Biological Exuberance: Animal Homosexuality and Natural Diversity

predator, they may depart with one another and temporarily leave their ducklings behind to fend for themselves. Occasionally three females join forces and raise their combined broods—as many as 50 or more ducklings—as a parenting trio. Interestingly, duckling survival rates are not significantly different in families with one as opposed to two (or three) female parents.

Female Australian Shelducks often court one another and form homosexual pair-bonds. In December, when birds begin pairing, females display to each other with ritual preening movements and chases. These often develop into a full-fledged WATER-THRASHING DISPLAY, in which one female swims toward the other while making sideways pointing movements with her outstretched head and neck. She may also dive and resurface, then chase after the other female. Her partner is frequently captivated by this performance and responds by enthusiastically diving and chasing in return; the two females may, as a result, form a bond that lasts until the next pairing season. Females that engage in homosexual courtship and pairing are usually younger adult or juvenile birds.

Male Musk Ducks perform an extraordinary courtship display that attracts both males and females. The male arches his back and lifts his head up, engorging his large throat pouch; at the same time he fans and bends his tail forward over his back at an extreme angle—a feat made possible because of two extra vertebrae. This gives the bird an astounding, reptilian appearance. While in this posture, he kicks both feet backward or to the side, producing enormously loud splashes or jets of water. Multiple kicks of various types are given in series, and often the courting male rapidly back-paddles in between kicks. He also produces a wide variety of sounds during these PADDLE-KICK, PLONK-KICK, and WHISTLE-KICK displays, including ker-plonks (made by the kicking and splashing) combined with whirr or cuc-cuc vocalizations, and even a distinctive whistling sound. In addition, many displaying males emit a musky odor (hence the name of the bird), and their plumage is so oily that puddles of oil may form on the surface of the water around them. This display—perhaps one of the most dramatic of all birds—draws both males and females, who crowd around the courting male. Often, males appear to be more attracted than females, swimming much closer to the displaying male and sometimes even making physical contact by gently and repeatedly nudging their breast against his shoulder. The displaying male is in a trancelike state and rarely responds directly to any of the onlookers. Indeed, although homosexual copulation has not been observed as a part of these displays, heterosexual mating has hardly ever been seen during such courtship sessions either.

A male Musk Duck (left) attracted to another male performing a “whistle-kick” as part of an elaborate courtship display sequence

Frequency: Homosexual mounting probably occurs only occasionally in Lesser Scaup Ducks, but female coparenting is a regular feature of some populations. As many as a quarter to a third or more of all families have two mothers, although in other populations they are less frequent, comprising about 12 percent of families in some years. Same-sex courtship and pairing occur frequently among younger Australian Shelduck females, while male Musk Ducks are routinely attracted to displaying males.

Orientation: A variety of bisexual arrangements characterize these duck species. Some female Lesser Scaups (perhaps 30–40 percent of the population) have a seasonal alternation between same-sex and opposite-sex pairings: they begin the breeding season in heterosexual pairs, but end it in same-sex associations. Most Australian Shelduck females in homosexual pairs probably go on to form heterosexual bonds as adults. Musk Duck males display to both females and other males; some of the males they attract are also interested in females, but others are apparently only attracted to the courting male.

Nonreproductive and Alternative Heterosexualities

As described above, separation of heterosexual pairs with subsequent female single-parenting (or coparenting) is the usual pattern for Lesser Scaup families. Several other alternative parenting and pairing arrangements occur in these species. Occasionally a female Lesser Scaup associates with a mated pair and even lays eggs in their nest. Musk Ducks often lay their eggs in other birds’ nests, where they are foster-parented by both their own and foreign species—including many other kinds of ducks (e.g., the blue-billed duck, Oxyura australis) as well as Dusky Moorhens. For their part, Lesser Scaups occasionally raise ducklings of other species of ducks, hatched from eggs that have been laid in their nests by, for example, redheads (Aythya americana). Australian Shelducks sometimes foster-parent chicks as well: about 5 percent of all broods contain “extra” ducklings from other families, and about 1 percent of all ducklings are adopted or “exchanged” between families. Lesser Scaup ducklings are occasionally abandoned by their mothers and may be adopted into other families. Abandonment of eggs is also prevalent: female Lesser Scaups may desert entire clutches, while egg DUMPING is common in Australian Shelducks. Many Shelduck pairs copulate but then lay or abandon the resulting eggs in caves, along the shore, or on islands, never incubating or hatching them. Most of these pairs—who may constitute close to half the population—have been unable to secure a breeding territory of their own. Many other birds are non-breeders as well: a large proportion of Lesser Scaups of both sexes, and Australian Shelduck females, are younger birds that are sexually mature but unpaired. In addition, it is thought that reproduction in younger male Musk Ducks may be suppressed by the presence of older males.

Although many Australian Shelducks form long-lasting heterosexual bonds, about 10 percent of breeding pairs divorce, and many more juvenile pairs separate. In Lesser Scaups, nonmonogamous copulations are common, accounting for more than half of all heterosexual activity. Many of these are rapes or forced copulations performed by paired males on females other than their mate; occasionally groups of up to eight males will pursue a female and try to mate with her. Only about 20 percent of such rapes involve penetration—the male Lesser Scaup, like most waterfowl (but unlike most other birds), does have a penis. More than a quarter of all such attempts are nonreproductive, occurring too early in the breeding season, during incubation, after breeding, or on nonbreeding females. In fact, the highest rates of attempted rape occur on females just before their molting period, when they are nonfertilizable. In Australian Shelducks, it is the females who vigorously pursue males, often courting already paired drakes in dramatic aerial chases. One or several females may try to maneuver in between a mated pair to separate the male, even grabbing at the tail feathers of his mate to force her to change direction. Females frequently suffer broken wings and may even be killed when they hit obstacles during such high-speed chases.

Other Species

Interspecies homosexual pairs involving several other kinds of ducks and geese have been observed in captive birds. A pair consisting of a female Common Shelduck (Tadorna tadorna) with a female Egyptian Goose (Alopochen aegyptiacus), for example, both laid eggs in a shared nest and jointly incubated them.

Sources

*asterisked references discuss homosexuality/transgender

*Afton, A. D. (1993) “Post-Hatch Brood Amalgamation in Lesser Scaup: Female Behavior and Return Rates, and Duckling Survival.” Prairie Naturalist 25:227-35.

———(1985) “Forced Copulation as a Reproductive Strategy of Male Lesser Scaup: A Field Test of Some Predictions.” Behavior 92:146–67.

———(1984) “Influence of Age and Time on Reproductive Performance of Female Lesser Scaup.” Auk 101:255–65.

Attiwell, A. R., J. M. Bourne, and S. A. Parker (1981) “Possible Nest-Parasitism in the Australian Stiff-Tailed Ducks (Anatidae: Oxyurini).” Emu 81:41–42.

Bellrose, F. C. (1976) Ducks, Geese, and Swans of North America. Harrisburg, PA: Stackpole.

Fullagar, P. J., and M. Carbonell (1986) “The Display Postures of the Male Musk Duck.” Wildfowl 37:142–50.

Gehrman, K. H. (1951) “An Ecological Study of the Lesser Scaup Duck (Aythya affinis Eyton) at West Medical Lake, Spokane County, Washington.” Master’s thesis, State College of Washington (Washington State University).

*Hochbaum, H. A. (1944) The Canvasback on a Prairie Marsh. Washington, D.C.: