Biological Exuberance: Animal Homosexuality and Natural Diversity

Large numbers of male Cowbirds are nonbreeders: more than half of all males in some populations are unpaired, and only a third of males actually copulate with females in some years. Brown-headed Cowbirds are also BROOD PARASITES, which means that females always lay their eggs in the nests of other bird species and take no part in raising their own young. Infanticide occurs in 9—12 percent of House Sparrow nests, often when a female who has lost her mate pairs with a new male (who pecks her young to death in order to father his own offspring). Females in polygamous trios also occasionally kill one another’s nestlings. Sometimes, however, a female whose mate has been replaced by an infanticidal male will stop laying eggs (by interrupting or delaying ovulation) in order not to lose any more young, and some replacement males adopt rather than kill their mate’s young.

Other Species

Male Sharp-tailed Sparrows (Ammodramus caudacutus), a North American species, sometimes mount other males. Adolescent male Yellow-rumped Caciques (Cacicus cela), a South American blackbird, frequently mount fledglings of both sexes. Sexual behavior toward these younger birds is usually part of an overall pattern of harassment, in which the adolescent males (often in groups) chase, peck, attack, and sometimes even knock fledglings from their perches (often resulting in their death by drowning if they fall into water). About 36 percent of such harassments (and the associated sexual behavior) involve same-sex interactions.

Sources

*asterisked references discuss homosexuality/transgender

Craig, A. J. F. K. (1996) “The Annual Cycle of Wing Moult and Breeding in the Wattled Starling Creatophora cinerea.” Ibis 138:448—54.

Darley, J. A. (1978) “Pairing in Captive Brown-headed Cowbirds (Molothrus ater).” Canadian Journal of Zoology 56:2249—52.

*Dean, W. R. J. (1978) “Plumage, Reproductive Condition, and Moult in Non-Breeding Wattled Starlings.” Ostrich 49:97-101.

Friedmann, H. (1929) The Cowbirds: A Study in the Biology of Social Parasitism. Springfield, Ill.: Charles C. Thomas.

*Greenlaw, J. S., and J. D. Rising (1994) “Sharp-tailed Sparrow (Ammodramus caudacutus).” In A. Poole and F. Gill, eds., The Birds of North America: Life Histories for the 21 st Century, no. 112. Philadelphia: Academy of Natural Sciences; Washington, D.C.: American Ornithologists’ Union.

*Griffin, D. N. (1959) “Apparent Homosexual Behavior Between Brown-headed Cowbird and House Sparrow.” Auk 76:238—39.

*Hamilton, J. B. (1959) “A Male Pattern Baldness in Wattled Starlings Resembling the Condition in Man.” Annals of the New York Academy of Sciences 83:429-47.

Laskey, A. R. (1950) “Cowbird Behavior.” Wilson Bulletin 62:157-74.

Liversidge, R. (1961) “The Wattled Starling (Creatophora cinerea [Menschen]).” Annals of the Cape Provincial Museums 1:71—80.

Lowther, P. E. (1993) “Brown-headed Cowbird (Molothrus ater).” In A. Poole, P. Stettenheim, and F. Gill, eds., The Birds of North America: Life Histories for the 21st Century, no. 47. Philadelphia: Academy of Natural Sciences; Washington, D.C.: American Ornithologists’ Union.

Lowther, P. E., and C. L. Cink (1992) “House Sparrow (Passer domesticus).” In A. Poole, P. Stettenheim, and F. Gill, eds., The Birds of North America: Life Histories for the 21 st Century, no. 12. Philadelphia: Academy of Natural Sciences; Washington, D.C.: American Ornithologists’ Union.

Møller, A. P. (1987) “House Sparrow, Passer domesticus, Communal Displays.” Animal Behavior 35:203—10.

*Robinson, S. K. (1988) “Anti-Social and Social Behavior of Adolescent Yellow-rumped Caciques (Icteri-nae: Cacicus cela).” Animal Behavior 36:1482-95.

Rothstein, S. I. (1980) “The Preening Invitation or Head-Down Display of Parasitic Cowbirds: II. Experimental Analysis and Evidence for Behavioral Mimicry.” Behavior 75:148—84.

Rothstein, S. I., D.A. Yokel, and R. C. Fleischer (1986) “Social Dominance, Mating and Spacing Systems, Female Fecundity, and Vocal Dialects in Captive and Free-Ranging Brown-headed Cowbirds.” Current Ornithology 3:127—85.

Scott, T. W, and J. M. Grumstrup-Scott (1983) “Why Do Brown-headed Cowbirds Perform the Head-Down Display?” Auk 100:139—48.

*Selander, R. K., and C. J. La Rue, Jr. (1961) “Interspecific Preening Invitation Display of Parasitic Cowbirds.” Auk 78:473—504.