Biological Exuberance: Animal Homosexuality and Natural Diversity

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; Bjork-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).

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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).

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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).

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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).

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And sometimes the correlation between the two end points is itself suspect. For example, it has been claimed that supernormal clutches are more common in Great Lakes populations of Herring Gulls than they are in New England, a fact that is attributed to greater levels of DDT poisoning in the Great Lakes (Conover 1984c:254) and/or the absence of available nesting sites in New England (Fry et al. 1987:40; see note 65 above). However, Nisbet and Drury (1984:88) show that the “higher rate” of supernormal clutches in the Great Lakes can be traced to only one particular colony site; in three other Great Lakes areas censused, the prevalence of supernormal clutches was no greater than in New England. Moreover, even if such clutches are more common in the Great Lakes area, the fact that they still occur in New England indicates that their presence cannot be due entirely to pollutant-related (or nest-site availability) factors.

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In Western Gulls, the correlation between toxins and supernormal clutches is claimed to be supported by chronological evidence: larger clutches were supposedly not common prior to the widespread use of pesticides in the 1950s–1970s in southern California, while female pairs are claimed to occur at a “much lower” rate (Hayward and Fry 1993:19) or to have all but disappeared (Pierotti and Annett 1995:11) now that pesticide use has stopped. However, no comprehensive survey of the affected areas has in fact been conducted to assess the actual incidence of female pairs today (even if such a study were to find consistently low levels, this would still be significant, since it would demonstrate a “residual” component of same-sex activity that is independent of toxin effects and of a “shortage” of the opposite sex, as is true for many other species). Nor have detailed longitudinal or geographic studies been conducted to track the putative correlations during this entire five-to-six-decade period. In fact, records of supernormal clutches in Ring-billed Gulls go back much earlier, to the early 1900s (and in other species back to the late 1800s), while in some Terns their frequency has actually decreased since the 1950s (Conover 1984c), so the chronological question is far from resolved. At least one researcher who has addressed the temporal issue rejects the DDT (or other pollutant) connection for the majority of cases: Conover (1984c:254) conducted an extensive survey of the occurrence of supernormal clutches in 34 species, including comparing pre- and post-1950 rates, and concluded that their frequency is not higher since the 1940s for most Gull and Tern species. Finally, no studies have yet determined the incidence of homosexual pairing/supernormal clutches in other regions of the world that have the highest levels of contamination from DDT and related pollutants, such as the Baltic Sea, the Waddensee, the Irish Sea, the Gulf of St. Lawrence, and the northern Gulf of Mexico (Nisbet, I. C. T. [1994] “Effects of Pollution on Marine Birds,” p. 13, in D. N. Nettleship, J. Burger, and M. Gochfeld, eds. Seabirds on Islands: Threats, Case Studies, and Action Plans, pp. 8–25. [Cambridge: BirdLife International]).

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Hayward and Fry 1993:19; Luoma, J. R. (1995) “Havoc in the Hormones,” Audubon 97(4):60-67; Robson, B. (1997) “A Chemical Imbalance,” Nature Canada 26(1):29-33; see also Coulson 1983 (Caspian Tern). The equating of homosexuality with environmental and physiological “havoc” has also entered the more popular discourse, as in a recent public radio broadcast that referred to lesbian pairs in Gulls as evidence of hormonal imbalances caused by environmental contamination (“Gator Envy,” All Things Considered, National Public Radio, February 1, 1995). Some things not considered in this report were the broader context of same-sex pairing in other species and the intricacies of the specific cases. For more on the pathologizing of homosexuality, see the following section “Gross Abnormalities of Behavior.”

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See, for example, Aiken (1981) on Water Boatman Bugs. Even this case is somewhat less than definitive, however, since more than half of all mating attempts in this species are by males on other males.

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Guianan Cock-of-the-Rock (Trail 1985a:238, 240); Giraffe (Spinage 1968:130); Black-billed Magpie (Baeyens 1979:39–40); Mountain Sheep (Geist 1968:208). For examples of homosexual interactions that are explicitly labeled “mistakes” or “errors” (including, but not limited to, cases of sex misrecognition), see Asiatic Mouflon (Schaller and Mirza 1974:318-20); Common Murre (Birkhead et al. 1985:610-11); Oystercatcher (Makkink 1942:60); Laughing Gull (Hand 1981:139–40); Greater Rhea (Fernandez and Reboreda 1995:323).

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Redshank (Hale and Ashcroft 1982:471). Other species in which the occurrence of homosexuality is taken as