Biological Exuberance: Animal Homosexuality and Natural Diversity

For further discussion of sexual orientation in animals, as well as comparisons between animal and human homosexuality, see chapter 2. Following Vasey (“Homosexual Behavior in Primates,” p. 175), the term homosexual is used to designate primarily the form of behaviors without necessarily implying anything about their “function or context or the actors’ ages and motivation.” For further consideration of the terminology used to describe same-sex activity in animals, including discussion of alternative definitions of the term homosexual(ity) as it is applied to animals (and some of the controversies that have surrounded its use in the zoological literature), see chapter 3. For more on the “functions” and contexts of homosexual behavior, see chapters 4-5.

6

Guianan Cock-of-the-Rock (Endler and Théry 1996); Anna’s Hummingbird (Hamilton 1965); Buff-breasted Sandpiper (Myers 1989).

7

For a general survey of play-fighting, see Aldis, O. (1975) Play Fighting. (New York: Academic Press).

8

Spinner Dolphin (Norris et al. 1994:250).

9

Ingestion of semen by both males and females during masturbation in heterosexual contexts also occurs among Golden Monkeys (Clarke 1991:371).

10

Supernormal clutches have also been reported for pairs of male Emus, probably because more than one female has laid in their nest. What might be termed “subnormal” clutches—i.e., nests containing fewer eggs than are usually found for heterosexual pairs—are reported for female pairs of Blue Tits. And “super-supernormal” clutches occasionally occur in heterosexual pairs of Roseate Terns: as a result of within-species parasitism and possibly also egg transfer (see chapter 5 for more on these phenomena), some nests contain more than double the number of eggs found even in supernormal clutches (as is also true for “dump” nests in many Ducks and Geese).

11

For discussion, and refutation, of the idea that same-sex pairs form in species such as these solely for the purpose of raising offspring, see chapter 5. In some birds such as grouse (e.g., sharp-tailed grouse, prairie chickens, white-tailed ptarmigan) and ducks (e.g., eiders, buffleheads) broods from more than one female are combined or “amalgamated” but no same-sex coparenting occurs (one female, or a heterosexual pair, look after all the offspring); cf. Bergerud and Gratson 1988:545 (Grouse); Afton 1993 (Ducks); Eadie, J. McA., E P. Kehoe, and T. D. Nudds (1988) “Pre-Hatch and Post-Hatch Brood Amalgamation in North American Anatidae: A Review of Hypotheses,” Canadian Journal of Zoology 66:1709-21.

12

Ring-billed Gull (Conover 1989:148).

13

In some bird species in which same-sex pairs are unable to obtain fertile eggs on their own (or in which homosexual parenting has yet to be observed in the wild), parenting skills have been demonstrated by supplying homosexual pairs with “foster” eggs or young in captivity. Same-sex pairs of Flamingos, White Storks, Black-headed Gulls, Steller’s Sea Eagles, Barn Owls, and Gentoo Penguins, for example, have all successfully hatched such eggs and/or raised foster chicks.

14

Black Swan (Braithwaite 1981:140—42); for more details, see chapter 5 and part 2.

15

Ring-billed Gull (Conover 1989:148); Western Gull (Hayward and Fry 1993:17—18); see chapter 2 for further discussion of same-sex pairs being limited to nonoptimal territories. Several other studies point to the possibility of more “attentive” parenting by female homosexual pairs. Researchers have found that female Ring-billed Gulls in same-sex pairs, for example, may have higher levels of progesterone—a female hormone associated with nest-building and incubation behavior—than females in heterosexual pairs (Kovacs and Ryder 1985); see chapter 4 for more on the hormonal profiles of animals involved in same-sex activity. In a related set of observations, some investigators have documented more “intense” nesting behavior in female homosexual pairs than heterosexual pairs in some captive studies. Allen and Erickson (1982:346, 350), for instance, found that female pairs of Ring Doves are more persistent incubators than heterosexual pairs, being less likely to abandon their nests and terminate incubation when they have infertile eggs than are heterosexual pairs. Brockway (1967:76) found that female Budgerigars in homosexual pairs begin continuous occupation of their nests significantly sooner than females in heterosexual pairs. However, because female pairs begin noncontinuous occupation of their nests significantly later than heterosexual pairs in this species, the overall amount of their nesting activity and the timing of their egg-laying essentially evens out.

16

See chapter 5 for further discussion of homosexual activity in communal groups and the often complex relationship between “helpers” and same-sex activity.

17