streaks on the head, and black-and-white eyes. DISTRIBUTION: Australia, Tasmania. HABITAT: Wetlands, estuaries, bays. STUDY AREA: Lake Bathurst, New South Wales, Australia.
Social Organization
Both of these species of Grebes commonly socialize in pairs or small groups, and sometimes in dense flocks (which may contain several thousand birds in Hoary-headed Grebes). They nest in large colonies—up to 400 nests for Hoary-headed Grebes—and most form monogamous pair-bonds.
Description
Behavioral Expression: Male Silvery Grebes occasionally mount other males, using the same position as for heterosexual copulation—although unlike in heterosexual mating, the mounted bird does not typically invite the other male to mount him. In Hoary-headed Grebes, two birds of the same sex sometimes perform courtship displays to each other on floating platforms, constructed of water vegetation, and perhaps also mount one another. One such display is called REARING, in which the bird lifts its body up, ruffles its mantle feathers, and extends its head and neck downward. This may lead to one bird INVITING the other to mount, by settling back down, kinking its neck, and resting its throat on the nest.
The “rearing” display of a Hoary-headed Grebe, used during courtships with same- and opposite-sex partners
Frequency: Same-sex activity occurs only occasionally in these two species of Grebes. In Silvery Grebes, for example, about 1 in 300 mounts is between two males.
Orientation: Grebes that participate in same-sex activities are probably bisexual, also courting and mating with members of the opposite sex.
Nonreproductive and Alternative Heterosexualities
In these two species of Grebes—as in many other Grebes—REVERSE heterosexual mountings are common. An average of 27 percent of all copulations among Silvery Grebes involve females mounting males, and early in the breeding season as many as 40 percent of all mounts are reverse. Their prevalence during this period—long before fertilization is possible—indicates that this form of behavior is decidedly nonprocreative. In addition, ejaculation does not usually occur during reverse mounts, although females typically perform tail thrusting, perhaps to facilitate genital contact. Grebes also copulate repeatedly, with as many as five or six matings taking place over 15—20 minutes; during this activity, males and females may also alternate positions in a form of reciprocal mounting. Although most heterosexual mating in Hoary-headed Grebes takes place between pair members, some copulations also occur between unpaired birds.
Sources
*asterisked references discuss homosexuality/transgender
*Fjeldsa, J. (1983) “Social Behavior and Displays of the Hoary-headed Grebe Poliocephalus poliocephalus.” Emu 83:129—40.
Fjeldsa, J. and N. Krabbe (1990) Birds of the High Andes. Copenhagen: Zoological Museum, University of Copenhagen; Svendborg, Denmark: Apollo Books.
Johnsgard, P. A. (1987) Diving Birds of North America. Lincoln and London: University of Nebraska Press.
*Nuechterlein, G. L., and R. W. Storer (1989) “Reverse Mounting in Grebes.” Condor 91:341—46.
*O‘Brien, R. M. (1990) “Hoary-headed Grebe, Poliocephalus poliocephalus.’ In S. Marchant and P. J. Higgins, eds., Handbook of Australian, New Zealand, and Antarctic Birds, vol. 1, pp. 100—107. Melbourne: Oxford University Press.
Storer, R. W. (1969) “The Behavior of the Horned Grebe in Spring.” Condor 71:180—205.
WADING BIRDS
IDENTIFICATION: A stocky, medium-sized (2 foot long) heron with a black crown and back, white underparts, gray wings, and white ribbon plumes at the nape of the neck. DISTRIBUTION: Over much of Europe, Asia, Africa, and North and South America. HABITAT: Wetlands. STUDY AREAS: American Museum of Natural History, New York; Altenberg, Austria; subspecies N.n. hoactli and N.n. nycticorax.
Social Organization
Black-crowned Night Herons are fairly gregarious birds, gathering in colonies that may contain hundreds or thousands of individuals nesting close together. Monogamous pairs predominate during the mating season.
Description
Behavioral Expression: Male Black-crowned Night Herons sometimes court other males and form homosexual pairs. To attract other birds, a male performs the SNAP-HISS CEREMONY, in which he repeatedly extends and lowers his head with erected plumes while “treading” with his feet and making a combined snapping (or clicking) and hissing sound. This courtship display is directed at both males and females. While most males are not interested in the ceremony, those that are attracted go on to participate in an OVERTURE display (also used in heterosexual courtship). In this activity, one or both males stretch their heads forward (again with feathers raised) while making their eyeballs protrude from their sockets, at the same time clicking and touching their bills. Males in homosexual pairs also mount each other (in the position used for heterosexual copulation); both males may mount or be mounted, although individuals sometimes show a preference for one or the other activity. Typically one male in the pair also builds a nest out of twigs; sometimes this occurs before the pair-bond forms, or else the two males may search for a nest site together. Once the pair-bond is established, both males vigorously defend their territory against other birds. Homosexual pair-bonds are strong, lasting the entire breeding season (as do heterosexual bonds). Young Black-crowned Night Herons also form pairs or “companionships,” some of which are between birds of the same sex (although no overt sexual behavior occurs between companions of either the same or opposite sex). Occasionally, a juvenile female may even bond with more than one other female. Although no homosexual pairs between adult females have yet been observed, females sometimes perform typically male courtship displays such as the snap-hiss ceremony.
Frequency: In some captive populations, homosexual pairs in adult males make up more than 20 percent of all pairings, while 38 percent of juvenile pairs are same-sex (three- quarters of which are between females). The incidence of same-sex pairs in the wild is not known. Adult male partners may mount each other more than 30 times over the mating season.
Orientation: During the courtship phase, males exhibit a form of simultaneous bisexuality by displaying to both sexes, and some males are clearly more attracted to same-sex courtships than others. Most young females that form same-sex bonds only pair with other females, while a few form both homosexual and heterosexual pair-bonds. Once a homosexual bond has formed, though, the birds will maintain the bond even if they are separated for several weeks, returning to their same-sex partner when reunited rather than establishing a heterosexual bond. Some birds may exhibit sequential bisexuality, forming heterosexual bonds after participating in homosexual pairings when young (or vice versa).
Nonreproductive and Alternative Heterosexualities
Male-female relations in Black-crowned Night Herons are sometimes fraught with complications.
