A Further Contribution

to Knowledge of the Host Relations

of the Parasitic Cowbirds

HERBERT FRIEDMANN, LLOYD F. KIFF,

and STEPHEN I. ROTHSTEIN

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 235
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SMITHSONIA N CONTRIBUTION S T O ZOOLOG Y • NUMBE R 235

A Further Contribution

to Knowledge of the Host Relations

of the Parasitic Cowbirds

Herbert Friedmann, Lloyd F. Kiff,

and Stephen I. Rothstein

SMITHSONIAN INSTITUTION PRESS

City of Washington

1977
ABSTRAC T

Friedmann, Herbert, Lloyd F. Kiff, and Stephen I. Rothstein. A Further Contribution to Knowledge of the Host Relations of the Parasitic Cowbirds. Smithsonian Contributions to Zoology, number 235, 75 pages, 1977.—A very large

amount of new information on cowbird parasitism, based on about 4750 instances reviewed since the senior author's 1971 addendum to his 1963 host

catalog, is here brought together. The data are presented in terms of the individual host species for each of the three species of parasitic cowbirds. In some

cases, especially of seldom used, or at least seldom reported, hosts, the additional

records supplement, but do not alter, our understanding of the host-parasite

relation; in some other cases the new data are of sufficient magnitude to support

convincingly a change of status. Also, in the case of some of the North American

host species, experimental studies of their reactions (as accepters or rejecters) to

the eggs of the parasites cause alteration from earlier estimates based solely on

empirical field observational data and help to define the nature of the hostparasite relationship more adequately and in a more meaningful way. Parasitism

by the brown-headed cowbird (Molothrus ater) is recorded for 26 species and

subspecies of birds not hitherto known to be victimized. In the case of the

Neotropical shiny cowbird (M. bonariensis) 32 new hosts are documented; for

the bronzed cowbird (M. aeneus) 7 new hosts are documented. In all, documentation, with such clarification as the new data permit, is given for 235 species of

hosts: 140 hosts of M. ater, 74 of M. bonariensis, and 21 of M. aeneus. In each

of these the new information is correlated with that presented in earlier papers,

so as to make the total current knowledge available to investigators studying any

one of these many species of birds in whose life histories the parasites may play

a major or even a very minor role.

OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded

in the Institution's annual report, Smithsonian Year. SERIFS COVKR DESIGN: The coral Montastrea

cavernosa (Linnaeus) .

Library of Congress Cataloging in Publication Data.

Friedmann, Herbert, 1900-

A further contribution to knowledge of the host relations of the parasitic cowbirds.

(Smithsonian contributions to zoology ; no. 235)

Bibliography: p.

Includes index.

1. Cowbirds. 2. Parasitic birds. 3. Birds-America. I. Kiff, Lloyd F., joint author. II. Rothstein, Stephen I., joint author. III. Title. IV. Series: Smithsonian Institution. Smithsonian

contributions to zoology ; no. 235.

QL1.S54 no. 235 [QL696.P2475] 591'.08s [598.8'81] 7&-608075
Contents

Page

Introduction 1

Methods and Procedures 2

Acknowledgments 3

Brown-headed Cowbird (Molothrus ater) 5

Discussion 5

New Hosts 5

Data Derived from Egg Collections 6

Nest Record Files and Their Biases 6

Methods of Dealing with Biases in Empirical Data 7

Designation of Species as Accepters and Rejecters 7

Other Problems in the Determination of the Cowbird's Host

Preferences 8

Data on the Effects of Parasitism 9

Data on Individual Host Species 10

Shiny Cowbird {Molothrus bonariensis) 51

Discussion 51

New Hosts 51

Data on Individual Host Species 52

Bronzed Cowbird (Molothrus aeneus) 64

Discussion 64

New Hosts 64

Dump Nests and Multiple Parasitism 65

Data on Individual Host Species 66

Depositories of Unpublished Data 69

Literature Cited 70

Index to Host Species Discussed 74

in

A Further Contribution

to Knowledge of the Host Relations

of the Parasitic Gowbirds

Herbert Friedmann, Lloyd F. Kiff,

and Stephen I. Rothstein

Introduction

The present paper brings together a vast amount

of new information documenting and clarifying

the relations existing between the many kinds of

victims of the several cowbird species and their

respective parasites. It is based on observational

and specimen data, supplemented by the results of

still continuing experiments conducted by one of

us (S.I.R.) over a number of years. It also critically

reviews data available from the recent work of

others in this currently very active field of research.

Even the mere accumulation of additional instances

of cowbird parasitism on some of the less well

documented host species, while often fragmentary

in nature and not always conducive to immediate

biological conclusions, has a value for investigators

of those individual species as well as a cumulative

value and meaning in the overall problems of

brood parasitism.

This report adds a very considerable number of

species and subspecies of birds to the previously

Herbert Friedmann, Director Emeritus, Museum of Natural

History of Los Angeles County; Research Associate, Smithsonian Institution; 350 South Fuller Avenue, Los Angeles,

California 90036. Lloyd F. Kiff, Western Foundation of

Vertebrate Zoology, 1100 Glendon Avenue, Los Angeles, California 90024. Stephen I. Rothstein, Department of Biological

Sciences, University of California, Santa Barbara, California

93106.

known hosts of three species of cowbirds, the brownheaded (Molothrus ater), the shiny (M. bonariensis),

and the bronzed (M. aeneus). As additional kinds

of birds are found to be victimized, it becomes

increasingly evident that mere additions are not

necessarily meaningful in themselves, except where

they are related to changes in the environment—

either as replacements of other hosts, or as hosts

newly available to the parasites because of recent

extensions of the geographical or ecological ranges

of the latter. As one example, out of a number

that might be cited, concerning the expanding

breeding range of the brown-headed cowbird, we

may mention southern Vancouver Island, an area

where the species was unknown prior to 1955, but

where it is now a very well-established and common summer resident (Davidson, 1966; Tatum,

1969, 1970). Evidence of this expansion is comprised by the many instances of parasitism, on a

dozen or so kinds of birds there, mentioned in this

report.

The biological problems raised by the intrusion

of a brood parasite into a new area or a new ecological zone have been discussed briefly by one of us

(Friedmann, 1971:249-250). In all such areas it

would be worthwhile to record the early host

choices and preferences, and those of subsequent

years, as well as the reactions of "new" hosts to the

parasites. By "new" is meant not merely additions
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

to previously recorded host species, but, primarily,

hosts (or even local populations of known hosts)

previously in no danger of cowbird parasitism.

The problems are difficult to evaluate because the

parasites are not individually host-specific, and,

therefore, are not density-dependent on any one

host species. Related problems exist in areas where

the cowbird population has grown very greatly,

causing critical damage to local potential hosts, as

in Michigan (Mayfield, 1960, 1973; Van Velzen,

1972) and the Edwards Plateau, Texas (Oberholser,

1974).

METHODS AND PROCEDURES.—Since the last addendum (Friedmann, 1971) to the 1963 host catalog by the senior author, we have reviewed 4750

additional instances of cowbird parasitism, well

over half of which, especially if not accompanied

by other pertinent data, are considered as merely

repetitive evidence of earlier information. The remainder are presented or summarized in this paper. Our basic interest in studying all these data is

to document and, where possible, to clarify the

mutual relations between the parasites and their

hosts.

There is still a need for increased and statistically

more significant information on the relative frequency with which many individual host species

are selected by the parasites, and on the incidence

of parasitism that each host experiences. This is

true for even some of the familiar hosts of the

brown-headed cowbird, the most completely documented of all the cowbird species. Reliable, quantitative data are needed before answers may be

formed to such critical questions as the following.

How much of the cowbird's total reproductive

output is provided by a particular host species?

By how much does the cowbird reduce a host

species' reproductive output? Questions such as

these are of primary importance in considerations

of the demographic processes occurring in nature

and in the possible evolution of adaptations for

and against parasitism.

It is anticipated that these quantitative aspects

of the nature of brood parasitism will be enhanced

in the future with the growth of a number of comprehensive "nest record cards" depositories. These

should eventually provide much larger masses of

information on all the hosts of the brown-headed

and the bronzed cowbirds than have been available previously. Most of these files, presently held

by organizations too understaffed to do more than

make token searches, should offer large, useful

(because nonselectively chosen) samples from which

to estimate the relative frequency with which each

of the regularly parasitized host species is victimized

since they will be in a position to yield not only

instances of parasitism but also the number of

unparasitized nests of each species reported during

the same period of years. Important qualifying

limitations inherent in data of this kind are discussed below in our account of the brown-headed

cowbird. Further, when the information from all

of these depositories is combined, it should be

possible to note geographic variation in the incidence of parasitism within each kind of host.

We have not been able to visit these various

filing centers personally, but, as outlined later, we

have gotten the greatest part of their data (with

one exception) though the cooperation of persons

affiliated with them. Only in the case of the Ontario records is there a published compilation (Peck,

1975). These sources have given us nearly half of

the material assembled in the present report.

Furthermore, we have been able, through the

efforts of one of us (L.F.K), to incorporate in this

paper all the pertinent data on the largest collection of birds' eggs in North America, that amassed

by the Western Foundation of Vertebrate Zoology

(abbreviated to Western Foundation in our annotated catalog). Other egg collections that were used

as sources for data in this paper are listed in "Depositories of Unpublished Data."

Large egg collections, such as that held by the

Western Foundation, composed of specimens from

many smaller private collections, show an unnaturally low incidence of cowbird parasitism. Conversations with some of the older oologists, and

statements in the oological literature from the turn

of the century indicate that some early collectors

had a marked preference for sets of eggs "uncontaminated" by cowbirds, and in exchanges between

collectors there was also a bias against parasitized

sets, as though they were less "complete" than

they otherwise might be. This bias may not have

affected rare species of hosts, and did not develop

in Neotropical collecting because of the relatively

small numbers of sets of such host species that

became available to individual collectors.

Even in collections chiefly involving Molothrus

ater, the data, while not necessarily reflecting ac-
NUMBER 235

tual rates of natural parasitism on the various host

species, do yield reliable information of a comparative kind. Thus, there is little reason to think

that any personal bias against cowbird eggs on the

part of the earlier egg collectors would have resulted in their gathering of more, or of fewer,

parasitized sets of one host species than of any

other. Whatever biases they may have expressed

were applied equally to sets of eggs of all host species. It is true that the end results, as they appear

today in such a vast assemblage of specimens from

many sources, are somewhat complicated by the

fact that a few collectors seem to have had some

interest in sets with cowbird eggs, but they were

outnumbered by others with a marked preference

for sets without them. In each case it seems the individual collector's attitude was consistent, regardless of the host species involved. Because the majority of them did prefer unparasitized sets, it

seems safe to say that in a corpus of material of

the magnitude of the Western Foundation's, any

host that there shows an incidence of parasitism of

over 10 percent can only be looked upon as a very

frequent host choice in nature. This is examined

in detail below, in our account of the brown-headed

cowbird.

Aside from considerations of host-parasite relations, we are also concerned with the recent accumulations of empirical observational data on

cowbird parasitism in general. In reporting these

data, we have correlated them with earlier estimates, principally with the senior author's 1963

book.

The new information is presented separately for

each of three species of cowbirds—the brownheaded (Molothrus ater), the shiny (M. bonariensis), and the bronzed (M. aeneus). We have no new

information to report on the screaming cowbird

(Af. rufo-axillaris), or the giant cowbird (Scaphidura oryzivora). Inasmuch as each of the three

species dealt with in this paper, as well as a great

many of their hosts, are polytypic, we have referred the various records to their proper subspecies, both of the parasites and of the hosts,

although we have stressed the species as the basic

biological taxon. At the start of the account of

each of the three cowbird species, we have included

a list of the hosts herein reported for the first time

for each of the subspecies of the parasites.

In the list relative to the brown-headed cowbird,

special mention is made in cases in which the

species discussed is known to be a rejecter (defined

below), and the experimental data for each are

summarized. These experiments are important in

uncovering various observational biases in the determination of the relative incidences of parasitism

these hosts suffer. Their significance is explained

in the "Discussion" at the opening of the section

of this paper dealing with the brown-headed cowbird. Aside from this work by one of us (S.I.R.), it

may be noted that in the course of his extensive

and illuminating work on the giant cowbird in

Panama, Neal G. Smith (1968) has done a considerable number of experiments on the reactions to

parasitic eggs by the limited number of hosts of

that cowbird. His complete report on the giant

cowbird will be a great addition to our knowledge

of brood parasitism in the family Icteridae. However, Scaphidura oryzivora is not as closely related

to Molothrus ater as are the other two species dealt

with in this paper. Experiments on the hosts of M.

bonariensis and M. aeneus are needed before any

meaningful comparisons may be made.

The nomenclature and sequence of the North

American birds involved in the present paper

follow the usage of the fifth edition of the American Ornithologists' Union's Check List of North

American Birds (1957), and the changes recommended in the thirty-second check-list supplement

(in Auk, 1973:411-419). We also follow Parkes and

Blake (1965), in placing Tangavius in Molothrus,

and in adopting the subspecific name loyei for the

northwestern race of the bronzed cowbird (M.

aeneus loyei, formerly M. aeneus milleri). Otherwise, we have not attempted to anticipate what

nomenclatorial changes may be recognized in the

sixth edition, still in preparation. The "common

names" of South American birds are taken from

the lists of Eisenmann (1955) and of Meyer de

Schauensee (1966). We continue to recognize melanogyna as a race of Molothrus bonariensis.

ACKNOWLEDGMENTS.—In the course of assembling the data for this paper, from sources other

than the literature, we have had the kind cooperation and assistance of many persons associated with

institutions possessing egg collections or files of

"nest record cards." (All such institutions are listed

in "Depositories of Unpublished Data.") Thus, we

have all the data, through 1974, in the files of the

Ontario nest records at Toronto, given us partly
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

by J. C. Barlow and R. D. James and completed

by Peck's 1975 tabulation of all the data included

there. Mrs. W. J. Smith kindly sent us all the cowbird records through 1973 from the files at the

University of British Columbia, Vancouver. We

have also had all the data through 1975 from the

Prairie nest records files at Winnipeg, where Mrs.

J. T. Barber supplemented the data supplied us

earlier by H. W. R. Copland and Dr. R. M. Hatch.

From the extensive files maintained at Cornell

University, Ithaca, New York, Mrs. Ruth Pantle

sent us computerized data from the parts of the

files available in that form, which parts are unfortunately limited in coverage. There must be a

large amount of additional information still to be

extracted from these files. In addition, a number of

private individuals generously sent us their records,

observations, or tangential information. To all of

these, listed alphabetically immediately below, we

express our thanks. Throughout this paper, wherever information is credited to any of these names, it

is understood that it reached us by personal communication, unless a publication reference is given.

G. D. Alcorn, University of Puget Sound, Tacoma, Washington; M. Alvarez del Toro, Tuxtla

Gutierrez, Chiapas, Mexico; Mrs. J. T. Barber,

Winnipeg, Manitoba; J. C. Barlow, Royal Ontario

Museum of Zoology, Toronto, Ontario; Dra. Nelly

A. Bo de Sorrentino, Museo de la Plata, La Plata,

Argentina; Dr. J. I. Borrero, Cali, Colombia; R.

Broder, Santa Barbara, California; J. Bull, American Museum of Natural History, New York, New

York; S. Burr, Corpus Christi, Texas; A. Galileu de

Miranda Coelho, Universidad Federal, Pernambuco, Brazil; H. W. R. Copland, Manitoba Museum

of Man and Nature, Winnipeg, Manitoba; Humberto G. Diaz, Museo de Historia Natural, Popayan,

Colombia; J. E. duPont, Delaware Museum of

Natural History, Greenville, Delaware; P. F. Elliott,

Kansas State University, Manhattan, Kansas; A. J.

Erskine, Canadian Wildlife Service, Ottawa, Ontario; S. Ervin, California State University, Fresno,

California; R. D. Etchecopar, Museum National

d'Histoire Naturelle, Paris; R. P. ffrench, St. Peter's

School, Pointe-a-Pierre, Trinidad; H. H. Frost,

Brigham Young University, Provo, Utah; R. K.

Furrer, Schwerzerische Vogelwart, Sempach, Switzerland; Alfredo Gepp, Montevideo, Uruguay; E.

Gerzenstein, Seattle, Washington; M. Gochfeld,

American Museum of Natural History, New York,

New York; R. R. Graber, Urbana, Illinois; T. W.

Haislip, Jr., East Linn, Oregon; Edward M. Hall,

Whittier, California; J. A. Hamber, Santa Barbara

Museum of Natural History, Santa Barbara, California; E. N. Harrison, Western Foundation of

Vertebrate Zoology, Los Angeles, California; D. R.

M. Hatch, Manitoba Museum of Man and Nature, Winnipeg, Manitoba; Jose Hidasi, Cuiaba,

Mato Grosso, Brazil; H. S. Horn, Princeton University, Princeton, New Jeresy; Gunnar Hoy, Salta,

Argentina; R. D. James, Royal Ontario Museum

of Zoology, Toronto, Ontario; J. R. King, Washington State University, Pullman, Washington; E. E.

Klaas, Iowa State University, Ames, Iowa; P. M.

Lais, Museum of Natural History, Oregon State

University, Corvallis, Oregon; D. W. Lamm, Tucson, Arizona; J. Lane, Hales Museum of Natural

History, Brandon University, Brandon, Manitoba;

E. K. Lemon, Victoria, Vancouver Island, British

Columbia; G. McCaskie, San Diego Natural History Museum, San Diego, California; R. McCracken, Corpus Christi, Texas; R. M. Mengel,

University of Kansas, Lawrence, Kansas; R. S.

Miller, Yale University, New Haven, Connecticut;

E. S. Morton, United States National Zoological

Park, Washington, D. C; S. Narosky, Lanus, Buenos

Aires, Argentina; R. W. Nero, Winnipeg, Manitoba; D. M. Niles, Delaware Museum of Natural

History, Greenville, Delaware; R. F. Norman,

Queens University, Kingston, Ontario; F. F. Nyc,

Jr., New Braunfels, Texas; Padre Antonio Olivares,

Universidad Nacional de Colombia, Bogota, Colombia; C. C. Olrog, Tucuman, Argentina; Gordon

H. Orians, University of Washington, Seattle,

Washington; Mrs. Rita Pantle, Cornell Univeristy,

Ithaca, New York; G. K. Peck, Royal Ontario

Museum of Zoology, Toronto, Ontario; O. S.

Pettingill, Wayne, Maine; W. H. Phelps, Jr., Caracas, Venezuela; A. Pistorius, Berkeley, California;

R. J. Quigley, Western Foundation of Vertebrate

Zoology, Los Angeles, California; R. J. Robertson,

Queens University, Kingston, Ontario; S. A.

Rohwer, Burke Memorial Museum, Seattle, Washington; S. M. Russell, University of Arizona,

Tucson, Arizona; P. A. Schwartz, Instituto

Neotropical, Caracas, Venezuela; N. J. Schmitt,

Western Foundation of Vertebrate Zoology, Los

Angeles, California; D. A. Schroeder, University
NUMBER 235

of California, Santa Barbara, California; H. Sick,

Museu Nacional, Rio de Janeiro, Brazil; Mrs. W. J.

Smith, University of British Columbia, Vancouver,

British Columbia; D. W. Snow, British Museum

(Natural History), Tring, England; D. E. Snyder,

Peabody Museum, Salem, Massachusetts; K. Steele,

University of California, Santa Barbara, California;

R. E. Stewart, Jamestown, North Dakota; J. B.

Tatum, Victoria, Vancouver Island, British Columbia; D. F. Tomback, University of California,

Santa Barbara, California; R. H. Wiley, University

of North Carolina, Chapel Hill, North Carolina;

and P. Woodward, University of Maryland, College Park, Maryland.

The Western Foundation of Vertebrate Zoology

generously contributed the costs involved in a

computer printout of data from the Cornell University nest record files. The University of California, Santa Barbara, supported the field studies

of one of us (S.I.R.), whose wife, Marian Rothstein,

assisted in typing his notes for use in this paper.

We are greatly indebted also to Mrs. Reese Hale

Taylor, for her generous volunteer work in typing

the present paper.

Brown-headed Cowbird

Molothrus ater

Discussion

Because of its abundance and its great geographic range in an area with many observers, we

have far more new information on this species of

cowbird than on the other two considered in this

paper. Also, it is the only one of these three species

that has been studied experimentally as yet, with

the result that it is possible to interpret some of

its host relations in greater depth and accuracy

than may be done for the others.

NEW HOSTS.—Some 6 species, or 26 species and

subspecies, new to its host catalog are herein reported, with their pertinent data, bringing the total

host list for this parasite up to 216 species, or 375

species and subspecies of birds. Aside from the 26

additions, there are some hosts that have been

found to be parasitized by races of the cowbird

other than those previously reported. As a result,

we have 7 new hosts for M. ater ater, 18 for M.

ater artemisiae, and 19 for M. ater obscurus.

Seventeen species are added to the list of victims

definitely known to have reared the young parasite: Tyrannus verticalis, Empidonax wrightii, Pyrocephalus rubinus, Auriparus flaviceps, Regulus

satrapa, Sturnus vulgaris, Vermivora celata, Dendroica townsendi, Dendroica striata, Sturnella

magna, Enphagus cyanocephalus, Carpodacus purpureus, Spinus psaltria, Pipilo fuscus, Ammodramus

savannarum, Zonotrichia leucophrys, and Melospiza lincolnii. This brings the total of true fosterers (as opposed to mere victims) up to 139 out

of the 216 species.

Hosts new to the previous lists are given below

for each race of the cowbird. Those that are new

to the total host catalog of the species are marked

by an asterisk.

New hosts for Molothrus ater ater: *Rallus limicola limicola, Actitis macularia, *Regulus satrapa

satrapa, *Dendroica striata, *Quiscalus quiscula

stonei, Passerina ciris pallidior, and Carpodacus

mexicanus frontalis.

New hosts for Molothrus ater artemisiae: Charadrius vociferus vociferus, *Empidonax hammondii,

* Empidonax wrightii, * Auriparus flaviceps acaciarum, Psaltriparus minimus minimus, *Vireo huttoni insularis, Vermivora chrysoptera, * Vermivora

celata celata, *Dendroica townsendi, Dendroica

castanea, *Dendroica striata, Icterus spurius, *Carpodacus purpureus californicus, *Spinus tristis

jewetti, Amphispiza bilineata deserticola, *Junco

hyemalis shufeldti, *Zonotrichia leucophrys pugetensis, and *Melospiza lincolnii alticola.

New hosts for Molothrus ater obscurus: Zenaida

macroura marginella, Tyrannus verticalis, Sayornis

phoebe, Sayornis saya saya, *Polioptila melanura

melanura, *Chamaea fasciata intermedia, Bombycilla cedrorum, Sturnus vulgaris vulgaris, *Vireo

huttoni carolinae, *Agelaius tricolor, * Icterus cucullatus californicus, *Pheucticus melanocephalus

maculatus, *Pipilo erythrophthalmus falcinellus,

*Pipilo fuscus crissalis, *Pipilo fuscus carolae, Spizella pusilla pusilla, Zonotrichia leucophrys nuttalli, *Passerella iliaca stephensi, and *Melospiza

melodia mailliardi.

Including these additions to the host catalog, the

new information brought together in this report
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

adds to, if only to a minor degree, or alters our

understanding of the host relations of the brownheaded cowbird with more than half (140) of its

known species of victims.

DATA DERIVED FROM EGG COLLECTIONS.—Mention

was made in our introductory paragraphs that

the vast number of parasitized sets of eggs in the

collections of the Western Foundation do not necessarily reflect actual rates of natural parasitism, but

do give us valuable comparative data. Inasmuch

as the greatest part of these records have to do

with the brown-headed cowbird, we may consider

them at this point. The detailed data from this

collection are given in the accounts of the individual host species. In some cases the numbers of

such sets are too small to be interpretable, but in

others it is possible to see some trends. The magnitude of the material may be appreciated from

the count that shows that brown-headed cowbird

eggs are present in 472 sets belonging to 35 commonly parasitized species, which, in turn, are

represented by a total of 7368 sets of eggs. There

are also 168 parasitized sets of less frequently reported victims.

In some species of hosts that have a large breeding range extending across the North American continent and that are represented in the collection by

sizeable numbers of sets of eggs, there is a higher

frequency of parasitism in the eastern than in the

western parts of their range. Examples are the yellow warbler with 85 sets of the eastern race (Dendroica petechia aestiva), 13 of which (15.3 percent)

are parasitized, and 228 sets of the western race

(D. petechia morcomi), with 13 (5.7 percent) parasitized; the yellowthroat, with 124 sets of its eastern

races, 13 (10.5 percent) of which are parasitized, and

159 sets of its western subspecies, 12 (7.6 percent)

of which have cowbird eggs; the cardinal, with 76

sets of the eastern, nominate race, 8 of which (10.5

percent) are parasitized, as compared with 104 sets

of the races Richmondena cardinalis magnirostris

and superba, 9 of which (8.7 percent) have cowbird

eggs; and the rufous-sided towhee, with 55 sets of

its eastern, typical subspecies, 9 of which (16.4 percent) are parasitized, as compared with 300 sets of

8 western races, only 2 of which (0.7 percent) are

parasitized.

Notable exceptions to this trend are the lark

sparrow represented by 33 sets of its eastern (not

as far east as in the above mentioned species) nominate form, none of which have cowbird eggs, and

195 sets of its western race (Chondestes grammacus

strigatus), 17 of which (8.7 percent) are parasitized;

and, to some extent, Wilson's warbler, which, in

the eastern part of its range, is largely restricted to

northern areas where neither cowbirds nor observers are abundant; of this species, 10 (6.8 percent) of 147 sets of the western race (WUsonia

pusilla chryseola) are parasitized, and none of 26

eastern sets have any cowbird eggs. Some species,

such as the American goldfinch and the song sparrow, show local variation in frequency of parasitism, but reveal no significant, broad, longitudinal

trends.

NEST RECORD FILES AND THEIR BIASES.—In earlier

papers on cowbird hosts, particularly of M. ater,

where published sources had given total numbers of

nests found, as well as the number that were parasitized, these figures were duly noted; there is no

need to repeat them herein. When all the large

"nest record cards" depositories are examined in

greater detail, these may become sources of supplementary information.

In his useful summary of the cowbird data in

the Ontario nest records files, Peck (1975:7) has

listed four factors that bias the apparent percentages of parasitism, all causing a lowering of the

figures: (1) host nest cards where contents were not

checked; (2) inability of observer to recognize cowbird eggs; (3) failure of contributor to make out a

second card for the cowbird; (4) resemblance of cowbird eggs to those of the host. To these we may

add a fifth, based on our experience, namely errors

in assembling data for computerization.

Even allowing for these factors, the data banks

of the main "nest record cards" files still present a

serious problem common to all data based on empirical studies of brood parasitism: observations

of natural parasitism may lead to incorrect conclusions concerning the actual incidences of parasitism. Given the dynamics of evolution, especially

of responsive behavior, it is reasonable to assume

that victimized species may develop reactions to, or

against, parasitism because of its effect on their own

reproductive output. If the reaction is against parasitism, and if this is manifested by ejection of the

cowbird eggs, it is clear that much parasitism will

go undetected, since many cowbird eggs will be

ejected before investigators ever see them. Thus,

cowbird parasitism on some species may be much
NUMBER 235

higher than suggested by observations. One of us

(Friedmann, 1963:133) emphasized this problem

when discussing brown-headed cowbird parasitism

on the northern (Baltimore) oriole. At that time

only 13 cases of parasitism were known, but in 3

of these instances cowbird eggs had been found on

the ground beneath the nests, indicating ejection

by the orioles. It was suggested that ejection "might

play a role in the apparent paucity of records of

cowbird parasitism." In assessing research on

cuckoo parasitism, one of us (Rothstein, 1971) has

more recently discussed the problems that may occur when frequencies of observed parasitism are

equated with frequencies of actual parasitism. Because of the possibility of host rejection, we must

be cautious in interpreting the significance of field

observations.

It should be stressed that even if observations of

a particular host species demonstrate little or no

ejection of parasitic eggs, it is by no means certain that ejection is unimportant in that species.

Inevitably, there is a strong bias toward seeing precisely those cowbird eggs that are not ejected. It is

conceivable that all, or nearly all, of the observations of cowbird parasitism on a particular host

species could appear to demonstrate acceptance

even if ejection were its typical response to parasitism, because only the acceptances would be observed.

METHODS OF DEALING WITH BIASES IN EMPIRICAL

DATA.—Fortunately, there is a partial solution to

this problem. By experimentally placing cowbird

eggs into nests one can determine accurately a species' response to parasitism and whether ejection

introduces a bias into interpretations drawn from

observations of naturally parasitized nests. Experiments allow an accurate determination of the frequency of ejection because the investigator can ascertain the fate of every cowbird egg in his sample.

One of us (S.I.R.) is conducting a systematic program of experimental cowbird parasitizations of

North American birds, using artificial, as well as

real, cowbird eggs. Results of experiments on 640

nests of 43 species are summarized (Rothstein,

1975a) and detailed analyses of experiments on

single species will be presented in other papers. In

general, the results of these experiments have

been surprisingly straightforward. Most (80.4 percent) of 245 rejections of experimental cowbird

parasitism were accomplished by the host ejecting

the cowbird egg from the nest. Smaller numbers

were accomplished by nest desertion, by damaging

(but not ejecting) the cowbird egg, or by burying

the cowbird egg under new nesting material. Because ejection was the most common form of rejection, or of host defense, the experiments indicate the host defenses can strongly bias quantitative

conclusions based solely on observations of natural

parasitism. Other modes of host defense, such as

nest desertion, do not introduce so serious a bias

because deserted nests retain the evidence of parasitism; the cowbird eggs are still present. However,

even nest desertion does introduce some bias. Desertion tends to deflate the number of cases of parasitism observed and to inflate the apparent percentage of acceptances because deserted nests are

less likely to be found than active ones, since their

builders are not around to call attention to them

by their behavior.

DESIGNATION OF SPECIES AS ACCEPTERS AND REJECTERS.—The experiments have demonstrated that

host rejections occur and can strongly conceal the

actual rates of natural parasitism. Besides this, the

experiments help to elucidate the critical point of

specific host response, in terms of acceptance and

rejection, that each species shows. Again the experimental results have been straightforward. Some

species show close to 100 percent rejection, i.e., rejection occurs in nearly all the experimentally

parasitized nests of the species. Other species show

close to zero rejection. No really intermediate species have been found, and a suitable statistical test

shows a highly significant tendency for all species

to show either total rejection or total acceptance

(Rothstein, 1975b). Accordingly, all host species may

be readily placed in one of two groups: rejecter and

accepter species.

These results have important consequences in

formulating estimates of rates of natural parasitism. As the experiments showed that nearly total

rejection or total acceptance is the rule, it follows

that observations of nests of rejecter species are of

little help in revealing actual rates of natural parasitism, whereas observations of nests of accepter

species provide reliable data. A few accepter species may show occasional rejections, but the frequency of this response is so slight that the bias,

while still real, is not very important statistically.

Experiments (by S.I.R.) have determined that the

gray catbird, American robin, eastern kingbird,
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

cedar waxwing, blue jay, brown thrasher, and

northern oriole are rejecter species (based on experiments on at least 10 nests of each species). The

western kingbird, less adequately tested (2 nests)

also seems to be a rejecter. Experiments on 10 or

more nests of each showed the following birds to

be accepter species: red-winged blackbird, common

grackle, eastern phoebe, chipping sparrow, yellow

warbler, mourning dove, barn swallow, black-billed

cuckoo, and American goldfinch. Experiments on

6 to 9 nests of each species, gave similar accepter

status to the song sparrow, cardinal, and wood

thrush; experiments on fewer nests (2 to 5 of each)

gave accepter responses for the rose-breasted grosbeak, mockingbird, vesper sparrow, eastern meadowlark, red-eyed vireo, prairie warbler, rufous-sided

towhee, rough-winged swallow, starling, house finch,

and yellow-headed blackbird. In some of the above

there is no reason to assume frequent cowbird

parasitism (common grackle, mourning dove, barn

swallow, black-billed cuckoo, rough-winged swallow, and starling) but the tests reveal that, if parasitized, they would react as accepters.

The species mentioned above are those whose

responses to cowbird eggs have been tested experimentally. While only experiments can help us to

determine reliably whether a species is a rejecter

or an accepter, the experimental results allow us

to decide, with a fair degree of certainty, the accepter status of some species that have not been

experimented upon and thus allow us to determine

whether observations of natural parasitism on these

species give a true or a biased picture. Inasmuch as

the experiments show a significant tendency toward

either almost total rejection or acceptance by each

species, it follows that in the absence of experimental data, a species can be assumed to be an accepter if a large proportion (more than 20 percent)

of its nests show natural parasitism and if this

parasitism is always, or nearly always, accepted.

This assumption is reasonable because if 20 percent or more of the nests show natural cowbird

parasitism that is accepted, then at least 20 percent

of the individuals must be accepters. No rejecter

species tested has shown more than 13 percent acceptance. Such an assumption may introduce occasional errors because a species with a moderate level

of rejection might show much cowbird parasitism

that was accepted and be designated incorrectly as

an accepter. But the assumption is valuable because errors are likely to be few, as results to date

indicate that truly intermediate species are very

rare or lacking. This allows us to categorize as accepters many species that have not yet been experimented upon. For example, no experiments have

been made on the Kirtland's warbler, the dickcissel,

or the lark sparrow, but these species have, in particular studies on large samples of nests, shown

rates of parasitism of 55 percent (Mayfield, 1960),

78 percent (Zimmerman, 1966), and 45 percent

(Newman, 1970), respectively. There can be little

doubt that these species are accepters. It should

be stressed, however, that no matter how much

natural parasitism has been observed on a species,

it is still worthwhile to test its reaction experimentally. Only experiments can determine accurately the frequency with which a species rejects,

and experiments will be essential in elucidating

the true nature of any species that may appear to

show an intermediate level of rejection.

Unlike species that are known to be frequently

parasitized, species found to be rarely or never

parasitized naturally, must be subjected to experiments to determine their rejecter-accepter status.

Species observed to be commonly parasitized are

almost certainly accepters, but species rarely found

to be parasitized may be either rejecters or accepters that are rarely parasitized, or they may be effective rejecters that are, in fact, parasitized quite

commonly. In such species the need for experiment

is essential, but experimentally induced cases of

parasitism cannot tell us how frequently rejecter

species are normally parasitized. Basically, we can

conclude that the incidence of actual parasitism of

a rejecter species must be higher than the incidence

of observed parasitism, but we cannot be certain

as to how much higher. It would seem to be maladaptive for cowbirds to parasitize rejecters, but

this, by itself, does not mean that such parasitism

is in fact insignificant in a quantitative sense.

OTHER PROBLEMS IN THE DETERMINATION OF THE

COWBIRD'S HOST PREFERENCES.—The above discussion shows how difficult it is to determine rates of

parasitism. But even if rates of actual parasitism

could be determined accurately for all species, the

data would not necessarily provide reliable information on another critical aspect of cowbird parasitism, namely the presence and strength of preferences cowbirds may have for particular host species. Rates of parasitism and host preferences may
NUMBER 235

not correlate well because the degree of preference

for a particular host species is not the only factor

determining the frequency with which the host is

actually parasitized. Given a choice, a cowbird may

strongly prefer a particular host species but may

rarely succeed in parasitizing it because the species

may have an especially well hidden nest or be especially effective at guarding its nest. Information

on nest crypticity could be gathered by analyzing nest sites and the areas surrounding them. Information on nest guarding could be gathered experimentally by testing the responses of hosts to

mounted or live cowbirds placed near nests. For

the present, it is sufficient to emphasize that the

unknown variables of nest crypticity and guarding

make it difficult to infer host preferences from rates

of parasitism. Importantly, Robertson and Norman

(1975), have recently begun a systematic investigation of nest guarding. By placing mounted cowbirds close to active nests during controlled

experiments these authors found that some species

react more strongly to cowbirds than to mounted

song, savannah, and house sparrows. Robertson

and Norman's work also indicates that within a

taxon the intensity with which accepter species

react to mounted cowbirds is directly proportional

to the intensity of parasitism suffered by each species. Further studies by these authors will be directed toward determining whether intensely parasitized species are most aggressive toward cowbirds

because natural selection has produced a stronger

innate response in such species or because these

species are so commonly parasitized that many individuals had had prior experience with cowbirds,

before Robertson and Norman's experiments, and

had learned that cowbirds are likely to interfere

with their nests. For our immediate purposes the

important point about Robertson and Norman's

work is that species may differ in the efficiency

with which they can repel cowbirds, and thus, even

if cowbirds have equal preferences for various

hosts, the amount of parasitism each host experiences may differ.

There are also the problems of equating cowbird and host preferences from data on rates of

parasitism. The need to equate densities of cowbirds (when comparing data from different areas)

is straightforward. Equating host densities when

comparing samples may be necessary because cowbirds may form search images for common host

species in the same manner in which some predators are believed to form search images for their

most abundant prey. Formation of search images

for hosts would, everything else being equal, result in common species being parasitized at a

higher rate than rare ones.

DATA ON THE EFFECTS OF PARASITISM.—Despite

the enormous numbers of publications on cowbird

parasitism, there are few species for which there

are data of sufficient quality and quantity to allow

an accurate determination of the effects cowbird

nestlings have on the host's own young. There are

also few host species for whose nests there are sufficient data on the success rates of cowbird nestlings. These data have great importance in theoretical considerations. The ecological and evolutionary

significance that cowbird parasitism has for a particular host species is proportional to the degree

of reproductive loss caused by each instance of

parasitism (Rothstein, 1975b). It follows that any

discussion of "reproductive strategy" by the cowbird must take into consideration the quality (from

the parasite's point of view) of the various hosts

available to it.

The paucity of data on the consequences of parasitism is due to the fact that it is much easier to

observe a nest once or twice and report whether

parasitism occurred than to visit a nest repeatedly

to weigh nestlings and to note the number and

condition of the nestlings. Notable exceptions to

this important deficiency in the cowbird literature

are studies on the song sparrow by Nice (1937),

Brewer's blackbird by Furrer (1974), the eastern

phoebe by Klaas (1975), Kirtland's warbler by Mayfield (1960), and the red-eyed vireo by Southern

(1958). Many other valuable studies have reported

the outcome at small numbers of parasitized nests

of other species but in general the data are still too

few. Perhaps the simplest, yet most effective, way

to report data is to use Southern's (1958) tabular

scheme. In a simple table Southern presented the

individual outcome, in terms of host and parasite

success, at each of 104 parasitized and unparasitized

nests. The value of this method is that it places on

record the crucial data for every nest and makes it

possible for the reader to conduct his own analyses.

Extensive analysis would not be possible if the data

were presented merely in summary form.

One of us (S.I.R.) is actively pursuing the experimental study of host reactions to cowbird
10 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

parasitism and has a number of further reports in

hand. Pending further elucidation of this sort, we

present the following new information based on a

large number of observations and of record specimens concerning a great many individual host species. It is our hope that the data here presented and

the questions discussed may stimulate others to further studies of the many problems raised by the

biology of brood parasitism.

Data on Individual Host Species

VIRGINIA RAIL

Rallus limicola Vieillot

On 7 June 1971 at McGarry Township, Kearns,

Ontario, Mr. J. S. Nickerson found a nest of a Virginia rail containing 8 eggs of the rail and 1 of the

brown-headed cowbird (Ontario nest records, Toronto). This is the first time a cowbird has been

reported laying an egg in a nest of this species.

The rail can only be looked upon as an accidental

host choice, an error on the part of the parasite.

KILLDEER

Charadrius vociferus (Linnaeus)

The killdeer, an obviously unsuitable bird as a

host for the brown-headed cowbird, has figured

hitherto in the host catalog of that parasite solely

on the basis of its inclusion in a list of cowbird

victims compiled by Oberholser prior to 1920.

When he was asked about it in 1921 he could not

recall the source or the locality of the record, but he

considered it to be valid and that it pertained to the

nominate race of the cowbird.

Recently Harold Mossop (1963) reported a cowbird's egg with 4 eggs of the killdeer in a nest of the

latter in Manitoba. On geographic grounds this

must involve the northwestern race of the cowbird,

M. ater artemisiae, for which it is a "first." The

fact that there is now a second "record" (both

without detailed data) does not alter the status of

the killdeer as a cowbird "host." It is to be looked

upon as a purely accidental involvement.

SPOTTED SANDPIPER

Actitis macularia (Linnaeus)

This unlikely host was first reported as a victim

of the brown-headed cowbird at Edmonton, Alberta

in 1964 (Friedmann, 1966:2) and since then, surprising as it may seem, 4 additional instances have

beeen reported: 1 from Utah (Friedmann, 1971:241);

another from Alberta (near Leduc, 5 June 1960)

and 1 from Manitoba (Lake Manitoba, 26 June

1970) reported by Hatch (1971); and 1 from Ontario (5 June 1965) in the nest records index at the

Royal Ontario Museum. The Ontario record is

the first one that involves the nominate race of the

parasite; the others all refer to M. ater artemisiae.

WILSON'S PHALAROPE

Steganopus tricolor Vieillot

To the 2 earlier records of this improbable victim parasitized in Utah (Friedmann, 1963:45) may

be added another from Manitoba. Hatch (1971:17)

found a nest of this phalarope at Watchorn Bay,

Lake Manitoba, about 10 miles west of Moosehorn,

Manitoba, 15 June 1970, containing 1 cowbird egg

and 4 eggs of the host.

MOURNING DOVE

Zenaida macroura (Linnaeus)

The number of records of parasitized nests of the

mourning dove continues to grow slowly, although

the dove is hardly a likely host species. To the

half dozen earlier records (Friedmann, 1971:241)

may be added 1 taken in Kent County, Delaware,

24 May 1958, now in the Delaware Museum of

Natural History, and another from Cameron

County, Texas, 22 May 1927, now in the collection

of Oregon State University. The last one is the

first record involving the small race of the cowbird

(M. ater obscurus).

Aside from the fact that this bird is, like all

doves, not suitable as a host for the cowbird, the

fact remains that when parasitized it accepts the

alien egg.

GROUND DOVE

Columbina passerina (Linnaeus)

A third record of this ground dove (subspecies

C. passerina pallescens) was collected by R. D.

Camp at Brownsville, Texas, on 24 May 1927, and
NUMBER 235 11

is now in the collections of the Western Foundation. A fourth instance, also from Cameron County,

Texas (not certainly from Brownsville), 4 June

1927, is in the collection of Oregon State University. The earlier 2 records were also from the

Brownsville area of Cameron County. Four records

from this area suggest that it is not unusual for the

dwarf cowbird to lay into nests of this dove, even

though such actions are not likely to be fruitful.

YELLOW-BILLED CUCKOO

Coccyzus americanus (Wilson)

A sixth instance of cowbird parasitism on this

species was reported from Kansas by "Woods"

(1972:14-15), a case observed 10 years earlier than

his published note. This record enlarges the geographical area over which such parasitism has been

found (the earlier records were from Connecticut,

Pennsylvania, Ohio, Illinois, and Michigan), but

the fact remains that the cuckoo is generally unmolested by the parasite.

BLACK-BILLED CUCKOO

Coccyzus erythropthalmus (Wilson)

A fifth case of parasitism on this rarely chosen

host can be added to the 4 reported previously

(Friedmann, 1971:242). One of us (S.I.R.) found a

nest, on 24 June 1969, that contained 2 young

cuckoos about 3 or 4 days old and 1 cowbird egg.

This was 1 of 14 cuckoo nests studied in 1968 and

1969 in Cheboygan and Emmet counties, Michigan.

On 27 June the cowbird egg was missing, but 2

half-shells from it were found almost directly beneath the nest. The half-shells were dried out,

indicating that the cowbird egg had hatched. Probably, since the usual food of cuckoos—bristly caterpillars—was unsuitable to the cowbird infant, it

died shortly after hatching and its dead body was

removed by the host.

EASTERN KINGBIRD

Tyrannus tyrannus (Linnaeus)

An uncommonly reported host choice, the eastern kingbird was known earlier (Friedmann,

1963:49) to have been parasitized only from some

15 records. To these we may now add 9 more: 2

from Illinois (Graber, Graber, and Kirk, 1974:8); 4

from Ontario (Ontario nest records files, out of 716

nests reported); 1 from North Dakota (R. E.

Stewart); 1 from Maryland (Delaware Museum of

Natural History); and 1 from Cincinnatus, New

York (Western Foundation). One of the Illinois

records is of a nest containing a large young cowbird which "probably" fledged.

In attempting to evaluate this increase in the

number of instances of parasitism on this flycatcher,

we must take into consideration the fact that one

of us (S.I.R.) has found the eastern kingbird to be

a rejecter species. Experiments at each of 33 nests

resulted in ejection of an artificial or real cowbird

egg. These experiments involved samples of the

kingbird population in Connecticut, Maryland,

Michigan, and Manitoba. Because ejection of the

alien egg is the typical response, it follows that

much of the parasitism that may be perpetrated on

this species would go undetected. This makes it all

the more remarkable that there should be as many

as 5 additional observed records since the 1963

compilation; this can only mean that the eastern

kingbird is victimized somewhat frequently.

The Illinois instance (above) of a well-developed

young cowbird in a kingbird's nest suggests that

the host's usual rejection reaction is to the newly

laid cowbird egg, and that if it is not then ejected,

the kingbird will tolerate and incubate it, and rear

the young parasite. Whether, in this particular instance, there was some physical or other obstacle to

removal of the egg is not known.

WESTERN KINGBIRD

Tyrannus verticalis Say

This rarely recorded host, originally listed (Friedmann, 1963:49) without a definite case, has since

been reported 3 times as a cowbird host. T. S. Smith

(1972) found a parasitized nest in York County,

Nebraska, in June 1971, from which a young brownheaded cowbird and a young kingbird were fledged.

A parasitized set of eggs of this kingbird from

Merced County, California, collected by H. R.

Eschenburg, 23 May 1936, is now in the Delaware

Museum of Natural History; another set, taken
12 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

in Wasco County, Oregon, 11 June 1933, is in the

collection of Oregon State University.

Smith's observation adds the western kingbird

to the list of victims known to raise the young of

the parasite. The Merced County, California, egg

record is the first for the southwestern race of the

cowbird (M. ater obscurus).

This species has been designated tentatively as a

rejecter. Artificial cowbird eggs were ejected from

the 2 nests to which they were added (Rothstein,

1975a). The paucity of observed cases of natural

parasitism agrees well with this rejecter behavior

of the western kingbird.

GREAT CRESTED FLYCATCHER

Myiarchus crinitus (Linnaeus)

To the 5 earlier records (Friedmann, 1963:50) of

this rarely reported victim may be added 6 more, 3

from New York (Bull, 1974:537) and 3 from Ontario (out of 201 nest records in the files at Toronto). The great crested flycatcher seems to be

protected from cowbird parasitism by its pugnacity

and by its habit of nesting in holes.

EASTERN PHOEBE

Sayornis phoebe (Latham)

In the collections of the Western Foundation is a

set of 4 eggs of this species with 1 of the dwarf

cowbird (M. ater obscurus), taken at Marble Falls,

Texas, 20 May 1940, by F. F. Nyc, Jr. Mr. Nyc informs us that in 1974 he found 2 more parasitized

nests near Blanco, Texas. These 3 are the first records for the eastern phoebe as a victim of this subspecies of the parasite. The eastern phoebe has

long been known to be very frequently parasitized

by the eastern, nominate, race of the brown-headed

cowbird.

Although over 600 records of this flycatcher as a

cowbird victim have been reported, in only a few

"source studies" were the totals given of the number of nests, parasitized or not, found by the reporters. One of us (Rothstein, 1975b) found 136

nests in Connecticut and Michigan. Of these, 28

(20.6 percent) were parasitized. A survey of published studies in which were given the total numbers of nests found, as well as the number with

cowbird eggs or young, revealed another 358 nests,

64 of which (17.4 percent) were parasitized. Klaas

(1975) has reported that parasitism occurred at 95

(24.3 percent) of 391 phoebe nests in Douglas

County, Kansas, and Schukman (1974) noted 6 out

of 66 nests (9.1 percent) were so affected in Ellis

County, Kansas. Inasmuch as a fairly large part of

these cases were early in the breeding season of the

phoebe (Friedmann, 1929:207), and inasmuch as

the incidence of parasitism probably decreases as

the season progresses (Friedmann, 1963:51), it is

likely that the early losses incurred by the host are

offset by gains made later in the summer.

Cowbird parasitism is extremely deleterious to

the eastern phoebe because of the great disparity in

the incubation periods of the 2 species. The cowbirds generally hatch 4 to 6 days before the phoebes.

Data on 19 parasitized nests followed to completion

show that only 6 phoebes were fledged, a rate of 0.3

host young per parasitized nest (Rothstein, 1975b).

Similarly, Klaas (1975:8) found that only 3 of 100

phoebe eggs resulted in fledglings in 39 nests in

which 1 or more cowbird eggs hatched and which

were not destroyed by predation, storms, or other

factors which bring about loss of an entire nest.

Besides these 3 host fledglings, parasitized nests

produced another 26 phoebes, but all of these were

from nests at which cowbird eggs failed to hatch.

Considering all sources of mortality, 46.0 percent

of 1203 phoebe eggs in unparasitized nests produced fledglings, while only 9.0 percent of 323

phoebe eggs in parasitized nests were productive.

As for cowbird eggs in Klaas's study, 41.7 percent

of 139 produced fledglings.

The frequency of parasitism on the phoebe varies

greatly in adjoining and not dissimilar areas. Thus,

in their detailed account of this flycatcher in

Illinois, Graber, Graber, and Kirk (1974:24-26)

state that while it is a common host choice in most

of the state, with 29 percent of the nests parasitized

in central Illinois, and 33 percent in a southern

part (north of Franklin County), yet in one extreme

southern area (south of Saline County), where 7

nests were studied, not a single one had any cowbird eggs or young. The collections of the Western

Foundation contain 90 sets of eggs of this species,

10 of which (11.1 percent) have cowbird eggs with

them. The nest records files at Cornell University

have data on 2679 nests from all parts of the

range of the eastern phoebe. Of these, only 121

(4.5 percent) were parasitized. The Ontario nest
NUMBER 235 13

records at Toronto show that 91 (9.1 percent) of

995 nests reported were parasitized.

In the northwestern part of its range—Saskatchewan and Manitoba—the eastern phoebe appears to

be seldom molested by the brown-headed cowbird;

in the Prairie Nest Records at the Manitoba Museum there are data on 177 nests of this flycatcher,

only 1 of which was parasitized.

SAY'S PHOEBE

Sayornis say a (Bonaparte)

Donald W. Lamm reported a nest of Say's phoebe

at Tucson, Arizona, 22 March 1973, with 3 eggs of

the host and 1 of the brown-headed cowbird (M.

ater obscures). When revisited later there were 3

young phoebes and no cowbird. This is the first

time Say's phoebe has been reported as a victim of

the southwestern race of the parasite. The small

number of previous instances (Friedmann, 1963:53)

all involved the nominate race. To these may be

added 2 more Kansas records: 1 from Oberlin,

Decatur County, 31 May 1909 (now in the collections of the Western Foundation); and the other

from Ellis County, 1974 (Schukman, 1974).

This species and the related black phoebe

(Sayornis nigricans) provide a marked contrast with

the eastern phoebe, as they are only seldom found

to be parasitized. Schukman's study provides some

direct, comparative data because he studied Say's

phoebe and the eastern phoebe in the same area.

The 1 parasitized Say's phoebe nest he found was

among 30 nests of that species studied, whereas 6

of 66 eastern phoebe nests in this area were parasitized.

ACADIAN FLYCATCHER

Empidonax virescens (Vieillot)

To the data previously available (Friedmann,

1963:53-54), which indicated that the Acadian flycatcher was a not uncommon host, but usually not

a very frequently chosen one in many areas, it may

be added that in Pope County, Illinois, a high

incidence of parasitism, as much as 50 percent (of

12 nests examined), was noted by Graber, Graber,

and Kirk (1974:35). This is higher than has been

found elsewhere, although in parts of Indiana and

of Pennsylvania this flycatcher is a regular, fairly

frequent host. Ontario may be added to the areas

where this flycatcher is known to be parasitized; 1

nest (out of a total of 24 reported) has been so recorded (Peck, 1975).

TRAILL'S FLYCATCHER

Empidonax traillii (Audubon)

The division of the "Traill's flycatcher complex"

into 2 species, the willow flycatcher, E. traillii, and

the alder flycatcher, E. alnorum, necessitates a review of the records of cowbird parasitism of the

former composite. So far as may be judged from the

data available (the original data slips, from which

the early (Friedmann, 1929) compilation was made,

are no longer available), most of the eastern records

appear to deal with the willow flycatcher. The alder

flycatcher, now restricted to the boreal forest region,

may be largely allopatric with the brown-headed

cowbird.

The following comments, therefore, refer to the

willow flycatcher portion of this complex. In their

detailed study of the flycatchers of Illinois, Graber,

Graber, and Kirk (1974:42) write that "Traill's flycatcher must be very uncommonly parasitized by

cowbirds in Illinois, as we know of but 1 other

record (Poling 1889) than the 1 reported by Friedmann (1963)." (The latter was a case found near

Chicago in 1947.) The absence of Illinois records is

certainly puzzling, particularly when we consider

the number of cases reported from nearby areas in

Michigan and Ohio. We have noted numerous

records subsequent to the 1963 compilation (Friedmann, pp. 54-55) from many areas, but none from

Illinois. Yet there is no dearth of nest records year

after year in Illinois for this flycatcher, and there

is no scarcity of cowbirds there.

The Western Foundation's collections contain

237 sets of eggs of this species, 20 of which (8.4

percent) are parasitized. Breaking this down by subspecies, there are 57 sets of nominate E. traillii, 7 of

which (13.7 percent) have cowbird eggs, and 186

sets of E. traillii brewsteri, 13 of which (6.9 percent)

are parasitized. This difference seems to be borne

out generally: the western populations of E. traillii

(E. t. brewsteri) experience only about half as

much parasitism as do the eastern ones (E. traillii,
14

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

possibly plus E. alnorum). The Cornell University

nest records files have entries on 130 nests of the

Traill's flycatcher (not broken down by races).

Only 6 (4.6 percent) of these were parasitized. In

Nebraska, Holcomb (1972:55) studied 88 nests of

this flycatcher; 7 of these (8.0 percent) were parasitized, but in none of them were any cowbird

fledglings produced. The Ontario nest record files

have data on 159 nests of the entire Traill's flycatcher complex. Of these, 27 (17.0 percent) were

parasitized. Of these 27 cases, 5 are definitely known

to refer to E. traillii and 1 to E. alnorum.

LEAST FLYCATCHER

Empidonax minimus (Baird and Baird)

To the relatively few (19 in Friedmann, 1963:55)

earlier records of this flycatcher as a victim of the

brown-headed cowbird, we may now add 20 additional instances, an increase of over 100 percent. In

1970, the least flycatcher was noted for the first time

in southern Vancouver Island, near Victoria, and

was found to be parasitized. This record involves

the parasite race M. ater artemisiae, as does also a

parasitized set of eggs from Alberta, now in the

collection of the Delaware Museum of Natural History. Also pertaining to M. ater artemisiae are 5

records of parasitized nests of the least flycatcher

in Manitoba, 1960-1971, in the files of the Prairie

Nest Records Scheme at the Manitoba Museum of

Man and Nature.

Two additional records for the eastern race of

the cowbird, M. ater ater, are: 1 from Marlboro,

Massachusetts, 2 June 1912, in the collections of

the Western Foundation; and 1 from Ontario in

the Ontario nest card files at the Royal Ontario

Museum of Zoology. Bull (1974:537) lists 7 instances of parasitism on the least flycatcher in New

York State; 6 of these are additions to the 1963

compilation. The Ontario nest records files at

Toronto have data on 151 nests of the least flycatcher and 3 of these (2.0 percent) were parasitized.

HAMMOND'S FLYCATCHER

Empidonax hammondii (Xantus)

E. M. Hall found a nest of this flycatcher containing 3 eggs of the host and 1 of the brownheaded cowbird (M. ater artemisiae) at Virginia

Lakes, Mono County, California, 29 June 1950.

This is the first time Hammond's flycatcher has

been reported as a victim of the parasite to our

knowledge.

DUSKY FLYCATCHER

Empidonax oberholseri Phillips

Previously known (Friedmann, 1971:242) as a victim of the brown-headed cowbird in California (1

record), Washington (1 record), and British Columbia (2 records), the dusky flvcatcher has now been

found to be parasitized in southern Alberta

(Kondla and Pinel, 1971), near Conquest, Saskatchewan (Prairie Nest Records Scheme), and near Jefferson, Colorado (Kingery, 1974:932). Also, 5 more

California records, all from Mono County, may be

added: a set of eggs taken 10 June 1934, now in

the Santa Barbara Museum of Natural History; 2

other parasitized sets, from June Lake, in the collections of the Western Foundation; and 2 instances

of parasitism observed (not collected) by Schmitt—

on 21 July 1973 near Poison Creek, and on 31 July

1973 near the Little Walker River—both of fledged

young cowbirds attended and fed repeatedly by

dusky flycatchers.

This rapid increase in the number of records

makes it apparent that the dusky flycatcher is a

fairly frequent host choice of the brown-headed

cowbird (race M. ater artemisiae).

GRAY FLYCATCHER

Empidonax wrightii Baird

Yaich and Larrison (1973:14-16) found a nest of

this flycatcher at Wenas Park, 10 miles from Naches,

Washington, 26 May 1972. The following day a

brown-headed cowbird laid an egg in it alongside

the 2 eggs of the host. This is the first record in

print for this species as a cowbird victim. Mr.

R. M. Lais informed us that another parasitized

nest was found in the Malheur Lake area, central

Oregon, by T. W. Haislip. In reply to request for

more explicit data on this record, Mr. Haislip generously expanded it, as follows. In 1970 and 1971,

in the western juniper woodlands of central

Oregon, he found the gray flycatcher to be the

most abundant breeding bird, averaging about 25

pairs per 100 hectares (cowbirds averaged about 3

"pairs" per 100 hectares). Of 28 nests found, 7 were

parasitized; there was 30 percent parasitism in
NUMBER 235 15

1970, and 20 percent in 1971. Of the 7 parasitized

nests only 3 fledged a single cowbird apiece. In

none of the 7 did any of the host young survive,

and in no nest was more than a single cowbird egg

found.

It appears that the gray flycatcher is a regular

host choice of the brown-headed cowbird in central

Oregon, and probably is more affected elsewhere

than the absence of published records would indicate.

WESTERN FLYCATCHER

Empidonax difficilis Baird

The report of two additional instances of cowbird parasitism on the western flycatcher at Victoria, southern Vancouver Island, by Lemon (1969)

bears out the inference derived from earlier cases

in that area that this species is probably regularly

affected by the parasite. Since Miss Lemon's paper,

still another similar case has been reported from

the same area on 29 August 1970, a very late date,

but considered a valid record by the group of

observers at Victoria. In California, from whence 7

records were formerly known (Friedmann, 1963:55-

56) 4 more are now added, 3 from Santa Clara

County, all presently in the collections of the Western Foundation, and 1 from Solvang, Santa Barbara

County, in the Santa Barbara Museum of Natural

History.

While the records of cowbird parasitism are increasing in number, the western flycatcher does

seem to enjoy a very low frequency of this intrusion, compared to other members of its genus. Of

157 sets of eggs of this species in the Western Foundation, only 6 (3.8 percent) contain cowbird eggs.

This relative immunity may be due to the bird's

choice of nest sites—cliffs and manmade structures,

such as barns and bridges. In this the western

flycatcher is similar to the western species of Sayornis and the house finch, which use similar nest

sites, with similarly slight cowbird parasitism.

WESTERN WOOD PEEWEE

Contopus sordidulus Sclater

To the 7 earlier records of this flycatcher as a

victim of the brown-headed cowbird (Friedmann,

1963:57; 1971:242) may be added 2 more: a set of 2

eggs of the host and 1 of the parasite (subspecies

M. ater obscurus) taken at Santa Paula, Ventura

County, California, 7 July 1934; and another (involving the cowbird race M. ater artemisiae) at

Mammoth, Mono County, California, 29 June 1974.

Both records involve the host subspecies C. sordidulus veliei, and both sets of eggs are now in the

collections of the Western Foundation.

OLIVE-SIDED FLYCATCHER

Nuttallornis borealis (Swainson)

A fourth instance of this flycatcher as a cowbird

victim was noted in southern Vancouver Island,

British Columbia, in 1969: a nest containing 3 eggs

of the host and 1 of the parasite, reported to us by

Dr. J. B. Tatum. The 3 earlier records were from

Alberta and Mono County, California (Friedmann,

1963:57).

VERMILION FLYCATCHER

Pyrocephalus rubinus (Boddaert)

Previously reported as a victim of the brownheaded cowbird a small number of times in Texas,

Arizona, and California, the vermilion flycatcher

has recently been found to be parasitized at Redrock, Gila Valley, southwestern New Mexico

(Hubbard, 1971:25), where, on 13 June 1968, a male

vermilion flycatcher was watched repeatedly feeding a recently fledged young brown-headed cowbird.

In addition to this record, 3 others—2 of them from

Imperial County, California, and 1 from Huachuca

Plains, Arizona—are in the collections of the Western Foundation, and 2 from Tucson, Arizona,

are in the Santa Barbara Museum of Natural History. All the records from southwestern New Mexico west to California involve the host race P.

rubinus ftammeus and the cowbird subspecies Af.

ater obscurus.

HORNED LARK

Eremophila alpestris (Linnaeus)

Kondla and Pinel (1971) noted the horned lark

as a cowbird victim in southern Alberta, the fourth

instance known to us of parasitism on the lark

race E. alpestris leucolaema. Previously we knew

but a single record for the subspecies E. alpestris
16

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

enthymia, to which may now be added 9 more: 4

from Manitoba (3 in the Prairie Nest Records

Scheme, and 1 from Lake's End, Manitoba, in the

collections of the Western Foundation), and 5 from

North Dakota, reported to us by R. E. Stewart. In

this latter area the 5 parasitized nests constituted

19.2 percent of a total of 26 active nests noted, a

much higher incidence of parasitism than has been

reported elsewhere for the horned lark. In 1 of

these nests there was excessive multiple parasitism

—6 cowbird eggs with 2 of the host's. In New

York State, Bull (1974:537) reports 2 parasitized

nests of E. alpestris praticola. The Ontario nest

record files at Toronto reveal that 5 (4.2 percent)

of 119 nests reported from that province were parasitized. The Cornell files contain 1 record of a

parasitized nest, from Holstein, Nebraska.

BARN SWALLOW

Hirundo rustica Linnaeus

A parasitized nest of this uncommonly victimized

bird was collected in McHenry County, North Dakota, 1 July 1931, and is now in the Santa Barbara

Museum of Natural History. This is only the second record for the barn swallow (race H. rustica

erythrogaster) as a host of the northwestern race of

the brown-headed cowbird, M. ater artemisiae, the

previous one being from Manitoba (Friedmann,

1971:243). To the few instances of parasitism by

the nominate race of the cowbird known earlier

(Friedmann, 1963:59-60) may be added 2 from

Ontario (Peck, 1975:10), and a parasitized set of eggs

collected in St. Marys County, Maryland, now in

the Delaware Museum of Natural History.

Inasmuch as the barn swallow has been found

experimentally to be an accepter species, the small

number of observed instances of parasitism on it

indicates that it is really very infrequently victimized by the cowbird. This is borne out by the fact

that in the nest records files at Toronto, the 2 Ontario records were the only ones out of 1977 nests;

in the files at Cornell University, of 3676 nests reported, none were parasitized.

BLUE JAY

Cyanocittn cristata (Linnaeus)

The blue jay is a rarely reported victim; in the

1963 review (Friedmann, p. 61) only 3 (possibly 4)

records were known. Our purpose in discussing it

here is merely to point out that it is a rejecter

species. Artificial or real cowbird eggs were experimentally placed in 24 nests in Connecticut; these

were ejected by the jays from 22 of them. The 2

remaining nests were deserted. A similar experiment on 1 nest in Michigan resulted in an ejection

(Rothstein, 1975a). Whether the small number of

known cases of parasitism on this species is due to

a low rate of actual parasitism, as well as to the

observational bias caused by egg ejection, remains

to be determined. Purely casual observations, unreliable as they may be, suggest that the blue jay

is too large and too aggressive for the cowbird to

parasitize to any extent; in other words it seems

likely that the actual incidence of parasitism is

low.

BLACK-CAPPED CHICKADEE

Parus atricapillus Linnaeus

Previously (Friedmann, 1963:62; 1966:2) only 5

instances were known to us of this bird as a cowbird victim. To these may be added another, from

Ontario, the only nest parasitized out of 223 active

nests reported to the Ontario nest records files at

Toronto.

VERDIN

Auriparus flaviceps (Sundevall)

Austin (1970:432) observed a fledged young

brown-headed cowbird (M. ater artemisiae) attended

and repeatedly fed by a verdin in southern Nevada.

This is the first record for the subspecies A. flaviceps acaciarum as a cowbird host; there were earlier

records for the eastern race, A. flaviceps ornatus

(reported as A. flaviceps annexus in Friedmann,

1963:64). All of the few earlier records were of

eggs only; the present case is the first one of a

verdin rearing the young cowbird.

BUSHTIT

Psaltriparus minimus (Townsend)

To the 5 earlier records of this bird as a cowbird

victim (Friedmann, 1963:64; 1966:3) may be added
NUMBER 235 17

2 more: 1 observed near Victoria, British Columbia

(Crowell and Nehls, 1973:911), and 1 at North

Saanich, Vancouver Island, 10 June 1973, observed

by Stuart Johnston. On geographic grounds these

records must refer to the nominate race of the

bushtit and to the subspecies M. ater artemisiae of

the parasite; they are the first records for that race

of the cowbird parasitizing the bushtit.

In the case of the record from North Saanich,

the nest had been under observation since 1 June,

but was found to be damaged, with the entrance

enlarged, on 10 June. By 13 June, it was evident

that the bushtits had deserted. The nest was then

examined and was found to contain three bushtit

eggs and one cowbird egg; the nest and eggs are

now in the British Columbia Provincial Museum.

WHITE-BREASTED NUTHATCH

Sitta carolinensis Latham

This rarely used host was previously (Friedmann,

1963:64-65) known as a cowbird victim only 5

times, from Pennsylvania, Illinois, and New York

(once). Bull (1974:537) mentions 3 New York instances, 2 of which are obviously additions to our

earlier records.

WRENTIT

Chamaea fasciata (Gambel)

Baptista (1972:881) noted a pair of wrentits attending a fledged young brown-headed cowbird at

Lake Merced, San Francisco, 21 July 1969. He

correctly allocated this record to the subspecies

C. fasciata intermedia, the first one reported for

that race as a victim of the cowbird (M. ater obscurns). Baptista also reported two additional instances of cowbird parasitism on the subspecies C.

fasciata rufula, observed by Stewart in the Point

Reyes Bird Sanctuary, 3.5 miles south of Bolinas,

Marin County, California. One of these cases is

reported in greater detail by Stewart, Chamberlain,

and Story (1971:1004): on 18 May, the nest contained 3 eggs of the wrentit and 1 of the cowbird;

on June 9 it contained only the young parasite,

which fledged on the following day.

There are still less than a dozen recorded instances of the wrentit as a cowbird victim, but no

less than 3 races of the host are involved in them.

BEWICK'S WREN

Thryomanes bewickii (Audubon)

This wren is seldom reported as victimized by the

brown-headed cowbird, but 4 of its subspecies—

T. b. bewickii, T. b. cryptus, T. b. altus, and T. b.

calophonus—are involved in the 8 previously

known instances (Friedmann, 1971:243). We may

now add 6 more records, as follows. To the single

previous case of T. b. calophonus as a victim

(Friedmann, 1971:243) may be added 4 more:

Lemon (1969:395) found a parasitized nest at Victoria, southern Vancouver Island, on 12 June 1967,

and 3 additional cases from the same area since

then have been reported to us by J. B. Tatum,

suggesting that in southern Vancouver Island this

wren may be more frequently parasitized than it is

known to be elsewhere. In the nest reported by

Lemon, the wrens reared the young parasite but

none of their own young.

A third record for the nominate race of the

wren, observed in Tennessee (Cornell University

nest record cards), is also mentioned in Lemon's

paper. Finally, an additional instance of the race

T. b. cryptus as a cowbird victim is a parasitized

set of eggs, taken at San Angelo, Tom Green

County, Texas, 30 April 1954, in the collection of

the Delaware Museum of Natural History.

CAROLINA WREN

Thryothorus ludovicianus (Latham)

Previously (Friedmann, 1963:39, 68) this uncommonly selected host had been known on 1

occasion, out of a dozen instances of parasitism, to

rear a young cowbird to the fledging stage. A new

observation indicates a much greater successful

host potential for this wren. Luther (1974) reported a nest in which no fewer than 3 of the young

parasites were reared to the fledging stage, an unexpected proof of the ability of a pair of these

wrens to raise, not I, but 3 nestlings, each larger

than their own. There were originally 2 young

wrens in the nest as well, but they died early in

the competition for food with their parasitic nestmates.

At the time of the 1963 compendium (Friedmann, p. 68) only 14 instances of cowbird parasitism on this wren were reported. To these may
18

be added the following. In Anne Arundel County,

Maryland, in 1973 and 1974, Paul Woodward, together with Eugene S. Morton, found 13 nests of

this bird, 9 in "natural" settings and 4 on manmade structures. Of these, 5 (all nests in natural

sites) were parasitized, and each of these fledged 1

or more young cowbirds but no young wrens. The

failure of the wren nestlings may be due to the

much longer incubation period of their species,

giving too great an advantage to the more rapidly

developing parasites. In Ontario the Carolina wren

appears to be free of cowbird parasitism (16 nests

reported to the files at Toronto, none with cowbird eggs).

GRAY CATBIRD

Dumetella carolinensis (Linnaeus)

Before the experimental studies discussed earlier

in this paper, the gray catbird and the American

robin were the only species known to eject cowbird eggs frequently. But the actual incidence of

ejection was not known. Experiments on 53 catbird

nests resulted in 50 (94.3 percent) ejections. The

cowbird eggs in the 3 remaining nests were accepted. The experiments were conducted in Connecticut, Manitoba, Nebraska, Michigan, and Maryland (Rothstein, 1975a).

Experiments on 17 additional nests show that

after egg laying has ceased, catbirds correctly distinguish between their own and foreign eggs in a

number of different contexts. Catbirds always

ejected cowbird or other types of foreign eggs even

when these egg types outnumbered the catbird's

eggs or were the only types present (Rothstein,

1975c). These experiments were done to test

Rensch's (1925) question of whether birds that reject parasitic eggs actually recognize either their

own or the parasitic egg, or whether they simply

reject the egg type that is in the minority. In nearly

all cases the parasitic egg is in the minority, so

rejection could function efficiently as a host defense even if birds did not recognize their own or

a parasitic egg. Contrary to the generally held belief, the experiments showed that catbirds do indeed "know" the appearance of their own eggs.

Other experiments (Rothstein, 1974) suggested that

catbirds learn the appearance of their egg type from

the first egg(s) they lay and that it is possible to

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

"teach" a catbird that a cowbird egg is its own egg

type if eggs are experimentally switched shortly

after laying begins.

The Ontario nest records files at Toronto include

9 instances of cowbird parasitism on the gray catbird; these constitute 1.3 percent of 707 nests reported; the files at Cornell University record 4

instances (out of 367 nests in all), 3 from Michigan

and 1 from Kentucky.

BROWN THRASHER

Toxostoma rufum (Linnaeus)

Experiments showed this species to be a rejecter.

Artificial or real cowbird eggs were ejected from 25

nests and accepted at only 1 (Rothstein, 1975a).

These experiments were conducted in Connecticut,

Nebraska, Michigan, and Manitoba. It was not

previously known that the brown thrasher typically

ejects cowbird eggs but there are at least 5 known

cases in which naturally deposited cowbird eggs

disappeared from thrasher nests (see Rothstein,

1975a, and Graber, Graber, and Kirk, 1970:30). In

1 instance reported by Mengel and Jenkinson

(1970) the investigators believed that the cowbird

rather than the thrashers removed the cowbird

egg. But because Mengel and Jenkinson did not

actually see the cowbird remove her own egg and

because their belief is based on only 1 nest, their

suggestion that cowbirds remove their own eggs is

in need of further substantiation. Whether thrashers alone or cowbirds and thrashers remove cowbird eggs, it is clear that the amount of parasitism

detected is only a fraction of the actual parasitism

that occurs. Graber, Graber, and Kirk (1970) detected parasitism at 2 percent of all brown thrasher

nests in their study area of northern Illinois. This

sounds like a very low figure until the biases are

accounted for. The 2 percent of thrasher nests

recorded as parasitized were probably ones at

which acceptance (as well as parasitism) occurred;

parasitism was unlikely to have been detected at

other nests where ejection occurred. The experiments cited above showed that acceptance occurs

at only 1 in 26 nests. This means that if each of the

2 percent of the nests recorded as parasitized was

an acceptance, then the actual rate of parasitism

was about 26 times as high, or 52 percent. If only

half the nests observed to be parasitized resulted
NUMBER 235 19

finally in acceptances, then the actual rate of parasitism was 26 percent.

The brown thrasher is the only rejecter species

discovered so far that may on occasion have difficulty distinguishing between its eggs and those of

the cowbird. Thrasher eggs are larger and are

evenly marked with fine speckles throughout their

surface while cowbird eggs have fewer but larger

speckles that are often concentrated at the wider

pole. Unusually large cowbird eggs with a thrasherlike maculation, however, are sometimes found

(S.I.R., pers. observ.). If thrashers, on occasion,

have difficulty distinguishing cowbird eggs from

their own eggs, then the experiments may have

slightly overestimated the rate of rejection that

would occur in natural parasitism because the artificial and real cowbird eggs used in the experiments were strongly distinct from thrasher eggs.

The experiments, however, still provide a reliable

measure of the frequency of thrasher nests at which

rejection of nonmimetic eggs occurs. P. F. Elliott,

moreover, has informed us that in Riley County,

Kansas, in 1974 and 1975, 3 of 8 brown thrasher

nests were parasitized and in none of them were the

cowbird eggs ejected. One nest fledged 3 thrashers

and a cowbird.

Throughout the total range of the brown

thrasher the number of observed cases of parasitism

reported shows a growth from 31 in 1963, to 79 in

1975. The fact that this species is known to be a

rejecter makes it probable that it is parasitized

considerably more frequently than the relatively

small number of records indicate (relative, that is,

to the total number of nests found by observers).

The nest records at Cornell University show 15

instances of parasitism among 1038 nests reported.

These are distributed as follows: Kansas 2, Maryland 1, Michigan 1, Minnesota 1, Missouri 2, Nebraska 4, New York 2, Wisconsin 2. The Ontario

nest record files at Toronto include 14 such cases

out of 484 nests reported. The collections of the

Western Foundation have 156 sets of eggs of this

bird, 3 of which (1.9 percent) were parasitized.

Indeed, if we may cite negative evidence, it seems

that thrashers generally are not molested to any

degree by the brown-headed cowbird. Some 9 species of thrashers are sympatric in their breeding

range with the cowbird, but the brown thrasher

is the only one for which there are numerous

records of parasitism. Three other species of Toxostoma (T. longirostre, T. bendirei, and T. curvirostre) and 1 of Oreoscoptes (O. montanus) have

but a single record apiece; the other 4 species of

Toxostoma (T. redivivum, T. lecontei, T. dorsale,

and T. occelatum) have never been reported as

cowbird victims. We have no information as to the

reactions (accepter or rejecter) of any of these

species except T. lecontei, which is an accepter

(S.I.R., unpublished experiments).

Lest it seem that the paucity, or absence, of instances of cowbird parasitism on thrashers of the

genus Toxostoma, other than T. rufum, be due to

small numbers of nests found, it may be mentioned

that the Western Foundation's collections contain

the following large series of sets of eggs, all from

areas of sympatry with the brown-headed cowbird,

and none of them with any of the parasite's eggs:

T. longirostre, 62 sets; T. bendirei, 88 sets; T. curvirostre, 228 sets; T. redivivum, 245 sets; T. lecontei, 140 sets; and T. dorsale, 83 sets.

The absence of cowbird eggs in all these sets may

be due to absence of parasitism or to a possible

rejecter response to them by the species of thrasher.

AMERICAN ROBIN

Turdus migratorius (Linnaeus)

Information on natural parasitism of the robin

has changed little since the 1963 review (Friedmann, pp. 72-73). We include this species mainly to

report the experimental parasitizations. The experimental results confirm the widespread belief

that the robin typically rejects cowbird eggs and

allow a quantification of that belief. Artificial or

real cowbird eggs were rejected at 45 of 46 nests.

Seven of the rejections were by nest desertion and

the remainder by egg ejection (Rothstein, 1975a).

These experiments were done in Connecticut,

Michigan, Nebraska, Maryland, Manitoba, and

New Brunswick.

Recent data of considerable magnitude on the

incidence of parasitism on the robin are as follows.

The files at Cornell University show 7 instances

among 7482 nests reported (a little over 0.1 percent) distributed among Maryland, Massachusetts,

Nebraska, New York, and Wisconsin; the files at

Toronto show 9 instances among 3586 nests (a little

under 0.3 percent) in Ontario. An unusually high

incidence of parasitism was reported to us by P. F.
20

Elliott who found cowbird eggs in 2 out of 5 nests

in Riley County, Kansas, in 1974 and 1975. The

cowbird eggs disappeared, presumably ejected by

the robins, on the day they were laid or on the next

day. Also, robin eggs disappeared from both parasitized nests, possibly by removal by the cowbirds.

It is of interest that cowbirds are able to carry off

eggs as large as those of the robin (see also Blincoe,

1935; Rothstein, 1975a).

The robin and the gray catbird both show close

to 100 percent rejection, but they differ in the

time taken for rejection. Forty-five robin and 52

catbird nests were visited the day after they were

parasitized experimentally. The cowbird egg had

not yet been rejected at 42.2 percent of the robin

nests but only 23.1 percent of the catbirds had not

rejected after 1 day. This comparison is statistically

significant. Other lines of evidence also indicate

that catbirds are more intolerant than robins of

foreign eggs (Rothstein, 1975c). Thus, cowbird eggs

placed in robin nests are more likely to be found

and reported than those placed in catbird nests.

Therefore, if numbers of cases of observed parasitism are similar in both species, then the actual

parasitism is likely to be higher in the catbird. As it

happens, the 1963 review (Friedmann, pp. 69-70,

72-73) noted 26 cases of parasitism for both species.

Furthermore, the total number of robin nests that

have been examined is greater than that of catbird

nests, since the former species is more abundant, is

more widespread, and has a more easily found nest.

Thus cowbird eggs are observed in a higher percentage of the total of catbird nests examined than

of robin nests, even though they probably disappear more rapidly from the former.

These findings strongly imply that cowbirds

parasitize catbirds more frequently than they do

robins, although they have virtually no chance of

success with either species. Whether this probable

difference is due to host preference by the cowbird

or to some other factor (such as differences in defense of the nest) is uncertain.

WOOD THRUSH

Hylocichla mustelina (Gmelin)

The high incidence of cowbird parasitism on the

wood thrush in Iowa and Minnesota noted earlier

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

(Friedmann, 1963:73-74) is repeated in Illinois according to Graber, Graber, and Kirk (1971:16).

They write that, from their own records and from

the literature, they have egg data on 69 nests, 33

of which (47.8 percent) were parasitized. Their

records cover various parts of Illinois, and the incidence of parasitism is similar in all areas covered.

The Western Foundation has 97 sets of eggs of the

wood thrush, 6 of which (6.2 percent) have 1 or

more cowbird eggs. The Cornell University files

have data on 409 nests of this thrush, 55 of which

(13.4 percent) were parasitized; the Ontario nest

records files show a higher incidence of parasitism—

36 cases (30.5 percent) of 118 nests. Harrison (1975:

204) found an even greater frequency in Pennsylvania, where 11 out of 12 nests observed had cowbird eggs.

HERMIT THRUSH

Catharus guttatus (Pallas)

The subspecies C. guttatus sequoiensis had been

previously reported as a victim of the brown-headed

cowbird but once (Friedmann, 1963:75, at which

time the record was erroneously referred to the race

C. guttatus polionotus). Two additional records are

in the collections of the Western Foundation; they

are, like the first one, from Mono County, California—10 June 1936 and 12 June 1950, respectively. Bull (1974:537) reports a surprising 16 instances of parasitism in New York State on the

eastern hermit thrush, C. guttatus faxoni; 14 of

these are additions to our earlier records. From

Ontario (Ontario nest records files, Toronto), come

another 5 instances out of 84 nests reported, an

incidence of parasitism of 6.0 percent in that

province.

SWAINSON'S THRUSH

Catharus ustulatus (Nuttall)

The nominate race of this thrush had previously

(Friedmann, 1963:75) been recorded only twice as

a victim of the dwarf race of the brown-headed

cowbird (M. ater obscurus). Five more records, from

Santa Barbara, Los Angeles, and San Luis Obispo

counties, California, may now be added; the sets
NUMBER 235 21

are in the Santa Barbara Museum of Natural History and the Western Foundation. In Alberta,

Kondla and Pinel (1971) reported a sixth instance

of parasitism on the race C. ustulatus swainsoni by

the cowbird, M. ater artemisiae. In southern Vancouver Island, in July 1971, 2 records of parasitism

on this thrush were noted, and were reported to

us by Dr. J. B. Tatum.

VEERY

Catharus fuscescens (Stephens)

Although the veery subspecies C. fuscescens salicicola was previously known to be parasitized by

the brown-headed cowbird, a new picture of the

extent to which it is imposed upon in the western

prairie provinces of Canada is revealed by the files

of the Prairie Nest Records Scheme which include

14 such instances in Alberta, Saskatchewan, and

Manitoba, out of a total of 28 nests reported, or an

incidence of 50 percent. These records suggest

some geographical difference in the frequency of

parasitism. In Alberta and Manitoba 8 nests were

reported, all but 1 of which were parasitized, while

in Saskatchewan 20 nests were reported, 7 of which

(35.0 percent) had cowbird eggs or young in them.

One of us (S.I.R.) noted 2 additional cases of

parasitism among 3 nests of this thrush found near

Delta, Manitoba, in late June and July 1970. When

found, 1 of the nests had 3 veery nestlings, 1 cowbird nestling, and 1 veery egg. The other nest

eventually held 1 veery egg and 4 cowbird eggs although initially 3 veery eggs were present with the

4 of the cowbird. The single veery egg left in the

nest hatched on 3 July, even though its shell had

3 or 4 small holes in it 4 days earlier, presumably

inflicted by an adult cowbird. The nest was destroyed by a predator before any of the cowbird

eggs hatched. That the veery may be prone to multiple parasitism is suggested by Harrison's experience (1975:161); he found 3 parasitized nests at

Oconto, Wisconsin, containing 3, 3, and 5 cowbird eggs, respectively.

In the collections of the Western Foundation, 5

(9.6 percent) of 52 sets of eggs of this species are

parasitized. The Ontario nest records files at Toronto have data on 139 nests, 28 of which (20.1

percent) were parasitized.

EASTERN BLUEBIRD

Sialia sialis (Linnaeus)

An unusually high incidence of cowbird parasitism on this ordinarily infrequently reported victim

was reported by Musselman (1946) in Illinois,

where, in 1945, out of a total of 268 active nests

examined, 7 (2.6 percent) contained eggs of the

brown-headed cowbird. Previously (Friedmann,

1963:76-77) only a single Illinois record, and only

30 from the entire range of the eastern bluebird,

were known to us. Two further Illinois records may

be noted: 1, from Bureau, is now in the Santa

Barbara Museum of Natural History; another, from

near Amboy, is in the collections of the Western

Foundation. Pinkowski (1974:45) has recently reported 2 parasitized nests in Michigan. The nest

data in the files at Cornell University contain records of 8435 nests, of which only 6 (0.07 percent)

had cowbird eggs in them. The Toronto files show

3 parasitized nests out of 1367 reported, an incidence of 0.2 percent in Ontario.

MOUNTAIN BLUEBIRD

Sialia currucoides (Bechstein)

Dr. J. Lane informs us that 1 egg of the brownheaded cowbird was found with 3 of the mountain

bluebird in a nest box 4 miles southwest of Kimnay,

Manitoba, in July 1972. This is only the third

record for this bluebird as a cowbird victim; the

others were in Alberta and British Columbia

(Friedmann, 1963:77; 1971:244). That the mountain bluebird is really an extremely unusual host is

evidenced by the fact that the Brandon, Manitoba,

junior bird students have erected 3500 bluebird

nest boxes since 1959, at intervals of a few hundred

feet, on tops of fence posts, for about 1Q00 miles

in southwestern Manitoba, and this was the only

instance of cowbird parasitism they noted. In 1971,

646 pairs of bluebirds, mostly mountain bluebirds,

raised their young in these boxes and over 2600

nestlings were banded; in 1972, over 4100 nestling

bluebirds were banded, with no young cowbirds

among them. As mentioned in an earlier compendium (Friedmann, 1963:77), the British Columbia nest records scheme showed no instance of

cowbird parasitism in their records of 115 nests of

the mountain bluebird.
22

BLUE-GRAY GNATCATCHER

PolioptUa caerulea (Linnaeus)

The blue-gray gnatcatcher is now a fairly well

documented host of the brown-headed cowbird (39

records in Friedmann, 1963:77-78), and the only

reason for mentioning it in this paper is to add a

notable increase in our data for its western subspecies P. caerulea amoenissima in California. In

the collections of the Western Foundation there are

8 parasitized sets of eggs from California, from

Stockton south to San Diego County. The total

number of sets of blue-gray gnatcatcher's eggs (all

races), from the United States and Canada, but not

counting Mexico, in the Western Foundation's collections is 153, out of which 13 (8.5 percent) are

parasitized. Breaking this down to subspecies, we

have P. caerulea caerulea, 48 sets, 5 (10.4 percent)

parasitized; P. caerulea amoenissima, 105 sets, 8 (7.6

percent) with cowbird eggs.

BLACK-TAILED GNATCATCHER

PolioptUa melanura Lawrence

In central Coahuila, Mexico, W. K. Taylor

(1966:136-137) found the nominate race of this

gnatcatcher to be victimized by the brown-headed

cowbird (M. ater obscurus). Previously 3 other races

of this host had been so recorded—P. m. calijornica,

P. m. lucida, and P. m. margaritae—but Taylor's

record is the first one for typical P. melanura in

print. A second record is a parasitized nest found

in the Big Bend National Park, Texas, 6 June

1969, reported by Wauer (1973:143); a third and

fourth are 2 sets of eggs from near Gonzalez,

Tamaulipas, Mexico, now in the collections of the

Western Foundation. Inasmuch as the total number of records for all races of this gnatcatcher is

fairly few, it may be noted that the Western Foundation has in its collections 4 more parasitized sets

of eggs of P. m. lucida from Arizona and Sonora,

and 1 more of P. m. californica from Riverside

County, California. These bring the number of

records up to 27.

The Western Foundation has 87 sets of eggs of

this gnatcatcher, not counting some from Baja

California. Of these, 10 (11.5 percent are parasitized; of nominate P. melanura there are 2 sets,

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

both with cowbird eggs; of P. melanura lucida, 34

sets, 7 (20.6 percent) parasitized; of P. melanura

californica, 51 sets, only 1 of which has a cowbird

eggGOLDEN-CROWNED KINGLET

Regulus satrapa (Lichtenstein)

To the 2 earlier records of the kinglet as a host

of the brown-headed cowbird (Friedmann,

1971:245) may be added 4 more. Lemon (1969)

mentioned a fledged young cowbird attended by a

golden-crowned kinglet near Victoria, southern

Vancouver Island, 1 August 1967, the same area

from which both of the earlier records had come.

This makes it seem that this unusually small host

may be victimized there fairly regularly. Near Bellingham, Washington, on 2 August 1973, another

instance of a young cowbird with golden-crowned

kinglets as its fosterers was observed by Lavers

(1974). All these records involve the host race R.

satrapa olivaceus (the allocation of the 2 earlier

records to R. satrapa amoenus was an error), and

the parasite race M. ater artemisiae. A record from

Highland Forest, Onandaga County, New York

(Crumb, 1974) is the first for R. satrapa satrapa

and M. ater ater. A second, from Maine, is recorded

by Harrison (1975:164).

RUBY-CROWNED KINGLET

Regulus calendula (Linnaeus)

In spite of its diminutive size, the ruby-crowned

kinglet must be rated as a regular, if not a favorite,

host choice of the brown-headed cowbird. To the

10 previously reported instances of parasitism

(Friedmann, 1971:245) may be added 4 more, 3

from Mono County, California. These 3 are represented by 2 sets of eggs in the Santa Barbara Museum of Natural History and another set in the

Western Foundation. These California records all

refer to the race R. calendula cineraceus of the host

and M. ater artemisiae of the parasite. The fourth

record is from Mt. Desert Island, Maine (Harrison,

1975:165).
NUMBER 235 23

CEDAR WAXWING

Bombycilla cedrorum Vieillot

Since the last review, significant new information

on this species has come to light. Experiments show

it to be a rejecter species. Rejection of artificial or

real cowbird eggs occurred at 40 of 58 nests, 69.0

percent (Rothstein, in press(b)). Two of these nests

were located in Manitoba, 1 in New Brunswick,

and the rest in Michigan. Unlike other rejecters,

waxwings showed a nest stage-dependent response.

Waxwings parasitized on or before the third day of

incubation rejected at an 87.5 percent rate. Those

parasitized after the third day of incubation rejected at a 40.0 percent rate. Since most natural

parasitism occurs during the host's laying period,

87.5 percent is close to the figure for the rate at

which natural parasitism is rejected. Instead of

ejecting cowbird eggs, the rejection mode used almost exclusively by most rejecters, most (60.0

percent) waxwing rejections were by nest desertion.

In addition to these differences, most waxwings

wait at least 1 day before rejecting, whereas in

other species most individuals reject within 1 day.

The fact that waxwings reject cowbird eggs helps

to explain the small number of observed cases of

parasitism on this widespread, abundant species.

In the 1966 paper (Friedmann, p. 3) only 22 cases

were noted, but this figure has now more than

doubled. In the collections of the Western Foundation there are 3 parasitized sets of eggs, 1 each from

Illinois, Massachusetts, and Ontario; the Delaware

Museum has 1 parasitized set from New York; the

Toronto files include 24 parasitized nests, constituting 6.5 percent of 372 nests reported from Ontario;

in the Prairie Nest Cards Scheme are 2 more from

Manitoba. Bull (1974:537) notes 7 cases of parasitism in New York State; 5 of these are additional to

our earlier figures. One of us (Rothstein, in

press(a)) has surveyed data on 334 nests from

Cheboygan and Emmet counties, Michigan. Cowbird eggs or young were seen in 25 (7.5 percent) of

these Michigan nests. The Michigan data were collected between 1924 and 1969. These new data show

that in at least one area the waxwing is a regular

host. Furthermore, the rate of observed parasitism

is just a minimum figure for the rate of actual

parasitism, as the bulk of cowbird parasitism on

this rejecter species may go undetected.

The partly frugivorous diet waxwings feed their

nestlings makes it probable that cowbirds, even if

accepted, would often die because of inadequate

nourishment. Thus, the waxwing offers cowbirds

little chance of reproductive success. But the fact

that there are now over 50 known cases of parasitism on this species shows that the cowbird not infrequently victimizes unsuitable hosts to its own

loss. Such a wastage of reproductive potential seems

contrary to basic evolutionary principles. At the

same time, it is not always to its loss, as instances

have been reported where the waxwings accepted

and reared the young parasites (Friedmann,

1963:40,81).

It may well be that the waxwing's habit of rejecting the cowbird eggs as a rule played an important role in the experience of the late L. M.

Terrill (1961:5) in southern Quebec, where, in over

50 years of field work, he found 329 nests of this

species, but found cowbird eggs in only 4 of them.

The fact that the waxwing is a relatively late

breeder and often nests after the cowbirds laying

season is past its height, probably is also partly

responsible for the low incidence of parasitism in

Terrill's observations.

Recently De Sante and Le Valley (1971:904) reported a parasitized nest from near Berkeley, California. This is the first record of the waxwing as a

host of the dwarf race of the cowbird M. ater

obscurns, and is also an extension of the breeding

range of the waxwing in California.

STARLING

Sturnus vulgaris Linnaeus

At Berkeley, California, on 10 May 1969, Harriet

P. Thomas (1973:207) watched a starling repeatedly

feeding a large fledgling brown-headed cowbird.

The repetitive feeding indicated a foster-parentparasite relationship, not a casual response to the

food call of a strange fledgling. This observation is

the first evidence that the starling can and does rear

the parasite, and it is also the first record of the

starling's being parasitized by the southwestern

race of the cowbird M. ater obscurus. The two

previous records of the starling as a cowbird victim

were in Maryland and Illinois. The aggressive and

pugnacious nature of the starling, coupled with its

habit of nesting in holes, apparently keeps it largely

free of cowbird molestation.
24

BLACK-CAPPED VIREO

Vireo atricapilla Woodhouse

Although no quantitative data are given, Oberholser (1974:842) implies that this vireo is becoming increasingly imposed upon in Texas, where

manmade changes have resulted in growth of the

cowbird population, especially in the Edwards

Plateau. There the black-capped vireos are said to

be "finding it more difficult to raise their own

young" because of the greater abundance of the

parasites. This does not support Graber's contention (1961:325-326) that the black-capped vireos

(both sexes) tend to sit on the nest after the first

egg is laid, a habit of covering the eggs that might

safeguard them from cowbird parasitism. However,

Graber's own observations show that this is far

from totally protective, as she writes (p. 335) that

this vireo suffers large reproductive losses due to

cowbird parasitism: "Its nesting success is low compared to that of other passerines, but not lower

than that of a closely related, more widely distributed species, Vireo bellii."

In Graber's experience cowbird eggs are usually

deposited before the vireo's clutch is completed.

The cowbird egg hatches 2 to 4 days before those

of the vireo,

and by the time the young vireos hatch, the cowbird outweighs each of them more than ten times. In one nest, a

three-day old cowbird weighed 11.31 grams while its nest

mate, a newly hatched vireo, weighed 0.86 grams. The

cowbird is able to raise its head far above the vireo in

begging, and gets most of the food. The cowbird requires

about as much food as four vireo chicks so it is hungry and

begs most of the time. The vireo chick gets scarcely any food,

and is trampled and crushed by its parasitic nestmate. After

a day or two, the vireo chick dies and its body is removed

(p. 330).

In addition to the one-sided competition between

nestlings of the vireo and the cowbird, Graber's

figures on egg losses are impressive evidence of

what the vireo suffers. In 76 active nests that she

studied, a total of 243 vireo eggs were laid, more

than half of which, or 134 (55 percent), were lost

before hatching, and of these she estimates cowbird

parasitism was responsible for the loss of 97 (72 percent). She concludes that the black-capped vireo's

low reproductive success is "probably compensated

for by the survival rate and longevity of adults.'

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

WHITE-EYED VIREO

Vireo griseus (Boddaert)

Two instances of parasitism in Ontario (out of

2 nests reported to the nest records files, Toronto)

extend to the northwest the area over which the

white-eyed vireo is known to be affected by the cowbird.

HUTTON'S VIREO

Vireo huttoni Cassin

To the 8 earlier records of this vireo as a victim

of the brown-headed cowbird (Friedmann, 1963:83)

may be added 5 more: 3 from California (San Luis

Obispo, Ventura, and Santa Barbara counties) in

the Santa Barbara Museum of Natural History and

the Western Foundation; 1 from near Victoria,

British Columbia (Crowell and Nehls, 1973:911);

and 1 from Oregon, reported by Anderson

(1970:420). In the 1963 summary of available information, 2 records were considered as involving

the host race V. huttoni stephensi, 1 from New

Mexico, and 1 from Brewster County, Texas. The

former is correctly allocated to V. h. stephensi, but

the latter can only refer to V. huttoni carolinae, a

subspecies not hitherto reported among the victims

of the parasite. The record from Victoria, Vancouver Island, refers to the host race V. huttoni

insularis, which is the first one reported for that

form.

BELL'S VIREO

Vireo bellii Audubon

The various races of Bell's vireo have long been

known to be frequent victims of the brown-headed

cowbird, a situation that is even more strongly emphasized by the rapid accumulation of additional

instances. In 1963 there were some 82 actual instances compiled; by 1975 this has grown by more

than 50 percent. The Western Foundation alone

has in its collections some 46 parasitized sets of

eggs (23.3 percent) out of a total of 197 sets. By

subspecies, the figures are: V. bellii bellii and V.

bellii medius, 58 sets, 17 (29.3 percent) parasitized;

V. bellii anzunae, 13 sets, 5 (38.4 percent) parasitized; V. bellii pusillus, 120 sets, 24 (20.0 percent)

parasitized.
NUMBER 235 25

There is a possibility that the high incidence of

parasitism on this bird in southern California,

coupled with an accelerated rate of destruction of

its habitat may be causing it locally to diminish

critically in numbers. Similarly, in the central valley of central and northern California, Remsen and

Gaines (1973:916) considered that this vireo, as

well as the yellow warbler and the yellowthroat,

were nearly extinct, "probably due to cowbird parasitism." The excessive victimization of Bell's vireo

is also noted in southern Texas, where, in 1971, 23

nests were reported and 17 of these contained cowbird eggs or young (Webster, 1971:877).

YELLOW-THROATED VIREO

Vireo flavifrons Vieillot

In 1963 (Friedmann, pp. 85-86) it was concluded

that the frequency of cowbird parasitism on this

vireo varied from place to place, but that quantitative data were still meager. It may be noted that the

Ontario nest records files at Toronto reveal that 17

(32.7 percent) of 52 nests reported from the province were parasitized.

SOLITARY VIREO

Vireo solitarius (Wilson)

New information has been amassed on the western race of this vireo, V. solitarius cassinii, hitherto

reported as a victim of the brown-headed cowbird

only 7 times in print (Friedmann, 1963:87). To

these records may be added 10 more: 3 from southern Vancouver Island—Victoria (Crowell and

Nehls, 1973:911), Alouette Lake, 1 August 1970,

and Saanich, 28 July 1973 (the last 2 reported to

us by Dr. J. B. Tatum); and 7 from California—

Tulare, Santa Barbara, Ventura, Tuolumne, and

Alameda counties—4 of which were found by E. M.

Hall or by R. J. Quigley.

The vireo subspecies V. solitarius plumbeus was

previously reported as a victim even less frequently

than V. s. cassinii, but here again, hitherto unpublished records raise the number by 4 cases, all from

Arizona, reported to us by Hall. The Western

Foundation's collections contain a total of 166 sets

(of all races of the vireo), 8 of which (4.8 percent)

are parasitized. It so happens that all 8 are of the

subspecies V. solitarius cassinii, forming 6.1 percent

of the 131 sets of eggs of that race in the collections.

That the solitary vireo is, indeed, more often victimized in the west than in the east is shown by the

total of all records known to us: V. solitarius

solitarius, 6; V. solitarius alticola, 2; V. solitarius

plumbeus, 15; V. solitarius cassinii, 17.

RED-EYED VIREO

Vireo olivaceus (Linnaeus)

Of 27 nests from Saskatchewan, Manitoba, and

Alberta reported to the Prairie Nest Cards files

at the Manitoba Museum, 5 had cowbird eggs in

them, a lower incidence of parasitism than obtains

farther south and east. We may recall that in the

Douglas Lake area of Michigan, Southern (1958)

reported cowbird eggs in 72.1 percent of the nests

of this vireo (75 parasitized out of 104 active nests

studied). Other sizeable samples reported in the

1963 compilation (Friedmann, pp. 88, 89) showed

36.4 percent parasitism in Ohio and 41.3 percent in

southern Quebec. The nest records files at Toronto

show 65 cases of parasitism out of 240 nests in

Ontario (27.1 percent).

Although this vireo often deserts its nest if a

large number of cowbird eggs are laid or if all the

vireo eggs are removed by cowbirds (Southern,

1958), there are several cases known in which vireos

continued to incubate clutches consisting only of

cowbird eggs. Incubation of 5 cowbird eggs continued at 1 of the nests studied by Southern

(1958:195) after the 2 vireo eggs that were present

were removed (presumably by cowbirds). Harrison

(1975:172) cites a bird incubating at a Pennsylvania

nest that contained 4 cowbird and no vireo eggs.

One of us (L.F.K.) found that incubation of 3 cowbird eggs continued after he removed the only

vireo egg from a nest in Cabell County, West Virginia. Another of us (S.I.R.) studied a comparable

nest at the University of Michigan Biological Station, Pellston, Michigan. This last nest had a number of unusual features. Two cowbird eggs were

laid on one morning and the 6 cowbird eggs the

nest eventually held were laid over a span of at

least 9 days. When discovered on 18 June 1963, the

nest held 1 vireo egg and 2 cowbird eggs. The vireo

egg disappeared on 25 or 26 June, but incubation

of the 6 cowbird eggs then present continued until

at least 8 July. The nest was probably abandoned
26

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

on 9 July, and the cowbird eggs were removed

(presumably by a predator) by 10 July. Thus, incubation continued for about 21 days, during the

last 13 or 14 of which the nest held no host eggs.

It is likely that the cowbird eggs failed to hatch

because their combined mass was too great to allow

successful incubation by a bird as small as a vireo

(see Friedmann, 1963:21-22 for a discussion of the

incubation capabilities of hosts).

PHILADELPHIA VIREO

Vireo philadelphicus (Cassin)

To the 2 earlier records (Friedmann, 1963:89) of

this very rarely reported victim may be added 4

more: 2 parasitized nests found in Ontario (out of

a total of 24 nests) recorded in the Ontario nest

records files at the Royal Ontario Museum of

Zoology; another, also from Ontario (Humber

River, 15 June 1915), now included in the collections of the Western Foundation; and a sight

record of a Philadelphia vireo attending a fledged

young cowbird near Pyramid Lake, Jasper National

Park, Alberta, noted by Rogers (1972:881).

Inasmuch as very few sets of eggs of the Philadelphia vireo are to be found in collections, it may

be that these 6 records of parasitism indicate a relatively high incidence of cowbird interference.

WARBLING VIREO

Vireo gilvus (Vieillot)

While the warbling vireo, as a species, is well

known as a frequent victim of the brown-headed

cowbird, its western population, forming the race

V. gilvus leucopolius, has been so reported in print

only twice (Friedmann, 1963:90). Six more instances

may be added: a parasitized set of eggs taken in

Tuolumne County, California, 6 June 1939, now in

the collections of the Western Foundation; a statement (Crowell and Nehls, 1973:911) of this vireo's

being parasitized in the Victoria area, Vancouver

Island; and 4 records from Saskatchewan and Manitoba in the Prairie Nest Records files at the Manitoba Museum. In Ontario the incidence of cowbird

parasitism on this vireo (V. g. gilvus) is unusually

low: 1 such nest out of a total of 62, or 1.6 percent

(Peck, 1975).

BLACK-AND-WHITE WARBLER

Mniotilta varia (Linnaeus)

In the earlier compendium (Friedmann, 1963:91)

but a single instance was noted of this warbler as a

victim of the northwestern race of the cowbird, M.

ater artemisiae. We may now add 2 more cases observed in Alberta (Prairie Nest Records).

SWAINSON'S WARBLER

Limnothlypis swatnsonii (Audubon)

To the 14 earlier records of the Swainson's

warbler as a cowbird victim (Mississippi, North

Carolina, Oklahoma, and West Virginia) may be

added 1 more—a set of 2 eggs of the warbler and 1

of the cowbird, collected at Phyzizzy's Swamp,

Savannah River, South Carolina, on 2 June 1899,

now in the holdings of the Western Foundation.

TENNESSEE WARBLER

Vermivora peregrina (Wilson)

To the small number of previous records (Friedmann, 1963:94-95) of this warbler as a cowbird

victim may be added 2 more from Alberta, 1 in

1956 (Prairie Nest Record Cards), a nest containing

two half-grown young cowbirds and one addled

warbler egg, and another in 1974, which was 1 out

of 4 nests found that year.

GOLDEN-WINGED WARBLER

Vermivora chrysoptera (Linnaeus)

A nest of this warbler containing 3 eggs of the

host and 1 of the brown-headed cowbird, found on

Little George Island, in Lake Winnipeg, Manitoba,

5 July 1971, reported by Houston (1971:872), is the

first record of this species as a victim of the northwestern cowbird, M. ater artemisiae. The nominate

race of the parasite was previously reported as

imposing on the golden-winged warbler only occasionally; a total of 17 instances up to 1963 (Friedmann, p. 93) had been recorded. To these may be

added 19 more: 2 from Massachusetts (from Maiden

and Bradford), now in the collections of the Western Foundation; 9 from New York (Bull (1974:537)

lists II cases, 2 of which were included in our ear-
NUMBER 235 27

Her figures); and from Ontario, 8 out of 22 nests

reported (Ontario Nest Records) an incidence of

36.4 percent.

BLUE-WINGED WARBLER

Vermivora pinus (Linnaeus)

In the 1963 compilation (Friedmann, p. 94) mention was made of 35 records of this warbler as a

cowbird victim. Only 1 of these instances was from

New York State. Bull (1974:537) notes 16 such cases

of parasitism from that area, a notable increase in

the available data, both locally and generally. One

record from Ontario, out of 4 nest cards in the files

at Toronto, extends the area where this warbler

and the brown-headed cowbird are mutually involved.

ORANGE-CROWNED WARBLER

Vermivora celata (Say)

Two parasitized nests of the nominate race of the

orange-crowned warbler were found near Saskatoon,

Saskatchewan, by Gehlert (1969:223), 23 and 29

June 1969, 1 with eggs of the 2 species, the other

with 2 young cowbirds nearly ready to fledge. These

are the first instances known to us of V. celata

celata as a victim of the brown-headed cowbird (M.

ater artemisiae), and the first record of this warbler's rearing the young parasites.

Previously we knew of 3 records for the race V.

celata lutescens (Friedmann, 1971:246). To these

we may now add 7 more: 6 cases from southern

Vancouver Island, British Columbia, where this

warbler appears to be parasitized regularly (Tatum,

1973:51; Crowell and Nehls, 1973:911; and a report received from Dr. J. B. Tatum); and one

from Samish Island, western Washington (Lavers,

1974:830).

NASHVILLE WARBLER

Vermivora ruficapilla (Wilson)

This infrequently reported victim of the brownheaded cowbird was known (Friedmann, 1963:95)

to be parasitized in 16 instances in Quebec, Massachusetts, New York, Michigan, Ontario, Minnesota, and Manitoba. Nine more cases may be added:

a set of 2 eggs of the host and 1 of the parasite,

collected near Oconto, Wisconsin, 28 May 1962,

now in the holdings of the Western Foundation; 4

instances in Ontario, (7 parasitized nests—3 previously known to us—out of 48 nests (14.6 percent)

reported to the nest records file of the Royal Ontario Museum); and 4 instances of parasitism in

New York State (out of 5 mentioned by Bull,

1974:537). The Ontario data are the first to reveal

a high incidence of parasitism anywhere.

LUCY'S WARBLER

Vermivora luciae (Cooper)

To the few earlier reports of cowbird parasitism

on this warbler in California, Arizona, and Texas,

may be added 7 more, 6 from Arizona and 1 from

New Mexico. The Arizona records are 1 each from

Yavapai County, 9 May 1946, and from Fort Lowell,

26 May 1908, and 3 from near Wickenburg, Maricopa County (all these 5 are presently in the collections of the Western Foundation), and 1 from

Tucson (in the Santa Barbara Museum of Natural

History). In New Mexico, Hubbard (1971:25)

found a parasitized nest of Lucy's warbler near

Cliff, Gila Valley, 20 June 1968.

This warbler is relatively seldom observed, but

the number of instances of parasitism on it reported suggests that it is probably a fairly frequent

host choice. The Western Foundation has 44 sets of

eggs, 5 of"which (11.4 percent) are parasitized.

YELLOW WARBLER

Dendroica petechia (Linnaeus)

The chief reason for mentioning this very commonly imposed upon host is to note a sizeable

group of northwestern records from Saskatchewan,

Manitoba, and Alberta, in the Prairie Nest Cards

at the Manitoba Museum. Of 194 nests reported, 31

(15.9 percent) were parasitized. This is relatively

similar to data from southern Quebec, where of 307

nests examined, 42 (13.6 percent) were parasitized

(Friedmann, 1963:98), but is much lower than in

Ohio and Michigan, where various observers reported an incidence of parasitism of from 35.6 to

42.0 percent. In Ontario, the nest records on file in

Toronto reveal a lesser frequency of parasitism,

25.7 percent (218 parasitized nests out of 848 nests
28 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

reported). The files at Cornell University show that

115 (22.4 percent) of 513 yellow warbler nests reported (all races) were parasitized. The great collections of the Western Foundation contain 348

sets of eggs of the yellow warbler (all races sympatric to the brown-headed cowbird); 28 of these

(8.0 percent) are parasitized. These data, broken

down by subspecies shows: D. petechia aestiva, 85

sets, 13 (15.3 percent) parasitized; D. petechia morcomi, 228 sets, 13 (5.7 percent) parasitized; D.

petechia rubiginosa, 12 sets, 1 of them parasitized;

D. petechia sonorana, 8 sets, 2 (25.0 percent) parasitized; D. petechia amnicola, 15 sets, none of them

parasitized.

MAGNOLIA WARBLER

Dendroica magnolia (Wilson)

The Ontario nest records files at Toronto reveal

that 6 (10 percent) of 60 magnolia warbler nests

found in that province were parasitized, the highest

frequency yet reported for this species as a cowbird

host. Harrison (1975:184) reported 2 parasitized

nests in Maine, out of 16 observed, a still higher

incidence (12.5 percent), but based on a much

smaller sample. He also found 2 nests in Pennsylvania, both of which were parasitized. Previously

(Friedmann, 1963:100) only 17 records were known

in all (including 2 of the above noted Ontario

ones). With 25 instances now known to us, it appears that the magnolia warbler, while infrequently reported as a cowbird host, is regularly

victimized.

BLACK-THROATED BLUE WARBLER

Dendroica caerulescens (Gmelin)

This infrequently reported victim was known

earlier (Friedmann, 1963:100) on the basis of only

10 records, 3 of which were from New York. Bull

(1974:537) increases the New York instances to 7.

Peck (1975) reports that in Ontario 2 out of 21

nests reported (9.1 percent) were parasitized.

YELLOW-RUMPED WARBLER

Dendroica coronata (Linnaeus)

The first section of notes following have to do

with that portion of this species previously considered a separate species, the Audubon's warbler

(D. coronata auduboni). In the Santa Barbara Museum of Natural History there is a set of four eggs

of Audubon's warbler with one of the brownheaded cowbird (subspecies M. ater artemisiae),

collected 26 June 1937, at Mammoth, Mono

County, California. This is the second record for

that area, and only the fifth one known to us for

this race of the yellow-rumped warbler throughout

its entire range. Rogers (1971:881) has recently

listed this race as a cowbird victim, as has Tatum

(1973:62) in Vancouver Island. The Prairie Nest

Records files have 3 more records from Alberta, 1

of which is the first one showing that the Audubon's warbler can and does rear the young parasite

(at Exshaw, Alberta, 13 July 1968). Pettingill and

Whitney (1965:102) report a young cowbird attended by a female Audubon's warbler in the Jewel

Cave National Monument, in the Black Hills,

South Dakota, on 26 July 1958. This record refers

to the host subspecies D. coronata memorabilis, for

which race it is the second record; the first one

(Friedmann, 1963:102) was from Montana.

Of the nominate, eastern race, formerly called

the myrtle warbler, Bull (1974:537) lists 5 instances

of parasitism in New York State. Peck (1975) reports

21 (27.3 percent) of 77 Ontario nests were

parasitized.

BLACK-THROATED GRAY WARBLER

Dendroica nigrescens (Townsend)

To the 5 earlier records (Friedmann, 1963:102;

1971:246) of parasitism on this warbler may be

added 2 more. In the collections of the Western

Foundation is a parasitized set of eggs taken at Red

Bluff, Tulare County, California, 19 May 1937, by

C. Andresen. Mr. Alan Pistorius writes us that he

and his companions watched a male black-throated

gray warbler repeatedly feeding a young fledgling

brown-headed cowbird more than twice its own

size, at 3000 feet on the east slope of the California

coast range southwest of Lodoga, near the Colusa

County-Lake County line, on 6 July 1972.

TOWNSEND'S WARBLER

Dendroica townsendi (Townsend)

Dr. J. B. Tatum (1973:62) notes that there was re-
NUMBER 235 29

ported to him 1 record of this warbler as a victim

of the brown-headed cowbird in southern Vancouver Island. He considered the record acceptable,

since the warbler is a common summer resident

there. He did not have an exact date for the observation, which is the first one involving Townsend's

warbler as a cowbird host. The record involved a

fledged young cowbird attended by its fosterers.

BLACK-THROATED GREEN WARBLER

Dendroica virens (Gmelin)

To the 15 earlier records of parasitism on this

warbler gathered over several decades (Friedmann,

1963:103) may be added 18 more: a parasitized set

of eggs taken near West Haven, Connecticut, 12

June 1916; 4 Ontario records, out of 26 nests (15.4

percent) reported to the nest card files at Toronto;

another Ontario record, from Kingston, mentioned

by Quilliam (1973:174); and 12 instances of parasitism in New York State (out of 14 mentioned by

Bull, 1974:537).

GOLDEN-CHEEKED WARBLER

Dendroica chrysoparia Sclater and Salvin

Recent manmade changes in the ecology of much

of the Edwards Plateau, Texas, have caused a great

increase in the cowbird population there, and this,

in turn, may have seriously affected the goldencheeked warbler. This bird is said (Oberholser,

1974:842) to be parasitized much more frequently

than previously, and while no figures are given, it

is suggested that the incidence of parasitism may be

excessive.

CERULEAN WARBLER

Dendroica cerulea (Wilson)

In the 1963 compilation (Friedmann, p. 104) only

12 records were known of cowbird parasitism on this

warbler. The number, while still small, may be increased to 18. Bull (1974:537) lists 5 instances from

New York State (1 of which was included in the

earlier statement), and 2 other cases were found

in Ontario (out of 29 nests reported to the Ontario

nest records files, Toronto).

BLACKBURNIAN WARBLER

Dendroica fusca (Miiller)

This very uncommonly reported victim was

known until now as a cowbird host on the basis

of only 10 records (Friedmann, 1963:105). Four

more may be added: a set of 3 eggs of the host and

1 of the parasite, collected 2 miles south of Hamilton, New York, 3 June 1925, by R. C. Harlow, now

in the collections of the Western Foundation; another from New York (Bull, 1974:537); a parasitized

nest found at MacLennon, Algoma District, Ontario, reported to the Ontario nest records files at

Toronto (this finding and 1 of the records included

in the 1963 compendium comprised 2 out of 14

nests reported); and another from Kingston, Ontario, listed by Quilliam (1973:159, 174). The last

is one of the few instances in which the warbler

was reported as rearing the young parasite.

CHESTNUT-SIDED WARBLER

Dendroica pensylvanica (Linnaeus)

In Ontario this warbler seems to be more frequently parasitized than was previously (Friedmann, 1963:106) reported. In the nest record files

at Toronto are data on 150 nests found in that

province, and of them no fewer than 30 (20.0 percent) were parasitized. Of these 30 records, 28 are

additional to what we had known previously, a

notable increase, from 75 records in 1963 to 103

in 1975.

BAY-BREASTED WARBLER

Dendroica castanea (Wilson)

Previously (Friedmann, 1963:107) the baybreasted warbler was known as a victim of the

nominate race of the brown-headed cowbird in

Quebec Province, Canada. There were only 2 records. We may now add 2 more, from the Prairie

Nest Cards files in Winnipeg, which add this species to the host list of the northwestern race of the

parasite, M. ater artemisiae. One record was observed in Alberta in 1965, the other in 1974.
30 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

BLACKPOLL WARBLER

Dendroica striata (Forster)

The blackpoll warbler was added to the known

hosts of the brown-headed cowbird by Gilligan and

Wright (1969) at Sauvie Island, near Portland,

Oregon, 24 July 1969, when they saw a fledged

young cowbird attended and repeatedly fed by one

of these warblers. The locality is somewhat outside

the warbler's normal breeding range, but the record seems acceptable, since the identification was

corroborated by several other observers and was

accepted as valid by the editors of Audubon Field

Notes, who were aware of the geographic problem

it presented. The cowbird in this case is the northwestern race, M. ater artemisiae.

In the east, Bull (1974:537). notes 1 record of

parasitism on the blackpoll warbler in New York

State, by the nominate race of the parasite, a nest

found at Balsam Round Top Mountain, Ulster

County, 24 June 1969, with 4 eggs of the warbler

and 1 of the cowbird.

PINE WARBLER

Dendroica pinus (Wilson)

The pine warbler was known as a rarely reported

victim of the brown-headed cowbird, on the basis of

10 instances (Friedmann, 1963:107), either of collected eggs or of observations of the warbler feeding

a young cowbird. To these may now be added 2

more; a parasitized set of eggs in the Royal Ontario

Museum of Zoology and an observed (not collected)

instance in Ontario, 7 June 1916, reported to the

Ontario nest records files at that museum. Ontario

is the only "region" (in an admittedly loose use of

the term) where there is reason to believe the pine

warbler is a regular, if not frequent, host choice;

4 of the 12 records are from Ontario.

The paucity of records of cowbird parasitism on

this warbler is borne out by the fact that the Western Foundation's collection contains 29 sets of eggs

of the pine warbler from within the breeding range

of the brown-headed cowbird, but not one of them

is parasitized.

NORTHERN WATERTHRUSH

Seiurus noveboracensis (Gmelin)

In 1963 (Friedmann, pp. 113-114) only 15 instances of cowbird parasitism on this warbler were

mentioned, 1 of them from New York State. The

recorded situation in that state is now greatly

changed. Bull (1974:537) mentions 20 more records

from that area, where, in suitable localities, this

species must be a frequently chosen victim. Part of

Bull's data stems from the studies of S. W. Eaton

(1957) published unfortunately in a seldom consulted journal of limited availability. In Ontario,

the only area from which a fairly high incidence of

parasitism had been recorded earlier—8 (20.0 percent) of 40 nests examined—only a single additional

case has been reported in the past 20 years, although

there were, in 1974, data on 74 Ontario nests in

the nest records files at Toronto, causing the incidence of parasitism to drop from 20.0 to 12.2

percent (9 out of 74 nests).

LOUISIANA WATERTHRUSH

Seiurus motacilla (Vieillot)

Bull (1974:537) mentions some 30 instances of

cowbird parasitism on this warbler in New York,

of which the earlier compendium (Friedmann,

1963:114-115) included 15. These 15 additions

bring the total known records up to 86. While over

a third of the total are from one state, there is no

reason to think there is a greater frequency of parasitism there than elsewhere.

MACGILLIVRAY'S WARBLER

Oporornis tolmei (Townsend)

To the 9 earlier records of this warbler as a

host of the brown-headed cowbird (Friedmann,

1963:117) may be added 4 more instances: a parasitized nest found at Lake Tahoe, California, 14

June 1938, now in the Santa Barbara Museum of

Natural History; another from Laurel Creek, Mono

County, California, in the Western Foundation's

collections; a record noted in Tatum (1971:51) of

an observation near Victoria, Vancouver Island,

of a fledged cowbird attended by foster parents of

this species; and a similar observation, 5 August

1975, at an elevation of 8000 feet, near Mammoth,

California (S.I.R.).
NUMBER 235 31

YELLOW-BREASTED CHAT

Icteria virens (Linnaeus)

To the few earlier records (Friedmann, 1963:120-

122) from western Canada may be added 3 more

parasitized nests found in Alberta (Prairie Nest Records), the first instances reported from that province.

YELLOWTHROAT

Geothlypis trichas (Linnaeus)

Over 300 cases of cowbird parasitism on this warbler have been reported. These should yield some

significant indices, but the evidence is mixed. Thus,

in the collections of the Western Foundation, 124

sets of eggs of eastern races include 13 that are parsitized (10.5 percent); 159 sets of California races

include 12 parasitized sets (7.5 percent). However,

data from a few eastern areas where sizeable samples are available (Friedmann, 1963:117-120), yield

the following: southern Quebec, 113 nests, 8 of

which (7.1 percent) are parasitized; Ohio, 41 nests,

19 (46.3 percent) parasitized; Michigan, 90 nests,

35 (38.8 percent) parasitized.

Two records of parasitized nests of the host race

G. trichas campicola from Alberta, in the Prairie

Nest Cards Scheme, are the third and fourth instances for that subspecies of the yellowthroat. Another record, from Canston, British Columbia,

listed previously (Friedmann, 1963:120) as G.

trichas occidentalis is probably better considered as

G. trichas campicola. A new, and valid, record for

G. trichas occidentalis, from Barr Lake, Colorado,

is in the collections of the Western Foundation.

As an indication of the ability of the yellowthroat

to rear a sizeable brood, mention may be made of a

nest observed in the Goleta Slough, Santa Barbara

County, California, by Kelly Steele, that fledged 1

young cowbird and 3 young yellowthroats.

HOODED WARBLER

Wilsonia citrina (Boddaert)

In the 1963 compilation (Friedmann, pp. 122—

123) some 32 instances of parasitism on this warbler

were noted, but the number seemed to have grown

slowly enough to suggest that the bird was generally

an infrequently selected host. This was concluded although there were a number of records from

Michigan and from Maryland, where the hooded

warbler was imposed upon more often than elsewhere. This picture is changed now, since in New

York State alone, Bull (1974:537) mentions 27 records, all but 3 of which are new to our earlier

figures. These indicate that there this bird is a

common host choice. A single instance of parasitism in Ontario (out of data on 3 nests in the files

at Toronto) adds a new northern locality of record.

WILSON'S WARBLER

Wilsonia pusilla (Wilson)

Until now this warbler has been reported as a

cowbird host only a small number of times, but it

appears, from recent evidence, that it must be a

fairly regular, possibly even a favorite choice of the

parasite in southern Vancouver Island and in southern California, if not elsewhere. In the former area,

Lemon (1969) reported a fledged young cowbird

attended by a Wilson's warbler (race W. pusilla

chryseola) near Victoria, on 13 August 1968. This

is the first time the subspecies W. p. chryseola has

been found to rear the young parasite (one previous

instance is known for the subspecies W. pusilla

pileolata). Since Lemon's paper, 2 additional observations of fledged young cowbirds attended by

adults of this warbler have been reported in the

same area (J. B. Tatum).

From southern California there are no fewer than

16 additional records, all of sets of eggs with cowbird eggs; 6 of these are in the Lawrence Stevens

collection in the Santa Barbara Museum of Natural

History (all from San Luis Obispo and Santa Barbara counties); 10 are in the collections of the

Western Foundation (Santa Clara, San Benito, Alameda, Ventura, and Los Angeles counties). The 6

parasitized sets from San Luis Obispo and Santa

Barbara counties allow some idea of the rate of

parasitism there. These 6 sets are among only 11

sets from these 2 counties in that museum. This

rate of parasitism, 6 out of 11 (54.6 percent), is the

highest for any species of host on which that museum has data from the adjacent coastal counties

of San Luis Obispo, Santa Barbara, and Ventura.

The fact that the subspecies W. p. chryseola is

the segment of the total population of Wilsonia

pusilla that is affected heavily by the parasite is
32 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

shown by the holdings of the Western Foundation,

which contain 174 sets of eggs of the species as a

whole, 11 of which (6.3 percent) are parasitized; all

11 of these are W. pusilla chryseola (out of 148 sets

of that subspecies). Of the 34 known records of

parasitism, no less than 28 are from California

(Mono County south to Los Angeles County); the

others are from southern British Columbia, Alberta,

and Colorado.

CANADA WARBLER

Wilsonia canadensis (Linnaeus)

In 1963 (Friedmann, pp. 123-124) only 11 records

were given for this bird as a cowbird host. Bull

(1974:537) gives that number for New York State

alone (1 of his records was included in the earlier

account). To the 3 cases from Ontario reported in

the 1963 compilation may be added 1 more (4 cases

out of data on 19 Ontario nests in the files at

Toronto). It appears that in suitable localities the

Canada warbler may be fairly regularly parasitized.

HOUSE SPARROW

Passer domesticus (Linnaeus)

That the house sparrow is only a very occasional

host choice of the brown-headed cowbird is suggested by the small number of definite records of

parasitism out of many hundreds of nests examined

(742 in Ontario alone, none of them parasitized),

and especially by the fact that in most areas only

single instances have been reported—1 each from

California, Kentucky, Maryland, New York, and

Ohio, and 2 each from Colorado and Michigan. In

the 1963 compilation (Friedmann, p. 125) were

noted indefinite statements of "regular" parasitism

of house sparrows in Pennsylvania and in eastern

Kentucky, but no numbers or cases were given in

their original support. To all these we may add the

following: Bull (1974:537) lists 2 more instances

from New York; "Woods" (1972:14-15) mentions

1 from Kansas; Bennett (1973:9) reports 1 from

Nebraska; and Wauer (1973:178) lists the house

sparrow as a cowbird host in the Big Bend National Park, Texas. This last record involves the

race M. ater obscurus of the parasite, previously

noted but a single time in this relationship—in

southern California (Friedmann, 1963:125).

The fact that the eggs of the house sparrow and

of the brown-headed cowbird are quite similar may

have caused other cases of parasitism to remain

undetected.

BOBOLINK

Dolichonyx oryzivorus (Linnaeus)

A parasitized nest found near Oak Lake, Manitoba, 3 July 1959, is the second recorded instance of

the bobolink as a victim of the northwestern race

of the parasite, M. ater artemisiae. The record is in

the files of the Prairie Nest Records Scheme.

Throughout its breeding range the bobolink is relatively seldom victimized by the brown-headed cowbird. Since the 1963 compilation (Friedmann, p.

125) when 22 records of parasitism were reported,

only 11 additional ones have come to our attention

—from New York, Illinois, Wisconsin, and Ontario,

and the above case from Manitoba. In Ontario, 6

out of 58 nests reported had cowbird eggs in them,

an incidence of parasitism of 10.2 percent (Peck,

1975), a higher incidence than elsewhere.

EASTERN MEADOWLARK

Sturnella magna (Linnaeus)

Previously (Friedmann, 1963:126-127) there were

some 32 records of cowbird parasitism on this uncommonly reported host. We may now more than

double this number, as follows. In the nest record

files at Cornell University there are data on 244

nests of the eastern meadowlark, 15 of which (6.1

percent) had cowbird eggs in them. In Nebraska

Bennett (1973, 1974) reported 3 more instances of

parasitism; the Western Foundation has a parasitized set of eggs from Amboy, Illinois. In Ontario,

the nest records files at Toronto show that 8 (3.9

percent) of 206 nests reported were parasitized

(Peck, 1975). P. F. Elliott informs us that in Riley

County, Kansas, in 1974 and 1975 he found 28

(70.0 percent) of 40 nests to be parasitized. These

data support the earlier (1963) statement that the

eastern meadowlark is parasitized most heavily in

the central part of North America, although none

of the data previously available showed an incidence of parasitism approaching that of Elliott's

sample. The meadowlarks in Elliott's study fledged

a number of cowbirds. These are the first cases
NUMBER 255 33

known in which cowbird parasitism of this species

was successful. Elliott also found some evidence that

cowbirds in his area had specialized on and adapted

to particular host species, as indicated by the fact

that cowbird eggs found in meadowlark nests were

significantly heavier than those found in the nests

of smaller hosts such as the grasshopper sparrow

and the dickcissel (Elliott, 1975).

YELLOW-HEADED BLACKBIRD

Xanthocephalus xanthocephalus (Bonaparte)

To the few (11) records of parasitism on this

blackbird available in 1963 (Friedmann, pp. 127-

128) may be added 5 more: 2 from Spokane County,

Washington, where M. F. Willson (1966) examined

371 nests, 2 of which contained cowbird eggs; 1

from Sea Island, Victoria area, Vancouver Island,

13 June 1971, reported to us by Dr. J. B. Tatum;

and 1 each from Illinois and Minnesota, in the collections of the Western Foundation. Willson's report gives a clear indication of the very infrequent

parasitism this host experiences, which helps to

explain the paucity of published records. The only

observer who considered the yellow-headed blackbird to be a frequent victim was F. C. Lincoln

(1920:69), who gave no figures but merely stated it

to be so in the Clear Creek district of Colorado. In

light of more recent knowledge, Lincoln's statement

appears to be open to question.

RED-WINGED BLACKBIRD

Agelaius phoenicew (Linnaeus)

It has long been known that the red-winged

blackbird's suffering from the intrusions of the

brown-headed cowbird varies greatly in different

areas of the continent. In the eastern United States

and Canada it is seldom molested, but in the western prairie regions the picture is quite otherwise.

Thus, the Prairie Nest Records Scheme has no

fewer than 62 cases of parasitism on this host in

Alberta, Manitoba, and Saskatchewan in recent

years alone, a third as many as were available from

the entire range of the blackbird in 1963 (Friedmann, p. 130). The total number of records for the

host throughout its range has grown from about

180 in 1963 to over 500, and, as might have been anticipated, by far the most of these are from the central part of the United States and Canada. In the collections of the Western Foundation there are 1210

sets of eggs of this blackbird, 28 of which (2.3 percent) are parasitized. However, 17 of these are from

the Gulf Coast of southeastern Texas (23.9 percent

of 71 sets from there); 3 are from the Rocky Mountains (6.0 percent of 50 sets); elsewhere the incidence of parasitism is 1.9 percent (of 155 sets) from

the eastern and midwestern states, and 0.6 percent

(5 out of 779 sets) from California. In the Prairie

Nest Records at the Manitoba Museum there are

cards for 707 nests of the redwing, 62 of which (8.7

percent) were parasitized. An unusually high incidence of parasitism was reported from Arrowwood Refuge, North Dakota, where 13 of 17

redwing nests were so affected, with the result that

only 11 redwings and 3 cowbirds fledged from 5

successful nesis (Houston, 1973:885). This is almost as high an incidence of parasitism as was reported earlier (Friedmann, 1963:130) from Decatur

County, Kansas, but is based on more explicit

figures than was Colonel Wolfe's Kansas estimate.

The data in the Cornell University files, unfortunately given to us without geographical sources,

show that 176 (4.0 percent) of 4293 nests reported

had cowbird eggs in them. The Ontario files, at

Toronto, include 84 instances of parasitism in that

province, out of a total of 3376 nests reported, an

incidence of 2.5 percent.

As previously noted (Friedmann, 1963:128-130;

Dappen, 1967) several observers have suggested that

redwings in some areas are relatively free from

parasitism because breeding in colonies results in

efficient communal defense against cowbirds. Also

Robertson and Norman (in press) found that redwings attack mounted cowbirds placed near their

nests. While nest defense almost certainly reduces

the incidence of parasitism, it would seem that some

other factor must account for the virtual lack of

parasitism that occurs in some parts of the redwing's range because nest defense could not forestall all cases of attempted parasitism. One way to

determine whether low incidence of parasitism in

some areas is due completely to nest defense by

redwings or whether low preference for redwings

by cowbirds is also a factor is to determine the

incidence of parasitism of species nesting among

redwing colonies. If nest defense is the only explanation for the low incidence of parasitism, the
34 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

other species breeding with the redwings should

also experience little parasitism as the "communal

defense" should exclude cowbirds from the entire

area. Interestingly, Kelly Steele found that 2 of 3

yellowthroat nests in the Goleta Slough, Santa Barbara County, California, were parasitized, whereas

none of at least 20 redwing nests among which the

yellowthroat nests were built were affected. Similarly, Harrison (1975:249) reports "frequent" parasitism of swamp sparrow nests built among redwing

nests which were "rarely" parasitized.

TRICOLORED BLACKBIRD

Agelaius tricolor (Audubon)

A set of 4 eggs of the tricolored blackbird with

1 of the brown-headed cowbird (M. ater obscurus)

was collected in Merced County, California, 21 May

1944, by G. Brem, Jr., and is now in the collections

of the Western Foundation. The record is the first

one for this blackbird as a cowbird victim.

The tricolored blackbird can only be considered

as a species that is parasitized extremely seldom, as

vast numbers of its nests have been studied in the

past by several students, and unpublished experiments (by S.I.R.) have shown it to be an accepter

species. Thus, Orians (1961) and Payne (1969) between them examined thousands of clutches of eggs

of this species during the spring breeding season,

and never found a cowbird egg among them. More

recently Payne (1973:95) has suggested that the

excessive density of nests characteristic of the tricolored blackbird colonies may act as a deterrent

to the cowbird, either by intimidation or confusion,

and in this way keeps the species free from parasitism. Although this density of nests does seem to

prevent the red-winged and the yellow-headed

blackbirds from nesting in the same marshes, it is

not certain that this nest density would also totally

exclude the cowbird. If the deterrent effect of the

tricolor's nesting density were the only factor limiting the incidence of cowbird parasitism we might

see occasional cases of parasitism, as such a deterrent could hardly provide complete protection.

Yet the fact that only 1 instance of parasitism is

known among the tens of thousands of nests inspected suggests that cowbirds do not often attempt

to parasitize this species (although the deterrent

effect proposed by Payne may also be a factor).

Interestingly, a recent survey of A. tricolor colonies

(Dehaven, Crase, and Woronecki, 1975) finds a

tendency for smaller colonies than prevailed in the

past. If the deterrent effect of large numbers of tricolors is the only factor limiting cowbird parasitism,

then the latter phenomenon may become more

prevalent as this tendency toward smaller colonies

progresses.

ORCHARD ORIOLE

Icterus spurius (Linnaeus)

The total number of actual records of this oriole

as a cowbird victim was only 18 until recently

(Friedmann, 1963:131), but we may now add 17

more: 1 from Illinois, 1 from Iowa, 1 from Pennsylvania, 7 from Texas, 1 from Kansas, 1 from South

Dakota, and 5 from Ontario. The Pennsylvania instance and 3 of the Texas records are in the Western Foundation; another of the Texas sets is in the

Santa Barbara Museum of Natural History, and

still another in the Delaware Museum of Natural

History; 1 was reported to us by its finder, F. F.

Nyc, Jr.; and 1 was observed in the Big Bend country by Wauer (1973a). The Ontario records are in

the collection or in the nest card files of the Royal

Ontario Museum of Zoology. The others are observational records: South Dakota by Houston

(1972:872), and Kansas by Williams (1972:874). The

Texas set in Santa Barbara is unusual in that it

contains 5 eggs of the cowbird (M. ater obscurus)

and 3 of the oriole; it was taken near Henley,

Brazos County, Texas, 30 May 1951. The instance

reported by Nyc, found at Kingsville, Texas, contained eggs of both the brown-headed and the

bronzed cowbirds, with those of the oriole. The

Western Foundation has 83 sets of eggs of the

orchard oriole, 6 (7.2 percent) of which are parasitized.

The South Dakota record involves the northwestern race of the cowbird, M. ater artemisiae, for

which subspecies the orchard oriole is a "new"

victim.

The incidence of parasitism reported from Ontario, 5 nests out of 31 (16.1 percent), is so high as

to suggest that this oriole, like the hooded and

unlike the northern oriole, may be an accepter

species.
NUMBER 235 35

HOODED ORIOLE

Icterus cucullatus Swainson

The status of this oriole as a cowbird host choice

has become more fully documented in the past few

years. In the 1963 compilation (Friedmann, pp.

131-132) the total number of actual records was

only 10, to which figure we may now add 34 more.

One of us (S.I.R.), in 1975, found that 15 (71.4

percent) of 21 nests found in suburban areas of

Goleta and Santa Barbara were parasitized; also 1

nest (the only one found) at Carpinteria was so

affected, but not the single nest seen at Refugio State Beach. These findings show the hooded

oriole to be a major host in Santa Barbara County,

at least in the areas altered by man.

Of the remaining new records, more than half

are in the collections of the Western Foundation:

5 from California, involving the host race /. cucullatus californicus (from Fresno, Los Angeles and

San Diego counties), a race previously reported as

a cowbird host by Rowley (in Friedmann, 1963:

132) and, recently, by H. and O. Clarke (in

McCaskie, 1970:718) near Glendale, Los Angeles

County; 4 from Cameron County, Texas, and 1

each from Reynosa and from Matamoros, Tamaulipas, involving the host race /. cucullatus sennetti, and 1 from Arizona, involving the host race

/. cucullatus nelsoni. In the collections of Oregon

State University there are 2 more Cameron County

sets with cowbird eggs. Wauer (1973a) noted this

oriole as a cowbird victim in the Big Bend area,

Texas.

In 1 of the parasitized nests from Los Angeles

County, the orioles had built a new lining to the

nest over the cowbird eggs and had not yet deposited any of their own. This behavior has not

been noted before for the hooded oriole, but it has

been described (Friedmann, 1963:132-133) in the

case of the northern oriole, /. galbula. One other

instance, from Santa Barbara County, reported to

one of us by Richard Broder, was of a female

hooded oriole feeding a fledged young cowbird, 13

to 20 August 1974. No other fledglings were present

during the week-long observation, which suggests

that no young orioles survived. Earlier in the same

year, Broder saw the same individual oriole (or, at

least, one breeding in the same spot) with two

fledged young orioles, probably a first brood.

The Western Foundation's collections contain

148 sets of eggs of this oriole from within the area

of its sympatry with the brown-headed cowbird;

12 of these (8.1 percent) are parasitized. Unpublished experiments (by S.I.R.) have shown the

hooded oriole to be an accepter species.

NORTHERN ORIOLE

Icterus galbula (Linnaeus)

Experiments involving the addition of foreign

eggs to nests that contained 2 or more oriole eggs

demonstrated that this oriole is a rejecter species.

Artificial cowbird eggs were rejected at 18 nests.

Real cowbird or house sparrow eggs (which are

similar to cowbird eggs) were rejected at another 5

nests. The experiments, involving many species,

indicate that while ejection is the normal type of

rejection, this oriole is distinctive in that it ejects

by spiking cowbird eggs. Other rejecters eject by

lifting the eggs in their bills. These experiments

were done in California, Manitoba, Ontario, and

Connecticut and thus tested both the Bullock's and

Baltimore forms of this species (Rothstein, in

press (c)). Additional evidence of rejection was sent

to us by R. Robertson and R. Norman, who placed

real cowbird eggs in 5 nests at Delta, Manitoba.

Each cowbird egg was ejected.

The least demanding explanation for the origin

of rejection behavior is that it evolved in response

to brood parasitism and that it decreases the deleterious effects of the parasitism. This interpretation

will be supported if it can be shown that cowbird

parasitism, if accepted, reduces the oriole's reproductive output. Reproductive loss due to allowing

a cowbird egg to hatch is too poorly known to be

measured accurately, but that it occurs is indicated

in the case of every nest we know of in which a

cowbird egg hatched. One cowbird, but no orioles,

fledged from a nest reported by Nauman (1930).

Gregg (in Friedmann 1963:133) noted a nest containing a cowbird "big enough to fly" and 2 orioles

much less advanced in development. Tate (in Friedmann, 1963:133) found 2 dead oriole nestlings below a nest that contained 1 oriole and 2 cowbirds.

M. R. White (unpublished 1945 MS in files of the

University of Michigan Biological Station) described a nest in which a cowbird hatched 1 to 2

days before 4 orioles hatched. One of the orioles

died before it was 4 days old and the cowbird was
36

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

so advanced in development that it fledged when

the remaining orioles were only 6 to 7 days old.

(Orioles fledge after 11 to 14 days; Bent, 1958.)

Each nest demonstrates either the death of some

oriole young or such a great disparity in size between cowbird and oriole nestlings that the viability of the latter was almost certainly reduced. Also,

Newman (1969) reported a fledged cowbird being

fed by a female oriole that appeared to have no

young of her own. Thus, the rejection behavior

elucidated by the experiments has adaptive value

that is potentially very high, although knowledge

of the actual rate of parasitism of the oriole is

needed before the adaptive value can be quantified (Rothstein, 1975b).

Only a small number of additional records of

natural parasitism have come to light in recent

years but the oriole's rejecter status makes the

paucity of records more understandable. In New

York, Bull (1974:537) reported 6 instances of parasitism, 5 of which are additional to the 1963 compilation (Friedmann, pp. 132-133). T. S. Smith

(1972) observed the ejection of a naturally deposited cowbird egg. This occurred in Nebraska

and involved the eastern race of the cowbird, M.

ater ater. The records reported by White and

Newman (above paragraph) which occurred near

Pellston, Michigan, and in Johnston County, Oklahoma, respectively, also refer to M. a. ater. Eight

cases of parasitism by this race were reported from

Ontario (Peck 1975). (Possibly some of these Ontario cases are referable to M. ater artemisiae since

this race replaces M. a. ater in extreme western

Ontario.) The Western Foundation has 2 sets

parasitized by M. a. ater, 1 from Pennsylvania, the

other from Ontario. There are 4 new records for

the northwestern race of the parasite, M. ater artemisiae. One, published by Nero (1971), was the

first record for Manitoba. A second Manitoba case

was found by R. S. Miller in 1972 at Delta, Manitoba. The third case, now in the Delaware Museum

of Natural History, was collected at Belvedere,

Alberta. The fourth case, from Minnesota, is at

the Western Foundation.

Except for Newman's (1969) record which may

have involved a hybrid, all the above records of

parasitism refer to the eastern (Baltimore) form of

this oriole. There are 5 new records for the western

(Bullock's) form. The Santa Barbara Museum of

Natural History has a set of 4 oriole eggs and 1

cowbird egg taken at Vernon, Texas, 31 May 1966,

and one of us (S.I.R.) found 3 cases of parasitism

(described below) near Shandon, San Luis Obispo

County, California. The Western Foundation has

a parasitized set from El Centro, Imperial County,

California. The Texas record is referable to M. ater

ater, the 4 California records to M. ater obscurus.

While isolated reports of parasitism of the oriole

are important, data on the incidence of parasitism

in large series of nests have greater value. The

Western Foundation has 283 sets of eggs, only 4 of

which (1.4 percent) contain cowbird eggs. The 8

Ontario records reported by Peck (1975) make up

2.5 percent of the total sample of 318 nests in the

Ontario Nest Record Scheme. The 3 records from

Shandon, California, make up 8.8 percent of the

34 nests S.I.R. found in that area in 1974 and

1975. Of course, even these data do not accurately

reflect the proportion of northern oriole nests actually parasitized because orioles may remove most

cowbird eggs before the eggs are seen.

Techniques to estimate the amount of parasitism

of rejecter species that goes unseen are discussed

elsewhere (Rothstein, in press (b)). Two additional

techniques that are especially applicable to this

oriole are as follows. (1) Although these orioles

usually drop ejected cowbird eggs at least several

meters from their nest (Rothstein, in press (c)),

some apparently drop them directly from the nest

(see Friedmann, 1963:132-133; Smith, 1972). Inspection of the ground beneath oriole nests might reveal some of the cowbird eggs ejected before the

inspection of the nest by an observer. Parasitism

at 1 of the Shandon nests was detected in this

manner when pieces of cowbird eggshell were

found directly beneath an oriole nest that was not

close to any other nests. (2) Experiments on the

ontogeny of the northern oriole's egg recognition

(S.I.R., in prep.) showed a small proportion of

orioles learn to accept artificial cowbird eggs added

to nests before the onset of laying. Orioles breeding

for the first time apparently imprint on the first

eggs that appear in their nest. The remaining

orioles reject artificial cowbird eggs added before

the onset of laying but most of them do not succeed

in ejecting the artificial (plaster) egg because they

cannot spike it. They peck at it and damage it but

after several days some (perhaps all) habituate to

the egg and cease their rejection attempts. The end

result, whether the orioles initially accept the arti-
NUMBER 235 37

ficial egg or first try to eject it and then habituate,

is that rejection behavior is "turned off" during

part or all of the laying stage, if an artificial cowbird egg is added before laying begins. Thus, a

sample of birds subjected to this experiment should

reveal much of the natural parasitism that occurs,

although some parasitism might still be missed if

cowbirds lay before orioles have habituated and if

the appearance of a naturally deposited cowbird

egg is very different from that of the artificial egg

to which the orioles imprinted or habituated. The

presence of the artificial cowbird egg in such nests

should not alter the likelihood of natural parasitism because the presence of a cowbird egg has

little or no effect on the probability that a nest will

receive additional cowbird eggs (Mayfield, 1965).

One nest in the ontogeny experiments at which

orioles accepted the artificial cowbird egg was naturally parasitized as was another nest at which the

orioles habituated to the artificial cowbird egg

(nests 75-96 and 75-116, respectively). The cowbird

eggs in these nests were laid between 22 and 28

May 1975. Both were accepted since they were still

present and undamaged on 5 June. The cowbird

egg was missing from nest 75-116 on 12 June but

as the nest then contained 1 dead plus 1 live oriole

nestling and an addled oriole egg, the cowbird

could have hatched, then died and been removed.

The cowbird egg in nest 75-96 did not hatch. It

and 2 dead oriole nestlings were in the nest on

17 June.

Thus, the 3 cases of parasitism near Shandon

would probably not have been detected had not

special techniques been applied (checking the

ground beneath nests, imprinting and habituating

orioles to cowbird eggs). These special techniques

were not applied at most of the other 34 nests

studied near Shandon so the incidence of parasitism could have been higher than 3 of 34 (8.8

percent), since much natural parasitism would still

have gone undetected. It is important to point out

that cowbirds are uncommon near Shandon so the

relatively high figure (8.8 percent) for the minimum incidence of parasitism was not due to an

unusually large number of cowbirds. Rather, it was

most likely due to the fact that the special techniques applied made it possible to detect parasitism that normally goes unseen. Application of

these techniques in other areas where cowbirds are

more common might reveal much higher incidences

of parasitism. As with the cedar waxwing (discussed previously) these data on cowbird parasitism

near Shandon imply that cowbirds not infrequently

parasitize rejecter species even though their chances

for reproductive success are virtually nil.

RUSTY BLACKBIRD

Euphagus carolinus (Miiller)

In the collections of the Royal Ontario Museum

of Zoology is a set of 5 eggs of the rusty blackbird

with one of the brown-headed cowbird (M. ater

artemisiae) taken at Okotaks, Alberta, 24 June 1917,

by E. Beaupre. Previously (Friedmann, 1963:134),

there were only 3 records known to us, 2 definite

and 1 indefinite, of parasitism on this blackbird, all

from Alberta.

BREWER'S BLACKBIRD

Euphagus cyanocephalus (Wagler)

It was known previously (Friedmann, 1963:134)

that Brewer's blackbird was a frequent host of the

brown-headed cowbird in Alberta and Montana,

but the actual extent to which it is imposed upon

in the northwestern prairie areas could hardly be

appreciated from the nonquantitative information

previously available. The Prairie Nest Records

Scheme has kindly sent us copies of all their cowbird data up to mid-1975, and this reveals that of

420 records of cowbird parasitism on 37 species of

hosts in Alberta, Saskatchewan, and Manitoba, no

fewer than 85 were on Brewer's blackbirds, the

most frequently victimized of any of the resident

passerine species in terms of total number of nests

found to be parasitized, not in percentages. Next

in order of total number of parasitized nests came

the clay-colored sparrow and the red-winged blackbird, each with 65 instances in the same area. There

were, in all, records of 371 nests of Brewer's blackbird in the Prairie Nests Record Scheme, so the

85 instances with cowbird eggs amount to 22.9 percent of the total, a fairly high incidence of parasitism.

Even more numerous and illuminating data are

provided by Furrer (1974 and personal communication) who studied this species in the "Potholes

Region" (Grant and Adams counties) of eastern
38 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Washington in 1969 and 1970. Overall parasitism

on 837 nests was 32.0 percent. There was much

seasonal variation in the intensity of parasitism.

Cowbirds did not become common in the area until

late April, and consequently early nests suffered

much less parasitism than later ones. In 1969, there

was 8.0 percent parasitism of 138 nests in which

the first egg was laid between 10 April and 9 May,

whereas 50.9 percent of 177 clutches started between 10 May and 20 June were parasitized. Similarly, in 1970, 6.5 percent of 277 clutches started

in the early interval were parasitized while 59.6

percent of 245 clutches in the later interval were

parasitized. The incidence of parasitism of late

nests reached such a high level in 1970 that 87.5

percent of 32 clutches begun after 8 June were

victimized. Parasitism at very early nests resulted

in total failure for the cowbirds; the cowbird eggs

laid in all 10 nests parasitized between 10 April

and 3 May (1969, 1970) were laid so late in the

host's nesting cycle that they could not have received sufficient incubation for hatching.

In addition to the incidence of parasitized nests,

the incidence of multiply parasitized nests also increased as the season progressed. Multiple parasitism peaked between 9 and 14 June. Nests parasitized during this period received an average of

2.67 cowbird eggs. Several times 5 cowbird eggs

were laid in the same nests and 1 nest (that was

probably abandoned) contained 7 cowbird eggs and

1 Brewer's egg. Some nests subjected to multiple

parasitism received cowbird eggs after earlier eggs

had already hatched. The unusually intense parasitism of Brewer's in the Potholes Region may not

be due to cowbirds in that area having an especially

strong preference for parasitizing this species.

Furrer points out that the area has a depauperate

avifauna; there are few potential hosts besides

Brewers blackbird.

Furrer estimates that about 50 percent of the

female cowbirds that parasitized Brewer's nests removed a host egg. Surprisingly, the data showed no

decrease in host fledging success attributable to the

presence of cowbird nestlings although Furrer suggested that post-fledging success might be reduced

among host young reared with cowbirds. It is also

worth pointing out that caring for a cowbird can

reduce fitness even if the normal number of host

young are fledged from an individual nest because

the parents' chances of surviving to breed again

may be reduced. The extra care devoted to the

cowbird produces an additional strain on the

parents with no immediate increased output of host

offspring and perhaps with a decrease in subsequent output of the breeding pair.

Furrer's work makes it evident that numerous

cowbirds are reared by this species. About onethird of all cowbird eggs resulted in fledglings. The

success rate of cowbird eggs in nests in bushes over

land was higher than that in nests over water or on

the ground. Furrer found several nests in each year

of his study that fledged only cowbirds. In 1970 he

found 6 nests, each of which contained 3 cowbirds

that reached ages of at least 8 days and therefore

probably survived long enough to fledge. That

Brewer's rear large numbers of cowbirds is also

shown by Gordon H. Orians' studies in the Potholes Region (pers. coram.). Despite its large size,

Brewer's blackbird is evidently a good host.

We have compared Furrer's data from 1969 and

1970 with data Henry S. Horn (pers. comm.) collected in the same region in 1964, 1965, and 1966.

The general trends Furrer found are also shown by

Horn's data. The only major difference between

the 2 bodies of information is that Horn found less

parasitism. In Horn's study 2.6 percent of 234

clutches started on or before 10 May were parasitized, whereas Furrer's study showed 6.5 and 8.0

percent parasitism for the period. Similarly, 26.8

percent of 56 clutches started after 10 May were

parasitized according to Horn's study whereas

Furrer found 50.9 and 59.6 percent parasitism for

this period. Quantitative comparisons are difficult

but it is evident that the incidence of multiple

parasitism was higher in Furrer's study than in

Horn's. This increase in parasitism over a 7 year

period, revealed by a comparison of Horn's and

Furrer's studies, is almost certainly a reflection of

the fact that the cowbird is a relative newcomer to

the Potholes Region and that it increased in population between the two studies. We are indebted

to Drs. Furrer, Horn, and Orians for making their

data available to us. Dr. Furrer will publish more

detailed analyses of his information elsewhere.

All the data discussed above refer to the northwestern race of the cowbird (M. ater artemisiae).

Previously (Friedmann, 1963:134-135) there was

but a single instance on record of Brewer's blackbird as a victim of the dwarf or southwestern race

of the cowbird (M. ater obscurus). A second record,
NUMBER 235 39

from near Buckeye, Maricopa County, Arizona, is

in the collections of the Western Foundation. During May 1975, one of us (S.I.R.) found 4 additional cases of parasitism by M. a. obscunis, 1 near

Tupman and 3 near Shandon in Kern and San

Luis Obispo counties, California, respectively. The

3 Shandon nests constituted 3.6 percent of 83 nests

found in 1974 and 1975. The Tupman nest was 1

of 2 found on 20 May 1975. Cowbirds were abundant at Tupman, but uncommon near Shandon. An

interesting facet of parasitism by M. ater obscurus

is that the size differential between it and Brewer's

blackbird is even greater than is the case for M.

ater artemisiae. In marked contrast to Furrer's experience in Washington is the situation in western

Ontario, where Peck (1975) reported not a single

one of 171 nests recorded in the Ontario nest

records files was parasitized.

Strangely enough, in earlier records, Brewer's

blackbird was never mentioned as having actually

reared young cowbirds. This omission has now been

corrected by Furrer's and Orians' numerous observations. In a similar vein, Dr. J. B. Tatum sends

us a record from Saanich, near Victoria, Vancouver

Island, 23 July 1973, of a Brewer's blackbird feeding 2 fledged cowbirds. Also, 1 of the parasitized

nests S.I.R. observed near Shandon produced a

fledgling cowbird. Lastly, on 3 August 1975, S.I.R.

observed a female Brewers feeding a fledged cowbird near Crowley Lake, Mono County, California

at an altitude of 7200 feet. This is an unusually

late date and an unusually high altitude for cowbird parasitism.

COMMON GRACKLE

Quiscalus quiscula (Linnaeus)

The grackle has been reported very rarely as a

cowbird victim. To the six earlier records (Friedmann, 1963:135) may be added 5 more: a parasitized nest in Greeley County, Nebraska (Bennett,

1974), 1 in Ontario (Ontario nest records files,

Toronto), 1 at Seneca, Maryland, 22 April 1941 (in

the Delaware Museum of Natural History); and

2 other records from New York State (Bull, 1974:

537). The record from Maryland is the first one

involving the host subspecies Q. quiscula stonei

(all the others refer to Q. quiscula versicolor). The

Nebraska record is the second for the cowbird race

M. ater artemisiae.

It should be pointed out that numerous experiments have shown the grackle to be an accepter

species (Rothstein, 1975a). Therefore, the small

number of records of parasitism cannot be due to

rejection behavior by the host, but must reflect an

actual absence of parasitism by the cowbird. The

reason for the lack of parasitism is not clearly

known. The cowbird may avoid parasitizing species

as large as the grackle, but the American robin

and brown thrasher are nearly as large and have

been found to be parasitized many more times than

the grackle, even though they are rejecter species.

Perhaps the grackle's colonial nesting may be a

factor. It may be difficult for cowbirds to escape

detection when entering grackle colonies. But many

grackles do not nest in colonies, in which case

other factors may be responsible for the low incidence of parasitism. In the nest card records files

at Cornell University there are data on 1795 nests

of the grackle, none of which contained cowbird

eggs. (There were indefinite statements of 2 ot

them being parasitized, but nothing in the way

of a reliable record). In the Ontario files at Toronto

are data on 1399 nests, only 1 of which was parasitized.

WESTERN TANAGER

Piranga ludoviciana (Wilson)

To the 5 previous records (Friedmann, 1963:135;

1971:246) of the western tanager as a victim of the

brown-headed cowbird may be added three more,

all from Mono County, California: one in the

Western Foundation; one in the Santa Barbara

Museum of Natural History; and one found, but

not collected, by John Schmitt, along the Little

Walker River, 30 June 1973. This nest contained

two newly hatched tanagers, one tanager egg, and

one egg of the cowbird. The western tanager is

still to be looked upon as an uncommonly reported host. Whether the rarity of reported parasitism is due to a lack of observations or to a very

low rate of parasitism, or even to rejection behavior, is an interesting question, since this species'

eastern counterpart, the scarlet tanager, seems to

be very heavily parasitized.
40

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

SCARLET TANAGER

Piranga olivacea (Gmelin)

The true status of this species as a cowbird host

is not well understood. Only about 50 cases were

known as of the 1963 review (Friedmann, p. 136).

This is not a large number for such a common

and widespread species. However, the relative

paucity of records may be due largely to the fact

that this species has a nest that is difficult to find

and to reach, since it is usually 7 or more meters

above the ground. Several studies listed in 1963,

and based on a series of nests, reported high rates

of parasitism. The situation is further clarified by

Prescott's (1965) monograph. Eleven of 14 (78.6

percent) nests of known contents found in southern Michigan from 1947 to 1949 contained cowbird eggs. An additional nest contained only an

advanced cowbird nestling when found. Six nests

(among the 11 parasitized ones) whose contents

were known and that were successful fledged

7 cowbirds and 8 tanagers. The detrimental effects

of cowbird parasitism were great and seemed to

be due largely to egg removal by adult cowbirds

and/or to decreased egg production by female tanagers. Prescott occasionally observed female cowbirds visiting tanager nests. Some visits even occurred while nestling cowbirds were in the nest,

but no adult cowbirds were seen to feed nestlings.

On one occasion Prescott watched a female cowbird lay in a tanager nest. This observation was

unusual because the cowbird removed a host egg

6 seconds before laying her own egg, whereas workers who investigated other species of hosts reported that host eggs are not removed at the time

the cowbird deposits her own egg. A very high incidence of parasitism is also shown by nests studied

near Pellston, Michigan. A survey of unpublished

reports filed (as of 1969) at the University of Michigan Biological Station shows that all 5 scarlet

tanager nests studied there between 1940 and 1966

were parasitized. One nest, studied by J. K. Boon

in 1966, had 2 tanager and 4 cowbird eggs.

Since a number of investigators working in diverse areas (data listed herein from Norris, 1947,

and in the Friedmann, 1963, review) have reported very high rates of parasitism, it is possible

that the scarlet tanager is one of the most heavily

parasitized host choices in certain areas. Bull (1974:

537) mentions 12 instances of parasitism in New

York State; 9 of these are additional to our earlier

compilation. In the files of the Ontario nest records,

at Toronto, are 2 more cases out of 36 nests reported from that province, a much lesser frequency

of parasitism.

SUMMER TANAGER

Piranga rubra (Linnaeus)

In view of the infrequency with which this tanager had been reported earlier as a cowbird victim

(only 18 records in Friedmann, 1963:136) we may

add that in the 12 years since then, only a single

further instance has come to our notice—a parasitized set of eggs from Mena, Arkansas, 25 May

1955, in the collections of the Western Foundation.

CARDINAL

Richmondena cardinalis (Linnaeus)

Previously (Friedmann, 1963:137-138; 1966:5) a

large number of records had been noted, with an

unusually wide disparity in the incidence of parasitism in various areas (from "rarely parasitized" to

over 60 percent). This lack of uniformity made it

desirable to seek further quantitative data. Toward

this end we may note that in the Ontario nest

records files at Toronto there are 35 instances of

parasitism (19.0 percent) of a total of 184 Ontario

nests reported. The files at Cornell University, unfortunately given us without localities, show 49

parasitized nests out of a total of 1018 reported

(4.8 percent).

PYRRHULOXIA

Pyrrhuloxia sinuata (Bonaparte)

To the 9 records of this bird as a cowbird

victim previously reported (Friedmann, 1963:138;

1971:246-247) may be added 2 more: 1 in the

collections of the Western Foundation, taken at

Corpus Christi, Texas, 30 May 1912; and 1 in the

Delaware Museum of Natural History, from Lytle,

Texas, 20 July 1932.
NUMBER 235 41

ROSE-BREASTED GROSBEAK

Pheucticus ludovicianus (Linnaeus)

A new northwesternmost record of this bird as a

victim of the brown-headed cowbird is a parasitized

nest found at Leduc, Alberta (Prairie Nest Records,

Manitoba Museum); previously (Friedmann, 1963:

138) Saskatchewan and North Dakota were the only

areas where this grosbeak was known to be parasitized by the northwestern race of the cowbird (M.

ater atemisiae). In the files of the Ontario nest

records, Toronto, are data on 193 nests, 12 of

which (6.2 percent) were parasitized (by M. ater

ater).

BLACK-HEADED GROSBEAK

Pheucticus melanocephalus (Swainson)

A parasitized nest of the black-headed grosbeak

reported from Butte County, California, by Dembosz, Fickett, and Manoles (1972:979) refers to the

host race P. melanocephalus maculatus, a subspecies

not hitherto recorded as a cowbird victim. A second instance, from San Luis Obispo County, California, 1 May 1937, is in the Lawrence Stevens

Collection in the Santa Barbara Museum of Natural History. The cowbirds involved in these 2

cases are of the race M. ater obscurus, a subspecies

not previously reported as a parasite on any race of

this grosbeak.

The nominate race of the grosbeak has been reported as a cowbird host a number of times in

British Columbia (Friedmann, 1971:247), and in

Montana, Utah, Colorado, Nebraska, and Kansas

(Friedmann, 1963:139). Still, on the whole, the

black-headed grosbeak appears to be parasitized

much less frequently than the rose-breasted species.

In the holdings of the Western Foundation are 271

sets of eggs of P. melanocephalus, none of which

are parasitized, while of P. ludovicianus there are

59 sets, 5 of which (8.1 percent) have cowbird eggs.

BLUE GROSBEAK

Guiraca caerulea (Linnaeus)

The Western Foundation's collections contain 10

parasitized sets of eggs of this bird, about a fifth as

many as the total number of records known earlier

(Friedmann, 1963:140; 1971:247). These add considerably to the documentation of the blue grosbeak-brown-headed cowbird relationship. If we

consider them according to the subspecies of the

host and in relation to the total number of sets

of eggs of each in the Western Foundation, we get

the following: G. caerulea caerulea, 23 sets, 4 of

which (17.4 percent) are parasitized; G. caerulea

interfusa, 9 sets, 2 of which (22.2 percent) are parasitized; G. caerulea salicaria, 37 sets, 4 of which

(10.8 percent) have cowbird eggs.

LAZULI BUNTING

Passerina amoena (Say)

A few years ago (Friedmann, 1971:247) it was

erroneously stated that the lazuli bunting had been

listed many times as a victim of the brown-headed

cowbird. Actually, including the data therein presented, there were then available only 13 records of

parasitism on it. To these we may now add 10

more: 2 from California (Madera and Calaveras

counties), 3 from Oregon (Wasco County), all in the

collections of the Western Foundation; 3 from Utah

(1 from Springdale, in the collections of the Western Foundation, and 2 from Washington and Provo

counties in the collections of Brigham Young University); another from San Luis Obispo County,

California, in the Santa Barbara Museum of Natural History; and 1 from Maricopa County, Arizona, in the Western Foundation's collections. This

remarkable increase in the number of records suggests that the lazuli bunting may yet uphold

the statement made prematurely (not proleptically)

in 1971. The Western Foundation has a total of 107

sets of eggs of this bunting; 7 of these (6.5 percent)

have cowbird eggs.

The closely related indigo bunting has a much

higher incidence of parasitism, 9 of 63 sets (14.3

percent) in the Western Foundation. In sizeable

data brought together in 1963 (Friedmann, pp. 140—

141) the indigo bunting was found to show a still

higher rate of parasitism, 40 to 42 percent in Ohio.

Peck (1975) notes that 19 of 88 (21.6 percent)

Ontario nests were parasitized.

PAINTED BUNTING

Passerina ciris (Linnaeus)

A set of 2 eggs of this bunting with 1 of the

brown-headed cowbird, taken 2 miles north of
42 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Royse City, Washington County, Texas, on 23 May

1939, and now in the Western Foundation, is the

first for the host-parasite combination P. ciris pallidior and M. ater ater, although the area is fairly

close to where the ranges of M. ater ater and M.

ater obscurus meet. The latter race of the cowbird

has long been known to parasitize this subspecies

of the bunting, while M. ater ater has been known

to victimize P. ciris ciris.

DICKCISSEL

Spiza americana (Gmelin)

P. F. Elliott has informed us that parasitism of

this species is very frequent in Kansas. Working in

Riley County during 1974 and 1975, he found that

18 (94.7 percent) of 19 nests were parasitized,

whereas the previous "high" for parasitism of this

species was 78.2 percent (Zimmerman, 1966), also in

Kansas.

PURPLE FINCH

Carpodacus purpureus (Gmelin)

Dr. J. B. Tatum informs us of an observation of

an adult purple finch feeding and attending a recently fledged brown-headed cowbird near Victoria,

southern Vancouver Island, British Columbia, in

1969, and of a second, similar instance at North

Saanich, southern Vancouver Island, observed by

Stuart Johnston, 9 June 1973. Crowell and Nehls

(1973:911) noted still another case in the same general area. Aside from the relative rarity of records

for the purple finch as a cowbird host, these are

the first ones reported for the western race of the

finch (C. purpureus californicus). There had been

only 1 previous record of the purple finch's rearing

the young cowbirds.

Data on the nominate race of the purple finch

from Cheboygan and Emmet counties, Michigan, in

the area around the University of Michigan Biological Station, indicate that this species is, in at

least this one region, a common host. In the files of

the station are student reports on 14 nests studied

between 1926 and 1968. Eight (57.1 percent) of

these were parasitized. This species is a cardueline

finch and since this group feeds its young on a type

of food—regurgitated plant seeds—unusual for a

passerine its members may be among the few passerines whose diet is unsuitable for cowbirds. Thus,

it is of interest to determine what proportion of

cowbird nestlings are able to survive under this

feeding regime. Four of the 8 parasitized nests are

irrelevent to this question because of nest predation, or insufficient data, or because the observers

removed the cowbird eggs. At 1 of the remaining 4

nests (studied by C. V. Davis in 1941) a cowbird egg

disappeared about the time the finch egg hatched.

Possibly the cowbird hatched, but soon died, and

was then removed by the finches. At another nest

(studied by W. F. Sell in 1962) a cowbird nestling

disappeared when it was 2 to 3 days old. But at the

last 2 nests (studied by W. F. Sell in 1965 and by

A. P. Sibole and S. I. Rothstein in 1968) a cowbird

nestling fledged. In assessing the potential threat

that the parasitism poses to the finch's reproductive

output, it is important to note that the cowbird

hatched 1 to 3 days earlier than the finches at each

of 3 nests at which investigators reported hatching

times. It is also important to note that the high rate

of parasitism in this Michigan area is not a transitory phenomenon. The 2 oldest nests in the sample, studied in 1926 and 1941, were parasitized as

were the 2 most recent nests, studied in 1968.

Apparently the situation described for Michigan

applies also to New York, from which state Bull

(1974:537) mentions 15 instances of parasitism. Of

these, 10 are additional to the earlier compilation

(Friedmann, 1963:144). In Ontario, as well, the

purple finch is a frequent host; in the nest records

files at Toronto, 27 out of 70 nests reported (38.6

percent) were parasitized, a higher incidence of parasitism than for any other host species of which at

least 20 nests were reported. All these new data

provide a great change in our knowledge since the

1963 compendium.

HOUSE FINCH

Carpodacus mexicanus (Miiller)

The house finch has been reported as a victim of

the brown-headed cowbird relatively seldom (11

records, Friedmann, 1963:145; 1966:6). It may therefore be worth noting 7 more records: a set of 4 eggs

of the finch and 1 of the cowbird, taken in San

Luis Obispo County, California, 21 May 1933, now

in the Santa Barbara Museum of Natural History;

an observation in southern Vancouver Island (Vic-
NUMBER 235 43

toria area), 15 July 1970; a parasitized set collected

at Mesa, Maricopa County, Arizona, 29 June 1922,

now in the Delaware Museum of Natural History;

another found at Fresno, California, 14 May 1975;

a parasitized set taken at Hunter, Salt Lake

County, Utah, 15 June 1916, by J. W. Sugden, now

in the Western Foundation; a cowbird egg from a

nest of a house finch at Carlsbad, Eddy County,

New Mexico, 10 July 1922, in the Thomas Burke

Memorial Museum, University of Washington; and

a record from Premont, Jim Wells County, Texas

(Cornell University files). The record from Carlsbad, New Mexico, involves the nominate, eastern

race of the parasite, for which it is the second case

reported. All of the present records involve the host

race C. mexicanus frontalis.

In the early 1940's the house finch was introduced

on Long Island, New York, and has become established there. According to Bull (1974:537) it has

been found to be parasitized there in at least 3 instances. Here the parasite is nominate, M. ater ater.

Bull has kindly supplied the data for 2 of these

cases: Bellport, Suffolk County, 3 May 1965, with

1 finch egg and 2 cowbird eggs; Lloyd's Harbor,

Suffolk County, 29 May 1966, nest in a hanging

flower pot on a house porch, 5 eggs of the finch and

1 of the parasite.

COMMON REDPOLL

Acanthis flammea (Linnaeus)

This far northern finch was previously known as

a victim of the brown-headed cowbird on the basis

of a single record, a parasitized nest found at

Castor, Alberta, 25 June 1959 (Friedmann,

1963:146). The Prairie Nest Records Scheme includes 2 such cases, both found on the same day in

the same place; 1 of them is most probably the same

as the record previously mentioned.

PINE SISKIN

Spinus pinus (Wilson)

To the 11 earlier records of parasitism on this

bird (Friedmann, 1963:146-147) may be added 3

more. One of these, from Manitoba (Prairie Nest

Records, Winnipeg) is the third case known to us

involving the cowbird race M. ater artemisiae. The

other 2, from Ontario, out of 11 nests reported to

the nest records files at Toronto, refer to the nominate race of the parasite.

AMFRICAN GOLDFINCH

Spinus tristis (Linnaeus)

Lemon (1969) reported a goldfinch parasitized by

a brown-headed cowbird near Victoria, southern

Vancouver Island. This record must refer to the

host subspecies S. tristis jewetti, which is an addition to the host catalog. Of the subspecies S. tristis

salicamans, no fewer than 13 parasitized sets of

eggs, all from California (Merced, San Benito,

Ventura, Los Angeles, and San Diego counties) are

in the collections of the Western Foundation.

These 13 constitute 6.8 percent of 191 sets of that

subspecies in that collection; the host frequency

is about the same for the Foundation's material of

eastern S. tristis tristis—3 parasitized sets (6.6 percent) of 45 sets there. However, in 4 "source studies"

of the eastern goldfinch population from Quebec

and Michigan (Friedmann, 1963:147-148) there

were only 19 parasitized nests out of 1484 reported,

an incidence of only about 1.3 percent. Of 49 nests

from Saskatchewan, Manitoba, and Alberta reported to the Prairie Nest Cards files at Winnipeg,

only 2 (4.0 percent) were parasitized; of 439 nests in

Ontario, 18 (4.1 percent) were parasitized (Ontario

Nest Records, Toronto); the files at Cornell University show 12 (3.1 percent) of 390 nests were so

affected.

During 1968 and 1969, one of us (S.I.R.) found 12

nests of this species in Cheboygan and Emmet counties, Michigan. One of these nests was parasitized.

The cowbird egg hatched 2 to 4 days before the 5

goldfinch eggs began to hatch. However, the cowbird showed little weight gain. On 22 July 1968, the

day it probably hatched, the cowbird weighed 2.8 g.

On 23 July, it was 3.5 g, and on 24 July it was

dead and weighed 2.5 g. Evidently, the cowbird

was not adequately nourished by the diet of regurgitated seeds this cardueline finch normally feeds

to its young. Interestingly, on 24 July, the dead

cowbird was draped over the nest rim in a manner

similar to that in which cardueline finches drape

fecal sacs around the sides of their nest.
44 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

LESSER GOLDFINCH

Spinus psaltria (Say)

To the few (7) records of this goldfinch as a cowbird victim in California (Friedmann, 1963:148)

may be added 6 more, 5 of which, are among a total

of 8 parasitized sets of eggs in the collections of

the Western Foundation, an incidence of parasitism

of 5.2 percent out of 153 sets there; the other 3

of these 8 were included in the 1963 statement.

The sixth record, observed by D. A. Schroeder at

Three Pines Campground, Ventura County, is the

first case in which a cowbird was successfully reared

by this species of host. When first found, on 12 May

1972, the nest contained 3 goldfinch eggs and 1 cowbird egg. Between 12 and 21 May, 2 of the goldfinch eggs fell from the nest when a late snowstorm

caused the branches supporting the nest to tilt

over. The cowbird hatched on 21 or 22 May and

fledged on 31 May. The 1 remaining goldfinch egg

hatched on 24 May, but the nestling disappeared 2

days later.

GREEN-TAILED TOWHEE

Chlorura chlorura (Audubon)

Previously (Friedmann, 1963:150) we knew but a

single record of this towhee as a victim of the

northwestern race of the brown-headed cowbird,

M. ater artemisiae. We may now add 3 more instances, 2 from Mono County and 1 from Tuolumne County, California, all in the collections of

the Western Foundation. There still are only a

small number of reports of parasitism on the greentailed towhee by the nominate race of the cowbird, although it has been said to be a favorite host

choice in Mesa County, Colorado, and in San

Miguel County, New Mexico (Friedmann,

1963:150).

RUFOUS-SIDED TOWHEE

Pipilo erythrophthalmus (Linnaeus)

In the last general survey of the brown-headed

cowbird's hosts (Friedmann, 1963:150-151), it was

noted that few instances of parasitism on this towhee had been reported from California, but that

the recent spread and increase of the parasite in the

southern parts of that state would probably result

in further records. Three such instances have come

to light: 1, collected in San Luis Obispo County,

2 June 1934, is now in the Santa Barbara Museum

of Natural History, and 2 more—1 from near

Mendota, Fresno County, 1 June 1935, and 1 from

near Stockton, 21 June 1942—are in the collections

of the Western Foundation. The San Luis Obispo

record involves the host subspecies P. erythrophthalmus megalonyx; the other 2 have to do with

the race P. erythrophthalmus falcinellus. The last

mentioned subspecies is new to the host catalog of

the parasite.

The Western Foundation's collections contain

393 sets of eggs of this towhee (all races), 11 of

which (2.8 percent) are parasitized. A list of only

those races of the host known to be victimized by

the cowbird, yields the following data: P. erythrophthalmus erythrophthalmus, 55 sets, 9 (16.3 percent) parasitized; P. erythrophthalmus falcinellus,

8 sets, 2 (25.0 percent) parasitized; P. erythrophthalmus canaster, 3 sets, none parasitized; P. erythrophthalmus arcticus, 7 sets, none parasitized; P. erythrophthalmus montanus, 14 sets, none parasitized;

P. erythrophthalmus curtatus, 1 set, not parasitized;

P. erythrophthalmus oreganus, 37 sets, none parasitized; P. erythrophthalmus falcifer, 57 sets, none

parasitized; and P. erythrophthalmus megalonyx,

173 sets, none parasitized.

The Ontario nest records files at Toronto have

data on 70 nests, 14 of which (20.0 percent) were

parasitized.

BROWN TOWHEE

Pipilo fuscus Swainson

McCaskie (1970:718) reported that H. and O.

Clarke found a young brown-headed cowbird

reared by a brown towhee in 1970, near Glendale,

Los Angeles County, California, where the breeding

race of the host is P. fuscus senicula, according to

the fifth edition of the A. O. U. Check-List

(1957:583). A little further to the north, in Santa

Barbara and San Luis Obispo counties, one of us

(S.I.R.) found 7 nests of the subspecies P. fuscus

crissalis in 1974. Two of these nests were parasitized,

constituting the first records for that race of the

brown towhee as a cowbird victim. Aside from

this, they give an indication that the brown towhee

may be a more common host than was indicated
NUMBER 235 45

by previously available data. One nest was already

abandoned when found and the other was destroyed by a predator before the cowbird egg

hatched. It is possible that cowbird parasitism of

this towhee is increasing in southern California,

with the increase of the cowbird population. No

parasitism was found in 6 towhee clutches collected in previous years in Santa Barbara and San

Luis Obispo counties and now at the Santa Barbara Museum of Natural History. Otherwise the

brown towhee is known as a very occasional victim

of the cowbird in New Mexico (3 records) and

Arizona (several records); these instances all relate

to the host race P. fuscus mesoleucus.

A parasitized nest found east of Stone Corral,

California, 4 May 1941, by W. B. Sampson, and

now in the Western Foundation, is the first record

of parasitism on the subspecies P. fuscus carolae.

The Glendale record is the first one of the host

species rearing the young parasite; all the other

records were of eggs only.

ABERT'S TOWHEE

Pipilo aberti Baird

To the 10 times this towhee had been previously

noted (Friedmann, 1963:152) as a cowbird victim

may be added 11 more instances, 10 of them in

the collections of the Western Foundation, and 1

in the Delaware Museum of Natural History. The

records in the Western Foundation are as follows:

of nominate P. aberti aberti there are 34 sets, 7

of which (20.6 percent) are parasitized, all 7 from

Maricopa County, Arizona (as is the set in the

Delaware Museum); of P. aberti dumeticolus there

are 69 sets, 3 (4.3 percent) are parasitized, all from

California—near El Centro, near Blythe, Riverside

County, and from Bard, Imperial County.

LARK BUNTING

Calamospiza melanocorys (Stejneger)

A set of eggs of the lark bunting containing an

egg of the brown-headed cowbird, now in the

Western Foundation, taken at Seven Persons, Alberta, adds a new northwestern limit to the range

over which this species has been found to be parasitized. The earlier records (Friedmann, 1963:153;

1971:247-248) were from North Dakota, Montana,

and Saskatchewan. The Prairie Nest Records files

at the Manitoba Museum contain records of 6 parasitized nests of this bird. A record from Nebraska,

reported by Bennett (1974), is the southernmost

record of parasitism on the lark bunting.

SAVANNAH SPARROW

Passerculus sandwichensis (Gmelin)

This sparrow has recently been reported as a

cowbird victim in southern Alberta by Kondla and

Pinel (1971). This refers to the host race P. sandwichensis nevadensis, for which there were previously only 3 records from Alberta. Information

received from the Prairie Nest Records Scheme

adds no fewer than 18 more records of parasitism on

this bird in Alberta, Saskatchewan, and Manitoba,

out of a total of 111 nests reported, an incidence

of parasitism of 16.2 percent. It follows that in the

prairie provinces of Canada the savannah sparrow

can be looked upon as a regular victim of the

parasite, quite a different situation than could

have been visualized from the few earlier data. A

record from Utah (Brighton, 3 May 1906), not

hitherto reported, is in the Western Foundation's

collections; 1 from Jefferson, Colorado, is reported

by Kingery (1974:932). Of the host race P. sandwichensis oblitus the following may be recorded:

in Ontario, out of 240 nests reported to the Ontario nest records at Toronto, 32 (13.3 percent)

were parasitized; the Delaware Museum of Natural

History has a parasitized set of eggs from Illinois;

Potter (1974:58) in southeastern Michigan, noted 1

parasitized nest out of 54 nests observed by him.

Of the host race P. sandwichensis savanna we may

add 3 more records, from Cape Cod, Massachusetts

(Hill, 1965:280), and New York (Bull, 1974:537).

The total number of records for the species known

to us is now 84, as compared with 28 in 1963.

GRASSHOPPER SPARROW

Ammodramus savannarum (Gmelin)

In view of the fact that there still are but a

relatively small number of records of this secretive

sparrow as a cowbird victim (18 records known in

Friedmann, 1971:248), we may note that in Ontario

(Peck, 1975), 6 (11.7 percent) of 51 nests reported

were parasitized. P. F. Elliott informs us that he

found an even higher rate of parasitism in Riley
46

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

County, Kansas, where 9 out of 18 nests (50 percent) were so affected. He also found the grasshopper sparrow successfully raises cowbird nestlings,

the first evidence for this on record. Peck's and

Elliott's data indicate that this sparrow and the

cowbird are, at least in their regions, quite important in each other's economy. The Prairie nest

records at Winnipeg show a paratitized nest found

at Woodlands, Manitoba, 2 July 1962. These Ontario, Kansas, and Manitoba records involve the

host race, A. savannarum perpallidus. The eastern

race, A. savannarum pratensis, has recently been

noted as a cowbird victim on Cape Cod, Massachusetts (Hill, 1965:280).

HENSLOW'S SPARROW

Ammodramus hensloxvii (Audubon)

To the small number of cases of parasitism on

this sparrow previously known to us (Friedmann,

1963:156) may be added one more, from near

Augusta, Michigan, reported by Robins (1971).

This record involves the nominate races of the host

and of the parasite. Although the total number of

records is still small, it is significant in proportion

to the number of nests, parasitized or not, reported

of this unobtrusive species. In Maryland, from

whence 5 records of parasitism are known, the Henslow's sparrow must be a regular and a fairly common host choice.

VESPER SPARROW

Pooecetes grammineus (Gmelin)

A new concept of the frequency with which the

vesper sparrow is imposed upon by the brownheaded cowbird in the western prairie provinces

of Canada is afforded by the files of the Prairie

Nest Records Scheme which include no fewer than

23 instances (11.8 percent) of parasitism in Alberta,

Saskatchewan, and Manitoba, out of a total of 195

nests reported. The Ontario nest records files, at

Toronto, have data on 242 nests, 35 of which (14.5

percent) were parasitized. These figures reflect a

higher incidence of parasitism than either of two

sizeable "lots" of data reported earlier (Friedmann,

1963:157), where it was noted that 9 nests (8.0 percent) were parasitized out of 112 found in Ohio

by Hicks, and 3 out of 74 nests examined in southern Quebec by Terrill (4.0 percent). The experience of Harrison (1975:249) in Pennsylvania and

Wisconsin suggests that such parasitism is not always the case. He found 18 nests, none of which

held any cowbird eggs.

Low frequency of parasitism is shown in the material in the Western Foundation's collections. Out

of 107 sets of eggs, only 3 have cowbird eggs (only

2.8 percent). All these are of the nominate race of

the host where they constitute 5.7 percent of 53

sets; completely unparasitized are 29 sets of P.

grammineus confinis and 25 sets of P. grammineus

affinis.

LARK SPARROW

Chondestes grammacus (Say)

The recent work of Newman (1970) reveals again

the difficulty of properly evaluating the frequency

of host selection by the brown-headed cowbird. At

the time of the 1963 compilation (Friedmann,

p. 158) only 30 instances were on record, and the

only valid conclusion then seemed to be that this

bird was a relatively seldom chosen victim. Newman's paper not only adds half as many more

records, but shows that in his study area, Marshall

County, Oklahoma, the lark sparrow was heavily

parasitized; 15 (45.5 percent) of 33 nests under observation were so affected. Newman's data reveal

that only 3 of the parasitized nests actually fledged

young cowbirds, while the fledging success of the

host was 20.0 percent of the eggs laid in parasitized nests as compared with 55.2 percent in nonparasitized nests. Analysis of Newman's data shows,

interestingly, that parasitized nests were much less

successful in producing young of either species

than were unparasitized nests (28.6 percent of the

former and 58.8 percent of the latter produced

young). This difference, while not statistically significant, suggests that parasitized nests may have a

higher predation rate than unparasitized ones. If

this is indeed the case, one wonders if the former

are relatively easier for predators to find, perhaps

because of the louder and more persistent begging

of the nestling cowbirds.

To Newman's cases we may now add 25 more, a

total of 70, or over twice the number known to us

in 1963. Four of these additions are from Oklahoma (Wiens, 1963); 1 from Texas is in the collec-
NUMBER 235 47

tions of the Delaware Museum of Natural History;

3 parasitized nests out of 15 from Saskatchewan,

Manitoba, and Alberta are in the Prairie Nest

Records; 17 others, including sets from Texas,

California, and Oklahoma, are in the Western

Foundation's collections. These 17 sets constitute

7.4 percent of the 228 sets of lark sparrow eggs

in that large collection, or 8.7 percent of 195 sets

of the host race C. grammacus strigatus. Of the

nominate, eastern race of the lark sparrow there are

33 sets of eggs, not one of which contains cowbird

eggs. Lest it seem that this low percentage of parasitism in this extensive series is at odds with Newman's findings, discussed above, it should be said

that this may reflect the bias some of the early egg

collectors had against parasitized sets, many of

whose eggs are now in the Western Foundation. It

cannot be merely assumed that the frequency of

parasitism on the lark sparrow has increased in

recent years.

RUFOUS-WINGED SPARROW

Aimophila carpalis (Coues)

To the little known of this sparrow as a victim

of the brown-headed cowbird (M. ater obscurus)

may be added 2 instances, both from near Tucson,

Arizona: a parasitized set of eggs taken on 7 May

1897, now in the holdings of the Western Foundation, and an observation reported to us by D. W.

Lamm, who found a parasitized nest, 15 August

1971, at Santa Rita Experimental Range, south of

Tucson. Apparently in that part of Arizona the

rufous-winged sparrow is not infrequently imposed

upon by the parasite.

CASSIN'S SPARROW

Aimophila cassinii (Woodhouse)

To the few previous records of this sparrow as

a victim of the brown-headed cowbird (Friedmann,

1963:159) may be added one more. Kingery and

Julian (1971:439) found a parasitized nest in the

Comanche National Grassland, 11 miles southeast

of Campo, Baca County, extreme southeastern

Colorado. This record refers to the nominate race

of the parasite, for which subspecies there was

earlier but a single record, an instance reported

by Strecker (1927:47) from McLennon County,

Texas.

BLACK-THROATED SPARROW

Amphispiza bilineata (Cassin)

To the total number of instances of cowbird

parasitism on this sparrow previously known

(Friedmann, 1963:160) we may now add the following additional cases: 5 from the Texas counties

Cameron, Tom Green, and Webb, distributed

among the Western Foundation, the Delaware Natural History Museum, and the collections of Oregon

State University; a "few nests" all of which were

parasitized, found in southern Texas (Webster,

1972:878); one from southwestern Texas.—Big Bend

National Park (Wauer, 1973:178); and one from the

Malheur National Wildlife Refuge, southeastern

Oregon, reported to us by T. W. Haislip, Jr. This

last record, the first authenticated breeding record

for the black-throated sparrow in Oregon (A. bilineata deserticola), is also the first record for this

species as a host of the northwestern race of the

parasite (Af. ater artemisiae).

DARK-EYED JUNCO

Junco hyemalis (Linnaeus)

The dark-eyed junco, as presently understood,

includes the races of the previously separated "Oregon" junco as well as those of the "slate-colored"

junco.

Of the race /. hyemalis cismontanus, previously

(Friedmann, 1963:161) known as a cowbird victim

in British Columbia, we may note a parasitized set

from the Fort Assiniboine District, Alberta, 8 June

1946, now in the collections of the Western Foundation. Of the "Oregon" junco portion of the

species we may add the first records of cowbird

parasitism on the subspecies /. hyemalis shufeldti—

from near Victoria, southern Vancouver Island

(Lemon, 1969), and from near Portland, Oregon, a

set now in the collections of the Western Foundation. The small number of previous records for

the races of the "Oregon" junco were of the subspecies J. h. montanus, J. h. thurberi, and /. h.

pinosus. Three additional instances of parasitism

on /. h. thurberi are mentioned by Rogers (1971:

881) and 11 more by White (1974) out of a total

of 40 nests studied by her in meadow sites in the

Sierra Nevadas, Nevada County, California. Fur-
48

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

ther south in the Sierras (Mono County) one of

us (S.I.R.) found a parasitized nest with 2 cowbird

eggs laid during the first 3 days of August, a very

late date.

In New York, from whence we previously knew

of only 2 records, Bull (1974:537) has added 6

more cases.

CHIPPING SPARROW

Spizella passerina (Bechstein)

At the time of the 1963 compendium (Friedmann,

p. 162) but a single instance was known of parasitism on the subspecies S. passerina arizonae by

the dwarf cowbird M. ater obscurus. A second case

may be added, a set of 4 eggs of the sparrow and 1

of the parasite, taken in San Luis Obispo County,

California, 28 April 1939, now in the Santa Barbara Museum of Natural History.

The collections of the Western Foundation contain 267 sets of eggs of the chipping sparrow, only

8 of which (3.0 percent) are parasitized. This is to

some extent a reflection of the bias against sets

with cowbird eggs of some of the early collectors

whose materials are now incorporated in the

Western Foundation, and may also suggest a geographical difference in the incidence of parasitism

on this sparrow in the west as compared with the

east. We may recall (Friedmann, 1963:162) that in

Ohio, Hicks had found that 60 out of 115 nests

examined (over 50 percent) were parasitized, and

that in southern Quebec, Terrill had found cowbird eggs or young in 16 out of 138 nests (11.6 percent). One of us (S.I.R.) studied 83 nests in Cheboygan and Emmet counties, Michigan, in 1968

and 1969, and found that 30 (36.2 percent) of them

were parasitized. Of 155 nests found in Manitoba,

Saskatchewan, and Alberta, reported to the Prairie

Nest Cards files at the Manitoba Museum, 20 (12.9

percent) were parasitized. Of 733 nests in Ontario

reported to the files at Toronto, 216 (29.5 percent)

were parasitized. On the other side of the picture

is the experience in Pennsylvania of Harrison

(1975:244) who found cowbird eggs in only 2 out

of 29 nests examined, a very low incidence of 6.9

percent.

CLAY-COLORED SPARROW

Spizella pallida (Swainson)

This sparrow was previously known (Friedmann,

1963:163) to be parasitized by the brown-headed

cowbird frequently in Alberta, but there were only

scattered records from elsewhere, e.g., only 1 such

case from North Dakota. Now there is evidence that

this sparrow is frequently imposed upon in that

state. Dr. R. E. Stewart informs us that he has data

on 14 North Dakota instances of parasitism, including the 1 referred to above. The 13 additional

cases represent 39.4 percent of 33 active nests examined, a high rate of parasitism, a rate exceeded in

North Dakota only by the yellow warbler (44

percent) in Dr. Stewart's state files. In the files of

the Prairie Nest Records Scheme are 65 instances

of cowbird parasitism on this sparrow in Alberta,

Saskatchewan, and Manitoba. In these prairie provinces the clay-colored sparrow is a very common

victim, second in frequency only to Brewer's blackbird. The 65 Prairie records more than equal in

number all the records from the entire range of

the sparrow known a decade earlier. These 65

records constitute 23.6 percent of a total of 275

clay-colored sparrow nests reported to the Scheme

up to mid-1975. In Ontario, 3 nests out of 13 reported to the Toronto files were parasitized. What

degree of biological success for the cowbird is involved in this excessive host selection is, however,

uncertain, in view of Salt's (1966) conclusion that

in his area of Alberta the clay-colored sparrow did

not tolerate, or, at least, did not incubate, the eggs

of the parasite. Salt's conclusion needs to be corroborated by experiments as he does not state how

many parasitized nests served as the basis for his

statement, and the intolerance he noted consisted

largely of nest desertion. Inasmuch as birds may

desert their nests for various reasons, the mere fact

of desertion cannot be rigidly connected with cowbird parasitism however much the two may seem

to have a cause-and-effect relationship.

BREWER'S SPARROW

Spizella breweri Cassin

To the little that was previously known of

Brewer's sparrow (nominate subspecies) as a host of

the brown-headed cowbird (Friedmann, 1963:163-
NUMBER 235 49

164) may be added 2 more records; a set of 3 eggs

of the host and 1 of the parasite, taken in Mono

County, California, 15 June 1940, and now in the

Santa Barbara Museum of Natural History (Lawrence Stevens Collection); and a parasitized nest

found in North Dakota, reported to us by Dr. R. E.

Stewart.

FIELD SPARROW

Spizella pusilla (Wilson)

Kondla and Pinel (1971) have recorded the field

sparrow (subspecies S. pusilla arenacea) as a victim

of the brown-headed cowbird (M. ater artemisiae)

in southern Alberta, the northwesternmost area yet

reported for this victim. Actually Alberta is just

north of the range of the host as given in the 1957

A. O. U. Check-List (pp. 616-617). Either the sparrow is extending its range or the paucity of local

observers has limited our knowledge of its occurrence in southern Alberta before now. While the

field sparrow is a frequent victim of the cowbird,

with over 125 records of parasitism (Friedmann,

1963:164-165), there were only 2 earlier records

for the race S. pusilla arenacea, both from South

Dakota.

Mr. F. F. Nyc, Jr. has informed us that he found

a parasitized nest of the field sparrow in Caldwell

County, Texas. The brown-headed cowbird in that

area is of the race M. ater obscurus, a subspecies of

the parasite not previously noted as affecting this

sparrow.

Since the 1963 compilation some 66 additional instances of parasitism on the nominate race of the

sparrow have come to our notice. In the collections

of the Western Foundation there are 122 sets of

eggs of the field sparrow, 9 of which (7.4 percent)

were parasitized. In Ontario, of 179 nests reported

to the files at Toronto, 36 (20.1 percent) were

parasitized.

WHITE-CROWNED SPARROW

Zonotrichia leucophrys (Forster)

The white-crowned sparrow has long been known

as an infrequent victim of the brown-headed cowbird. The few instances on record (Friedmann,

1971:249) pertained to 3 races of the host—Z. I.

leucophrys, Z. I. oriantha, and Z. /. gambelii (now

shown to refer to Z. I. pugetensis). To these may

be added the race Z. leucophrys nuttalli, which was

so reported by Baptista (1972) in the San Francisco

Bay area. Baptista also suggested that the records

previously assigned to Z. /. gambelii were more accurately referable to Z. /. pugetensis in the light of

Banks's detailed study (1964) of the geographic

variations of this sparrow, a decision here accepted.

Lemon (1969) found Z. /. pugetensis to be parasitized near Victoria, Vancouver Island, where still

additional instances were reported later in the

annual bird reports for southern Vancouver Island

(Tatum, 1970: [unpaged]; 1971:51; and 1973:62),

and by Crowell and Nehls (1973:911). Still more

recently, Lewis (1973) and Lavers (1974) found this

race of the sparrow to be parasitized on Camano

and on Samish Islands, western Washington (1 instance out of over 100 active nests found on

Camano Island, 3 instances on Samish Island). A

record of a parasitized nest from Skull Creek, Saskatchewan, 2 July 1961, (files of the Prairie Nest

Records Scheme) may be noted as well as the mention of 3 fledged young cowbirds attended by whitecrowned sparrows in the "Great Basin-Central

Rocky Mountain Region" (Kingery, 1972:886). It

is not clear from Kingery's note whether these were

3 separate observations or 1 instance involving 3

young cowbirds. Dr. James R. King informs us

that in his studies of this sparrow, race Z. leucophrys oriantha, in Hart Mountain National Antelope Refuge, Lake County, Oregon, in June 1975,

he found that 6 (14.3 percent) of 42 nests observed

were parasitized. It appears from all these recent

records that the white-crowned sparrow is becoming

a regular host of the parasite in the recent extension of range of the latter in Oregon and Washington.

WHITE-THROATED SPARROW

Zonotrichia albicollis (Gmelin)

Of 236 nests of this bird found in Ontario and

reported to the nest record files at Toronto, 17

(7.2 percent) were parasitized, a higher incidence

than the 4.0 percent (20 out of 507 nests) found in

southern Quebec (Friedmann, 1963:166). Of these

17 records, 12 are additional to those listed in the

earlier compilation, increasing the total from 36

to 48 instances.
50 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Fox SPARROW

Passerella iliaca (Merrem)

The fox sparrow is infrequently reported as a

cowbird victim. To the single previous record for

the subspecies P. iliaca monoensis (Friedmann,

1963:167) as a victim of the brown-headed cowbird,

may be added 2 more from Mono County, California, now in the collections of the Western Foundation.

A first instance of cowbird parasitism on the race

P. iliaca stephensi was found by E. M. Hall at

Barton Flat, San Bernardino County, California, on

21 July 1973, a late breeding date. In this case the

cowbird egg was found at one side of the nest and

possibly was not being incubated by the sparrow.

LINCOLN'S SPARROW

Melospiza lincolnii (Audubon)

Kingery (1974:932) listed the Lincoln's sparrow

as a cowbird host at Jefferson, Colorado; one of

us (S.I.R.) noted another instance of parasitism

on it in Mono County, California, 4 August 1975,

a nest with 2 young cowbirds and 2 young sparrows,

all ready to fledge. These are the first records of

the host subspecies M. lincolnii alticola as a victim

of the cowbird, and also the first report of Lincoln's sparrow's rearing the young of the parasite to

the fledging stage. In both cases, the parasite was

of the race M. ater artemisiae. The nominate race

of the sparrow was previously known (Friedmann,

1963:167-168) as a host on the basis of only 10

records, occurring over more than half a century,

ranging from northern New York State to Saskatchewan, Manitoba, and Alberta. To these may be

added 1 more, from Ontario, in the nest record

files at Toronto (the only instance out of 15 nests

reported to the files).

SWAMP SPARROW

Melospiza georgiana (Latham)

To the data previously compiled (Friedmann,

1963:168) may be added 20 more records of parasitism on the swamp sparrow: 1 from near Chicago,

Illinois, 3 from Wisconsin (Dana and Oconto counties), and 1 from New York (Monroe County), all

in the collections of the Western Foundation; 1

from South Dakota in the Delaware Museum of

Natural History, and 14 records from Ontario. The

Ontario nest records show 18 parasitized nests out

of 112 nests reported (of these, 4 were included in

the earlier compilation). This is an incidence of

16.0 percent, a high frequency of parasitism. Harrison (1975:249) noted that the swamp sparrow was

a "frequent" victim in marshy areas in Pennsylvania

and Wisconsin, in spots where nearby red-winged

blackbird nests were rarely affected by the cowbirds.

It becomes obvious that the incidence of parasitism

on this sparrow varies in different areas; in most

places it is an uncommon host choice.

SONG SPARROW

Melospiza tnelodia (Wilson)

The song sparrow may be discussed here chiefly

to put on record the greatly increased number of

known instances of cowbird parasitism on some of

the sparrow's less well-known western subspecies, including one, M. melodia mailliardi, that had not

been reported as a cowbird victim until now. In the

vast collections of the Western Foundation are

the following parasitized sets of eggs: M. melodia

montana, 2 sets from Utah (Hunter and Ft. Douglas Creek, Salt Lake County); M. melodia fallax, 1

set from near Phoenix, Arizona; M. melodia cooperi,

16 sets from Los Angeles, San Diego, and San Luis

Obispo counties, California; M. melodia saltonis, 5

sets from Yuma and Maricopa counties, Arizona,

and near Bard, Imperial County, California; M.

melodia heermanni, 4 sets from Los Banos, Merced

County, Fresno, Fresno County, and Buena Vista

Lake, Kern County, California. M. melodia gouldii,

5 sets from Alameda and Santa Clara counties,

California; M. melodia fisherella, 2 sets from Mono

County, California, and 2 sets from Oregon; M.

melodia morphna, 2 sets from Oregon; and M.

melodia mailliardi, 2 sets taken near Stockton,

California.

In the collections of the University of Puget

Sound there is a parasitized set of eggs of the

rarely reported subspecies M. melodia merrilli,

taken at Satus, Washington, 17 June 1928. For this

subspecies there was previously a single record

from British Columbia.

Aside from being a very commonly selected host,
NUMBER 235 51

the song sparrow is also a remarkably good one

from the standpoint of the parasite (McGeen,

1972:379).

The great number of instances on record of the

song sparrow as a cowbird host choice gives the

impression that it is very heavily parasitized. If we

add together the figures from all studies where the

total number of song sparrow nests found is given,

as well as the number that were parasitized, the

resulting figure comes to 385 nests parasitized out

of 1286 active nests observed, or a parasitism incidence of 29.9 percent. As might be expected, the

percentage varies in different sets of data (see

Friedmann, 1963:170), with a high of 62.7 percent

(37 out of 59 nests) in Michigan and a low of 12.7

percent (62 out of 486 nests) in southern Quebec.

At its most intense local rate, the cowbird parasitism on the song sparrow comes about up to the

level experienced on the whole population of the

Kirtland's warbler. Mayfield (1973) found that the

warbler had from 60 to 70 percent of its nests parasitized, with heavy loss of host young. In the collections of the Western Foundation there are 847 sets

of eggs of the song sparrow (all races, but not including eggs taken in Baja California, or Alaska,

or off-shore islands, localities outside the cowbird's

breeding range). Out of these, 44 (5.19 percent) have

cowbird eggs in them. Regionally these figures break

down as follows: eastern races, 131 sets, 9 (6.9 percent) parasitized; California races, 582 sets, 24 (4.1

percent) parasitized; Pacific Northwest races, 86

sets, 4 (4.7 percent) parasitized; Rocky Mountain

races, 38 sets, 3 (7.9 percent) parasitized; and southwest races, 10 sets, 4 (40.0 percent) parasitized.

Of 152 nests found in Saskatchewan, Manitoba,

and Alberta reported to the Prairie Nest Card files,

at the Manitoba Museum, 30 (19.7 percent) were

parasitized. These 30 records refer to the host race

M. melodia juddi and the parasite race M. ater

artemisiae. Of 773 nests of the song sparrow (all

races) listed in the data bank at Cornell University,

74 (10 percent) were parasitized; of 1002 nests found

in Ontario and reported to the files at Toronto,

251 (25.1 percent) were parasitized.

CHESTNUT-COLLARED LONGSPUR

Calcarius ornatus (Townsend)

Previously known as a victim of the brownheaded cowbird in North Dakota and Saskatchewan, this longspur has recently been found to be

imposed upon in southern Alberta as well (Kondla

and Pinel, 1971). In North Dakota, where most of

the older records were noted, the incidence of parasitism may be higher than was hitherto assumed.

Dr. R. E. Stewart informs us that out of 37 nests

examined there, 8 were parasitized, a rate of 21.6

percent. Until now there were only a dozen or so

records in all. To these may be added two more

from Moose Jaw, Saskatchewan (Prairie Nest Records Scheme), and one from near Esmond, North

Dakota, in the collections of the Western Foundation.

Shiny Cowbird

Molothrus bonariensis

Discussion

The small number of bird students throughout

much of South America is reflected in the slow

accretion of new published information on this

species of cowbird. Inexpliacably, Sick's important

paper of 1958 was overlooked in the 1963 compilation, but was subsequently assumed to have been

included in it. The information it contains, together with what we have been able to learn from

extensive correspondence with many generous and

cooperative observers, who have very kindly made

their unpublished notes available to us for the

present report, has enabled us to appraise and to

review some 262 more instances of the parasitism

of the shiny cowbird since the 1971 paper.

NEW HOSTS.—These records add 33 new hosts

(27 species, plus 6 subspecies) to those previously

reported. Four races of the parasite are involved

in these records, as listed below. In addition to

these 33 new hosts, a few species previously known

to be among the victims of one race of the shiny

cowbird have been found to be parasitized by

another subspecies as well. The additions to the

host catalogs for each of the 4 cowbird subspecies

are listed below; those that are new to the total
52 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

host list of the species are marked with an asterisk.

No new information has come to us concerning

the other races of the shiny cowbird.

New hosts for Molothrus bonariensis bonariensis:

*Zenaida auriculata chrysochenia, *Pseudoseisura

cristata, *Phacellodomus striaticeps, *Phacellodomus rufifrons, *Phacellodomus sibilatrix, *Phleocryptes melanops, *Tityra cay ana braziliensis,

"Alectruris tricolor, Arundinicola leucocephala,

*Serpophaga subcristata, *Myiarchus tyrannulus

tyrannulus, *Phytotoma rutila angustirostris, *Anthus furcatus, *Psarocolius decumanus, *Schistoclamys melanopis olivina, *Ramphocelus carbo

centralis, *Donacospiza albifrons, *Arremon flavirostris d'orbignii, *Sporophila Hneola, and *Spinus

magellanicus tucumanus.

New hosts for Molothrus bonariensis melanogyna:

Anumbius annumbi, Passer domesticus domesticus,

*Icterus icterus jamacaii, *Hemithraupis guira

guira, and Thlypopsis sordida sordida.

New hosts for Molothrus bonariensis venezuelensis: *Machetornis rixosus flavigularis, *Campylorhynchus nuchalis brevipennis, Thryothorus rutilns, *Catharus aurantiirostris aurantiirostris,

*Turdus nudigenis nudigenis, *Turdus serranus

atrosericeus, Vireo olivaceus vividior, *Basileuterus

flaveolus, Agelaius icterocephalus icterocephalus,

*Rhodinocichla rosea rosea, Sicalis flaveola flaveola,

*Atlapetes semirufus denisei, and *Arremonops

conirostris conirostris.

New hosts for Molothrus bonariensis cabanisii:

* Troglodytes aedon striatulus, Agelaius icterocephalus icterocephalus, and *Zonotrichia capensis costaricensis.

These additions bring the total host catalog of

the shiny cowbird up to 176 species, or 240 species

and subspecies of birds. Future field studies in the

many parts of South America that are still imperfectly known, should increase the numbers. However, more important than mere additions to this

catalog will be quantitative data establishing the

relative frequency of host choice in different areas.

We know, for example, that the house wren is

seldom parasitized in Argentina, but is a primary

host in Trinidad and in parts of northern South

America. The rufous-collared sparrow is clearly

the most frequently selected victim in Argentina,

Uruguay, parts of Brazil (east and southeast), and

of Venezuela (Caracas area), but its role is assumed

by a grackle, Quiscalus lugubris, in Anzoategui

Province, northeastern Venezuela. In Chile, where

the parasite is considered to be a relatively recent

addition to the fauna, a very considerable portion

of the burden of its reproduction has fallen on the

diuca finch, Diuca diuca, while in the Lesser Antilles the spread of the shiny cowbird has caused

critically great damage to the golden warbler, Dendroica petechia. On the other side of the picture,

in many parts of South America we still have insufficient data to suggest the relative frequency of

specific host choices by the parasite.

Among the records here brought together are

observations adding 9 species to the list of those

that have been reported as rearing the young shiny

cowbirds. Previously (Friedmann, 1963:197; 1971:

250) 27 species had been found to do so, i.e., to be

true fosterers, not merely victims. The additions

are: Tityra cayana, Campylorhynchus nuchalis,

Thryothorus rutilus, Thraupis sayaca, Ramphocelus

carbo, Donacospiza albifrons, Atlapetes semirufus,

Spinus magellanicus, and Poospiza nigrorufa.

In some of the following accounts we state that

a species has been found to be parasitized, but give

no details other than the name of our informer.

This means that we do not have any more explicit

data.

Data on Individual Host Species

EARED DOVE

Zenaida auriculata (Des Murs)

Gunnar Hoy informs us that in December 1972,

he found a nest of this dove containing an egg

of the shiny cowbird in Oran, northern Salta, Argentina. This is the first time this species has been

found to be victimized by the cowbird; it cannot

be looked upon as anything but an accidental host

choice, since pigeons are not suitable as fosterers

for the parasite. The pigeon involved is of the subspecies Z. auriculata chrysauchenia; the parasite is

the nominate race of Molothrus bonariensis.

RUFOUS CACHOLOTE

Pseudoseisura cristata (Spix)

Dr. Helmut Sick informs us that this furnariid

has been noted as a victim of the shiny cowbird
NUMBER 235 53

(M. bonariensis bonariensis) near Bahia, Brazil.

This is the first such instance to have come to our

notice.

RUFOUS-CAPPED ANTBIRD

Thamnophilus ruficapillus (Vieillot)

Previously (Friedmann, 1929:94) known as a cowbird host in Uruguay, this species is now the subject of a record from Gualeguaychu, Entre Rios,

eastern Argentina, where, on 21 December 1970,

Senor S. Narosky found a nest with 2 eggs of the

antbird and 4 of the shiny cowbird. The record

involves the nominate races of the host and the

parasite.

RUFOUS OVENBIRD

Furnarius rufus (Gmelin)

Previously known (Friedmann, 1929:94-97; 1931:

54) to be a frequent host in Argentina and in

southeastern Brazil, the rufous ovenbird is similarly

commonly parasitized in Uruguay, according to E.

Gerzenstein, and in Mato Grosso, Brazil, according

to J. Hidasi.

STRIPE-CROWNED SPINETAIL

Cranioleuca pyrrhophia (Vieillot)

Hoy (1971:160) found a parasitized nest of this

spinetail at Voile Lerma, Salta, Argentina. This is

the second record of this host-parasite combination;

the previous one (Friedmann, 1963:204) was also

found by Hoy in the same area. The records involve the nominate races of both the host and the

parasite.

WREN-LIKE RUSHBIRD

Phleocryptes melanops (Vieillot)

The Delaware Museum of Natural History has a

set of 2 eggs of this rushbird with 1 of the shiny

cowbird, taken at Buena Esperanza, San Luis Province, Argentina, 14 December 1912, by J. Goodall.

This is the first record known to us of this species

as a victim of the parasite (nominate races of both

P. melanops and M. bonariensis are involved).

FIREWOOD-GATHERER

Anumbius annumbi (Vieillot)

Previously known as a victim of the shiny cowbird in Argentina on the basis of a single record,

this bird has now been found to be parasitized in

southeastern Brazil as well, according to Dr. Helmut

Sick. The Brazilian record involves the cowbird

race M. bonariensis melanogyna; the Argentine

one, the nominate race.

RED THORNBIRD

Phacellodomus ruber (Vieillot)

This bird was previously known as a victim of

the shiny cowbird on the basis of a single instance

in Uruguay (Friedmann, 1934:342). Recently,

Hidasi informed us that he has observed a second

case near the Rio Pixaim, Mato Grosso, Brazil.

STREAK-FRONTED THORNBIRD

Phacellodomus striaticeps (d'Orbigny and

Lafresnaye)

Dr. C. C. Olrog informs us that he has found

this thornbird to be a victim of the shiny cowbird in

Tucuman, Argentina. It was not previously reported as a host. The nominate races of both the

victim and the parasite are here involved.

RUFOUS-FRONTED THORNBIRD

Phacellodomus rufifrons (Wied)

This is an addition to the known victims of the

shiny cowbird. Dr. C. C. Olrog informs us that he

has found it to be parasitized in Tucuman, Argentina. The record involves the nominate race of

the cowbird and the host subspecies P. rufifrons

sincipitalis.

LITTLE THORNBIRD

Phacellodomus sibilatrix (Sclater)

Senor S. Narosky writes us that at Zarate, Buenos

Aires Province, Argentina, on 14 January 1967,

he found a parasitized nest of this thornbird. It

is the first time this species has been reported as a

cowbird victim.
54 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

BLACK-TAILED TITYRA

Tityra cayana (Linnaeus)

This cotinga was added to the known victims of

the shiny cowbird by Jose Hidasi, who informed

us that some years ago he observed a young of

the parasite being attended and fed by a pair of

the tityra near Goiania, Mato Grosso, Brazil. This

record involves the nominate race of the parasite

and the host subspecies T. cayana braziliensis.

TROPICAL KINGBIRD

Tyrannus melancholicus Vieillot

The tropical kingbird was previously known

(Friedmann, 1929:105-106; 1931:55; 1934:343) to

be parasitized in western Argentina, Paraguay, and

Brazil. We may now add 2 records from eastern Argentina, kindly sent us by S. Narosky: one from

Atalaya, and one from San Vicente, both in Buenos

Aires Province.

COCK-TAILED TYRANT

Alectruris tricolor (Vieillot)

Dr. R. D. Etchecopar informs us that he has in

his collection a set containing 1 egg of this flycatcher and 2 of the shiny cowbird, taken in Tucuman, Argentina by Luis Dinelli over 70 years

ago. The record somehow never was published until now; it adds the present species to the parasite's host catalog.

WHITE-HEADED MARSH TYRANT

Arundinicola leucocephala (Linnaeus)

This flycatcher has long been known as a fairly

frequent host choice of the shiny cowbird in Guyana

and in Trinidad. Sick informs us that it has been

found to be parasitized in Brazil as well. While the

exact locality of the Brazilian record is not known

to us, the probabilities are that the case involves

the nominate race of the cowbird; in the Guyana

and Trinidad records the race M. bonariensis minimus is involved.

CATTLE TYRANT

Machetornis rixosus (Vieillot)

The southern, nominate race of this flycatcher

has long been known to be parasitized by the shiny

cowbird in Argentina (13 records from Tucuman

alone) and in Paraguay. We have been informed

by Mr. Paul Schwartz that he has found the northern subspecies, M. rixosus flavigularis, to be victimized in the Caracas area, Venezuela, by the local

race of the parasite, M. bonariensis venezuelensis.

FORK-TAILED FLYCATCHER

Muscivora tyrannus (Linnaeus)

This flycatcher has been known, since Hudson's

early work (1874:154; cited in Friedmann, 1929:

106), to be a frequently selected host of the shiny

cowbird in Argentina. Since most of the Argentine

records were from the eastern part of that country—

provinces of Buenos Aires and Entre Rios—it may

be noted that a similar incidence of parasitism also

obtains in Cordoba Province, central Argentina,

where, in 1907, Goodall collected no fewer than

10 parasitized sets of eggs, and, in 1912, 2 such sets

in San Luis Province, all currently in the Delaware Museum of Natural History and not previously reported in print.

WHITE-CRESTED TYRANNULET

Serpophaga subcristata (Vieillot)

This little flycatcher was added to the known

victims of the shiny cowbird when Eugene Gerzenstein found a parasitized nest on 6 November 1960,

southwest of Paso Real, on the Solis Chico River,

Departamento de Canelones, Uruguay.

CROWNED SLATY-FLYCATCHER

Empidonomus aurantioatrocristatus

(d'Orbigny and Lafresnaye)

To the 2 records of this flycatcher as a victim of

the shiny cowbird known to us earlier (Friedmann,

1929:105) may be added 3 more: 2 from Manchala,

Tucuman, northwestern Argentina, 20 October

1925 and 10 October 1930, taken by Pablo Girard,
NUMBER 235 55

and both now in the collections of the Museo de

La Plata; and 1 found in Entre Rios, 23 December 1970, by S. Narosky.

BROWN-CRESTED FLYCATCHER

Myiarchus tyrannulus (Miiller)

The Museo de La Plata has a set of 4 eggs of

this flycatcher with 1 of the shiny cowbird, collected at Manchala, Tucuman, Argentina, 10 November 1930, by Pablo Girard. No previous record

for this host species is known to us; the record involves the nominate races of both the host and the

parasite.

SUIRIRI FLYCATCHER

Suiriri suiriri (Vieillot)

Sefior S. Narosky writes us that he found a parasitized nest of this flycatcher at Pronunciamento,

Entre Rios Province, eastern Argentina, on 15

October 1968. Previously (Friedmann, 1929:103)

we knew of but 1 other record, from Mendoza,

western Argentina.

WHITE-TIPPED PLANTCUTTER

Phytotoma rutila Vieillot

This interesting bird was added to the known

host list of the shiny cowbird by Gunnar Hoy, in

January 1968, when he found a parasitized nest

near a small mountain settlement, 2800 meters

elevation, in the province of Salta, northwestern

Argentina. We are much indebted to Dr. Hoy for

this information, which it is expected he will amplify in a forthcoming description of the previously

unknown eggs of the plantcutter (P. rutila angustirostris); the parasite involved in this record is

M. bonariensis bonariensis.

Dr. C. C. Olrog has since informed us that he

has also found this species to be victimized, apparently in the province of Tucuman, some distance south of Salta.

STRIPE-BACKED WREN

Campylorhynchus nuchalis Cabanis

We have recently learned from Dr. R. H. Wiley

that he observed a fledged young cowbird (M.

bonariensis venezuelensis) cared for and repeatedly

fed by 2 stripe-backed wrens (C. nuchalis brevipennis) in Venezuela. This wren is an addition to

the shiny cowbird's host catalog.

RUFOUS-BREASTED WREN

Thryothorus rutilus Vieillot

As outlined in an earlier paper (Friedmann,

1931:56) this wren is frequently parasitized by the

shiny cowbird (M. bonariensis minimus) in Trinidad. All the records then available were of eggs

only, but recently R. P. ffrench has informed us

that he has found the young parasites to be reared

successfully by this host. In Tobago, Dr. D. W.

Snow observed a recently fledged young cowbird

attended and fed by an adult rufous-breasted wren.

Mr. Paul Schwartz informs us that he has observed this wren to be victimized in the Caracas

area of Venezuela by the local subspecies of the

cowbird (M. bonariensis venezuelensis) as well.

HOUSE WREN

Troglodytes aedon Vieillot

Miller (1963:47) found this wren to be a host

of the shiny cowbird at San Antonio, western

Andes, Colombia. The local race of the wren is T.

aedon striatulus, which has not otherwise been reported as a cowbird victim. Dr. J. I. Borero and

Father Antonio Olivares have informed us of numerous observations they have made of parasitism

on the house wren in the region of Cali, Colombia,

as well. Previously seven other subspecies, T. a.

albicans, T. a. tobagensis, T. a. musculus, T. a.

rex, T. a. audax, T. a. chilensis, and T. a. bonariae,

had been known to be parasitized. The present

record refers to the cowbird race Af. bonariensis

cabanisii, a subspecies not hitherto reported as including this wren among its victims.

From Trinidad there were earlier (Friedmann,

1963:207) a number of records of parasitism on this

wren (race T. aedon albicans, of which T. a. clarus

is a synonym). To these may be added 17 more

such instances, demonstrating beyond question that

the house wren, in spite of its small size, is the

most frequently reported host of the shiny cowbird

in that island that has many potential (and ac-
56

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

tual) hosts. Of these additional cases, 10 have

come to us through the kindness of Dr. D. W.

Snow, and the other 7 were reported to us by R. P.

ffrench. In 1 of the latter's instances there were 4

eggs of the wren and 9 of the cowbird, a nest that

could hardly have been successful. In 9 of the 10

cases observed by Snow, the parasite's eggs were

accepted and incubated and the young cowbirds

were reared; in only a single case were the "eggs

thrown out after cowbird visit."

From the combined evidence supplied by ffrench

and Snow, it becomes apparent that the cowbird

parasitizes other hosts in localities where the house

wren is absent, but that the parasite prefers the

wren when it is available. (See the note on Agelaius

icterocephalus in the present paper).

The house wren has also been found, by Paul

Schwartz, to be a victim of the shiny cowbird (race

M. bonariensis venezuelensis) in the vicinity of

Caracas, Venezuela.

This wren is of more than usual interest, since in

Argentina and Uruguay it is seldom imposed upon

(by M. bonariensis bonariensis) while in Guyana

and Trinidad it is a favorite host choice of M.

bonariensis minimus (Friedmann, 1963:207). By

way of contrast, it may be mentioned that in North

America the house wren is extremely infrequently

parasitized; thus in Ontario, only 1 out of 709

nests reported was parasitized by M. ater.

PATAGONIAN MOCKINGBIRD

Mimus patagonicus (Lafresnaye and d'Orbigny)

A fourth instance of parasitism on this mockingbird is a set of 2 eggs of the host and 1 of the

parasite, collected at Maquinehao, Rio Negro, Argentina, 26 October 1911, by J. R. Pemberton, now

in the collections of the Western Foundation. A

fifth instance was found near Patagones, Buenos

Aires Province, 15 December 1972, by S. Narosky.

CHILEAN MOCKINGBIRD

Mimus thenca (Molina)

To the 3 earlier recorded instances (Friedmann,

1929:110; 1934:544) of parasitism on this host in

Chile, may be added 3 more from that country, all

presently in the collections of the Western Foundation, all collected by J. D. Goodall, near Santiago (2 at Manquehue, 1 and 2 December 1967,

and 1 at Fundo La Montana on the road between

Santiago and Colina, 20 October 1968).

CHALK-BROWED MOCKINGBIRD

Mimus saturninus (Lichtenstein)

The race M. saturninus modulator, previously

(Friedmann, 1929:109-110) noted as a common

host of the shiny cowbird in Argentina, has been

found by Gerzenstein to be equally imposed upon

in Uruguay. Recently S. Narosky has informed us

of 3 more instances of cowbird parasitism on this

mockingbird in Buenos Aires Province: in one of

these nests there were 11 cowbird eggs, in the

others 1 and 5, respectively.

ORANGE-BILLED NIGHTINGALE-THRUSH

Catharus aurantiirostris (Hartlaub)

This thrush (nominate race) is now added to the

known hosts of the shiny cowbird (M. bonariensis

venezuelensis) on the strength of information received from Paul Schwartz, who has found it to be

parasitized near Caracas, Venezuela.

BARE-EYED THRUSH

Turdus nudigenis Lafresnaye

Mr. Paul Schwartz informs us that he has found

this thrush to be parasitized near Caracas, Venezuela. The local race of the cowbird is M. bonariensis venezuelensis, the local host is of its nominate subspecies, and is new to the known host list

of the parasite.

GLOSSY-BLACK THRUSH

Turdus serranus Tschudi

A nest of this thrush containing 1 egg of its own,

1 egg and 1 young of the shiny cowbird (subspecies

M. bonariensis venezuelensis) was found 17 October 1974 in the mountains (1600 to 1700 meters altitude) near Caracas, Venezuela, by W. H. Phelps,

Jr., to whom we are indebted for this information.

This constitutes an addition to the host catalog of

the shiny cowbird.
NUMBER 235 57

CREAMY-BELLIED THRUSH

Turdus amaurochalinus (Cabanis)

This thrush was previously reported (Friedmann,

1929:109; 1938:43) as a victim of the shiny cowbird

in the provinces of Tucuman and Cordoba, western Argentina, where a total of 6 instances of parasitism were known to us. Recently, R. D. Etchecopar has informed us that in his collection are 4

more parasitized sets of eggs, taken in 1903 or

1904 in Tucuman by Luis Dinelli. Two additional

Tucuman records, collected by Pablo Girard, are

in the Museo de La Plata. The total number of

Tucuman records is sufficient to show that the

creamy-bellied thrush is a frequent host choice of

the parasite in that area. Sefior S. Narosky informs

us that he found a parasitized nest of this thrush at

Pronunciamento, Entre Rios Province, eastern Argentina, 26 December 1970.

RUFOUS-BELLIED THRUSH

Turdus rufiventris (Vieillot)

Although this thrush has been reported (Friedmann, 1929:107; 1938:43) as a cowbird victim in a

few places in Argentina, Uruguay, and Brazil, the

number of records is small enough to warrant adding one more. Sefior S. Narosky writes us that he

found a nest of this species with 1 egg of its own

and 8 of the shiny cowbird at Pronunciamento,

Entre Rios, eastern Argentina, 24 December 1970.

YELLOWISH PIPIT

Anthus lutescens Pucheran

The yellowish pipit was formerly known as a

victim of the shiny cowbird on the basis of 1 record in Tucumdn Province, northwestern Argentina

(Friedmann, 1929:110). Recently, Sick has informed

us that it has been found to be parasitized in southeastern Brazil. In that region the cowbird is of the

race M. bonariensis melartogyna, for which the

pipit is a "new" host.

SHORT-BILLED PIPIT

Anthus furcatus Lafresnaye and d'Orbigny

Eugene Gerzenstein informs us that on 4 December 1966 he found a nest of this pipit containing

2 eggs of the shiny cowbird as well as several of

the host, near A0 Dulce, Polanes, Departamento de

Lavalleja, Uruguay. This is the first record for this

bird as a victim of the parasite.

RED-EYED VIREO

Vireo olivaceus (Linnaeus)

The South American populations of the redeyed vireo, formerly separated as Vireo chivi, have

at least 3 subspecies that are known to be parasitized by the shiny cowbird, but apparently the

species is not parasitized nearly so frequently in

South America as is its North American nominate

race by the brown-headed cowbird. The southernmost subspecies, V. olivaceus chivi, was known as

a victim of M. bonariensis bonariensis in Argentina

(Friedmann, 1929:110; 1938:43) and of M. bonariensis melanogyna in southeastern Brazil (Friedmann, 1934:344); the race V. olivaceus griseobarbatus is parasitized in southwestern Ecuador by M.

bonariensis aequatorialis (Friedmann, 1963:209),

and V. olivaceus vividior has been found to be

parasitized by M. bonariensis minimus in Trinidad

(Friedmann, 1949:156) and may be now stated to

be similarly affected by M. bonariensis venezuelensis near Caracas, Venezuela, according to information received from Paul Schwartz.

RUFOUS-BROWED PEPPERSHRIKE

Cyclarhis gujanensis Gmelin

Previously known as a cowbird victim in Tucuman, Argentina (Friedmann, 1929:110), this bird

has been found by S. Narosky to be victimized at

Embalse, Cordoba, 20 January 1969. The nest contained 3 eggs of the host and 2 of the parasite.

The record involves the host race C. gujanensis

viridis and the nominate race of the shiny cowbird.

BICOLORED HONEY-CREEPER

Conirostrum bicolor (Vieillot)

Previously (Friedmann, 1963:209) this bird was

known to be victimized by the small race of the

shiny cowbird (At. bonariensis minimus) on the

basis of 1 record from Trinidad and one from

Surinam. Recently, ffrench (1973:396-397) listed 3
58

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

records from Trinidad, including the one previously

mentioned. There had been some uncertainty about

the earlier Trinidad record since that particular

nest was described as domed, whereas all other

nests of this species found are open, cup-like structures. In 2 of ffrench's 3 records, the young cowbirds

were reared successfully by their hosts. Still another record from Trinidad comes to us from D. W.

Snow, who saw a pair of these honey-creepers

feeding a recently fledged young cowbird.

WHITE-STRIPED WARBLER

Basileuterus leucophrys Pelzeln

The white-striped warbler is an addition to the

known victims of the shiny cowbird. Sick has informed us that it has been found to be parasitized

in the Distrito Federal (Brasilia), eastern Goias,

Brazil. The cowbird in that area is the nominate

subspecies.

FLAVESCENT WARBLER

Basileuterus flaveolus (Baird)

The flavescent warbler may be added to the

known victims of the shiny cowbird. Mr. Paul

Schwartz informs us he has found this species to

be parasitized by the local race of the cowbird, M.

bonariensis venezuelensis, in the vicinity of Caracas, Venezuela.

HOUSE SPARROW

Passer domesticus (Linnaeus)

This introduced, but now widely distributed,

species was previously known to have been parasitized once in Chile by the shiny cowbird. Sick

informs us of a similar record from Sao Paulo,

Brazil. In an earlier paper (1957:16—17) Dr. Sick

reported that around Rio de Janeiro he found

house sparrows and shiny cowbirds congregating in

mixed flocks and sleeping together in small roosts,

but at that time he wrote that the house sparrow

had not been known to be used as a host by the

parasite. Judging by the more extensive data on

this bird in North America, the house sparrow

seems unlikely to become a regular host choice.

Its pugnacity alone would be a deterrent to the

would-be intruder. The Brazilian record involves

the cowbird race M. bonariensis melanogyna; the

earlier Chilean one had to do with M. bonariensis

bonariensis.

CRESTED OROPENDOLA

Psarocolius decumanus Pallas

We learn from the Museo de La Plata that

there is in that collection a set of 3 eggs of this

oropendola with 1 of the shiny cowbird, taken at

Atahona, Tucuman, Argentina, 19 November 1928,

by Pablo Girard. This is the only record known

to us for this host.

TROUPIAL

Icterus icterus (Linnaeus)

The race jamacaii of this oriole has been found

to be parasitized by the shiny cowbird (subspecies

M. bonariensis melanogyna) at Pirapora, Minas

Gerais, Brazil (H. Sick). This is a "first" record,

both for the race of the host and for the race of

the parasite. There was a single earlier record in

Guyana involving the host race /. icterus croconotus

and the parasite race M. bonariensis minimus

(Friedmann, 1963:211).

YELLOW-WINGED BLACKBIRD

Agelaius thilius (Molina)

To the 10 earlier records (Friedmann, 1929:120;

1931:58; 1934:344-345) of this blackbird as a victim of the shiny cowbird may be added 8 more.

One of these, taken at Lampa, north of Santiago,

Chile, 12 October 1956, by P. P. de Leon, is now

in the holdings of the Western Foundation. Another was found by S. Narosky, at Lobos, Buenos

Aires Province, Argentina, 8 January 1967. Dr.

Gordon H. Orians informs us that in OctoberNovember 1973, in the province of Buenos Aires,

he found 20 nests of this blackbird, 6 of which had

1 cowbird egg each, and in every instance these

were the unspotted, pure white morph. In the

same study sites, which consisted of wet areas along

a 16 kilometer stretch of road near Pinamar, Orians

also found the following nests of two other icterids:

51 of Pseudoleistes virescens and 9 of Ambly-
NUMBER 255 59

rhamphus holosericeus. None of the latter contained

cowbird eggs but 10 Pseudoleistes nests had 1 cowbird egg and 2 others had 2 cowbird eggs. Unlike

the case in the Agelaius nests, 13 of the 14 cowbird

eggs in the Pseudoleistes nests were of the speckled

morph; only 1 was unmarked white. The association

between A. thilius and white cowbird eggs and between P. virescens and speckled cowbird eggs is

highly significant statistically. The zero incidence

of parasitism on A. holosericeus is not significantly

different from the incidences of parasitism on A.

thilius and P. virescens but is suggestive of a real

difference.

The differential occurrences of white and speckled cowbird eggs cannot be due to differences in

microgeographical distribution. Agelaius nests were

mixed in with Pseudoleistes nests, sometimes within

a few meters of each other. Possibly individual cowbirds that laid each egg type parasitized the different

hosts preferentially. Or it is possible that the two

types of cowbird eggs are placed randomly and

that Agelaius selectively removes speckled eggs and

Pseudoleistes removes white ones. Conceivably,

some process combining selective egg placement by

the cowbirds and selective removal by the hosts

is responsible for Dr. Orians' observations. Interestingly, Hudson (1920:124-125; cited by Friedmann,

1929:120-121) suggested that Pseudoleistes ejects

white cowbird eggs but retains speckled ones. He

often found cowbird eggs on the ground under

nests. Also, Dr. Orians informs us that of the two

cowbird egg morphs, the white one most closely

resembles eggs of A. thilius, the speckled one most

closely resembles eggs of P. virescens, and neither

resembles eggs of A. holosericeus. Conceivably the

last mentioned species ejects both types of cowbird

eggs or, as Dr. Orians suggests, it may have escaped parasitism because its nests were further out

in extensive stands of marsh vegetation than were

nests of the other two icterids, and cowbirds may

rarely enter such areas. Dr. Orians also notes that

Amblyramphus is much more territorial than the

other two species and the fact that either the male

or female usually perches near the nest may also

deter cowbird parasitism. We are indebted to Dr.

Orians for informing us of his observations and for

the additional information he has so generously

provided. We have discussed this information at

length because it is the first evidence known to us

that shows that both white and speckled cowbird

eggs occur, in one area, at different frequencies,

with different hosts. This information poses significant biological questions concerning the factors

responsible for the differential occurrence of the

two types of cowbird eggs and it is hoped that

these will be dealt with in the near future. The

situation is especially intriguing because Dr. Orians'

experience with A. thilius differs from that of

Bullock who studied this host at Angol, Chile

(Friedmann, 1934:345-346). One of the' nests Bullock studied contained five cowbird eggs, each patterned so differently that he concluded 5 different

hens were involved. Obviously, these could not all

have been unmarked white eggs.

It may be recalled that there is 1 previous record

of a parasitized nest of Amblyrhamphus holosericeus near Buenos Aires (Friedmann, 1931:58).

YELLOW-HOODED BLACKBIRD

Agelaius icterocephalus (Linnaeus)

First added to the list of victims of the shiny

cowbird (M. bonariensis minimus) in Trinidad

(Friedmann, 1931:58) on the basis of G. M. Snooker's observations, this marshbird's status as a frequently selected host in that island, is now corroborated by R. P. ffrench, who informs us that out

of 10 nests found there by R. H. Wiley, 7 contained cowbird eggs. This host lives in marshy

areas where the house wren does not occur, and

in such situations it is the commonest host choice.

Dr. Wiley writes us that he found this blackbird

to be parasitized, not only in Trinidad, but also

in Guarico, Venezuela, and in Surinam. In Venezuela the parasite is of the subspecies M. bonariensis venezuelensis, for which race this is a "new"

host record. In the region of Popayan, Colombia,

Humberto Granados Diaz informs us he has twice

noted this marshbird as a victim of the parasite,

the local race of which is M. bonariensis cabanisii,

for which this is also a new host record.

CHESTNUT-CAPPED BLACKBIRD

Agelaius ruficapillus Vieillot

While there were some 50 or more records of

this blackbird as a cowbird host in earlier reports

(Friedmann, 1929:120; 1931:58) all were from Tu-
60 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

cunian, western Argentina. An instance from eastern Argentina comes to us from Senor S. Narosky,

who found a parasitized nest at Lobos, Buenos Aires

Province, 8 January 1967.

CHOPI BLACKBIRD

Gnorimopsar chopi (Vieillot)

Many years ago (Friedmann, 1934:346) it was

noted that Azara, in the opening years of the nineteenth century, had written that his Indian assistant, Noseda, had found this bird to be parasitized by the shiny cowbird, but he gave no definite

records. Noseda's observations were probably made

in southern Paraguay. Later, Sobrino made an observation similar to Noseda's in the province of

Minas Gerais, Brazil, but, again, mentioned no specific instances (Friedmann, 1938:45). The first definite specimen record seems to be a set of 3 eggs of

the host and 2 of the parasite (M. bonariensis melanogyna), taken in Arcos, Minas Gerais, October

1925, now in the Delaware Museum of Natural

History. We are indebted to Mr. John E. du Pont

for information about this set.

BROWN-AND-YELLOW MARSHBIRO

Pseudoleistes virescens (Vieillot)

Previously (Friedmann, 1929:120-121) this species was known to be a very frequent host choice

in Argentina, and that there it often had excessive

numbers of shiny cowbird eggs in its nests. Hudson

was quoted to the effect that he found as many as

14, and, in one case, 16 of the parasitic eggs in single nests. "In some seasons all the nests . . . found

and watched were eventually abandoned by the

birds on account of the number of parasitical eggs

dropped in them." Similarly, in the province of

Entre Rios, Smyth (1925) found nests of this host

with 8, 10, 11, 12, 15, and 17 cowbird eggs apiece!

Very different was the experience of Dr. Gordon H.

Orians in the province of Buenos Aires, in October-November 1973, discussed more fully under

Agelaius thilius herein. He found 51 nests

of this marshbird and 10 of these contained a single

cowbird egg apiece in addition to those of the host,

2 of the nests had 2 cowbird eggs each. Dr. Orians

informs us that 13 of the 14 cowbird eggs were of

the usual speckled coloration and 1 was unmarked

white. Hudson, the first man to study these birds,

thought that the Pseudoleistes may eject pure white,

unspotted cowbird eggs, but retain and incubate

mottled ones. He often found cowbird eggs on the

ground under the nests.

Santos (1940:271) found this bird to be victimized

in southeastern Brazil, and recently we have been

informed by Eugene Gerzenstein that it is often

parasitized in Uruguay as well.

RED-BREASTED BLACKBIRD

Leistes militaris (Linnaeus)

The southern race of this species, L. militaris

superciliaris, has been known earlier (Friedmann,

1963:211-212) as a fairly frequent host choice of the

shiny cowbird in Argentina. According to information received from Dr. Sick it is also parasitized in

southern Brazil.

GREATER RED-BREASTED MEADOWLARK

Pezites militaris (Linnaeus)

The little that was previously reported (Friedmann, 1929:121) of this bird as a victim of the

shiny cowbird made it seem a relatively infrequently selected host. The picture is now changed

by the observations of Dr. Michael Gochfeld. In

his study of this bird in 1970 and 1971 near Saavedra, in the pampas 90 kilometers north of Bahia

Blanca, Argentina, he found it to be very heavily

parasitized. Out of 23 active nests that came under

his notice, no fewer than 22 were parasitized. In

the same area and in the same years, 11 nests of

the related Pezites defilippii were found, none of

which contained eggs or young of the cowbird. Dr.

Gochfeld writes us that this striking difference in

the incidence of parasitism may be a reflection of

the differential nest site selection by the two species. P. defilippii tended to nest in open fields away

from elevated perches, while P. militaris tended to

nest in fence-row vegetation, which may have afforded elevated perches for the cowbird. Dr. Gochfeld's studies should be of much interest, and it is

hoped his report will provide further data to clarify

the situation more explicitly.

Another instance of parasitism on the greater
NUMBER 235 61

red-breasted meadowlark, from farther south and

west, was collected at Rio Limay, Rio Negro, Argentina, 28 December 1912, by C. L. Nelson; this

set of eggs is now in the collections of the Western

Foundation.

It may be recalled that there are still only 2

records of parasitized nests of P. defilippii, both

found as long ago as the 1880's, at Lomas de Zamora, Buenos Aires Province (Friedmann, 1929:121).

In the light of Dr. Gochfeld's experience these records may be looked upon with some suspicion as to

their identification, but without other evidence

they cannot be dismissed.

SAYACA TANACER

Thraupis sayaca (Linnaeus)

Previously (Friedmann, 1929:111; 1931:56) there

were 3 records of this tanager as a victim of the

shiny cowbird, both involving parasitic eggs found

in nests, 2 in Tucum£n, Argentina, and 1 near

Rio de Janeiro, Brazil. That the sayaca tanager is

a true fosterer and not merely a victim is now made

definite by an observation of a fledged young cowbird attended by this species in Tucuman, 8 January 1970, by J. R. King, to whom we are indebted

for this record. Still another Tucuman record, a

parasitized set of eggs taken at Manchala, 28 October 1929, is now in the Museo de La Plata.

GUIRA TANAGER

Hemithraupis guira (Linnaeus)

This tanager is a newcomer to the host catalog

of the shiny cowbird. Dr. Sick has informed us that

it has been found to be parasitized in Minas

Gerais, southeastern Brazil, on at least 1 occasion.

The record involves the nominate race of the

host, H. guira guira, and the subspecies M. bonariensis melanogyna of the parasite.

BLACK-FACED TANAGER

Schistoclamys melanopis (Latham)

The black-faced tanager was added to the known

victims of the shiny cowbird in Brazil, according

to information sent to us by Dr. Sick. The parasitism was noted near Brasilia, eastern Goias. The

host race there is the subspecies S. melanopis olivina, the parasite is M. bonariensis bonariensis.

SILVER-BEAKED TANAGER

Ramphocelus carbo (Pallas)

To the single earlier record (Friedmann, 1938:44)

from Trinidad, of this tanager as a victim of the

shiny cowbird may be added a second from that

island, communicated to us by D. W. Snow. This

was of a fledged young cowbird attended by one of

these tanagers. A third record, from Brazil, comes

to us from Dr. H. Sick. The Brazilian record involves the host race R. carbo centralis and the parasite race M. bonariensis bonariensis; the Trinidad

instances involve R. carbo magnirostris and M.

bonariensis minimus.

WHITE-LINED TANAGER

Tachyphonus rufus (Boddaert)

Previously (Friedmann, 1963:212) we knew of 3

records of this tanager as a victim of the shiny

cowbird, 2 from Venezuela and 1 from Colombia.

An additional instance from the vicinity of Caracas,

Venezuela may be mentioned, a case reported to us

by Paul Schwartz.

ORANGE-HEADED TANAGER

Thlypopsis sordida (Lafresnaye and d'Orbigny)

Previously known as a host of the shiny cowbird

on the basis of a single record from Tucuman,

northwestern Argentina, this tanager has been reported as a victim of the parasite in Brazil, as well,

by Dr. Sick. The instance he reported is from near

Rio de Janeiro, and involves the cowbird subspecies M. bonariensis melanogyna; both records

refer to the nominate race of the tanager.

ROSE-BREASTED THRUSH-TANAGER

Rhodinocichla rosea (Lesson)

This tanager is now added to the host catalog

of the shiny cowbird on the basis of information

received from Mr. Paul Schwartz, who found it to
62

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

be parasitized near Caracas, Venezuela. The record

involves the nominate race of the host and the

cowbird race M. bonariensis venezuelensis.

GOLDEN-BILLED SALTATOR

Saltator aurantiirostris (Vieillot)

Inasmuch as the total number of records of this

saltator as a victim of the shiny cowbird is still

small (Friedmann, 1929:112) it may be added that

the Museo de La Plata has 2 parasitized sets of

eggs, from Manchala, Tucuman, 18 and 28 November 1930.

ULTRAMARINE GROSBEAK

Cyanocompsa cyanea (Linnaeus)

The earlier (Friedmann, 1929:112) statement to

the effect that the grosbeak had been found to be

parasitized in Tucuman, northwestern Argentina,

may be extended by the information that it is there

a frequent host choice. There were no fewer than

8 parasitized sets of eggs from that province in the

J. P. Norris Collection, and another is in the Museo

de La Plata.

LONG-TAILED REED-FINCH

Donacospiza albifrons (Vieillot)

This species was added to the known victims of

the shiny cowbird in Uruguay by Eugene Gerzenstein. He found parasitized nests more than once in

Ban ado de Carrrasco (Montevideo-West) and near

Playa Penino (east of Sta. Lucia Bridge), and he

also has seen these reed finches feeding a fledged

young shiny cowbird.

OCHRE-BREASTED BRUSH-FINCH

Atlapetes semirufus (Boissonneau)

Mr. William H. Phelps, Jr., informs us that in

the mountains near Caracas, Venezuela, at about

1600 to 1700 meters, he observed young shiny cowbirds (Af. bonariensis venezuelensis) attended and

fed by this species (race A. semirufus denisei). Paul

Schwartz also reports this bird as a victim of the

shiny cowbird at Caracas. These records add this

finch to the known hosts of the parasite.

SAFFRON-BILLED SPARROW

Arremon flavirostris Swainson

This finch was added to the known victims of the

shiny cowbird by Gunnar Hoy, who informs us that

he found a nest containing 2 eggs of the host and 1

of the shiny cowbird at Lesser, Salta, Argentina, 22

December 1974. The record involves the host subspecies A. flavirostris d'orbignii, and the nominate

race of the parasite.

BLACK-STRIPED SPARROW

Arremonops conirostris (Bonaparte)

Mr. Paul Schwartz informs us that he has a record of this sparrow being victimized by the shiny

cowbird near Caracas, Venezuela. The record,

which is the first one for this bird, involves the

nominate race of the victim and the race M. bonariensis venezuelensis of the parasite.

LINED SEEDEATER

Sporophila lineola (Linnaeus)

Gunnar Hoy informs us that in December 1972,

at Oran, Salta Province, Argentina, he found many

nests of this seedeater, 2 of which contained eggs of

the shiny cowbird. This species is an addition to the

known hosts of the parasite.

HOODED SISKIN

Spinus magellanicus (Vieillot)

This species of siskin was previously known

(Friedmann, 1929:113) as a victim of the shiny cowbird solely on its having been so reported by Gibson, in the Cape San Antonio region in the province

of Buenos Aires, eastern Argentina. We are now informed by Dr. J. R. King that he saw a recently

fledged young shiny cowbird attended by a hooded

siskin in Tucuman, northwestern Argentina, 30

November 1969. The siskin in Tucuman is of the

subspecies C. magellanicus tucumanus, which is an

addition to the known hosts of the parasite. The

Cape San Antonio record, previously considered as

referring to C. magellanicus ictericus, is now relegated to the nominate race of the hooded siskin.
NUMBER 235 63

SAFFRON FINCH

Sicalis flaveola (Linnaeus)

To the relatively tew earlier records (Friedmann,

1929:111; 1934:345) of this finch (subspecies S.

flaveola pelzelni) as a victim of the shiny cowbird

in Argentina and Uruguay, the following may be

added. The Museo de La Plata has 2 parasitized sets

of eggs, 1 from Manchala, Tucuman, Argentina, 2

December 1930, and 1 from General Lavalle,

Buenos Aires, 9 January 1933. In Uruguay E. Gerzenstein informs us that he found it to be among

the frequent hosts of the parasite. The nominate

race of the saffron finch has also been found to be

victimized near Caracas, Venezuela, by the local

form of the shiny cowbird, M. bonariensis venezuelensis, according to Paul Schwartz.

GRASSLAND YELLOW FINCH

Sicalis luteola (Sparrman)

In the 1963 compendium (Friedmann, p. 213) it

was noted that this finch had been listed as a victim of the shiny cowbird in Argentina and in Uruguay. It was then stated that, "inasmuch as neither

the finch nor the cowbird are local or rare, and inasmuch as the nest of the former seems in every

way suitable, it is difficult to see why the misto

(grassland yellow) finch is not parasitized more frequently." Now Eugene Gerzenstein has informed

us that in Uruguay he found it to be a fairly frequent host choice of the parasite. An additional

Argentine record comes to us from Sefior S. Narosky, who found a parasitized nest at Atalaya,

Buenos Aires, 26 November 1967.

COMMON DIUCA FINCH

Diuca diuca (Molina)

Previously (Friedmann, 1929:117; 1949:157)

known as a victim of the shiny cowbird in western

Argentina and in Chile, we may add that it is also

parasitized in eastern Argentina. Sefior S. Narosky

informs us of a parasitized nest found at Patagones,

Buenos Aires, 14 December 1972.

PILEATED FINCH

Coryphospingus pileatus (Wied)

The pileated finch (nominate subspecies) was

first reported as a victim of the shiny cowbird in

Minas Gerais, Brazil, by Skinner (1928:64) who

recorded several sets of eggs taken by Goodall near

Arcos, every one of which was parasitized with from

1 to 3 cowbird eggs apiece. Nothing further has

been reported, but the degree to which the pileated

finch is victimized could not be realized from

Skinner's brief statement. However, the Delaware

Museum of Natural History acquired Goodall's egg

collection, and in it are no fewer than 8 parasitized

sets of eggs, all taken near Arcos in 1922, 1923, and

1924. It follows that this species must indeed be one

of the major supports of the shiny cowbird in southeastern Brazil, possibly as much so as the chingolo

sparrow, Zonotrichia capensis.

CHINGOLO, OR RUFOUS-COLLARED SPARROW

Zonotrichia capensis (P. L. S. Miiller)

The wide-ranging chingolo sparrow is perhaps

the commonest victim of the shiny cowbird, especially in Argentina and in eastern Brazil. Recently

Eugene Gerzenstein has informed us that it is also

the most frequent host in Uruguay, although no

specific instances from that country have so far appeared in the literature. The Uruguayan records

involve the host race Z. capensis hypoleuca.

The northeasternmost subspecies of the sparrow,

Z. capensis costaricensis, may now be added to the

10 others of its geographic races previously known

to be parasitized. A. H. Miller (1963:47) reported

it as a victim of M. bonariensis cabanisii in Colombia (San Antonio, western Andes). Dr. J. I. Borrero

informs us that he has observed similar cases near

Cali, Colombia. The fact that in Chile the chingolo

(Z. capensis chilensis) is frequently victimized by

the shiny cowbird is evidenced by 5 parasitized sets

of eggs, all collected by J. D. Goodall near Santiago,

and currently in the collections of the Western

Foundation.

The Venezuelan race of this sparrow (Z. capensis

venezuelae) was previously (Friedmann, 1949:157)

noted as a victim of the shiny cowbird on the basis

of a single record near Caracas. Recently, Mr.

W. H. Phelps, Jr., has informed us that in the past
64 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

few years he has noted many such cases in that area.

This is in keeping with the situation elsewhere in

South America; where the rufous-collared sparrow

and the shiny cowbird occur together, the former

seems usually to be a favorite host choice of the latter. In areas where the sparrow does not occur, as

in parts of the states of Monagas and Anzoategui,

in northeastern Venezuela, the shiny cowbird seems

to concentrate its parasitism on the grackle Quiscalus lugubris, as in the field experience of Foster

D. Smith (Friedmann and Smith, 1955:514). In

Trinidad, the wren, Troglodytes musculus, is the

favorite host choice, but in northeastern Venezuela

Foster Smith did not find the wren to be parasitized, although it breeds there.

King's study of the rufous-collared sparrow in

Tucuman, northwestern Argentina (1973) has corroborated, even extended, the almost incredibly

high incidence of parasitism previously noted for it

in that area (Friedmann, 1929:113-114)—66.0 percent of all the nests for the entire breeding season

(33 out of 50 nests under observation) contained 1

or more eggs of the shiny cowbird, and at the peak

of the sparrow's breeding season, 100 percent were

so affected!

BLACK-CAPPED WARBLING-FINCH

Poospiza melanoleuca (d'Orbigny and Lafresnaye)

Previously known (Friedmann, 1929:115) as a

shiny cowbird host in Tucumdn Province, northwestern Argentina, on the basis of 2 parasitized sets

of eggs taken at Manchala, by Pablo Girard, in

1925, there is now a third record from the same locality, by the same collector, 24 November 1930, in

the collections of the Museo de La Plata.

RINGED WARBLING-FINCH

Poospiza torquata (d'Orbigny and Lafresnaye)

To the single earlier record of this finch as a

victim of the shiny cowbird (Friedmann, 1971:251),

may be added a second, a nest with a well developed young cowbird, found in December 1967, in

the Lerma Valley, Salta Province, Argentina, by

Gunnar Hoy. The race P. torquata pectoralis is the

subspecies of the host involved in Salta, as in the

earlier record from San Luis, Argentina.

BLACK-AND-RUFOUS WARBLING-FINCH

Poospiza nigrorufa (d'Orbigny and Lafresnaye)

Previously (Friedmann, 1929:117) this warblingfinch was known as a victim of the shiny cowbird

in the Cape San Antonio region, Buenos Aires Province, Argentina, where Gibson had so recorded it.

We now learn of a later record from the same area,

taken 15 January 1933, by Col. R. Runnacles, and

now in the Museo de La Plata, and of another parasitized nest found 26 November 1967 at Atalaya,

Buenos Aires, by S. Narosky.

GREAT PAM PA-FINCH

Embernagra platensis (Gmelin)

To the few records previously reported (Friedmann, 1929:117; 1931:58) of this finch as a cowbird

victim in Argentina and Paraguay, may be added

one more Argentine instance. Senor S. Narosky informs us that he found a parasitized nest at Tapalque, Buenos Aires, on 7 December 1971.

Bronzed Cowbird

Molothrus aeneus

Discussion

Additional information on this cowbird is geographically "spotty," as much as the range of the

bird has few or no resident, local observers. The

data here brought together are dependent on specimen records (of eggs) in collections, on the kind

cooperation of a small number of collectorobservers, and on the literature.

NEW HOSTS.—Recently one of us (Kiff, 1973) reported 3 new hosts for this cowbird in Costa Rica:

Catharus gracilirostris, Amblycercus holosericeus,

and Ramphocelus passerinii. We now add 7 more

(6 species and 1 subspecies) from Arizona, Mexico,
NUMBER 235

65

and Guatemala. Since all are new to the total host

list of Molothrus aeneus, there is no need to mark

them with an asterisk.

New hosts for Molothrus aeneus aeneus: Turdus

grayi grayi, Zarhynchus wagleri wagleri, Icterus

wagleri wagleri, Habia juscicauda salvini, and

Melozone biarcuatum biarcuatum.

New host for Molothrus aeneus lloyei: Setophaga

picta.

New host for Molothrus aeneus assimilis: Piranga

flava dextra.

These bring the known host catalog of the

bronzed cowbird up to a total of 71 species, or 86

species and subspecies of birds. One report of a

species previously recorded (Friedmann, 1971:252)

as a victim, the brown-throated wren, Troglodytes

brunneicollisj has since been found to have been

erroneous, due to a confusion in the record, which

really refers to Thryothorus sinaloa, a species otherwise reported as a victim of the bronzed cowbird.

In the 1963 compendium (Friedmann, p. 175) 15

species of hosts were noted as having been found

to rear the young bronzed cowbirds. Only 5 others

have since been observed to do so; they are: Cyanocorax yncas, Thryomanes bewickii, Mimus polyglottos, Piranga bidentata, and Ramphocelus passerinii.

DUMP NESTS AND MULTIPLE PARASITISM.—Before

proceeding to the comments on individual species

of hosts, it should be mentioned that there is a

slowly growing mass of evidence suggesting that the

bronzed cowbird occasionally makes use of what

may be termed dump nests, in which excessive

numbers of eggs of multiple hens are deposited.

Since these nests are either old ones, already deserted by their builders, or since the unacceptably

large numbers of parasitic eggs cause the hosts to

desert, these eggs are wasted. A case in point, recently described to us by F. F. Nyc, Jr., is a dump

nest he found at Brownsville, Texas—a small

platform-like nest in a crotch about 7 feet up in a

tree, containing 14 eggs of the bronzed cowbird and

no eggs, or any other sign, of a host. It may be recalled that the South American shiny cowbird,

Molothrus bonariensis, is even more addicted to the

use of such dump nests, in which from 15, 17, 20,

25, 26, to, in one instance, an incredible maximum

of 37 of its eggs have been reported, and as many

as 13 female cowbirds have been found to lay their

eggs in one of these nests (Friedmann, 1929:86-87).

In these instances the circumstantial evidence suggests that the eggs, dissimilar enough to suggest

they were laid by 13 hens, were those of year-old

hens still living in loose flocks late in the season

and without individual breeding territories. It now

appears that a similar situation may be present in

the case of the bronzed cowbird. Aside from Nyc's

record of 14 eggs of this species in a deserted nest,

we may call atention to a record, given in our account of the green jay, below, also in southern

Texas, of a nest containing 10 of the parasitic eggs

together with 2 eggs of the host.

It is true there have been some records of excessive, multiple parasitism by the brown-headed

cowbird as well, but the number of such cases is

extremely small compared with the many thousands

of records of more limited, "normal" degrees of

parasitism. The number of these cases is so insignificant statistically that it is not possible to look

upon them as evidence for the dump nest habit in

that cowbird species—a total of only 21 nests with

5 or more (in one case up to 12) eggs of the brownheaded cowbird, against nearly a thousand times

that many "normal" nests, each with 1 or 2 eggs of

the parasite (Friedmann, 1963:12-13).

Another aspect of the matter of host selection by

the bronzed and the brown-headed cowbirds that

is becoming even more clearly discernable from the

total mass of records is that there are significant

differences between the two parasites that serve to

divide the available host species in a way to lessen

competition for victims in areas where the two cowbirds are sympatric and numerous. Vireos and wood

warblers are reported as victims far more often for

the brown-headed cowbird than for the bronzed

species. This does not mean that the overlapping of

the host choices of the two is insignificant; more

than half of all the species known to be parasitized

by M. aeneus are also molested by M. ater. For

that matter, it is not at all uncommon to find

individual nests containing eggs of both species of

cowbirds. However, most of these hosts are used

significantly more frequently by one than by the

other of the two species of brood parasites. The

trends are not as pronounced as they are in the

sympatric species of parasitic Cuculus in Africa,

for which the term "alloxenia" was proposed to

describe the situation where related species of parasites affect different species of hosts (Friedmann,

1967a; 1967b).
66 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Data on Individual Host Species

GREEN JAY

Cyanocorax yncas (Boddaert)

To the 3 records previously known to us (Friedmann, 1963:177) of this unusually large victim may

be added 3 more: a nest with 2 eggs of the jay and

1 of the bronzed cowbird, found at El Zapotal,

Tuxtla Gutierrez, Chiapas, 10 June 1959, by Miguel

Alvarez del Toro, and one found in the Santa Ana

Refuge area, southern Texas (Webster, 1971:878),

containing 2 eggs of the host and 10 of the parasite.

It is this second instance that is discussed as a case

of a dump nest in the paragraph above. Two years

later, Webster (1973:892) reported a pair of green

jays feeding a fledged young bronzed cowbird, the

first record of this jay's actually rearing the young

parasite.

MOCKINGBIRD

Mimus polyglottos Linnaeus

The mockingbird was known previously (Friedmann, 1963:178; 1966:8) as a rarely imposed upon

victim of the bronzed cowbird, with only 2 records,

both from southern Texas. Recent observations

have since necessitated a change in our estimate of

this host species. Four additional instances of parasitism, also from southern Texas, are now known to

us, and 3 of them were successful to the point of

rearing the young parasite to the fledging stage.

The 4 new records are: a parasitized set of eggs

found near Santa Maria, Cameron County, Texas,

29 June 1971, now in the collections of the Western

Foundation; and 3 separate records of fledged

young bronzed cowbirds attended and repeatedly

fed by mockingbirds, near Corpus Christi, late June

and August 1972, and August 1974, all observed

by Sheriton Burr to whom and to R. McCracken

we are indebted for the information. The 3 cases

observed by Burr were all fairly late in the mockingbirds' breeding season (they begin nesting in

March); it may be that their first broods of the season escape the intrusion of the parasite.

The fact that 3 cases of parasitism were noted in

one limited locality during a 3 year period is of

interest in a comparative way. The brown-headed

cowbird has been noted as using mockingbirds as

hosts quite infrequently, and as the mockingbird is

an "accepter species" the scarcity of records is

meaningful. By contrast, the neotropical shiny cowbird makes extensive use of the several species of

mockingbirds in South America. Inasmuch as all 3

species of cowbirds seem potentially similar in what

they require of a host, their relations with mockingbirds should be more alike than they seem to be.

LONG-BILLED THRASHER

Toxostoma longirostre (Lafresnaye)

Previously (Friedmann, 1963:179) this thrasher

had been reported as a victim of the bronzed cowbird only 3 times. To these may be added a fourth

record, observed in 1971, in the Santa Ana Refuge

area of southern Texas (Webster, 1971:878).

CLAY-COLORED ROBIN

Turdus grayi Bonaparte

This thrush is an addition to the known victims

of the bronzed cowbird. Two instances of its parasitism were found in Chiapas-El Zapotal, Tuxtla

Gutierrez, 20 May, and Meyapac, Ocozocoautla, 29

May—by Miguel Alvarez del Toro, to whom we

are indebted for this information. The records involve the nominate races of both the host and the

parasite.

YELLOW-BREASTED CHAT

Icteria virens (Linnaeus)

To the 2 earlier records of this warbler as a victim of the bronzed cowbird (Friedmann, 1963:180-

181) may be added 3 more. A set of 3 eggs of the

host and 1 of the parasite, found at Rio Grande

City, Texas, 1 May 1943, by F. F. Nyc, Jr., is now

in the collections of the Western Foundation.

Another instance, found by E. M. Hall at Sonoita

Creek, near Patagonia, Arizona, 9 June 1967, contained 3 eggs of the chat, 1 of the bronzed cowbird,

and 1 of the brown-headed cowbird. Such instances

of dual parasitism of this host in southeastern

Arizona may not be infrequent, as the same observer found another nest of this species in the same

locality on 3 June 1974, with 1 chat egg, 1 of the

bronzed cowbird, and 1 of the brown-headed cowbird.
NUMBER 235 67

The yellow-breasted chat seems to be less frequently victimized by the bronzed than by the

brown-headed cowbird, but the reason for this difference is not yet understood.

PAINTED REDSTART

Setophaga picta Swainson

On 11 June 1967, E. M. Hall found a nest of the

painted redstart containing 3 eggs of the warbler

and 1 of the bronzed cowbird at Madera Canyon,

Pima County, Arizona. This is the first time this

species has been noted as a victim of the bronzed

cowbird. It would seem that there cannot be many

areas where the breeding ranges of the two species

overlap, but they have both been noted (aside from

the present record) at Madera Canyon. The painted

redstart is one of the few ground-nesting birds affected by the bronzed cowbird.

CHESTNUT-HEADED OROPENDOLA

Zarhynchus wagleri (Gray and Mitchell)

A parasitized nest of this oropendola, found at

Kilometer 25, Ocozocoautla-Mal Paso road, Chiapas, 28 April 1972, by Miguel Alvarez del Toro, is

the first record for the species as a victim of the

bronzed cowbird. The record involves the nominate

race of the host and of the parasite.

YELLOW-BILLED CACIQUE

Amblycercus holosericeus (Deppe)

Miguel Alvarez del Toro informs us that he

found a nest of this cacique parasitized by the

bronzed cowbird at Isla La Concepci6n, Acapetahua, Chiapas, 20 May 1968. Previously the species

had been reported as victimized in Costa Rica

(Riff, 1973:241). In both the Mexican and the

Costa Rican instances the nominate races of the

host and of the parasite are involved.

RED-WINGED BLACKBIRD

Agelaius phoeniceus (Linnaeus)

In 1971 (Friedmann, p. 253) only 6 instances were

known to us of parasitism on the red-winged blackbird (subspecies A. phoeniceus megapotamus) by

the bronzed cowbird. To these may be added 2

more, both from the Brownsville, Texas, area, now

in the collections of the Western Foundation. It

appears that in extreme southern Texas the blackbird is parasitized fairly regularly.

ORCHARD ORIOLE

Icterus spurius (Linnaeus)

To the few earlier records (Friedmann, 1963:181)

may be added 1 more, a nest in southern Texas,

containing 5 eggs of the oriole and 4 of the bronzed

cowbird (Webster, 1972:878).

SCOTT'S ORIOLE

Icterus parisorum (Bonaparte)

W. J. Sheffler found a parasitized nest of this

oriole at Rancho Guirocoba, Sonora, 15 May 1949,

now in the collections of the Western Foundation.

This is the second known instance of this species'

being victimized by the bronzed cowbird. The earlier record was from southern Arizona (Friedmann,

1963:182).

BLACK-VENTED ORIOLE

Icterus wagleri Sclater

This oriole has been found to be victimized by

the bronzed cowbird in Chiapas—at El Sumidero,

Tuxtla Gutierrez, and at Meyapac, Ocozocoautla.

These occurrences were noted by Miguel Alvarez

del Toro, who has kindly informed us of his observations. The records involve the nominate races

of both the host and the parasite.

SPOTTED-BREASTED ORIOLE

Icterus pectoralis (Wagler)

This oriole was previously (Friedmann, 1963:182)

known to be victimized in the lowlands of El Salvador. Two recent records from Chiapas—La Encrucijada, Acapetahua, and El Carmen, Pijijiapam—are

the first from Mexico. We are indebted to their
68 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

observer, Senor Miguel Alvarez del Toro, for these

records. The nominate races of the host and the

parasite are here involved.

LICHTENSTEIN'S ORIOLE

Icterus gularis (Wagler)

To the few earlier records of this oriole as a victim of the bronzed cowbird (Friedmann, 1963:183;

1971:253) may be added three more from Tuxtla

Gutierrez, Chiapas, all found and reported to us by

Miguel Alvarez del Toro.

SCARLET-HEADED ORIOLE

Icterus pustulatus (Wagler)

While 4 races of this oriole have been known to

be parasitized by the bronzed cowbird, there was

until now but a single record involving the southern subspecies (/. pustulatus formosus). This was

from Oaxaca. We may now add 1 more from that

state (El Zapilote) in the collections of the Western

Foundation, and 4 records from Chiapas (Teran

and Tuxtla Gutierrez) reported to us by Miguel

Alvarez del Toro.

HEPATIC TANACER

Piranga flava (Vieillot)

One record, erroneously allocated to the host subspecies P. flava hepatica (Friedmann, 1971:253) collected at Rancho Vicente, Cerro Baul, Oaxaca,

really refers to P. flava dextra, which is an addition

to the host catalog of the bronzed cowbird. There

are 2 other earlier records for P. flava hepatica

(Friedmann, 1963:184).

RED-THROATED ANT-TANAGER

Habia fuscicauda (Cabanis)

This tanager was added to the known victims of

the bronzed cowbird by Miguel Alvarez del Toro,

when he found a parasitized nest at Meyapac,

Ocozocoautla, Chiapas, 30 May 1962. The record

involves the host race H. fuscicauda salvini and the

nominate race of the parasite.

PYRRHULOXIA

Pyrrhuloxia sinuata (Bonaparte)

Previously (Friedmann, 1971:253) there were 3

records known to us of this bird as a victim of the

bronzed cowbird. A fourth instance has been reported to us by its finder, Mr. F. F. Nyc, Jr., who

found a parasitized nest near Falcon Lake, Starr

County, Texas, 20 May 1970.

PAINTED BUNTING

Passerina ciris (Linnaeus)

The Western Foundation has in its collections an

egg of the bronzed cowbird taken from a nest of a

painted bunting, at Brownsville, Texas, 15 April

1900, by F. B. Armstrong. This is only the second

instance known to us of parasitism on this host by

the bronzed cowbird. The bunting is frequently imposed upon by the brown-headed cowbird, recalling

the case of the yellow-breasted chat, which shows

similarly a differential in its role as a victim of the

2 species of parasites.

WHITE-THROATED TOWHEE

Pipilo albicollis Sclater

To the 6 earlier records of this host (Friedmann,

1963:187; 1966:10) may be added 4 more, all similarly from Oaxaca, and all in the collections of the

Western Foundation. It is apparent that in that

part of Mexico, Sclater's towhee is a frequent host

choice of the bronzed cowbird.

PREVOST GROUND SPARROW

Melozone biarcuatum (Prevost and Des Murs)

One of us (L.F.K.) added this sparrow to the

known hosts of the bronzed cowbird when he collected a fledgling of the parasite being fed by two of

these sparrows, 16 August 1969, at Finca La Morena,

15 miles south of Guilapa, Department of Santa

Rosa, Guatemala. The cowbird was observed flying

from tree to tree with the two sparrows, and the

situation looked like a true family party, not an

"accidental feeding" due to response to the feeding

call of a strange fledgling.
Depositories of Unpublished Data

Egg Collections

Brigham Young University, Provo, Utah

British Columbia Provincial Musem, Vancouver, British

Columbia

Delaware Museum of Natural History, Greenville, Delaware

J. P. Norris Collection, dispersed: part at the San Bernardino

County Museum of Natural History, San Bernardino, California; part at Western Foundation; part at Nelson HoyCollection, Media, Pennsylvania

Museo dc La Plata, La Plata, Argentina

Oregon State University, Corvallis, Oregon

Royal Ontario Museum of Zoology, Toronto, Ontario

Santa Barbara Museum of Natural History, Santa Barbara,

California

Thomas Burke Memorial Museum, University of Washington, Seattle, Washington

University of Puget Sound, Tacoma, Washington

Western Foundation of Vertebrate Zoology, Los Angeles,

California

Record Files

British Columbia Nest Records, University of British Columbia, Vancouver, British Columbia

Cornell University Nest Records, Cornell University, Ithaca,

New York

Ontario Nest Records, Royal Ontario Museum of Zoology,

Toronto, Ontario

Prairie Nest Records, Manitoba Museum of Man and Nature,

Winnipeg, Manitoba

University of Michigan Biological Station (files, student

reports, unpublished manuscripts), Pellston, Michigan

69
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Anderson, S. H.

1970. The Avifaunal Composition of Oregon White Oak

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Austin, G. T.

1970. Breeding Birds of Desert Riparian Habitat in

Southern Nevada. Condor, 72:431-436.

Banks, R. C.

1964. Geographic Variation in the White-crowned Sparrow (Zonotrichia leucophrys). University of California Publications in Zoology, 70:1-123.

Baptista, L. F.

1972. Cowbird Parasitism on the White-crowned Sparrow

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Bennett, E. V.

1973. 1972 Nebraska Nesting Survey. Nebraska Bird Review, 41:3-9.

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NUMBER 2S5 71

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Index to Host Species Discussed

Acanthis flammea, 43

Actitis macularia, 10

Agelaius icterocephalus, 59

phoeniceus, 33, 67

ruficapillus, 59

thilius, 58

tricolor, 34

Aimophila carpalis, 47

cassinii, 47

Alectrurus tricolor, 54

Amblycercus holosericeus, 67

Ammodramus henslowii, 46

savannarum, 45

Amphispiza bilineata, 47

Anthus furcatus, 57

lutescens. 57

Anumbius annumbi, 53

Arremon flavirostris, 62

Arremonops conirostris, 62

Arundinicola leucocephala, 54

Atlapetes semirufus, 62

Auriparus flaviceps, 16

Basileuterus flaveolus, 58

leucophrys, 58

Bombycilla cedrorum, 23

Calamospiza melanocorys, 45

Calcarius ornatus, 51

Campylorhynchus nuchalis, 55

Carpodacus mexicanus, 42

purpureus, 42

Catharus aurantiirostris, 56

fuscescens, 21

guttatus, 20

ustulatus, 20

Charnaea fasciata, 17

Charadrius vociferus, 10

Chlorura chlorura, 44

Chondestes grammacus, 46

Coccyzus amcricanus, 11

ervthropthalmus, 11

Columbina passerina, 10

Conirostrum bicolor, 57

Contopus sordidulus, 15

Coryphospingus pileatus, 63

Cranioleuca pyrrhophia, 53

Cyanocitta cristata, 16

Cyanocompsa cyanea. 62

Cyanocorax vncas, 66

Cyclarhis gujanensis, 57

Dendroica caerulescens, 28

castanea, 29

cerulea, 29

chrysoparia, 29

coronata, 28

fusca, 29

magnolia, 28

nigrescens, 28

pensylvanica, 29

petechia, 27

pinus, 30

striata, 30

townsendi, 28

virens, 29

Diuca diuca, 63

Dolichonyx oryzivorus, 32

Donacospiza albifrons, 62

Dumatella carolinensis, 18

Embernagra platensis, 64

Empidonax difficilis, 15

hammondi, 14

minimus, 14

oberholseri, 14

traillii, 13

virescens, 13

wrightii, 14

Empidonomus aurantioatrocristatus, 54

Eremophila alpestris, 15

Euphagus carolinus, 37

cyanocephalus, 37

Furnarius rufus, 53

Geothlypis trichas, 31

Gnorimopsar chopi, 60

Guiraca caerulea, 41

Habia fuscicauda, 68

Hemithraupis guira, 61

Hirundo rustica, 16

Hylocichla mustelina, 20

Icteria virens, 31, 66

Icterus cucullatus, 35

galbula, 35

gularis, 68

icterus, 58

parisorum, 67

pectoralis, 67

pustulatus, 68

spurius. 34, 67

wagleri, 67

Junco hyemalis, 47

Leistes militaris, 60

Limnothlypis swainsonii, 26

Machetornis rixosus, 54

Melospiza georgiana, 50

lincolnii, 50

melodia, 50

Melozone biarcuatum, 68

Mimus patagonicus, 56

polyglottos, 66

saturninus, 56

thenca, 56

Mniotilta varia, 26

Muscivora tyrannus, 54

Myiarchus crinitus, 12

tyrannulus, 55

Nuttalornis borealis, 15

Oporornis tolmei, 30

Parus atricapillus, 16

Passer domesticus, 32, 58

Passerculus sandwichensis, 45

Passerella iliaca, 50

Passerina amoena, 41

ciris, 41,68

Pezites militaris, 60

Phacellodomus ruber, 53

rufifrons, 53

sibilatrix, 53

striaticeps, 53

Pheucticus ludovicianus, 41

melanocephalus, 41

Phleocryptes melanops, 53

Phytotoma rutila, 55

Pipilo aberti, 45

albicollis, 68

erythrophthalmus, 44

fuscus, 44

Piranga flava, 68

ludoviciana, 39

olivacea, 40

rubra, 40

Polioptila caerulea, 22

melanura, 22

Pooecetes grammineus. 46

Poospiza melanoleuca, 64

nigrorufa, 64

torquata, 64

74
NUMBER 235

75

Psaltriparus minimus, 16

Psarocolius decumanus, 58

Pseudoleistes virescens, 60

Pseudoseisura cristata, 52

Pyrocephalus rubinus, 15

Pyrrhuloxia sinuata, 40, 68

Quisculus quiscula, 39

Rallus limicola, 10

Ramphocelus carbo, 61

Regulus calendula, 22

satrapa, 22

Rhodinocichla rosea, 61

Richmondena cardinalis, 40

Saltator aurantiirostris, 62

Say onus phoebe, 12

sayaca, 13

Schistoclatuys melanopis, 61

Seiurus motacilla, 30

uovaboracensis, 30

Serpophaga subcristata, 54

Setophaga picta, 67

Sialia currucoides, 21

sialis, 21

Sicalis flaveola. 63

luteola, 63

Sitta carolinensis, 17

Spinus magellanicus. 62

pinus. 43

psaltria, 44

tristis, 43

Spiza americana, 42

Spizella breweri, 48

pallida, 48

passerina, 48

pusilla, 49

Sporophila lineola, 62

Steganopus tricolor, 10

Sturnella magna, 32

Stum us vulgaris, 23

Suiriri suiriri, 55

Tachyphonus rufus, 61

Thamnophilus ruficapillus, 53

Thlypopsis sordida, 61

Thraupis sayaca, 61

Thryomanes bewickii, 17

Thryothorus ludovicianus, 17

rutilus, 55

Tityra cayana, 54

Toxostoma longirostre, 66

rufum, 18

Troglodytes aedon, 55

Turdus amaurochalinus, 57

grayi, 66

migratorius, 19

nudigenis, 56

rufiventris, 57

serranus, 56

Tvrannus melancholicus, 54

tyrannus, 11

verticals, 11

Vireo atricapilla, 24

bellii, 24

flavifrons, 25

gilvus, 26

griseus, 24

huttoni, 24

olivaceus, 25, 57

philadelphicus, 26

solitarius, 25

Vermivora celata, 27

chrysoptera, 26

luciae, 27

peregrina, 26

pinus, 27

ruficapilla, 27

Wilsonia canadensis, 32

citrina, 31

pusilla, 31

Xanthocephalus xanthocephalus, 33

Zarhynchus wagleri, 67

Zenaida auriculata, 52

macroura, 10

Zonotrichia albicollis, 49

capensis, 63

leucophrys. 49

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must be submitted at the end of the manuscript—with as many legends typed, doublespaced, to a page as convenient.

Illustrations must not be included within the manuscript but must be submitted separately as original art (not copies). All illustrations (photographs, line drawings, maps, etc.)

can be intermixed throughout the printed text. They should be termed Figures and should

be numbered consecutively. If several "figures" are treated as components of a single larger

figure, they should be designated by lowercase italic letters (underlined in copy) on the illustration, in the legend, and in text references: "Figure 9b." If illustrations are intended to be

printed separately on coated stock following the text, they should be termed Plates and any

components should be lettered as in figures: "Plate 9b." Keys to any symbols within an

illustration should appear on the art and not in the legend.

A few points of style: (1) Do not use periods after such abbreviations as "mm, ft,

yds, USNM, NNE, AM, BC." (2) Use hyphens in spelled out fractions: "two-thirds." (3)

Spell out numbers "one" through "nine" in expository text, but use numerals in all other

cases if possible. (4) Use the metric system of measurement, where possible, instead of

the English system. (5) Use the decimal system, where possible, in place of fractions.

(6) Use day/month/year sequence for dates: "9 April 1976." (7) For months in tabular listings or data sections, use three-letter abbreviations with no periods: "Jan, Mar, Jun," etc.

Arrange and paginate sequentially EVERY sheet of manuscript—including ALL front

matter and ALL legends, etc., at the back of the text—in the following order: (1) title page,

(2) abstract, (3) table of contents, (4) foreword and/or preface, (5) text, (6) appendixes,

(7) notes, (8) glossary, (9) bibliography, (10) index, (11) legends.
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