Bruce Bagemihl - Biological Exuberance

Frequency: In Canada Geese, up to 12 percent of pairs in some (semiwild) populations are homosexual. The proportion is much smaller in Snow Geese: about 1 in 200 nests belongs to a pair of females. Approximately 4 percent of all mountings during Snow Goose rape attempts are between males.

Orientation: In one study of Canada Geese, 18 percent of the males formed homosexual pair-bonds while 6–12 percent of females did. Some birds in same-sex pairs appear to “prefer” their homosexual association, even if they have the opportunity for heterosexual interactions. In one case, a male harassed a female who was part of a long-lasting lesbian pair and separated her from her companion, mating with her. However, the next year she returned to her female partner and their pair-bond resumed. On the other hand, some birds have a preference for heterosexual pairings: many males remain unpaired if there are no available females rather than forming homosexual pair-bonds with each other. In Snow Geese, females in homosexual pairs may be functionally bisexual—they sometimes copulate with up to three different males to fertilize their eggs—although their same-sex pair-bond remains primary. Males who mount other males are otherwise primarily heterosexual, since most are paired with females and the majority of their sexual interactions are probably not with males.

As mentioned above, heterosexual rape is common in Snow Geese: during some mating seasons, each female is subjected to a rape attempt every five days (on average). Females are occasionally successful in thwarting such attacks, but males who rape can be very aggressive and may attack in groups. Sometimes the female’s mate can successfully chase an intruder off, but often he is not around to defend her because he is also raping another female. Significantly, most rapes are nonreproductive: more than 80 percent of all rape attempts are directed toward females that are nonfertilizable, such as incubating birds, and only about 2 percent of goslings are actually fathered this way. Rape is much less common among Canada Geese. However, ganders frequently harass and attack neighboring females when their mates are gone, often leading to abandonment of their eggs—as many as one-quarter of all nests may end up being deserted this way.

Several other variations on the heterosexual nuclear family occur in these species. Although most male-female pairs remain together for life, divorce and remating do occasionally take place in both Canada and Snow Geese. In addition, although most Snow Goose families remain together until the next breeding season, in some populations as many as 20 percent of the families split or break up before that time, usually because of separation of juveniles. Polygamous, heterosexual trios consisting of one male and two females sometimes form in Canada Geese (these differ from the bisexual trios described above in that the females are not bonded to each other). Some birds pair outside of their species, and Snow and Canada Geese may in fact mate with each other. CRÈCHES or combined broods—containing as many as 60 young—are sometimes found in Canada Geese, attended by one or several heterosexual pairs. In addition, families often “trade” goslings, caring for young other than their own on either a temporary or permanent basis. Up to 46 percent of Canada Goose broods and at least 13 percent of Snow Goose broods may contain adopted young, and over 60 percent of Canada broods in some populations experience a loss and/or gain of goslings due to adoption. Egg “adoption” is also common in Snow Geese because females often lay eggs in nests other than their own: 15–22 percent of all nests contain such eggs (although in some colonies more than 80 percent of nests may be affected), and more than 5 percent of all goslings are raised by a female other than their biological mother. Females that lay eggs in others’ nests are often aided by their mates, who distract the nest-owning gander by acting as a decoy for him to attack, allowing the female to approach the nest and lay her eggs. Sometimes the intruding female actually helps with building or repairing the nest; for her part, the nest-owning female often actively adopts foreign eggs that have not been laid directly in the nest by rolling them into her own clutch.

Snow Goose females also occasionally “abandon” their eggs by laying in what are known as DUMP NESTS, which contain large numbers of unincubated eggs from many different females. Abandonment of nests may also be triggered by the stresses of reproduction: females can lose up to a third of their body mass while incubating, and some individuals desert their clutches or even starve on the nest as a result of such hardships. Most Snow Goose nesting colonies also have a nonbreeding flock on their peripheries. In some years, the proportion of nonbreeding adults is sizable—as much as 40 percent of the population—and occasionally an entire colony will forgo breeding (for example if the weather is particularly adverse). Many Canada Goose heterosexual pairs are nonbreeding as well: in some populations, for example, more than a quarter of all male-female pairs do not procreate, although they may copulate frequently. In fact, some nonbreeders have sexual activity rates that are almost twice as high as pairs that do reproduce.

*asterisked references discuss homosexuality/transgender

*Allen, A. A. (1934) “Sex Rhythm in the Ruffed Grouse ( Bonasa umbellus Linn.) and Other Birds.” Auk 51:180–99.

Ankney, C. D., and C. D. MacInnes (1978) “Nutrient Reserves and Reproductive Performance of Female Lesser Snow Geese.” Auk 95:459–71.

*Collias, N. E., and L. R. Jahn (1959) “Social Behavior and Breeding Success in Canada Geese ( Branta canadensis ) Confined Under Semi-Natural Conditions.” Auk 76:478-509.

*Conover, M. R. (1989) “What Are Males Good For?” Nature 342:624–25.

Cooke, E, and D. S. Sulzbach (1978) “Mortality, Emigration, and Separation of Mated Snow Geese.” Journal of Wildlife Management 42:271-80.

Cooke, F., M. A. Bousfield, and A. Sadura (1981) “Mate Change and Reproductive Success in the Lesser Snow Goose.” Condor 83:322–27.

*Diamond, J. M. (1989) “Goslings of Gay Geese.” Nature 340:101.

Ewaschuk, E., and D. A. Boag (1972) “Factors Affecting Hatching Success of Densely Nesting Canada Geese.” Journal of Wildlife Management 36:1097–106.

*Grether, G. F., and A. M. Weaver (1990) “What Are Sisters Good For?” Nature 345:392.

*Klopman, R. B. (1962) “Sexual Behavior in the Canada Goose.” Living Bird 1:123–29.

Lank, D. B., P. Mineau, R. F. Rockwell, and F. Cooke (1989) “Intraspecific Nest Parasitism and Extra-Pair Copulation in Lesser Snow Geese.” Animal Behavior 37:74-89.

Luekpe, K. (1984) “A Strange Goose: Canada-Snow Hybrid?” Passenger Pigeon 46:92.

MacInnes, C. D., R. A. Davis, R. N. Jones, B. C. Lieff, and A. J. Pakulak (1974) “Reproductive Efficiency of McConnell River Small Canada Geese.” Journal of Wildlife Management 38:686–707.

Martin, K., F. G. Cooch, R. F. Rockwell, and F. Cooke (1985) “Reproductive Performance in Lesser Snow Geese: Are Two Parents Essential?” Behavioral Ecology and Sociobiology 17:257–63.

*Mineau, P., and F. Cooke (1979) “Rape in the Lesser Snow Goose.” Behavior 70:280–91.

Nastase, A. J., and D. A. Sherry (1997) “Effect of Brood Mixing on Location and Survivorship of Juvenile Canada Geese.” Animal Behavior 54:503–7.