Bruce Bagemihl - Biological Exuberance

56

Ring-billed Gull (Conover and Hunt 1984a); Greylag Goose (Huber and Martys 1993:157[fig.1]).

57

Willson, M. F., and E. R. Pianka (1963) “Sexual Selection, Sex Ratio, and Mating Systems,” American Naturalist 97:405-7; Verner, J. (1964) “Evolution of Polygamy in the Long-billed Marsh Wren,” Evolution 18:252— 61; Verner, J., and M. F. Willson (1966) “The Influence of Habitats on Mating Systems of North American Passerine Birds,” Ecology 47:143—47; Wittenberger, J. E (1976) “The Ecological Factors Selecting for Polygyny in Altricial Birds,” American Naturalist 109:779-99; Wittenberger, J. E (1979) “The Evolution of Vertebrate Mating Systems,” in P. Marler and J. Vandenbergh, eds., Handbook of Neurobiology: Social Behavior and Communication, pp. 271-349 (New York: Plenum Press); Goldizen et al 1998 (Tasmanian Native Hen). For examples of (heterosexual) mating systems actually determining the sex ratio rather than vice versa, see Hamilton, W. D. (1967) “Extraordinary Sex Ratios,” Science 156:477-88; Wilson, D. S., and R. K. Colwell (1981) “Evolution of Sex Ratio in Structured Demes,” Evolution 35:882-97.

58

In Roseate Terns, for example, homosexual pairs were initially taken as evidence of skewed sex ratios, even though the sex ratio in this species had not yet been reliably determined (owing to the difficulty, until recently, of accurately determining the sex of individuals) (Sabo et al. 1994:1023, 1026).

59

Western Gull (Hunt and Hunt 1977; Hunt et al. 1980; Wingfield et al. 1980; Fry and Toone 1981; Fry et al. 1987; Hayward and Fry 1993); Herring Gull (Fitch 1979; Shugart et al. 1987, 1988; Pierotti and Good 1994).

60

For explicit refutation of an association between female homosexual pairs and environmental toxins, see Hunt 1980 (Western Gull); Lagrenade and Mousseau 1983; and Conover 1984c (Ring-billed Gull).

61

Fry et al. 1987; Fry, D. M., and C. K. Toone (1981) “DDT-induced Feminization of Gull Embryos,” Science 213:922-24.

62

Fry et al. 1987:37, 39; Fry and Toone 1981:923. Behavioral changes that could potentially be relevant have only been observed in other bird species, and only as a result of direct injection with estrogen, a female hormone, and not as a result of exposure to toxins (which mimic some of the effects of estrogen).

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Indeed, if toxin-induced “feminization” resulted in behavioral changes, one might even expect this to be manifested directly as male homosexuality (especially under a “pseudoheterosexual” interpretation, or one in which homosexuality is equated with intersexuality), yet this has not been reported for these populations either. Even if such homosexuality were to occur, however, it would not necessarily argue for reduced numbers of breeding males: homosexually paired males in several bird species (including Black-headed and Laughing Gulls) sometimes continue to copulate with females (i.e., they are functionally bisexual and their same-sex pair bonds are nonmonogamous).

64

Herring Gull and other species (Fitch and Shugart 1983:6).

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Western Gull (Fry et al. 1987); Herring Gull (Burger and Gochfeld 1981; Nisbet and Drury 1984:88). In these populations scientists have suggested that perhaps a cofactor is involved: availability of nest sites (Fry et al. 1987:40). The hypothesis is that homosexual pairs will only form in sex-skewed populations if there are vacant nest sites, since female pairs presumably are less able to compete for territories in dense colonies. However, Hand (1980:471) argues that homosexual pairs can effectively obtain (and defend) territories even in dense colonies. In addition, Fetterolf et al. (1984) show that female pairs of Ring-billed Gulls in crowded colonies are simply relegated to less optimal nest sites, rather than failing to form in the first place (or disbanding) because of competition or crowding. This “cofactor” is also of limited applicability to other bird species. In Orange-fronted Parakeets, for example, female pairs compete successfully against heterosexual pairs for possession of nest sites (Hardy 1963:187), while in many species female pairs form regardless of whether they acquire nesting sites (i.e., homosexual pair-formation is independent of nesting).

66

Herring Gull (Shugart et al. 1987, 1988); Ring-billed Gull (Conover and Hunt 1984a,b).

67

Watson, A., and D. Jenkins (1968) “Experiments on Population Control by Territorial Behavior in Red Grouse,” Journal of Animal Ecology 37:595–614; Weatherhead, P. J. (1979) “Ecological Correlates of Monogamy in Tundra-Breeding Savannah Sparrows,” Auk 96:391-401; Smith, J. N. M., Y. Yom-Tov, and R. Moses (1982) “Polygyny, Male Parental Care, and Sex Ratio in Song Sparrows: An Experimental Study,” Auk 99:555–64; Hannon, S. J. (1984) “Factors Limiting Polygyny in the Willow Ptarmigan,” Animal Behavior 32:153–61; Greenlaw, J. S., and W. Post (1985) “Evolution of Monogamy in Seaside Sparrows, Ammodramus maritimus: Tests of Hypotheses,” Animal Behavior 33:373-83; Gauthier, G. (1986) “Experimentally-Induced Polygyny in Buffleheads: Evidence for a Mixed Reproductive Strategy?” Animal Behavior 34:300-302; Björk-lund, M., and B. Westman (1986) “Adaptive Advantages of Monogamy in the Great Tit ( Parus major ): An Experimental Test of the Polygyny Threshold Model,” Animal Behavior 34:1436–40; Stenmark, G., T. Slagsvold, and J. T. Lifjeld (1988) “Polygyny in the Pied Flycatcher, Ficedula hypoleuca: A Test of the Deception Hypothesis,” Animal Behavior 36:1646-57; Brown-headed Cowbird (Yokel and Rothstein 1991).

68

Western Gull (Hunt and Hunt 1977); Herring Gull (Shugart et al. 1988). Fertility rates for homosexual pairs in other Gull species (not associated with environmental toxins) vary considerably, from 0 percent fertile eggs in Kittiwake female pairs (Coulson and Thomas 1985), 33 percent for Silver Gulls (Mills 1991), and 8-94 percent for Ring-billed Gulls (Ryder and Somppi 1979; Kovacs and Ryder 1983). Incidentally, only some of the males that copulate with female Western Gulls in homosexual pairs are known to be already paired; the remainder may in fact be single males that females are bypassing for pair-bonding, while utilizing them to fertilize their eggs (see Pierotti 1981:538-39). Also, some Silver Gulls in homosexual pairs may be raped by males, i.e., their particiption in breeding may be “forced” rather than “consensual” (Mills 1989:397).

69

Herring Gull (Fitch and Shugart 1984:123); Ring-billed Gull (Conover 1984b:714–16; Fetterolf and Blokpoel 1984:1682); Western Gull (Pierotti 1980:292); Roseate Tern (Spendelow and Zingo 1997:553). In Roseate Terns, females with proven single-parenting abilities nevertheless sometimes still form homosexual pairs, indicating that their same-sex partnership is not due solely to the “necessity” of finding a coparent (e.g., one female formed a homosexual pair even though she had successfully raised a chick on her own when her male partner died the previous year).

70

For an extensive list of species in which supernormal clutches have been found—only a fraction of which involve verified female pairs—see Conover 1984c (Ring-billed Gull). For other sources of supernormal clutches (and the occurrence of female pairs with regular-sized clutches), see Western Gull and other species (Conover 1984); Ring-billed Gull and other species (Conover and Aylor 1985; Conover and Hunt 1984; Ryder and Somppi 1979); Common Gull (Trubridge 1980); Terns (Penland 1984; Shealer and Zurovchak 1995; Gochfeld and Burger 1996:631); loons (McNicholl, M. K. [1993] “Supernumerary Clutches of Common Loons, Gavia immer, in Ontario,” Canadian Field-Naturalist 107:356–58); sandpipers and related species (Mundahl, J. T., O. L. Johnson, and M. L. Johnson [1981] “Observations at a Twenty-Egg Killdeer Nest,” Condor 83:180-82; Sordahl, T. A. [1997] “Breeding Biology of the American Avocet and Black-necked Stilt in Northern Utah,” pp. 350, 352, Southwestern Naturalist 41:348-54); Laysan Albatross (Fisher 1968). On the nonoccurrence of female pairs in certain species with supernormal clutches, see Narita, A. (1994) “Occurrence of Super Normal Clutches in the Black-tailed Gull Larus crassirostris,” Journal of the Yamashina Institute of Ornithology 26:132–34; Chardine, J. W., and R. D. Morris (1996) “Brown Noddy ( Anous stolidus ),” in A. Poole and F. Gill, eds., The Birds of North America: Life Histories for the 21st Century no. 220, pp. 10, 18 (Philadelphia: Academy of Natural Sciences; Washington, D.C.: American Ornithologists’ Union).