Biological Exuberance: Animal Homosexuality and Natural Diversity

(less than 1 in 200 such matings result in insemination), and during group promiscuous matings, males often mount on any part of the female’s body, including her head. In addition, about 15—30 percent of promiscuous copulations occur outside of the female’s fertile period. The same is also true for sexual activity between mated partners: copulation begins as long as four to five months before the start of egg laying, and half of all heterosexual matings in some populations occur during nonfertilizable periods. In addition, almost a quarter of pair copulations do not involve genital contact. In Common Murres—as in most other birds—females have the remarkable ability to store sperm in special ducts in their reproductive tract, allowing them to inseminate their eggs even when not directly engaging in reproductive copulations.

Other forms of nonprocreative sexuality also occur. Nonbreeding female Common Murres often solicit promiscuous matings from males, while nonbreeding pairs or those who have lost their young (which can make up as much as a third of all pairs) frequently continue to copulate throughout the season. Nonbreeding Laysan Albatross pairs also sometimes engage in copulation. Birds in this species do not reproduce until they are 6—16 years old, even though they mature at one year old and may form pairs fully two years before they actually breed. Similarly, younger Common Murres usually delay breeding until they are five years old, congregating in CLUBS on the tidal rocks beneath the breeding colonies. Such nonbreeders make up approximately 13 percent of the population; among adults, 5—10 percent of birds do not breed each year, and more than a third skip breeding for at least one season during their life. In addition, masturbatory activity—birds mount and “copulate” with clumps of grass—was recently discovered in a closely related species, the thick-billed murre (Uria lomvia); it is likely that similar behavior also occurs in Common Murres.

A variety of alternative parenting arrangements are also found in these species. About 8 percent of all Common Murre chicks have “baby-sitters”—a pair of birds other than their parents who help brood (keep warm), protect, and sometimes feed the chick (even when the youngster’s parents are not away). Most such helpers are nonbreeders; others have tried but failed to breed, while some have finished raising their family or are also taking care of their own chick. In addition, pair separation and single parenting is routine in Common Murres: when a chick is old enough to leave the colony, only its father accompanies it to sea, feeding and chaperoning it for up to 12 weeks without his female partner. In Laysan Albatrosses, heterosexual parents are together at the nest for a remarkably short time—only 5—10 days out of the 230-day breeding season. Eggs are sometimes temporarily “adopted” by other birds who incubate them when the parents are away from the nest. Nonbreeding females have even been known to “join” existing pairs and regularly take turns with the parents incubating their egg. Sometimes females also lay a second egg in a stranger’s nest. Reproduction in this species is often fraught with difficulties, however. More than 20 percent of parents (both males and females) desert their nests—often when their partner fails to return for an incubation shift on time—and couples also occasionally divorce (2 percent of all pairs). Once the chicks have hatched, they are often subjected to abuse from neighboring birds, who may savagely peck, stab, bite, and occasionally even kill the youngsters if they stray too close.

Other Species

Homosexual copulations are common in another species of auk, the Razorbill (Alca torda), where 41 percent of nonmonogamous mountings (about 18 percent of all mountings) are between males. Up to 200 or more such mountings have been observed each season in some populations. Nearly two-thirds of all males mount other males (an average of 5 partners, sometimes as many as 16) and more than 90 percent of males receive mounts from other males. Older males participate more often than younger ones, and mountings are occasionally reciprocal. Like females, males usually resist such promiscuous mating attempts: although the mounter usually tries to achieve cloacal (genital) contact, only about 1 percent of same-sex mountings include genital contact or ejaculation (compared to 12 percent of promiscuous heterosexual mounts).

Sources

*asterisked references discuss homosexuality/transgender

Birkhead, T. R. (1993) Great Auk Islands. London: T. and A.D. Poyser.

*———(1978a) “Behavioral Adaptations to High Density Nesting in the Common Guillemot Uria aalge.” Animal Behavior 26:321—31.

———(1978b) “Attendance Patterns of Guillemots Uria aalge at Breeding Colonies on Skomer Island.” Ibis 120:219-29.

Birkhead, T. R., and P. J. Hudson (1977) “Population Parameters for the Common Guillemot Uria aalge.” Ornis Scandinavica 8:145—54.

Birkhead, T. R., S. D. Johnson, and D. N. Nettleship (1985) “Extra-pair Matings and Mate Guarding in the Common Murre Uria aalge.” Animal Behavior 33:608—19.

Birkhead, T. R., and D. N. Nettleship (1984) “Alloparental Care in the Common Murre (Uria aalge).” Canadian Journal of Zoology 62:2121—24.

Fisher, H. I. (1975) “The Relationship Between Deferred Breeding and Mortality in the Laysan Albatross.” Auk 92:433—41.

*———(1971) “The Laysan Albatross: Its Incubation, Hatching, and Associated Behaviors.” Living Bird 10:19—78.

———(1968) “The ‘Two-Egg Clutch’ in the Laysan Albatross.” Auk 85:134— 36.

Fisher, H. I., and M. L. Fisher (1969) “The Visits of Laysan Albatrosses to the Breeding Colony.” Micronesica 5:173—221.

Fisher, M. L. (1970) The Albatross of Midway Island: A Natural History of the Laysan Albatross. Carbondale, Ill.: Southern Illinois University Press.

*Frings, H., and M. Frings (1961) “Some Biometric Studies on the Albatrosses of Midway Atoll.” Condor 63:304—12.

Gaston, T., and K. Kampp (1994) “Thick-billed Murre Masturbating on Grass Clump.” Pacific Seabirds 21:30.

Harris, M. P., and S. Wanless (1995) “Survival and Non-Breeding of Adult Common Guillemots Uria aalge.” Ibis 137:192-97.

*Hatchwell, B. J. (1988) “Intraspecific Variation in Extra-pair Copulation and Mate Defence in Common Guillemots Uria aalge.” Behavior 107:157-85.

Hudson, P. J. (1985) “Population Parameters for the Atlantic Alcidae.” In D. N. Nettleship and T. R. Birkhead, eds., The Atlantic Alcidae, pp. 233—61. London: Academic Press.

Johnson, R. A. (1941) “Nesting Behavior of the Atlantic Murre.” Auk 58:153— 63.

Meseth, E. H. (1975) “The Dance of the Laysan Albatross, Diomedea immutabilis.” Behavior 54:217-57.

Rice, D. W., and K. W. Kenyon (1962) “Breeding Cycles and Behavior of Laysan and Black-footed Albatrosses.” Auk 79:517-67.

Tuck, L. M. (1960) The Murres: Their Distribution, Populations, and Biology. Ottawa: Canadian Wildlife Service.

*Wagner, R. H. (1996) “Male-Male Mountings by a Sexually Monomorphic Bird: Mistaken Identity or Fighting Tactic?” Journal of Avian Biology 27:209—14.

———(1991) “Evidence That Female Razorbills Control Extra-Pair Copulations.” Behavior 118:157-69.

GREAT CORMORANT

IDENTIFICATION: A large (3 foot), black, web-footed bird with a white throat and white filamentary plumes on the nape. DISTRIBUTION: Throughout Europe, Australasia, Africa, and Atlantic North America. HABITAT: Seacoasts, lakes, rivers. STUDY AREAS: Shinobazu Pond, Tokyo, Japan; Amsterdam Zoo, the Netherlands; subspecies P.c. sinensis and P.c. hanedae.