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NArURAL HISTORY.
SIIRVFY

'•'^'(.FIELDIANA • ZOOLOGY

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Published by
CHICAGO NATURAL HISTORY MUSEUM

Volume 44 March 23, 1965 No. 22

Taxonomy and Nomenclature
of the Bronzed Cowbird

KENhfETH C. PaRKES
Curator of Birds, Carnegie Museum

AND

Emmet R. Blake
Curator, Division of Birds

The Bronzed or Red-eyed Cowbird, currently called Tangavius
aeneus, has had a checkered nomenclatorial history, at the generic,
specific, and subspecific levels. In connection with the preparation
of the manuscript for the family Icteridae for the Peters Check-list
by the junior author, we have had occasion to look into both the
taxonomy and the nomenclature of this species.

The first edition of the A.O.U. Check-list (1886) and earlier litera-
ture placed aeneus in the genus Molothrus. In the appendix to his
Manual of North American Birds (1st ed., 1887, p. 589; 2nd ed.,
1896, p. 600), Ridgway proposed that two "species" (now considered
subspecies) of cowbirds, aeneus Wagler and robustus Cabanis, be sep-
arated from Molothrus. As generic characters he gave "feathers of
hind-part and sides of neck in the adult male much elongated, form-
ing a very conspicuous, soft, dense and erectile ruff; four outer pri-
maries with inner webs curiously sinuated and emarginated, the web
being expanded just beyond the middle portion, the posterior ex-
tremity of the widened part forming an acute point, projected longi-
tudinally (less marked on the first quill)." For this newly separated
genus Ridgway revived the name Callothrus Cassin (1866), originally
proposed as a subgenus of Molothrus to include aeneus (with which
Cassin synonymized robustus) and armenti Cabanis. The first of

Library of Congress Catalog Card Number: 65-19122

No. 989 207 NATURAL HISTORY SURVEY

JUL 22 1965
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208 FIELDIANA: ZOOLOGY, VOLUME 44

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these two species was later designated as the t3rpe of Callothrus by ^
Sclater (1884, p. 3). '' '

The segregation of the Bronzed Cowbird into a genus separate
from Molothrus was adopted in the second edition of the A.O.U.
Check-list (1895), and has been universally accepted in the subse-
quent literature. Only the number of species to be included in such
a genus and the names to be used for the included forms, as well as
for the genus itself, have varied.

Ridgway's concept of the genus Callothrus in his "Manual" in-
cluded aeneus as a west Mexican species, and robustus as a species
found from Texas to Panama. By 1902, when part II of "Birds of
North and Middle America" appeared he had added (without having
seen) the South American armenti as a third species, and recognized
two subspecies of aeneus, as Nelson, in the interim, had described
Callothrus aeneus assimilis as the form of southwestern Mexico.
Shortly afterward, Nelson (1905, p. 125) rediscovered the name
Tangavius involucratus Lesson, 1839, and showed that the type speci-
men probably came from eastern Mexico. The generic name Tan-
gavius was therefore substituted for Callothrus of later date, and
involucratus replaced robustus as the name for the form ranging from
Texas through eastern Mexico to Panama. Nelson, in the same paper
(1905, p. 126), showed that intergradation in the vicinity of the
Isthmus of Tehuantepec made it necessary to consider the three
Mexican forms as conspecific. The third edition of the A.O.U.
Checklist (1910) thus listed Tangavius aeneus aeneus (as the western
form had, since Ridgway wrote, invaded Arizona) and Tangavius
aeneus involucratus as the two forms found within its geographic
scope.

Friedmann (1927, 1929) was the first modern student to survey
the cowbirds over their entire geographic range, and he had the bene-
fit of field experience with many of the forms. He admitted the same
forms of Tangavius as had Nelson in 1905; i.e., two species, armenti
and aeneus, the latter with three races, aeneus, involucratus and as-
similis. At the generic level, Friedmann was then something of a
"splitter," preferring to recognize nomenclatorially certain natural
divisions among the cowbirds. Thus he not only continued to admit
both Tangavius and Molothrus, but coined a subgenus Strepitovagus
for M. rufoaxillaris, and segregated the non-parasitic cowbirds as a
third genus for which he revived the name Agelaioides Cassin. Fried-
mann redefined the genus Tangavius as follows: "Cowbirds with the
three outer primaries incised on their inner webs; the feathers of

PARKES AND BLAKE: THE BRONZED COWBIRD 209

the mantle enlarged to form a distinct ruff in the male; and the
plumage of the neck and breast somewhat hair-like."

Up until this point it had apparently not occurred to anyone that
the name aeneus Wagler, based on specimens collected by Deppe,
was almost certainly wrongly applied to the northwestern Mexican
race for which it had been used since the initial division of the
Bronzed Cowbird into two forms. It remained for van Rossem
(1934, pp. 354-355) to examine the Deppe specimens at the Zoolog-
ical Museum in Berlin, and to show that these were of the eastern
Mexican population. Although van Rossem plainly stated that the
specimen upon which Wagler based his description of aeneus (i.e.,
the type) came from the City of Mexico, and that a second specimen
came from "Lagunas" (identified by van Rossem as "Laguna, Vera
Cruz," but see below), Hellmayr (1937, p. 52) inexplicably cited the
type locality as "Laguna, Vera Cruz." This error has been perpetu-
ated in the most recent edition of the A.O.U. Check-list (1957), and
in the Mexican Check-list (Miller et ah, 1957).

Stresemann (1954) published a highly useful paper on the col-
lector Ferdinand Deppe, giving his itinerary, and listing the type
specimens, collected by Deppe, of species described by various nine-
teenth century ornithologists. In this paper he established the iden-
tity of Deppe's "Lagunas" as Laguna Huetulacan, Veracruz. However,
he lists a specimen from Oaxaca, Oaxaca, as the "lectotype" of Psaro-
colius aeneus Wagler, and mentions no specimen of this species from
Mexico City. Professor Stresemann has been kind enough to re-
examine the Deppe specimens in the Berlin Museum on our behalf
to clear up this discrepancy. He writes as follows (letter of 18 Au-
gust 1964) :

"In Lichtenstein's catalogue of about 1852 three specimens are listed under
the heading of 'Icterus (Molothrus) aeneus' :

7396 fern.

Oaxaca

Deppe

7397 mas. ad.

Mexico

Deppe

7398

Lagunas

Deppe

"The Oaxaca bird was destroyed in Feb. 1945, while the others are still in
best shape. Nr. 7398 is a female ad., collected in 1828 by Deppe and Schiede at
Laguna Huetulacan (Est. Veracruz). This specimen had apparently not yet
reached Berlin at the time of Wagler's visit in the autumn of 1828. Nr. 7397 is
a fine adult male, still bearing Lichtenstein's label: 'I. aeneus Wagl. Mas. Psaro-
colius aeneus Wagl. Mexico. Deppe.' In Deppe's lists of birds sent to Berlin, the
term 'Mexico' means always Mexico City. Nr. 7397 has, therefore, to be regarded
as the type of Wagler's bird. I made a mistake when writing in my 1954 article,
'Oaxaca, October 1825, lectotype' . . ."

The type locality of Tangavius aeneus aeneus may thus, thanks
to Dr. Stresemann, be firmly established as the City of Mexico.

210 FIELDIANA: ZOOLOGY, VOLUME 44

Having demonstrated that the subspecies in eastern Mexico must
bear the name aeneus rather than involucratus, van Rossem (1934,
p. 355) renamed the northwestern race T. a. milleri (type locality-
Tucson, Arizona) . The nomenclature thus established by van Ros-
sem was adopted by Hellmayr (1937) and has been universally em-
ployed ever since.

To turn from nomenclature to taxonomy, the generic distinctness
of the Bronzed Cowbird does not appear to have been questioned
since the separation was made by Ridgway. That author himself ad-
mitted (1902, p. 206) that "M. atronitens" [=M. bonariensis mini-
mus] has the inner webs of the three outer primaries with "an angu-
lar projection of the margin, much as in the species of Callothrus,
but much less pronounced, and there seems also to be a slight devel-
opment of the neck-ruffs of that genus." Ridgway's statement is
true of the other races of M. bonariensis, which he apparently did
not examine, as well as of minimus. The primaries of M. rufoaxillaris
are slightly sinuated in the same area.

Friedmann (1929, p. 319) stated that "in respect to the develop-
ment of the cape armenti is much nearer to T. aeneus than to any
species of Molothrus but is a fairly good intermediate link between the
two genera." We have examined the adult male specimen of armenti
in the American Museum of Natural History, and agree that it seems
to bridge in several ways the gap between Molothrus and Tangavius.
Although aeneus is a large, stoutly-proportioned cowbird, armenti, as
Friedmann {loc. cit.) points out, "seems to have the weakest bill and
feet of all the Cowbirds," and resembles M. ater more than T. aeneus
in these proportions. In addition, the brown color of the head and
body of armenti, while more iridescent, is not unlike that of the head
of male ater.

It is true that adult males of T. aeneus exhibit a peculiar tex-
ture of the breast feathers (described by Friedmann as "somewhat
hairlike"). This character appears to vary geographically in its ex-
pression within the species aeneus, and is definitely less conspicuous
in armenti. Isolated breast feathers of adult males of M. bonariensis
also have a decidedly "hairy" aspect, although this textural quality
is less conspicuous when the feathers are in place, as they are rela-
tively shorter than those of aeneus.

Thus every morphological character by which Tangavius and
Molothrus have traditionally been separated is seen to be bridged by
T. armenti, by M. bonariensis, or both. Recent studies of the be-
havior of icterids by Selander and others (see especially Selander

PARKES AND BLAKE: THE BRONZED COWBIRD 211

1964) have reinforced the earlier findings of Fried mann (1929) that
aeneus resembles the parasitic members of Moloihrus in displays and
vocalizations far more than does the non-parasitic badius, although
the latter is currently included in Molothrus. Friedmann charac-
terized the genus "Agelaioides" as "non-parasitic Cowbirds with
short, rounded wings, no sexual plumage dimorphism, and no court-
ship display." We agree with Hellmayr (1937, p. 68) that the wing
shape is not a very good generic character. As for the lack of sexual
plumage dimorphism, this is also true of M. rufoaxillaris, although
the latter might be considered "cock-feathered," while badius is "hen-
feathered." The differences in reproductive habits, displays and
vocalizations between badius and the other cowbirds are striking,
however, and a much better case could be made for recognizing
Agelaioides and Molothrus rather than Tangavius and Molothrus if
the cowbirds are to be divided into two genera. As emphasized by
Hoy and Ottow (1964), however, nestlings of M. rufoaxillaris are
virtually indistinguishable from those of M. badius; the latter spe-
cies is the chief and probably sole host of the former (Friedmann,
1963, pp. 216-217) . Friedmann (1929, p. 45) stated that rufoaxillaris
"shows in several ways that it is an offshoot from the Bay- wing
[badius] stock. . . ." Although, as agreed by all authors, badius is
undoubtedly the most "primitive" of living cowbirds, it seems best
to continue to consider it a member of the genus Molothrus.

Since the Bronzed Cowbird is shown above to lack any unique
character, whether morphological or behavioral, which would justify
continued recognition of the genus Tangavius, we hereby propose to
return it to Molothrus. The little-known armenti (for a summary of
its history see Friedmann, 1957) is a geographic representative of
aeneus. Although its difference in color and proportions suggest that
it might be specifically distinct, armenti is now considered by Dr.
Friedmann to be conspecific with aeneus. We propose to follow his
recommendation, based in part on observations of a living adult male
armenti in the National Zoo, and place armenti as a subspecies of
aeneus. Detailed distributional studies in Mexico may yet show that
the "gray female" and "black female" types of Bronzed Cowbird
are sympatric, in which case it will be necessary to return to the older
concept of two species.

Unfortunately, when Tangavius becomes a synonym of Molothrus,
it is necessary once again to rename the Bronzed Cowbird of Arizona
and northwestern Mexico, since Tangavius aeneus milleri van Ros-
sem, 1934, is preoccupied in Molothrus by Molothrus bonariensis

212 FIELDIANA: ZOOLOGY, VOLUME 44

milleri Naumburg and Friedmann, 1927, currently considered a syn-
onym of M. b. bonariensis. In order to honor van Rossem's intent
to name this race of Bronzed Cowbird for his friend and colleague
Dr. Loye Holmes Miller, we propose Molothrus aeneus loyei,
new name, to replace milleri van Rossem.

The Giant Cowbird or Rice Grackle, Scaphidura oryzivora (=PsO'
mocolax oryzivorus auct,; see Parkes, 1954), is undoubtedly related to
the Molothrus assemblage, and resembles them in certain of its dis-
plays (Harrison, 1963; Selander, 1964), However, oryzivora is quite
sharply set apart from the molothrine cowbirds in a number of mor-
phological particulars (very much larger size, different proportions,
peculiar bill shape, etc.), and appears worthy of continued separation
in the monotypic genus Scaphidura.

Friedmann (1963, pp. 2, 10, 173, 218) has arranged the cowbirds
in a proposed evolutionary sequence based chiefly on type of host
preference. Starting with the non-parasitic badius, he postulates the
first stage as the single-host rufoaxillaris. From this stock, one line
leads through bonariensis to ater, the species with the broadest host
tolerance. The other line, of more restricted host selection, leads
through oryzivora to aeneus (in which, contrary to his 1957 suggestion,
Friedmann includes armenti) . Friedmann admits that the "evidence"
for the latter sequence is almost entirely behavioral, and is merely
suggestive. Morphological evidence suggests a somewhat different
sequence. The shape of the outer primaries, incipient ruff, and
feather texture of males all point toward bonariensis as the nearest
living relative of the Bronzed Cowbirds. And Friedmann admits
that derivation of the Bronzed from the Giant Cowbird does seem
highly unlikely in many ways.

The most difficult species to place is the North American ater.
It is the most host-versatile species, but its plumage is less specialized
than that of either bonariensis or aeneus. Judging from statements in
the literature, especially in Friedmann (1929), the habit of associat-
ing with grazing ungulates is developed to the greatest extent in ater
(then, in descending order, aeneus, bonariensis, rufoaxillaris and ba-
dius; according to Skutch [1954, pp. 316-318], Scaphidura resembles
aeneus in feeding behavior) .

That there was a radiation in North America of cowbird-like
icterids is strongly suggested by the presence in Quaternary deposits
of the extinct genera Pyelorhamphus (New Mexico) and Pandanaris
(California, Florida; see Brodkorb, 1957) . Both of these most nearly
resemble cowbirds among living icterids, according to their describer.

PARKES AND BLAKE: THE BRONZED COWBIRD 213

Alden H. Miller. Significantly, these two are among the very few
extinct Quaternary land bird genera listed by Wetmore (1956), other
than the large falconiform birds, and they were the only extinct
Quaternary passeriform genera known at that time. A few addi-
tional extinct Pleistocene passeriform genera have since been de-
scribed, including one icterid, Cremaster (Brodkorb, 1959). The
latter resembles living oropendolas and caciques, but Dr. Brodkorb,
in conversation, states that he did not compare Cremaster with
Scaphidura. Such a comparison might prove to be of interest, as
the ecology deduced from the fauna associated with Cremaster does
not seem appropriate for an oropendola. At any rate, the deduction
seems inescapable that there were cowbird-like birds associated with
the extinct Pleistocene herbivore fauna, just as there were numerous
large extinct predators and scavengers, both avian and mammalian
(see Martin, 1959, p. 403). It is possible that living Molothrus ater
represents a survivor of this North American radiation (it is known
from the Pleistocene of Virginia; see Wetmore, 1962, p. 14), which
remained highly adaptable to new hosts, new herbivores, and new
geographic areas, as we know it to be today.

Friedmann (1963, p. 218) invoked geographic distribution as part
of his argument that aeneus may have been derived from oryzivora.
On the other hand, at least three species of cowbirds (ater, bonarien-
sis, aeneus) have expanded their ranges within historic times, and
Friedmann (1957) has himself suggested that the range of armenti
may have shifted away from the coast of Colombia within the past
century. It thus appears somewhat futile to try to reconstruct any
distributional history of cowbird evolution based on the present
ranges of living species.

For check-list purposes, as is well known, a three-dimensional re-
lationship must be forced into two dimensions. Up to a certain point,
a linear arrangement of the cowbirds reflects what seem to be true
relationships. As Friedmann has stated, more than one phyletic line
is almost certainly involved in the evolution of the living species.
If ater could be omitted, the sequence would be a rather straight-
forward one, progressing from lesser to greater development of para-
sitism, sexual dimorphism, and specialization of plumage. But, as
mentioned above, ater is in some ways the most advanced in behavior
characters while relatively unspecialized in plumage characters. The
latter is more likely to be a secondary development, although it is
possible that ater evolved directly from an unspecialized ancestral
molothrine. It seems that the best compromise is to place ater at

214 FIELDIANA: ZOOLOGY, VOLUME 44

the end of Molothrus, even though the following species, Scaphidura
oryzivora, has its closest affinities with aeneus. The proposed check-
list sequence of species of cowbirds, therefore, is as follows:

Molothrus badius

rufoaxillaris
bonariensis
aeneus
ater
Scaphidura oryzivora

Acknowledgments. — We are grateful to Dr. Erwin Stresemann for
information concerning the Deppe specimens of Molothrus aeneus in
the Berlin Museum, and to Dr. Allan R. Phillips for certain details
of the distribution of that species in Mexico, The authorities of the
American Museum of Natural History, New York, kindly permitted
the examination of specimens in that institution.

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