Female Brown-Headed Cowbird with Partial Male Plumage

2004·1.3 MB·English

by  Scott G Summers

Wilson Bulletin 116(4):293-294, 2004
FEMALE BROWN-HEADED COWBIRD WITH PARTIAL
MALE PLUMAGE
SCOTT G. SUMMERS^ 2 AND RICHARD M. KOSTECKEi
—
ABSTRACT. There are few records of functionally female birds exhibiting partial to total male plumages.
On 26 March 2004, we collected a female Brown-headed Cowbird {Molothrus ater) at Fort Hood, Texas, with
a presumably functional ovary and whose back and belly exhibited the glossy, greenish-black plumage typical
ofafter-hatch-year males. This individual is a unique specimen because (with the exception ofpartial albinism)
no aberrant plumages have been reported for Brown-headed Cowbirds. Received 27 May 2004, accepted 16
October2004.
Fort Hood, an active military installation ondary sexual characteristics, and expression
located in central Texas (Bell and Coryell of these genes is related to sex-specihe hor-
counties), practices Brown-headed Cowbird mones (i.e., estrogen and testosterone). Fur-
{Molothrus ater, hereafter cowbird) control as ther, Owens and Short (1995) suggested that
a means of reducing brood parasitism on en- the showier breeding plumage of males of
dangered songbirds that nest on the installa- many species is actually the neutral stage of
tion (Eckrich et al. 1999). On 26 March 2004, development and that more cryptic female
a cowbird with an unusual plumage was plumages are induced by estrogen production.
trapped at Fort Hood. The head and breast of Thus, the male plumage characteristics ob-
this bird were brownish-gray (i.e., typical fe- served on our female cowbird could have re-
male coloration; Fig. 1). Although individual sulted from reduced hormone secretion. Al-
and groups of feathers on its back and belly ternatively, the observed plumage may be the
were also brownish-gray, its back and belly result of a genetic abnormality. Cowbirds
were predominately a glossy, greenish-black maintain similar-looking plumage year-round;
typical of after-hatch-year males (Pyle 1997). therefore, hormones may not have a large in-
Upon dissection, we discovered that the cow- fluence on feather pigmentation (Lowther
bird had a reduced (i.e., follicles were small, 1993, Owens and Short 1995, Pyle 1997).
abuptprpoxriemsautmealbyly1 fmunmctiionnadli,ameotvearr,yaonnd withsitlee)f,t forReitgsaradblerersasntofpltuhmeagmee,cthhaencioswmbirredspwonesicbolle-
side. Wing chord (104 mm) and tail (71 mm) lected is a unique specimen. With the excep-
measurements were consistent with the cow- tion of partial albinism (Stewart 1963), few
bird being a large M. a. artemisiae female unusual plumages have been reported for
cowbirds (Lowther 1993, Ortega 1998). Fur-
(Pyle 1997).
Females that exhibit partial to total male ther, we have trapped and destroyed >19,512
plumages are rare but have been reported for female cowbirds at Fort Hood during 1999-
2003 (The Nature Conservancy ofTexas, Fort
Northern Bobwhite (Colinns virginianus\
Hood, Linpubl. data), and none of the birds
Buchanan and Parkes 1948), American (Falco exhibited unusual plumages. We deposited our
sparverius; Parrish et al. 1987) and Lesser (F. cowbird specimen (FMNH 440412) al the
naunianni\ Telia et al. 1996) kestrels. Bay- Field Museum of Natural History, Chicago,
breasted Warbler (Denclroica castanea\ Stod-
Illinois.
dard 1921), and Spotted Towhee (Pipilo ma-
culatus: Bergtold 1916). Male-like feather ACKNOWLEDGMENTS
pigmentation can result from hormonal ab-
normalities. Andersson (1994) suggested that All cowbirds were captured anti handletl uiKler l ed-
both sexes carry the genes that inlluence sec- eral Birtl Marking and .Salvage I’ennit 2299S-H. l ed-
eral Tish and Wildlife Permit MB()<S5693-0. and Texas
Scientilie I’ermit Number SI’K-()204-.336. V. A.
' The Nature Conservancy of Texas, F.O. Itox .'SI90, (ireene. I’ i;. Lowther. and ('. I’. Ortega commented on
Tort Hood, TX 76.S440190, U.SA. the manuscript, f unding was pro\itled by the Lnited
‘Corresponding author; e-mail: ssummers(otnc.org .States Army through ct)operative agreement DI’W-
293
294 THE WILSON BULLETIN • Vol. 116, No. 4, December2004
FIG. 1. Female Brown-headed Cowbird (Molothrus ater) trapped at Fort Hood, Texas, on 26 March 2004,
exhibiting brownish-gray head and breast typical of females, but a predominately glossy, greenish-black back
and belly typical ofafter-hatch-year males. Photograph by D. A. Cimprich.
ENV-02-A-0001 withTheNatureConservancyofTex- Ortega, C. P. 1998. Cowbirds and other brood para-
as. The content ofthis manuscriptdoes not necessarily sites. University ofArizona Press, Tucson.
reflect the position or policy ofthe United States gov- Owens, I. P. F. and R. V. Short. 1995. Hormonalbasis
ernment and no official endorsement should be in- of sexual dimoi-phism in birds: implications for
ferred. new theories of sexual selection. Trends in Ecol-
ogy and Evolution 10:44-47.
LITERATURE CITED
Parrish, J. R., J. Stoddard, and C. M. White. 1987.
Andersson, M. 1994. Sexual selection. Princeton Uni- Sexually mosaic plumage in a female American
versity Press, Princeton, New Jersey. Kestrel. Condor 89:911-913.
Bergtold, W. H. 1916. Pseudo-masculinity in birds. Pyle, P. 1997. Identification guide to North American
Auk 33:439. Birds, part I. Slate Creek Press, Bolinas, Califor-
Buchanan, F. W. and K. C. Parkes. 1948. A female nia.
Bob-white in male plumage. Wilson Bulletin 60: Stewart, P. A. 1963. Abnormalities among Brown-
19-120. headed Cowbirds trapped in Alabama. Bird-Band-
1
Eckrich, G. H., T. E. Koloszar, and M. D. Goering. ing 34:199-202.
1999. Effective landscape managementofBrown- Stoddard, H. L. 1921. Female Bay-breasted Warbler
headed Cowbirds at Fort Hood, Texas. Studies in in male plumage. Auk 38:1 17.
Avian Biology 18:267-274. Tella, j. L., j. a. Donazar, and F. Hiraldo. 1996.
Lowther, P. E. 1993. Brown-headed Cowbird {Mol- Variable expression of sexually mosaic plumage
othrus ater). The Birds ofNorth America, no. 47. in female Lesser Kestrels. Condor 98:643-644.