Biological Exuberance: Animal Homosexuality and Natural Diversity

Heterosexual copulation is often incomplete because females refuse to cooperate in mating. In addition, in the early stages of courtship, males are often aggressive toward any bird that approaches them, including females. Chicks that hatch late are usually deserted by their parents after their siblings have fledged; they often move to other nests and are adopted by those families. Adults also occasionally accept eggs laid in their nest by other herons such as great egrets (Casmerodius albus) or lay their own eggs in nests of other species such as snowy egrets (Egretta thula).

Sources

*asterisked references discuss homosexuality/transgender

Allen, R. P., and F. P. Mangels (1940) “Studies of the Nesting Behavior of the Black-crowned Night Heron.” Proceedings of the Linnaean Society of New York 50–51:1–28.

Cannell, P. E, and B. A. Harrington (1984) “Interspecific Egg Dumping by a Great Egret and Black-crowned Night Herons.” Auk 101:889-91.

Davis, W. E., Jr. (1993) “Black-crowned Night Heron (Nycticorax nycticorax) .” In A. Poole and F. Gill, eds., The Birds of North America: Life Histories for the 21 st Century, no. 74. Philadelphia: Academy of Natural Sciences; Washington, D.C.: American Ornithologists’ Union.

Gross, A. O. (1923) “The Black-crowned Night Heron (Nycticorax nycticorax naevius) of Sandy Neck.” Auk 40:1–30, 191–214.

Kazantzidis, S., V. Goutner, M. Pyrovetsi, and A. Sinis (1997) “Comparative Nest Site Selection and Breeding Success in 2 Sympatric Ardeids, Black-Crowned Night-Heron (Nycticorax nycticorax) and Little Egret (Egretta garzetta) in the Axios Delta, Macedonia, Greece.” Colonial Waterbirds 20:505–17.

*Lorenz, K. (1938) “A Contribution to the Comparative Sociology of Colonial-Nesting Birds.” In F. C. R. Jourdain, ed., Proceedings of the Eighth International Ornithological Congress, Oxford (July 1934), pp. 207–21. Oxford: Oxford University Press.

McClure, H. E., M. Yoshii, Y. Okada, and W. F. Scherer (1959) “A Method for Determining Age of Nestling Herons in Japan.” Condor 61:30–37.

*Noble, G. K., and M. Wurm (1942) “Further Analysis of the Social Behavior of the Black-crowned Night Heron.” Auk 59:205–24.

*Noble, G. K., M. Wurm, and A. Schmidt (1938) “Social Behavior of the Black-crowned Night Heron.” Auk 55:7–40.

Schorger, A. W. S. (1962) “Black-crowned Night Heron.” In R. S. Palmer, ed., Handbook of North American Birds, vol. 1: Loons through Flamingos, pp. 472–84. New Haven and London: Yale University Press.

CATTLE EGRET, LITTLE EGRET

IDENTIFICATION: Long-legged, typically white herons with ornamental, filamentous plumes on the back, breast, and nape; these are golden-buff-colored in the Cattle Egret. DISTRIBUTION: Throughout Africa, southern Europe, Australasia, and (in Cattle Egret) North and South America. HABITAT: Variable, including swamps, marshes, rivers, lakes, meadows. STUDY AREA: Near Tsu City, Japan; subspecies Bj. coromanda and E.g. garzetta.

LITTLE BLUE HERON

IDENTIFICATION: Similar to Little Egret but with slaty-gray plumage and a reddish brown head and neck. DISTRIBUTION: Southeastern United States to northern South America. HABITAT: Lakes, marshes, streams. STUDY AREA: Swan Lake, Arkansas; Cliftonville, Massachusetts.

GRAY HERON

IDENTIFICATION: A large (3 foot long) heron with a gray back, white head and neck, and black “eyebrow” stripe and nape plumes. DISTRIBUTION: Throughout Eurasia and Africa. HABITAT: Wetlands. STUDY AREA: Donana National Park, Spain; subspecies A.c. cinerea.

Social Organization

Herons and Egrets are highly social birds, nesting in dense colonies that may include birds of several different species. During the mating season the primary social unit is the monogamous pair, although several alternative mating systems occur (see below). Outside of the breeding season, they may be found either singly or in flocks.

Description

Behavioral Expression: In all four of these Heron and Egret species, males that are paired to females often copulate with birds other than their mates; in some cases, these involve homosexual copulations with other males who are themselves also paired to females. Homosexual mountings always take place during the mating season. In Little Egrets, mountings between males are most common during the early stages of heterosexual pair formation (before nest-building begins), while in Little Blue Herons at least some homosexual activity takes place during the incubation period, since males have been seen mounting other males that are sitting on eggs. Typically, males mount birds in neighboring nests, although in Little Egrets and Little Blue Herons males may travel to other areas of the breeding colony to engage in “extramarital” or promiscuous copulations (both homosexual and heterosexual).

In Cattle Egrets (and probably the other species as well), homosexual mountings always take place on the mountee’s nest. In a typical encounter, the male seeking an “extramarital” liaison approaches another male, uttering RICK RACK calls (a harsh double croaking sound, also used in heterosexual encounters). The first male then mounts the other bird and crouches on his back; some males only act as mounters in homosexual copulations, others only as mountees, while some males perform both roles. In Little Blue Herons and Cattle Egrets, homosexual mountings may also occur when one male mounts another male who is himself attempting to copulate with a female; sometimes, “pile-ups” of three or four males on top of each other may develop in this way. Usually the mountee is aggressive toward the male mounting him and does not permit cloacal contact. Similarly, male-female “extramarital” copulations are rarely completed, owing to resistance by the female or defense by her mate. In Cattle Egrets, nearly a quarter of all such heterosexual mounting attempts do not involve cloacal contact, while in Little Egrets more than 85 percent of such opposite-sex copulations are “incomplete.”

Frequency: Homosexual mountings can be quite common: in Little Egrets, for example, more than 100 mounts between males were recorded over four months in one colony, with such copulations comprising 5—6 percent of all “extramarital” sexual activity. In Little Blue Herons, homosexual mountings make up 3—6 percent of all copulations outside the pair-bond. Mounts between males represent 5 percent of “extramarital” copulations and 3 percent of all copulations in Cattle Egrets, while in Gray Herons they constitute 8 percent of all promiscuous mountings and 1 percent of the total number of copulations. In 18 percent of “extramarital” copulation attempts on female Cattle Egrets, additional males mount other males in a pile-up.

Orientation: Since males that participate in homosexual activity almost always have female mates, they are technically bisexual (and some birds may even participate in “group” sexual activity involving both males and females simultaneously, as in Little Blue Herons). In Little Egrets, about one-quarter of the male population engages in homosexual mounting, in Gray Herons 5—7 percent of males are involved in such activity, while in Cattle Egrets six out of ten males in one colony participated in same-sex mounting. Some individuals seem to show more of a “predilection” for homosexual behavior than others. In Cattle Egrets, for example, certain males engage in “extramarital” mountings only with males rather than females, while in