Biological Exuberance: Animal Homosexuality and Natural Diversity

Canberra, Australia; subspecies G.t. tenebrosa.

Social Organization

Pukeko are notable for their “communal” breeding system: they form stable groups of 4—14 birds during the mating season, usually with an equal number of males and females. All adult members (except nonbreeding “helpers,” see below) generally mate with each other, and both sexes take turns incubating the eggs, which are often laid by several females in the same nest. Some birds pair off into (heterosexual) couples or remain single rather than forming communal groups, and outside the breeding season Pukeko usually live in flocks. Many Tasmanian Native Hens and Dusky Moorhens also live in (generally smaller) communal breeding groups that have various types of polygamous or promiscuous mating arrangements. Some Tasmanian Native Hens also form monogamous pair-bonds.

Description

Behavioral Expression: Both male and female Pukeko engage in homosexual courtship and copulation with members of their communal group; these activities are more common and more developed between female birds. Lesbian courtship consists of a sequence of three activities (which also occur during heterosexual interactions). The courtship begins with ALLOPREENING: one female approaches another and bows to her, initiating mutual preening (stylized stroking of each other’s feathers with their bill). This is followed by COURTSHIP-FEEDING, in which the two females exchange ritual gifts of food (usually small leaves or shoots). Finally, copulation takes place: the courting bird approaches the other in a distinctive upright posture while making a nasal HUMMING CALL; her partner adopts a hunched posture and mounting takes place, often with full cloacal (genital) contact. Sometimes, the two females reciprocate, the bird who was mounted first then mounting the other. Male homosexuality usually involves copulation and sometimes allopreening, but not courtship-feeding. Unlike female same-sex interactions, sexual activity between males is often initiated by the bird that is mounted, who places himself in the hunched posture in front of the other male as an invitation to mount.

In Tasmanian Native Hens, homosexual copulations occur in both males (often younger birds) and females living in the same group, while only male Dusky Moorhens participate in same-sex mounting. In all three species, birds that engage in homosexual activities also undertake parental duties such as nest-building, egg laying, incubation, and care of chicks (whether their own or those of other members of their communal group). In fact, homosexual activity (like heterosexual activity) in female Pukeko is most frequent just before or during the period of egg laying. Because birds in Pukeko and Tasmanian Native Hen groups are often related to each other, at least some homosexual—as well as heterosexual—activity is incestuous (mostly between brothers in Tasmanian Native Hens).

Frequency: Homosexuality is common among Pukeko, occurring in nearly 45 percent of all communal groups. In this species, 7 percent of all copulations are homosexual, while 24 percent of courtship-feedings and 59 percent of courtship allopreening interactions are same-sex. In Tasmanian Native Hens and Dusky Moorhens, homosexual copulations make up 1—2 percent of all matings.

Courtship and sexual activity between female Pukeko: “allopreening” (above), approach with “humming call” (middle), and mounting

Orientation: Many adult breeding Pukeko are probably bisexual, capable of engaging in both homosexual and heterosexual courtship and copulation. In some cases, birds alternate between same-sex and opposite-sex copulations in quick succession. Nonbreeding helpers, however, generally participate in neither heterosexual nor homosexual activity. Far fewer individuals participate in homosexual behavior in Tasmanian Native Hens and Dusky Moorhens, but those that do are probably also bisexual.

Nonreproductive and Alternative Heterosexualities

As described above, the most common social unit among these species of Rails is not the heterosexual pair or nuclear family, but the communal group. In some populations of Pukeko, each such group may include up to seven nonbreeding individuals who assist in parental duties. These “helpers” (offspring from previous years) may delay their own reproductive careers for up to three years (one or two years in Tasmanian Native Hens, where an average of 18 percent of adults are nonbreeders). Some physiological mechanisms may be involved in this breeding suppression, since Pukeko helpers often have underdeveloped reproductive organs. In addition to several forms of polygamy, a number of other mating and parenting arrangements are found in these groups. For example, although all birds in Tasmanian Native Hen groups usually mate with each other, sometimes only one male-female pair actually has reproductive copulations. This social system has been called GENETIC MONOGAMY (because only one couple breeds) within SOCIAL POLYGAMY (since multiple partners mate with each other). In addition, although most group members remain together for life, females occasionally “divorce” their mates and join a new group; in some cases, this may lead to a female parenting young that are not her own. Occasionally, she may behave aggressively toward these foster chicks, even expelling them from the group. More violent confrontations sometimes occur when chicks stray into neighboring territories, where they may be killed by the resident group members. However, chicks are sometimes also adopted by neighboring groups, in both Tasmanian Native Hens and Dusky Moorhens.

Among breeding Pukeko, up to five males may court and mount the same female in quick succession—in these cases, one or more of the males may not actually inseminate the female. In fact, the “success” rate for most heterosexual copulations is not high: between one-half and two-thirds do not involve full genital contact and so do not result in insemination. Females often resist heterosexual advances by refusing to allow males to mount them, pecking at males who do mount them, preventing genital contact by not raising their tails, and prematurely terminating mating attempts. Copulations also occur when females are not fertile—for example, long before egg laying begins—and some males mate repeatedly without ever fathering any offspring that year. Similarly, mounts without genital contact account for more than a third of Dusky Moorhen matings and 60 percent of Tasmanian Native Hen matings. A few of these are REVERSE copulations, in which the female mounts the male. Incestuous matings are also common in Pukeko and Tasmanian Native Hens. Nearly two-thirds of all Pukeko heterosexual copulations in some populations are between related individuals, including mother-son, father-daughter, and brother-sister matings. More than 40 percent of Tasmanian Native Hen breeding groups contain related adults that mate with each other (mostly siblings); in addition, about 10 percent of copulations involve parents mounting their own offspring, including young chicks.

Other Species

Stable homosexual pairs often form among Cranes (e.g., Grus spp.) in captivity, a group of birds that is closely related to Rails.

Sources

*asterisked references discuss homosexuality/transgender

*Archibald, G. W. (1974) “Methods for Breeding and Rearing Cranes in Captivity.” International Zoo Yearbook 14:147-55.

Craig, J. L. (1990) “Pukeko: Different Approaches and Some Different Answers.” In P. B. Stacey and W. D. Koenig, eds., Cooperative Breeding in Birds: Long-term Studies of Ecology and Behavior, pp. 385-412. Cambridge: Cambridge University Press.

*———(1980) “Pair and Group Breeding Behavior of a Communal Gallinule, the Pukeko, Porphyrio p. melanotus.” Animal Behavior 28:593-603.

———(1977) “The Behavior of the Pukeko.” New Zealand Journal of Zoology 4:413—33.

Craig, J. L., and I. G. Jamieson (1988) “Incestuous Mating in a Communal Bird: A Family Affair.” American Naturalist 131:58-70.

*Derrickson, S. R., and J. W. Carpenter (1987) “Behavioral Management of Captive Cranes—Factors Influencing Propagation and Reintroduction.” In G. W. Archibald and R. F. Pasquier, eds., Proceedings of the 1983 International Crane Workshop, pp. 493—511. Baraboo, Wis.: International Crane