unlikely that homosexual matings are generally timed to take advantage of reproductive opportunities. In particular, they do not appear to be more prevalent earlier in the breeding season when putative “sperm-swapping” would be more likely to result in fertilizations (Lombardo, personal communication).
78
Pukeko: See Craig (1980:593, 601—2) for speculation on the “possible swapping of sperm during female homosexual cloacal contacts” as well as synchronization of egg laying. On the mechanisms that independently insure obscured paternity and shared parenting, see Jamieson et al. 1994:274—76; Jamieson and Craig 1987b:323 -25.
79
Best, R. L, and M. A. O’Brien (1967) The Book of Leinster, vol. 5, lines 35670— 35710. (Dublin: Dublin Institute for Advanced Studies); Greene, D. (1976) “The ‘Act of Truth’ in a Middle-Irish Story,” Saga och Sed (Kungliga Gustav Adolfs Akademiens Arsbok) 1976:30—37.
80
Boswell, J. (1994) Same-Sex Unions in Premodern Europe, pp. xxviii—xxix (New York: Villard Books). In discussing this story, Greene (1976:33-34) cites several “extremely rare” examples from the late 1800s, of questionable validity, in which women supposedly became pregnant from homosexual activity in this way. Regardless of whether conception by this means has been “documented” or is even biologically possible, what stands out in these descriptions of both human and animal homosexuality is their concern with heterosexuality. Namely, the putative role of same-sex activity in facilitating insemination is emphasized, and there is an insistence on ascribing a reproductive function to homosexual activity.
81
For a good summary and survey of some current strains of thought in this area, see Abramson, P. A., and S. D. Pinkerton, eds. (1995) Sexual Nature, Sexual Culture (Chicago: University of Chicago Press).
82
African Elephant (Sikes 1971:266).
83
Cordero, A. (1995) “Correlates of Male Mating Success in Two Natural Populations of the Damselfly Ischnura graellsii (Odonata: Coenagrionidae),” Ecological Entomology 20:213—22.
84
See the profiles for more information and references. Among those 48 species in which homosexuality has been documented and quantitative information on nonbreeders is available, an average of half of the population (or of one sex) does not participate in reproduction (independent of homosexuality).
85
Squirrel Monkey (Baldwin and Baldwin 1981:295; Baldwin 1968:296, 311); Grizzly Bear (Craighead et al. 1995:139).
86
Chalmers, N. R. (1968) “Group Composition, Ecology, and Daily Activities of Free-Living Mangabeys in Uganda,” Folia Primatologica 8:247–62; Musk-ox (Gray 1973:170—71).
87
Searcy, W. A., and K. Yasukawa (1995) Polygyny and Sexual Selection in Red-winged Blackbirds, pp. 6, 169 (Princeton: Princeton University Press). For the other species, see the profiles and the discussion of sexual orientation in chapter 2.
88
Bennett, N. C. (1994) “Reproductive Suppression in Social Cryptomys damarensis Colonies—a Lifetime of Socially-Induced Sterility in Males and Females,” Journal of Zoology, London 234:25—39; Northern Elephant Seal (Le Boeuf and Reiter 1988:351). In mole-rats, large numbers of adults are “permanently” nonbreeding, while in Northern Elephant Seals, many males simply do not survive to the relatively advanced age when breeding typically begins, and of those that do, less than half actually breed.
89
Waser, P. M. (1978) “Postreproductive Survival and Behavior in a Free-Ranging Female Mangabey,” Folia Primatologica 29:142—60; Ratnayeke, S. (1994) “The Behavior of Postreproductive Females in a Wild Population of Toque Macaques (Macaca sinica) in Sri Lanka,” International Journal of Primatology 15:445–69; Bester, M. N. (1995) “Reproduction in the Female Subantarctic Fur Seal, Arctocephalus tropicalis,” Marine Mammal Science 11:362–75. For further examples, see profiles of species indexed under “postreproductive individuals.”
90
Marsh, H., and T. Kasuya (1991) “An Overview of the Changes in the Role of a Female Pilot Whale With Age,” in K. Pryor and K. S. Norris, eds., Dolphin Societies: Discoveries and Puzzles, pp. 281–85 (Berkeley: University of California Press).
91
Canada Goose (Collias and Jahn 1959:505). It is not the case that these birds were simply “trying harder” to reproduce, since some of these pairs produced eggs but failed to incubate them. Rather, it appears that as nonparents, they were able to “indulge” in more sexual behavior.
92
Birkhead, T. R., and A. P. Moller (1993) “Why Do Male Birds Stop Copulating While Their Partners Are Still Fertile?” Animal Behavior 45:105—18; Eberhard, Female Control, p. 395.
93
Wasser, S. K., and D. P. Barash (1983) “Reproductive Suppression Among Female Mammals: Implications for Biomedecine and Sexual Selection Theory,” Quarterly Review of Biology 58:513-38; Abbott, D. H. (1987) “Behaviorally Mediated Suppression of Reproduction in Female Primates,” Journal of Zoology, London 213:455–70; Reyer et al. 1986 (Pied Kingfisher); Macdonald and Moehlman 1982 (Wild Dogs); Jennions, M. D., and D. W. Macdonald (1994) “Cooperative Breeding in Mammals,” Trends in Ecology and Evolution 9:89–93; Creel and Macdonald 1995 (Wild Dogs); Solomon, N. G., and J.A. French, eds. (1997) Cooperative Breeding in Mammals, pp. 304—5 (Cambridge: Cambridge University Press).
94
American Bison (Komers et al. 1994:324 [see also discussion in chapter 4]); Pied Kingfisher (Reyer et al. 1986:216); tamarins and marmosets (Snowdon, C. T. [1996] “Infant Care in Cooperatively Breeding Species,” Advances in the Study of Behavior 25:643—89, especially pp. 677-80); other species (Solomon and French, Cooperative Breeding in Mammals, p. 5).
95
Rohrbach, C. (1982) “Investigation of the Bruce Effect in the Mongolian Gerbil (Meriones unguiculatus),” Journal of Reproduction and Fertility 65:411–17.
96
Bighorn Sheep (Geist 1971:181, 295); Red Deer (Clutton-Brock et al. 1983:371–72); Northern Quoll and other carnivorous marsupials (Dickman and Braithwaite 1992); Ruffed Grouse (Gullion 1981:379–80); Western Gull (Pyle et al. 1997:140,145); Spotted Hyena (Frank and Glickman 1994). For further discussion of the avoidance of reproduction because of its stressful and potentially injurious effects on the individual, see Hand 1981:140—42 (Laughing Gull).
97
Wagner, R. H. (1991) “The Use of Extrapair Copulations for Mate Appraisal by Razorbills, Alca torda,” Behavioral Ecology 2:198—203; Sheldon, B. C. (1993) “Sexually Transmitted Disease in Birds: Occurrence and Evolutionary Significance,” Philosophical Transactions of the Royal Society of London, Series B 339:491–97; Hamilton, W. D. (1990) “Mate Choice Near or Far,” American Zoologist 30:341–52; Freeland, W. J. (1976) “Pathogens and the Evolution of
