Biological Exuberance: Animal Homosexuality and Natural Diversity

Field Ornithology 57:1—15.

*———(1980) “Nesting Success of Western Gulls on Bird Rock, Santa Catalina Island, California.” In D. M. Power, ed., The California Islands: Proceedings of a Multidisciplinary Symposium, pp. 467 -73. Santa Barbara: Santa Barbara Museum of Natural History.

*Hayward, J. L., and M. Fry (1993) “The Odd Couples/The Rest of the Story.” Living Bird 12:16—19.

*Hunt, G. L., Jr. (1980) “Mate Selection and Mating Systems in Seabirds.” In J. Burger, B. L. Olla, and H. E. Winn, eds., Behavior of Marine Mammals, vol. 4, pp. 113—51. New York: Plenum Press.

*Hunt, G. L., Jr., and M. W. Hunt (1977) “Female-Female Pairing in Western Gulls (Larus occidentalis) in Southern California.” Science 196:1466—67.

*Hunt, G. L., Jr., A. L. Newman, M. H. Warner, J. C. Wingfield, and J. Kaiwi (1984) “Comparative Behavior of Male-Female and Female-Female Pairs Among Western Gulls Prior to Egg-Laying.” Condor 86:157—62.

*Hunt, G. L., J. C. Wingfield, A.L. Newman, and D. S. Farner (1980) “Sex Ratio of Western Gulls on Santa Barbara Island, California.” Auk 97:473—79.

Paludan, K. (1955) “Some Behavior Patterns of Rissa tridactyla.” Videnskabelige Meddelelser fra Dansk naturhistorisk Forening 117:1—21.

Pierotti, R. J. (1991) “Infanticide versus Adoption: An Intergenerational Conflict.” American Naturalist 138:1140—58.

*———(1981) “Male and Female Parental Roles in the Western Gull Under Different Environmental Conditions.” Auk 98:532—49.

———(1980) “Spite and Altruism in Gulls.” American Naturalist 115:290—300.

*Pierotti, R. J., and C. A. Annett (1995) “Western Gull (Larus occidentalis).” In A. Poole and F. Gill, eds., The Birds of North America: Life Histories for the 21st Century, no. 174. Philadelphia: Academy of Natural Sciences; Washington, D.C.: American Ornithologists’ Union.

Pierotti, R. J., and E. C. Murphy (1987) “Intergenerational Conflicts in Gulls.” Animal Behavior 35:435—44.

Pyle, P., N. Nur, W. J. Sydeman, and S.D. Emslie (1997) “Cost of Reproduction and the Evolution of Deferred Breeding in the Western Gull.” Behavioral Ecology 8:140—47.

Roberts, B. D., and S. A. Hatch (1994) “Chick Movements and Adoption in a Colony of Black-legged Kittiwakes.” Wilson Bulletin 106:289—98.

Thomas, C. S., and J. C. Coulson (1988) “Reproductive Success of Kittiwake Gulls, Rissa tridactyla.” In T. H. Clutton-Brock, ed., Reproductive Success: Studies of Individual Variation in Contrasting Breeding Systems, pp. 251—62. Chicago and London: University of Chicago Press.

*Wingfield, J. C., A. L. Newman, G. L. Hunt, Jr., and D. S. Farner (1982) “Endocrine Aspects of Female- Female Pairings in the Western Gull, Larus occidentalis wymani.” Animal Behavior 30:9— 22.

*Wingfield, J. C., A. L. Newman, M. W. Hunt, G. L. Hunt, Jr., and D. Farner (1980) “The Origin of Homosexual Pairing of Female Western Gulls (Larus occidentalis wymani) on Santa Barbara Island.” In D. M. Power, ed., The California Islands: Proceedings of a Multidisciplinary Symposium, pp. 461—66. Santa Barbara, Calif.: Santa Barbara Museum of Natural History.

SILVER GULL

IDENTIFICATION: A medium-sized (16 inch) gull with gray back and wings; spotted black-and- white wing tips; bright red bill and legs; white iris. DISTRIBUTION: Australia, New Zealand, New Caledonia. HABITAT: Coasts, lakes, islands. STUDY AREA: Kaikoura Peninsula, New Zealand; subspecies L.n. scopulinus, the Red-billed Gull.

HERRING GULL

IDENTIFICATION: Similar to Silver Gull except larger (2 feet long), legs pinkish, bill yellow with a red spot, and iris yellow. DISTRIBUTION: North America, western Europe, Siberia; winters in Central America, N. Africa, southern Asia. HABITAT: Coasts, bays, lakes, rivers. STUDY AREAS: Gull Island National Wildlife Refuge, Lake Michigan; numerous other island locations in Lake Michigan, Lake Huron, and the Straits of Mackinac; Bird Island, Memmert, Germany; subspecies L.a. smithsonianus and L.a. argentatus.

Social Organization

Silver and Herring Gulls are usually found in flocks of several hundreds or thousands; they generally form monogamous pair-bonds and nest in colonies containing anywhere from several hundred to tens of thousands of nests.

Description

Behavioral Expression: In both Silver and Herring Gulls, females sometimes form lesbian pairs while males occasionally participate in homosexual mountings. Female pairs may develop between birds who were previously paired to a male, or they may involve birds who have never been paired before. In some cases, single, nonbreeding Herring Gull females visit the territory of a heterosexual pair and court the female, for example by performing HEAD-TOSSING, in which the head is hunched down and then repeatedly flicked upward. The heterosexually paired birds usually respond aggressively, but sometimes this behavior leads to a homosexual pairing the following season. Like heterosexual pairs, homosexual bonds are usually long-lasting and renewed each year: of those Herring Gull females in homosexual pairs that return to the same breeding grounds, 92 percent pair with the same female (compared to 93 percent of birds in heterosexual pairs). Of those that divorce, some remain single while others find a new (female) mate.

Females in same-sex pairs usually build nests and lay eggs. Silver Gull homosexual females generally begin nesting at a younger age than heterosexual females: females paired to other females start on average about a year earlier than females paired to males, and 11 percent of homosexual females begin nesting when they are two years old (heterosexual females never begin this early). Since both females lay eggs, nests belonging to same-sex pairs often have double or more the number of eggs found in nests of heterosexual pairs. These SUPERNORMAL CLUTCHES contain 4 or more eggs in Silver Gulls (compared to 2 eggs for male-female pairs) and 5—7 eggs in Herring Gulls (compared to 3 eggs for heterosexual pairs). Females sometimes mate nonmonogamously with males—or are raped by them (see below)—while still remaining paired to their female partner. Consequently, some of the eggs laid by female pairs are fertile—about a third in Silver Gulls, and 4—30 percent in Herring Gulls. Homosexual parents often successfully hatch these eggs and raise the chicks. Approximately 3—4 percent of all Silver Gull chicks are raised by same-sex pairs, and a further 9 percent of chicks are raised by male-female pairs in which the mother is bisexual. Overall, 7 percent of birds that go on to become breeding adults in this species come from families with two female parents. However, homosexual and bisexual females generally produce fewer offspring during their lifetimes than do heterosexual females.

In both Silver and Herring Gulls, males in heterosexual pairs often try to copulate with birds other than their mates, and in some cases they mount other males. Like females who are mounted by birds other than their mate, male Herring Gulls may respond aggressively to another male’s mounting them.

Frequency: About 6 percent of all pair-bonds in Silver Gulls are homosexual, while nesting attempts by female pairs occur in approximately 12 percent of all breeding seasons. In some populations of Herring Gulls, nearly 3 percent of the pairs are homosexual, while in other populations they are much less frequent, about 1 in every 360 pairs. In addition, approximately 2 percent of courtship behavior by unpaired females interacting with heterosexual pairs is directed toward the female partner. Male homosexual mountings account for 10 percent of the nonmonogamous copulations in Silver Gulls, and 2 percent of the total