Biological Exuberance: Animal Homosexuality and Natural Diversity

Orientation: To the extent that they mount both males and females in the group display, Acorn Woodpeckers are bisexual (although it must be remembered that such mounting is often ritualized, i.e., it may not always involve genital contact). Not enough is known about the life histories of individual Black-rumped Flamebacks to make any generalizations about their sexual orientation.

Nonreproductive and Alternative Heterosexualities

As described above, Acorn Woodpeckers have an unusual communal family organization that can involve different forms of polygamy. In addition, many birds are nonbreeding: more than a third of all groups may not reproduce in a given year, and one-quarter to one-half of all adult birds do not procreate. In some populations the proportion of nonbreeders may be as high as 85 percent. Many of these are birds who remain with their family group for several years after they become sexually mature, helping their parents raise young; some delay reproducing for three or four years. Other nonbreeders (as many as one-quarter) do not in any way help to raise young. Some groups are nonreproductive because all their adult members are of the same sex: nearly 15 percent of nonbreeding groups have no adult females and nearly 4 percent have no adult males. In addition to the nonprocreative heterosexual behaviors mentioned above (REVERSE mounting, group sexual activity, mounting without genital contact), female Acorn Woodpeckers also sometimes copulate with more than one male in quick succession. About 3 percent of families contain offspring that result from promiscuous matings with males outside the group. Incestuous heterosexual matings occasionally occur as well, although they seem to be avoided—in fact, incest avoidance may lead to a group’s forgoing breeding for an extended time. Parenting in this species is notable for a variety of counterreproductive and violent behaviors. Egg destruction is common—particularly among joint-nesting females, who often break (and eat) each other’s and their own eggs until they begin laying synchronously. Males also sometimes destroy eggs of their own group. In addition, infanticide and cannibalism occur regularly in Acorn Woodpeckers. A common pattern seems to be for a new bird in a group—often a female—to peck the nestlings to death and eat some of them in order to breed with the other adults in the group. Parents also regularly starve any chicks that hatch later than a day after the others do.

Sources

*asterisked references discuss homosexuality/transgender

*Koenig, W. D. (1995–96) Personal communication.

Koenig, W. D., and R. L. Mumme (1987) Population Ecology of the Cooperatively Breeding Acorn Woodpecker. Princeton, N.J.: Princeton University Press.

Koenig, W. D., R. L. Mumme, M. T. Stanback, and F. A. Pitelka (1995) “Patterns and Consequences of Egg Destruction Among Joint-Nesting Acorn Woodpeckers.” Animal Behavior 50:607–21.

Koenig, W. D., and P. B. Stacey (1990) “Acorn Woodpeckers: Group-Living and Food Storage Under Contrasting Ecological Conditions.” In P. B. Stacey and W. D. Koenig, eds., Cooperative Breeding in Birds: Long-Term Studies of Ecology and Behavior, pp. 415–53. Cambridge: Cambridge University Press.

Koenig, W. D., and F. A. Pitelka (1979) “Relatedness and Inbreeding Avoidance: Counterploys in the Communally Nesting Acorn Woodpecker.” Science 206:1103–5.

*MacRoberts, M. H., and B. R. MacRoberts (1976) Social Organization and Behavior of the Acorn Woodpecker in Central Coastal California. Ornithological Monographs no. 21. Washington, D.C.: American Ornithologists’ Union.

Mumme, R. L., W. D. Koenig, and F. A. Pitelka (1988) “Costs and Benefits of Joint Nesting in the Acorn Woodpecker.” American Naturalist 131:654–77.

———(1983) “Reproductive Competition in the Communal Acorn Woodpecker: Sisters Destroy Each Other’s Eggs.” Nature 306:583–84.

Mumme, R. L., W. D. Koenig, R. M. Zink, and J.A. Marten (1985) “Genetic Variation and Parentage in a California Population of Acorn Woodpeckers.” Auk 102:305–12.

*Neelakantan, K. K. (1962) “Drumming by, and an Instance of Homo-sexual Behavior in, the Lesser Gold-enbacked Woodpecker (Dinopium benghalense).” Journal of the Bombay Natural History Society 59:288–90.

Short, L.L. (1982) Woodpeckers of the World. Delaware Museum of Natural History Monograph Series no. 4. Greenville, Del.: Delaware Museum of Natural History.