ages are taken into account, nearly 20 percent of the male population at any given time is involved exclusively in homosexuality.
Nonreproductive and Alternative Heterosexualities
As described above, male and female Guianan Cock-of-the-Rock have essentially no contact with each other outside of the mating season. Even during the breeding season, their interactions are often unfriendly or overtly aggressive. Males frequently harass females by chasing them around the display court and in some cases attempt to forcibly copulate with them. Females struggle violently during these rape attempts and are usually able to get away, but are visibly stressed following such interactions. In fact, only 20 percent of all lek visits by females result in copulation. There is also a significant proportion of nonbreeding individuals in the population: an average of 20 percent of adult males do not have display territories (and thus rarely, if ever, court or mate with females), while nearly two-thirds of territorial males fail to mate each year. Moreover, males are rarely able to acquire their own territories (and therefore court females) before they are three to four years old. In addition, many females who visit the courtship grounds never actually mate with males during the entire breeding season.
Sources
*asterisked references discuss homosexuality/transgender
Endler, J. A., and M. Thery (1996) “Interacting Effects of Lek Placement, Display Behavior, Ambient Light, and Color Patterns in Three Neotropical Forest-Dwelling Birds.” American Naturalist 148:421–52.
Gilliard, E. T. (1962) “On the Breeding Behavior of the Cock-of-the-Rock (Aves, Rupicola rupicola).” Bulletin of the American Museum of Natural History 124:31– 68.
Trail, P. W. (1989) “Active Mate Choice at Cock-of-the-Rock Leks: Tactics of Sampling and Comparison.” Behavioral Ecology and Sociobiology 25:283–92.
*———(1985a) “A Lek’s Icon: The Courtship Display of a Guianan Cock-of-the-Rock.” American Birds 39:235–40.
———(1985b) “Courtship Disruption Modifies Mate Choice in a Lek-Breeding Bird.” Science 227:778–80.
*———(1983) “Cock-of-the-Rock: Jungle Dandy.” National Geographic Magazine 164:831–39.
*Trail, P. W., and D. L. Koutnik (1986) “Courtship Disruption at the Lek in the Guianan Cock-of-the-Rock.” Ethology 73:197–218.
IDENTIFIfATION: A crow-sized bird with cinnamon-brown plumage and a bare, blue-gray face. DISTRIBUTION: North-central South America, including Venezuela, the Guianas, Amazonian Brazil. HABITAT: Tropical forest. STUDY AREAS: Brownsberg Nature Park, Suriname; near the Kanuku Mountains, Guyana.
Social Organization
Calfbird males congregate, eight to ten at a time, on a display area or LEK in the understory of the rain forest canopy. Each lek consists of a central perch occupied by only one male, around which the remaining males cluster. Females (and males) visit the central male during courtship, usually at dawn; mating is polygamous or promiscuous, and females nest and raise the young on their own.
Description
Behavioral Expression: Male Calfbirds sometimes court other males who are attracted to the leks. A homosexual courtship begins when one male approaches the display site in a posture that females also adopt when entering the lek: the body is held in a horizontal position and all of the feathers are sleeked down, including the cowl feathers. He is attracted by the dramatic display of the central male, which consists of a loud, droning MOO call (hence the bird’s name) sounding something like grr-aaa- oooo. While mooing, the displaying male first puffs himself up, fluffing up his cowl feathers, and then sinks back down in a bowing motion while exposing two bright orange feather globes on either side of his tail. The male in horizontal posture gets close to the mooing bird, who may then direct his courtship displays directly at the other male—for example, by hopping closer while mooing intensely, or engaging in ritualized wing-preening. Usually the approaching male is then chased away if he gets too close, and in fact no homosexual copulations have yet been observed in this species. However, heterosexual mating itself is fairly rare (only occurring in 14 percent of dawn courtship visits by females), and displaying males also frequently chase females who approach them. Furthermore, males do sometimes mount or attempt to mount other males outside of the lek, though this may occur in an aggressive context. Calfbirds also typically form “companionships” with each other: the two males perform coordinated courtship displays, almost touching as they perch side by side, while they both moo and bow in precise alternation. In some cases, companions never perform courtship displays without their male partner. Companions also travel together on the lek and may even share a “home” with each other. Calfbirds typically have what is known as a RETREAT, a special location or tree where each male regularly spends time when not on the lek. Display partners sometimes share the same retreat.
Female Calfbirds also develop bonds with one another: the two companions keep each other company while feeding, travel together to and from the lek, and even nest close to each other. This is all the more remarkable considering that there are no heterosexual pair-bonds in this species. Female pairs use a number of distinctive calls to communicate with each other. While feeding together, for example, they maintain contact with soft wark calls. When one female sits on her nest, the other may perch nearby uttering a rasping waaa call regularly for over an hour, perhaps acting as a lookout for her companion. And two females nesting close to each other sometimes communicate with a unique low, growling call that sounds like grewer grewer, which is only heard in this context. Although no same- sex courtship or copulation has yet been observed, females do sometimes perform behaviors that are typically associated with displaying males. For example, one female was seen to call and posture repeatedly in the fashion of a male courting on a lek (though she did this away from the lek, at her nest). Her call was like the first half of the male’s mooing, and she displayed the orange tail ornaments usually seen in the male’s courtship sequence. Her voice was also raspier than other females’, and she built an exceptionally large nest. In addition, females sometimes adopt the male’s characteristic upright and fluffed appearance when they visit the lek.
Frequency: Approximately 1–2 percent of all courtship visits involve one male displaying to another, and all males (except for the central one) have male display partners. Mounting attempts between males occur fairly frequently, but it is not known how prevalent female same-sex activities are.
Orientation: Because only the central male ever copulates with females, the remainder of the male population is effectively involved only in same-sex activities for the duration of the breeding season, whether display companionships or courtship/mounting with other males. The central male, however, displays mostly to females and occasionally to males, so his behavior is bisexual—albeit primarily heterosexual. In addition, in the next breeding season another male may become the central one, so at least some of the males exhibit sequential bisexuality, while the remainder may continue to experience longer periods of more exclusive homosexuality.
Nonreproductive and Alternative Heterosexualities
As discussed above, the majority of the male population in any given year does not reproduce: only one male (the central one in the lek) ever breeds with a female. Moreover, only 12 percent of females mate during their dawn courtship visits, and heterosexual relations are frequently fraught with difficulty. Copulations are brief, often incomplete, and accompanied by aggression. Females visiting the lek are constantly chased by the noncentral males, while nearly one-third of male-female copulations and more than half of all courtship visits are disrupted and
