Biological Exuberance: Animal Homosexuality and Natural Diversity

IDENTIFICATION: A thrush-sized bird (12 inches) with velvety black plumage and brilliant golden yellow crown, nape, upper back, and wing feathers. DISTRIBUTION: East-central Australia. HABITAT: Humid forests. STUDY AREA: Sarabah Range, Queensland, Australia.

Social Organization

Regent Bowerbirds have a polygamous or promiscuous mating system: males court and mate with multiple partners on display territories (see below). Following the mating season birds often associate in cosexual flocks of 10—20 individuals.

Description

Behavioral Expression: Male Regent Bowerbirds build elaborate structures called BOWERS, in which they court both males and females. Bowers built by adult males form an “avenue” on the ground consisting of two parallel walls of twigs—10—12 inches high and 7—8 inches long—which are inserted into a platform of twigs on the ground. In some bowers the walls form a sort of arched walkway, while other bowers have triangular-shaped walls of different sizes. The bower is usually decorated with a dozen or so “display objects” or ornaments that are often selected for their color and strewn on the platform. These include brown snail shells, berries, green or purplish leaves, brown fruits and seeds, cicada husks, occasionally a yellow or pink flower petal, and even scavenged pieces of blue plastic. Remarkably, some birds also “paint” the walls of their bowers by applying, with their bills, macerated plant material mixed with saliva, giving some of the twigs a yellowish green coating. Adult males display in their bowers to females and younger males by flicking their wings and bowing their heads to show off their brilliant orange and yellow neck feathers. Sometimes they also ritually “present” display objects to the bird they are courting by picking up one of the ornaments from the avenue and holding it in their bill while facing their partner.

A bower constructed by a male Regent Bowerbird, used during courtship displays to both males and females

Juvenile males also build bowers and court both males and females. In some cases, they use the same bower shapes and displays as adults, but in other cases they utilize their own patterns, some of which may be unique to same-sex interactions. Some bowers built by younger males are more in the form of a horseshoe—open only at one end—with the sticks woven horizontally rather than vertically. When courtship-displaying to an adult male, the younger male enters the bower and squats with his tail toward the entrance. The adult male then rushes toward the juvenile, who is behind the closed end of the bower, or sometimes goes around to the entrance and tweaks the younger male’s tail. When courting other juvenile birds of both sexes, young males may perform a dance in the center of the bower, picking up an ornament and bobbing up and down with half-opened wings, then tossing the object over the bower wall. The bird(s) watching this display sweep and brush the ground with their wings.

Many younger males are transvestite, having a plumage coloration that more closely resembles that of adult females than adult males. It takes males up to seven years to develop the full yellow, orange, and black feathers typical of adult males, and during that time many actually exhibit plumages that are intermediate between the adult male and female patterns.

Frequency: Among adult male Regent Bowerbirds, 15 percent of their bower courtship time is spent displaying to other males, while 28 percent of juvenile males’ display time is same-sex.

Orientation: Regent Bowerbirds that court other males are probably bisexual, since they display to birds of both sexes.

Nonreproductive and Alternative Heterosexualities

A large segment of the male Regent Bowerbird population is nonbreeding: only about a third of all adult males maintain bowers, and of those that do, only a fraction actually mate with females. In addition, heterosexual courtship interactions rarely result in copulation: in only about 7 percent of female visits to bowers does mating actually take place, since the female often leaves while the male is displaying (and in 10 percent of female visits the male does not display at all).

Other Species

Adult male Satin Bowerbirds (Ptilonorhynchus violaceus) from Australia have also been observed performing courtship displays toward younger males.

Sources

*asterisked references discuss homosexuality/transgender