61

Fig. 1. Map of the coastal area of Surinam showing the names of places mentioned in the text.

The water level in the lagoons and the feeding possibilities for waders are highly variable depending on the amount of precipitation, the freciuency of inundation by the sea, and the amount of evaporation. The brackish herbaceous swamps found behind the belt of mangroves are mainly covered by the spike rush i Eleocharis mutata) and other Cyperaceae. During most of the year, the water level in these swamps is too high for waders. In the long dry season, however, there are extensive shallow and muddy areas, which attract large numbers of shorehirds.

Climate. — Surinam has a tropical climate; throughout the year, the mean daily tempera- ture remains between 26° and 28°C. The amount of rainfall varies seasonally. Most rain falls in April to July (long rainy season) with the least rain in September to November (long dry season). Between November and April, there is a short rainy season (December and January) and a short dry season (February and March), both with a moderate mean monthly precipitation ( Meteorologische Dienst 1965). There is, however, much variation in the onset of the seasons, both between coastal and inland Iccalities, and between years. Table 1 shows the distribution of the monthly rainfall at the mouth of the Matapicakanaal for 1961-70 and 1970-73.

Data collection. — To obtain a picture of the fluctuations in bird numbers, 1 made 6 series of regular counts:

1. From April 1971 through April 1973, the numbers of birds present during low tide at a mud flat 10 km northwest of Paramaribo, locally known as “Weg naar Zee” (= road to the sea), were counted at approximately 2 week intervals for one or more days from a fixed point near the high tide water mark. The area surveyed had the shape of an isosceles triangle with the observer placed at the apex ( 18° ) on the shoreline while the low tide water mark formed the base. At low tide, the flat extended about 1 km seaward ( i.e. height of the isosceles triangle).

62

THE WILSON BULLETIN • Vol. 90, No. 1, March 1978

Table 1

Monthly Rainfall (mm) at Matapicakanaal

Jan.

Kvhr.

.March

April

-May

June

July

Aug.

Sept.

Oct.

Nov.

Dec.

1970

n.a.*

67

57

313

168

244

164

77

6

48

87

225

1971

252

179

134

130

5.50

149

161

n.a.

n.a.

n.a.

n.a.

83

1972

260

53

598

634

542

54

87

40

16

0

149

278

1973

2

27

11

67

197

1961-70

182

96

100

138

252

225

131

64

11

28

40

169

( means)

* n.a. — not available.

Most counts were made late in the afternoon, when the sun interfered the least witli observation. Occasionally, however, I made counts in the early morning. Counts were made with a 40 X 00 telescope. On most days, I made several counts hetw'een 1 h before and 1 h after low' tide, from which I calculated the average numbers of birds present that day. These average nundjers formed the starting point for further analyses.

2 and 3. From March 1971 through August 1972, I made counts at 2-4 week intervals in 2 lagoons near Krofajapasi, and from May 1971 through November 1972 in 2 lagoons near Motkreek. Both complexes of lagoons were situated just behind a sandy beach and received sea water during spring tides. On several counting-days during the long dry season, the lagoons near Krofajapasi were completely dry', with the result that many w'aders had gone to feed elsewhere. In contrast, on some days during the long rainy season, the water level was too high for most species of waders. The lagoons near Motkreek also had a highly variable water level, but since these lagoons w'ere never completely dry, the fluctuations in bird numbers during the long dry' season were less than in the lagoons near Krofajapasi. In the long rainy season, however, there were some counting-days with such a high water level that it must have had an unfavorable effect on the numbers of waders present.

The length of the route taken in the lagoons of Krofajapasi covered about .7 km, that in the lagoons near Motkreek about 3.5 km. The counts near Krofajapasi were made in the afternoon, those near Motkreek in the morning. Along both transects, waders were counted on both sides as far as they could be identified with certainty using 10 X 40 binoculars. At Krofajapasi, I also used a 40 X 60 telescope. .\s a result, the width of the area covered was not the same for each species, and thus interspecific comparisons cculd not he made.

4. From December 1970 through December 1971, at 2-4 week intervals, I counted waders around low tide along the nearly 8 km sandy beach east of Krofajapasi, locally known as “Bigi Santi'’ (= large beach). The counts were made between 06:00 and 09:00 (local time). This census included both the littoral zone, which was only some tens of meters wide, and the beach. The latter was mainly covered by ipomoea (Ipomoea pes- caprae) and sea bean {Canavalia maritirna). During the long dry season, patches of the vegetation were burned. During the entire census period, the eastern end of the beach was fringed on the seaward side with a narrow', firm and tough eroding clay hank. During the first 9 months of the counting period, this hank was only a few hundred meters long, hut after .Vugust 1971 it rapiilly increased to 1.5 km. Since the bird density on the clay

Spaans • WADERS ALONG SURINAM COAST

63

bank differed from that on the sandy beach, the numbers of birds counted in these habitats will he given separately from September 1971 onward.

5. From March 1971 through October 1972, at Krofajapasi at 2-4 week intervals, I counted the numbers of Spotted Sandpipers (Actitis macularia) flying down the creek to their nightly roosts outside the mangrove swamps. Counts were made from about 17 :00 until dark, which occurred between 18:20 and 19:00 depending on the time of the year.

6. From December 1970 through December 1971, Spotted Sandpipers were also counted along the nearly 6 km long Matapicakanaal. This canal runs through a former plantation area, now mainly covered by mangroves. The counts were made at various times of the day, and at various tide levels.

Presentation of the results. — The results of the censuses are given as mean numbers per counting-day in 10 or 15 day periods. The status of each species will he given by an estimate of the maximum number present at one day during the season (s) involved. These estimates have been obtained by extrapolation of the transect counts for the entire coast, adjusted by the percentages of suitable habitat. Considering the small number of transects counted and the small area of each habitat they covered, these estimates, of course, give only a very rough picture of the numbers of birds. As an index of abundance, the following scale has been used:

very large numbers —100,000 or more individuals large numbers — 50,000-100,000 individuals

rather large numbers — 10,000-50,000 individuals rather small numbers — 2500-10,000 individuals small numbers — 500-2500 individuals

very small numbers — 1-500 individuals.

Data on the status only refer to the numbers present in the coastal area landward up to and including the zone of brackish herbaceous swamps. For some species, therefore, the number of birds in .‘Surinam may he higher than the numbers mentioned here.

RESULTS

In the following list, an account is given of the occurrence of the species which visit the Surinam coast yearly. For each species, data on the status, habitat selection, and numerical fluctuations will be given:

Black-l>elliecl Plover iPluvialis squatarola) . — This species is present throughout the year in rather small numbers, possibly in rather large numbers. It can he observed everywhere along the coast, both on soft or hard mud, and on sandy substrates.

Numbers of any importance were counted in the transects of Bigi Santi and Krofajapasi only. In both transects, the species was present throughout the year. In neither of the transects, however, was a clear-cut seasonal trend observed.

American Golden Plover {Pluvialis dominica) . — This species is a transient in very small numbers from September through November. It is mainly a bird of dry inland areas. Along the coast, I observed the species on the sandy beach of Bigi Santi in an area where ihe vegetation had recently been burned,

61

THK WILSON iaJLIi:riN • VuL 90, No. 1, March 1978

SEMIPALMATED PLOVER

MONTHS

Fig. 2. Seasonal variations in numbers of Seinipalinated Plovers along the Surinam coast. A. Beach of Bigi Santi, January through December 1971. The numbers counted on the sandy beach are indicated by cross-hatching; those on the clay hank are unshaded. B. Lagoons near Krofajapasi, March 1971 through April 1972. A cross indicates that no water was in the lagoons. The numbers at the top of the columns show the numbers of counts on which each datum is based.

and in parts of the lagoons near Motkreek that had dried up, between 15 Sep- tember (1 bird) and 17 November (3 birds). My observation dates match rather well the period of fall migration mentioned by Haverschmidt (1969). L ntil now, the latest date for a fall migrant was 8 Nov'ember (Haverschmidt op. cit. ) .

Seiiiipaliiiated Plover [Charadrius semipalmatus) . — This species is present throughout the year in rather large numbers. It is mainly distributed along the coast where it shows a strong preference for tidal flats and muddy lagoons.

Data on numerical fluctuations are available for the beach of Bigi Santi and for the lagoons near Krofajapasi (Fig. 2). At Bigi Santi, the species was seen throughout the year, except for a period of 2 months from mid-June through August. A pronounced peak in numbers occurred during late fall and early winter. In the lagoons near Krofajapasi, the species was observed

Spaans • WADERS ALONG SURINAM COAST

65

throughout the year with the same peak during the fall and winter periods. After December, numbers fell rapidly, both at Bigi Santi and near Krofajapasi. Since the drop in numbers coincides with the onset of the short rainy season, and hence with an enlargement of feeding areas in the lagoons, I suggest that it reflects a dispersal of birds to other feeding areas rather than a departure from Surinam.

During the spring, numbers remained low with no peak representing the passing of spring migrants. However, a small increase in numbers occurred in June. Since tbe increase was also noticed in other lagoons of the Krofajapasi area, I suggest that it reflects the arrival of summer visitors, probably from the South, rather than a concentration of birds that did not migrate to the North.

Upland Sandpiper { Bartramia longicaiida). — Along the coast, this species is a transient in very small numbers in September and an irregular winter visitor. There, I observed it mostly on the sandy beach where the vegetation was rather open or where it had recently been burned. My sightings occurred between 1 September (2 birds) and 19 February (1 bird). Observation dates all fall within the period mentioned by Haverschmidt (1966).

Whimhrel {Numenius phaeopus). — This species is present throughout the year in rather small numbers with highest numbers from August through October. It is confined to muddy substrates along the coast.

None of the transect counts showed significant numbers. The statement on status mentioned above is based on (jualitative data from outside the transects.

Lesser Yellowlegs {Tringa flavipes). — This species is a transient and winter visitor in very large numbers from mid-July through early May and a summer visitor in small to rather small numbers. The species is one of the most abundant waders on the tidal flats and in the shallow lagoons and brackish herbaceous swamps. Further inland, it is also numerous on flooded ricefields.

Data on numerical fluctuations are available for the mud flat near Weg naar Zee and for the lagoons near Motkreek and Krofajapasi (Fig. 3). Near Weg naar Zee, numbers increased from late July through mid-August, after which they remained high until early April. Near Motkreek, an increase in numbers occurred from mid- July through early August, after which they remained high until early March. Numbers then decreased rapidly. Near Krofajapasi, a moderate increase in numbers was seen in mid- July, followed by a decrease in September and an absence until mid- December. This was probably a result of poor feeding conditions there. From December through February, numbers remained moderate, followed by a peak abundance during March.

It might appear from the above data that a mass arrival of southbound transients did not occur before August. This, however, is not true. Large

66

THE W lESON BULLETIN • VuL 90, No. 1, March 1978

LT)

Cxi

LU

QQ

MONTHS

Fig. 3. Seasonal variations in numbers of Lesser Yellowlegs along the Surinam coast. A. Mud flat near eg naar Zee, April 1971 through April 1973. B. Lagoons near Motkreek, October 1971 through November 1972. C. Lagcons near Krofajapasi, March 1971 through August 1972. An arrow indicates a very high water level in the lagoons. P indicates a partial count. Other conventions as in Fig. 2.

numbers arrive in July but evidently, few make a stop for any length of time. This was corroborated by observations of large numbers of Lesser Yellowlegs beading eastward along the coast in the second half of that month.

On the mud flat near Weg naar Zee the highest numbers occurred from August through December ( long dry season I and in the lagoons near Motkreek

Spaans • WADERS ALONG SURINAM COAST

67

and Krofajapasi from December through March (short rainy season and short dry season). This indicates a shift from the mud flats to the lagoons with the onset of the rainy season.

The drop in numbers occurring after March near Motkreek and Krofajapasi suggests a mass departure from March onward. This was corroborated by observations of Lesser Yellowlegs departing the Motkreek lagoons on 10 March 1973. Data from mid-May through early July indicate that the species is a regular but not numerous summer visitor.

Greater Yellowlegs {Tringa melanoleuca) . — This species is a transient in large numbers and a winter visitor in rather large numbers from mid-Septem- ber through early May; it is a summer visitor in rather small numbers. Like the former, this species shows a strong preference for tidal flats and shallow lagoons; further inland, it is also common on flooded ricefields.

Data on numerical fluctuations are available for the mud flat near Weg naar Zee and for the lagoons near Motkreek (Fig. 4). The species was seen throughout the year in both transects with peak abundances during September— October (Weg naar Zee ) , in March ( Weg naar Zee ) , and in April ( Motkreek j . The absence of a peak near Motkreek during the fall is somewhat puzzling. The peaks in fall and spring may coincide with the passage of southbound and northbound transients.

Solitary Sandpiper [Tringa solitaria). — This species is a transient and winter visitor in rather small numbers from late July through early May; it is possibly present in rather large numbers during the fall. Along the coast, this is mainly a bird of shallow lagoons and brackish herbaceous swamps; further inland, it is also a common visitor of freshwater pools and ditches, and of flooded ricefields.

I observed the species during the transect counts only occasionally. The statement on status mentioned above is based on qualitative data from outside the transects. My observations of a Solitary Sandpiper on 19 July 1972 and one on 9 May 1971 are tbe earliest and latest dates respectively, for this species in Surinam ( see Haverschmidt 1968 ).

Spotted Sandpiper [Actitis macularia). — This species is a transient and winter visitor in rather large numbers from early July through early June; it is a summer visitor in very small, local numbers. The species is not con- fined to the coast and may be found everywhere that water is present. Along the coast, it shows a preference for shallow and muddy lagoons, but it may also be commonly found along creeks and canals, on firm and tough clay banks emerging from eroding coastline, and on higher parts of mud flats. During fall migration, it is also numerous on sandy beaches.

(){\

I HK W ILSON BULLETIN • VoL 90, No. 1, March 1978

MONTHS

Fig. 4. Seasonal variations in numbers of Greater Yellowlegs along the Surinam coast. A. Mud flat near W'eg naar Zee, April 1971 through April 1973. B. Lagoons near Mot- kreek, October 1971 through November 1972. Conventions as in Fig. 2 and 3.

Data on numerical fluctuations are available for Krofajapasi, Matapicaka- naal and the beach of Bigi Santi (Fig. 5). The first fall migrants arrive (luring early July. The earliest dates, based on records from places where the species was absent in the weeks before, are: 2 July 1971 (2 birds), 5 July 1972 (8 birds; these birds must have arrived during the night since the species was still absent the day before at each place of observation), and 6 July 1970 (1 bird). After then numbers built up rapidly, reflecting a mass arrival of migrants. From August through May, the numbers of birds flying down Krofajapasi Creek fluctuated heavily; highest numbers were in January and lowest numbers were in September. Along the Matapicakanaal, the num- bers remained high through January with much lower numbers occurring dur-

Spaans • WADERS ALONG SURINAM COAST

69

SPOTTED SANDPIPER

0-^ 1 ^ ^ W . I ,

J FMAMJJASOND MONTHS

Fig. 5. Seasonal variations in numbers of Spotted Sandpipers along the Surinam coast. A. Krofajapasi Creek, March 1971 through October 1972. B. Matapicakanaal, December 1970 through December 1971. C. Beach of Bigi Santi, December 1970 through December 1971. Conventions as in Fig. 2.

ing the spring months. At Bigi Santi, numbers decreased sharply during September, indicating that the peak of fall transients passed through mainly in August and early September. During the spring months, no migration peak was observed in any of the transects.

During June, only few Spotted Sandpipers were seen, either in or outside the transects. Of my 14 observations (25 birds) in June, 8 (18 birds) were

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THK WILSON BULLETIN • VoL 90, No. I, March 1978

WILLET

2

< ■ 2 ^B2±1 ^ 1 J

^ j 1 ■■ 1 1 1 1

F M A M J J A S O MONTHS

N D

Fig. 6. Seasonal variations in numbers of Vi illets along the Surinam coast ( mud flat near \\ eg naar Zee, May 1971 through April 1973). Conventions as in Fig. 2.

the entire month. The other 6 records ( 7 birds) were from other places, and all fell in the first week of June. The latter, therefore, are likely to be late spring migrants rather than summer visitors. The data show, however, that near Krofajapasi Spotted Sandpipers were present during the whole month of June. I feel justified in considering these as summering birds. Only 2 June records have previously been reported ( Haverschmidt 19681 .

Willel (Catoptrophorus semipalmatus) . — This species is a transient in rather large numbers, possibly in large numbers, from early July through mid- August; it is present during the other months in rather small numbers. The species is confined to the coast where it shows a strong preference for tidal flats. During the fall migration, however, large flocks may also be encountered in lagoons that have dried up.

Data on numerical fluctuations are only available for the mud flat near Weg naar Zee ( Fig. 6 ). The species was seen here throughout the year with a peak abundance from late July through mid-August, after which the mean numbers fluctuated around a low level. In March (1973) and April (1972), the numbers counted were somewhat higher, perhaps reflecting the passage of small numbers of spring migrants.

From these data, it might appear that a mass arrival of southbound tran- sients did not occur before the end of July, hut this is not true. Elsewhere along the coast, the species was already numerous in mid-July. In 1972, I observed several flocks of 10-50 birds heading east at Eilanti as early as 4 July. Al- though peak numhers are over by late August, transients may pass until well into October.

of birds flying down Krofajapasi Creek during the routine counts throughout

Spaans • WADERS ALONG SURINAM COAST

l

SHORT- BILLED DOWITCHER

3

MONTHS

Fig. 7. Seasonal variations in numbers of Short-l)illed Dowitchers along the Surinam coast. A. Mud flat near Weg naar Zee, April 1971 through April 1973. B. Lagoons near Motkreek, September 1971 through November 1972. Conventions as in Figs. 2 and 3.

Ruddy Turnstone [Arenaria interpres ) . — This species is present throughout the year in rather large numbers. It can be found everywhere along the coastal shore where the substrate is firm.

Counts were made along the beach of Bigi Santi and in the lagoons near Krofajapasi. The numbers counted in these transects show no clear-cut seasonal trend, except for an increase during the fall and early winter on the elay bank at the eastern end of Bigi Santi coincident with an increase in the length of this hank. In neither of the two transects was there any indication of a migration peak in the northern spring. In both transects, rather fair numbers were present during the northern summer months.

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TllK WILSON lUILLKTIN • Vul. 90, No. 1, March 1978

Fig. 8. Seasonal variations in numliers of Red Knots Spooled data) along the Surinam coast in 1970-73. Conventions as in Fig. 2.

Short-hilled Dowiteher ( Limnodromus griseus) . — This species is a transient in very large numbers during the fall, from mid-August through early October, and during the spring, from early March through late May; it is a winter and summer visitor in small numbers. This species was found almost exclusively in lagoons and on tidal flats. On the latter, it showed a strong preference for the zone of sling mud near the low-water mark.

Data on numerical fluctuations are available for the mud flat near Weg naar Zee and for the lagoons near Motkreek (Fig. 7). Near Weg naar Zee, numbers were high from late summer through early fall and in the spring. Numbers were low during the northern winter, and the species was absent during the northern summer. Near Motkreek, highest numbers were seen in late summer and early fall, and lowest numbers were seen during the northern winter and summer. The low spring numbers probably resulted from high water levels during the long rainy season.

Red Knot \Calidris canutus) . — This species is a transient in small numbers from mid- August through late October and in early May; it is a summer and winter visitor in very small numbers. Most Red Knots were observed on firm and tough clay banks emerging from eroding coastline and in shallow lagoons. I never observed the species on the soft tidal flats.

Since the species was not observed freiiuently in any of the transects all observations of knots along the coast have been lumped to obtain an idea about its occurrence ( iMg. 8 l. 1 he species was seen throughout the year with peaks from August tb rough October, and in May.

Spaans • WADERS ALONG SURINAM COAST

73

Fig. 9. Seasonal variations in numbers of Sanderlings along the Surinam coast (beach of Bigi Santi, January through December 1971). Conventions as in Fig. 2.

Sanderling ( Calidris alba I . — This species is a transient and winter visitor in small, possibly in rather small numbers, with highest numbers in fall; it is a summer visitor in very small numbers. The species, confined to the coast, was almost exclusively found on sandy beaches and on firm and tough clay banks emerging from eroding coastline.

Data on numerical fluctuations are available only for the beach of Bigi Santi (Fig. 9). The species was seen throughout the year with highest num- bers from September through December. On an average, the lowest numbers were seen from May through August, but in one census ( 17 June 1971) 33 birds were counted — almost as many as the average number during the first three months of the year. In September, there was an increase in numbers on the sandy beach. Some tens of birds were also observed then on the clay hank fringing the shore at the eastern end of the beach, where the species had not been seen in the months before. On the sandy beach, numbers remained more or less constant throughout the rest of fall, except for a peak in the second half of September. However, on the clay hank, parallel to an increase in its length, numbers increased from October onward. A pronounced migration peak in spring was not observed, hut it should he noted that no data were available for April.

"I

TIIK WII.SUN ItUl.I.KTIN • VoL VO, No. I, .March I97R

SEMIPALMATED SANDPIPER

MONTHS

Fig. 10. Seasonal variations in numbers of Semipalmated Sandpipers along the Suri- nam coast. A. Mud flat near Weg naar Zee, April 1971 through April 1973. B. Lagoons near Krofajapasi, March 1971 through April 1972. Conventions as in Fig. 2.

S(‘nii|)aliiiat(Ml Sandpiper iCalidris pusilla) . — This species is a transient and winter visitor in very large numbers from mid-August through mid-June, and a summer visitor in rather large numbers, possibly in large numbers. The species is mainly confined to the coast, where it shows a strong preference for tidal flats and shallow lagoons.

Data on numerical fluctuations are available for the mud flat near Weg naar Zee and for the lagoons near Krofajapasi (Fig. 10). Numbers near

Spaans • WADERS ALONG SURINAM COAST

Weg naar Zee increased gradually starting about mid-August with peak abundance in early November, after which they decreased. During the north- ern winter, numbers fluctuated heavily with fewer present in January and February than in December. From late February onward, numbers were somewhat higher, with a small peak in early May. After this, numbers de- creased to the low summer level.

Near Krofajapasi, no increase in numbers was observed after