heterosexual. About 30 percent of male Laughing Gull territorial intruders attempt to rape females, although such attacks are usually thwarted by the female and her mate; in addition, most are directed toward incubating females and hence are nonreproductive. Abuse and violence by heterosexual parents against chicks also occur in both species. During raids by predators such as snowy owls (Nyctea scandiaca), a pandemonium often develops in Ivory Gull breeding colonies, and groups of adult Gulls mob terrified chicks and sometimes even attack and kill them. The adults also puncture eggs and eat them; eggs containing fully developed embryos about to hatch are smashed and the yolk sac is eaten, but the down-covered embryo is discarded. Laughing Gulls also occasionally attack, kill, and even eat chicks (as well as eggs) on neighboring territories; cannibalism appears to be limited to a few individuals in dense colonies who repeatedly perform this behavior.
Sources
*asterisked references discuss homosexuality/transgender
Bateson, P. P. G., and R. C. Plowright (1959a) “The Breeding Biology of the Ivory Gull in Spitsbergen.” British Birds 52:105—14.
———(1959b) “Some Aspects of the Reproductive Behavior of the Ivory Gull.” Ardea 47:157—76.
Burger, J. (1996) “Laughing Gull (Larus atricilla).” In A. Poole and F. Gill, eds., The Birds of North America: Life Histories for the 21st Century, no. 225. Philadelphia: Academy of Natural Sciences; Washington, D.C.: American Ornithologists’ Union.
———(1976) “Daily and Seasonal Activity Patterns in Breeding Laughing Gulls.” Auk 93:308—23.
Burger, J., and C. G. Beer (1975) “Territoriality in the Laughing Gull (L. atricilla).” Behavior 55:301—20.
Hand, J. L. (1985) “Egalitarian Resolution of Social Conflicts: A Study of Pair-bonded Gulls in Nest Duty and Feeding Contexts.” Zeitschrift fur Tierpsychologie 70:123—47.
*———(1981) “Sociobiological Implications of Unusual Sexual Behaviors of Gulls: The Genotype/Behavioral Phenotype Problem.” Ethology and Sociobiology 2:135—45.
*Haney, J. C., and S. D. MacDonald (1995) “Ivory Gull (Pagophila eburnea).” In A. Poole and F. Gill, eds., The Birds of North America: Life Histories for the 21st Century, no. 175. Philadelphia: Academy of Natural Sciences; Washington, D.C.: American Ornithologists’ Union.
MacDonald, S. D. (1976) “Phantoms of the Polar Pack-Ice.” Audubon 78:2— 19.
*Noble, G. K., and M. Wurm (1943) “The Social Behavior of the Laughing Gull.” Annals of the New York Academy of Sciences 45:179—220.
Segre, A., J. P. Hailman, and C. G. Beer (1968) “Complex Interactions Between Clapper Rails and Laughing Gulls.” Wilson Bulletin 80:213—19.
CASPIAN TERN
IDENTIFICATION: A large (to 22 inches) gull-like bird with a black cap and crest, light gray back and wings, forked tail, and long red bill with a black tip. DISTRIBUTION: Throughout much of North America, Europe, Australasia, Africa. HABITAT: Coasts, lakes, estuaries. STUDY AREA: Columbia River in eastern Washington and Oregon.
ROSEATE TERN
IDENTIFICATION: Similar to Caspian Tern but smaller (to 17 inches) and with a more deeply forked tail and slighter bill. DISTRIBUTION: North Atlantic, Caribbean, Africa, Australasia. HABITAT: Seacoasts, islands. STUDY AREAS: Bird Island, Marion, Massachusetts; Falkner Island, Connecticut; subspecies S.d. dougallii.
Social Organization
During the mating season, Caspian and Roseate Terns usually congregate in large colonies which may contain up to 500 pairs in Caspians and several thousand in Roseates. The typical social unit is the monogamous mated pair. Outside of the mating season, Terns are less gregarious and are usually found alone or in small groups.
Description
Behavioral Expression: In both Caspian and Roseate Terns, two females may pair with each other, associating together the way a male-female pair does. Usually such homosexual pairs also build nests and lay eggs. Since both females typically lay, the result is a SUPERNORMAL CLUTCH containing up to twice the number of eggs found in nests of heterosexual pairs—4—6 eggs for Caspian homosexual pairs, and 3—5 eggs for Roseates. Both females take turns incubating the eggs (as do mates in heterosexual pairs). Sometimes the eggs are infertile, but in many cases they do hatch. There are several possible sources for fertile eggs in same-sex pairs: for example, one or both females may copulate with a male while still remaining bonded to her female mate. In addition, it appears that females in some populations occasionally “steal” eggs from others’ nests, sometimes transferring eggs from as many as three other nests into their own. Approximately 13 percent of supernormal clutches in some locations have at least one “stolen” egg in them, so it is likely that at least some females in homosexual pairs utilize this strategy. Once the eggs hatch, both females share parenting duties (as do partners in heterosexual pairs), which include feeding the young, protecting the chicks from predators, sheltering them against the sun, and defending the nesting territory.
Frequency: In Caspian Terns, 3–6 percent of pairs are homosexual; in Roseates, about 5 percent of chicks are tended by female pairs in some populations.
Orientation: Females in homosexual pairs that copulate with males in order to fertilize their eggs are functionally bisexual, although they retain their primary bond with the other female. Other female pairs may be exclusively homosexual for the duration of their pair-bond, since they do not lay fertile eggs. Some females are also sequentially bisexual, alternating between male and female partners in different breeding seasons.
Nonreproductive and Alternative Heterosexualities
Terns occasionally “steal” eggs from other clutches, as described above for homosexual pairs; birds in heterosexual pairs probably do so, since some nests with transferred eggs do not have supernormal clutches. In addition, female Roseate Terns sometimes lay eggs in nests other than their own, resulting in “super-supernormal clutches.” In one colony, for example, about 1 percent of the nests had 7 eggs—more than twice the number found even in supernormal clutches. Most such nests appear to belong to heterosexual pairs. Caspian Terns also have a high divorce rate: more than half of all male-female pairs do not last more than one season. Female Roseate Terns sometimes successfully raise chicks as a single parent when their male partner dies. As in many Gulls, infanticide and aggression toward chicks also occur in some Tern species. Caspian Terns, for example, often violently attack—and may even kill—chicks that wander onto their territories and may break eggs during their squabbles as well. Caspian Terns also commonly form CRECHES, dense herds of chicks attended by a few adults who watch over them while their parents are away foraging.
Sources
*asterisked references discuss homosexualityltransgender
*Conover, M. R. (1983) “Female-Female Pairings in Caspian Terns.” Condor 85:346–49.
Cramp, S., ed. (1985) “Caspian Tern (Sterna caspia)” and “Roseate Tern
