Biological Exuberance: Animal Homosexuality and Natural Diversity

the sole evidence of faulty sex recognition or “indiscriminate” mating or courtship include Cavies (Rood 1970:449), Little Brown Bats (Thomas et al. 1979:134), Shags (Snow 1963:93-94), Little Egrets (Fujioka 1988), Oystercatchers (Makkink 1942:67–68), Black-headed Gulls (van Rhijn 1985:87, 93), Superb Lyrebirds (Lill 1979a:496), and King Penguins (Murphy 1936:340). It should also be pointed out that the claim of “indiscriminate” sexual activity is often quite exaggerated: it is not uncommon for the mere existence of same-sex activity to be interpreted as evidence that the sex of the partner is immaterial, even when the animals show clear partner preferences, sometimes even favoring homosexual activity. For example, Trail and Koutnik (1986:210–11) claim that yearling Guianan Cock-of- the-Rock will mount any bird that sits still long enough; in fact, only one attempted heterosexual mount by a yearling was recorded during their study, compared to hundreds of homosexual mounts, and certain adult males were clearly mounted more often than others (ibid., 211–12, 215).

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Yellow-eyed penguin (Richdale, L. E. [1951] Sexual Behavior in Penguins, p. 73 [Lawrence, Kans.: University of Kansas Press]); Silvery Grebe (Nuechterlein and Storer 1989:344); Red-faced Lovebird (Dilger 1960:667).

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For species with adult-female/younger-male resemblances, see Rohwer, S., S. D. Fretwell, and D. M. Niles (1980) “Delayed Maturation in Passerine Plumages and the Deceptive Acquistion of Resources,” American Naturalist 115:400-437; for species with adult-female/adult-male resemblances, see Burley, N. (1981) “The Evolution of Sexual Indistinguishability,” in R. D. Alexander and D. W. Tinkle, eds., Natural Selection and Social Behavior, pp. 121-37 (New York: Chiron Press). A caveat about these cases is that the absence of homosexuality in a species is not necessarily a reliable form of evidence, since (as discussed in chapters 1-3) homosexual behavior is often hard to observe, easy to overlook, or deliberately ignored in the field.

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Blackbuck (Dubost and Feer 1981:74-75); Guianan Cock-of-the-Rock (Trail and Koutnik 1986:199; Trail 1983); Swallow-tailed Manakin (Foster 1987:549; Sick 1967:17; 1959:286); Blue-backed Manakin (Snow 1963:172); Raggiana’s Bird of Paradise, Victoria’s Riflebird (Gilliard 1969:113, 223); Regent Bowerbird (Gilliard 1969:337); Superb Lyrebird (Smith 1982 and personal communication).

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Mountain Goat (Chadwick 1983:14, 189–91); Bishop Birds (Craig and Manson 1981:13); Galah (Rogers and McCulloch 1981:81; Rowley 1990:4); Humboldt Penguin (Scholten 1987:200); King Penguin (Stonehouse 1960:11); Superb Lyrebird (Smith 1982 and personal communication); Ocher-bellied Flycatcher (Westcott and Smith 1994:678, 681; Snow and Snow 1979:286); Tree Swallow (Stutchbury and Robertson 1987c); Anna’s Hummingbird (Ortiz- Crespo 1972; Wells et al. 1996).

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Andersson, S., J. Ornborg, and M. Andersson (1998) “Ultraviolet Sexual Dimorphism and Assortative Mating in Blue Tits,” Proceedings of the Royal Society of London, Series B 265:445–50; Hunt, S., A. T. D. Bennett, I. C. Cuthill, and R. Griffiths (1998) “Blue Tits Are Ultraviolet Tits,” Proceedings of the Royal Society of London, Series B 265:451-55; Witte, K., and M. J. Ryan (1997) “Ultraviolet Ornamentation and Mate Choice in Bluethroats,” in M. Taborsky and B. Taborsky, eds., Contributions to the XXV International Ethological Conference, p. 201, Advances in Ethology no. 32 (Berlin: Blackwell Wissenschafts-Verlag); Roper, T. J. (1997) “How Birds Use Sight and Smell,” Journal of Zoology, London 243:211-13; Bennett, A. T. D., I. C. Cuthill, J. C. Partridge, and E. J. Maier (1996) “Ultraviolet Vision and Mate Choice in Zebra Finches,” Nature 380:433-35; Waldvogel, J. A. (1990) “The Bird’s Eye View,” American Scientist 78:342-53; Cabbage White Butterfly (Obara 1970 and personal communication; Obara, Y [1995] “The Mating Behavior of the Cabbage White Butterfly,” paper presented at the 24^th International Ethological Conference, Honolulu, Hawaii); Superb Lyrebird (Reilly 1988:45).

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Mountain Goat (Geist 1964:565); Musk-ox (Smith 1976:56); Cavies (Rood 1972:27, 54, 1970:443); Bighorn Sheep (Geist 1968:208); Common Murre (Birkhead et al. 1985:610-11); Flamingo (C. E. King, personal communication); Pronghorn (Kitchen 1974:44 [table 22]). In addition, some homosexual activity in Mountain Goats and Pronghorns also involves age-mates interacting with each other (adult males in Mountain Goats, younger males in Pronghorns). See also Wagner (1996) on Razorbills.

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Swallow-tailed Manakin (Foster 1987:555); Laughing Gull (Noble and Wurm 1943:205); Black-headed Gull (van Rhijn and Groothuis 1985:163). Conversely, homosexuality has sometimes been attributed to behavioral identity between males and females. In Ruffed Grouse, for example, the nonaggressive or “submissive” posture of a male is similar to the behavior of a female during courtship, and that males court both sexes is attributed to their inability to distinguish “female-acting” males from actual females (Allen 1934:185; see also the discussion of “pseudoheterosexuality” earlier in this chapter). Aside from the fact that males and females are very different visually from each other in this species and therefore “there is no excuse for a male not recognizing a female” (as Allen [1934:180-81] observes), in the related red grouse there is a parallel identity between male “submissive” and female courtship behavior, yet males do not court other males in this species (Watson, A., and D. Jenkins [1964] “Notes on the Behavior of the Red Grouse,” British Birds 57:157).

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Tree Swallow (Stutchbury and Robertson 1987a:719-20, 1987b:418). It is also unlikely that homosexual activity between adult males results from their mistaking one another for (adult) females. As Lombardo et al. (1994) point out, although the two sexes in this species look similar, the sex of at least one male involved in homosexual activity was nevertheless identifiable from his cloacal (genital) protuberance, lack of brood patch, and wing length. Most adult females are also visually distinct from males owing to the presence of a brown patch on the forehead (shorter wings also distinguish subadult females from subadult males) (Stutchbury and Robertson 1987c). In addition, same-sex copulations appear to be fairly uncommon in this species (Lombardo, personal communication)—certainly they are not nearly as frequent as one would expect if “mistakes” in sex recognition were prevalent.

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Black-headed Gull (van Rhijn 1985:87, 100).

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Hooded Warbler (Niven 1993:191) (cf. Lynch et al. [1985:718] for mean dimensions of other males). Niven (1993 and personal communication) suggests that it was also the female behavior patterns of this male that “triggered” the homosexual pairing, yet this bird’s behavior was actually a mixture of male and female patterns, involving, for example, incubation (female duties) as well as singing (male). Moreover, male Hooded Warblers are particularly attuned to differences in song pattern, using this information to recognize individual birds and then storing it in long-term memory for future use (Godard 1991). Because this male’s singing was highly distinctive, it is improbable that other males simply “disregarded” this aspect of his behavior or were “unaware” of his male status (especially given his physical characteristics). Furthermore, all “female” behaviors recorded in this individual occurred after the formation of the pair-bond—since pairs were not observed early in the breeding season, we do not in fact know whether this individual exhibited any (or only) “femalelike” patterns during courtship and pair- formation.

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Hooded Warbler: differential attacking of males (Stutchbury 1994:65-67); mating success of malelike females (as evidenced by the fact that nests are fairly equally distributed between dark and light females) (Stutchbury et al. 1994:389[fig.6]; Stutchbury and Howlett 1995:95); promiscuous mating attempts on hooded females (Stutchbury et al. 1994:388).

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Common Garter Snake (Mason 1993:261, 264; Mason et al. 1989:292; Mason and Crews 1985; Noble 1937:710–11); other species (Muma, K., and P. J. Weatherhead [1989] “Male Traits Expressed in Females: Direct or Indirect Sexual Selection?” Behavioral Ecology and Sociobiology 25:23-31; Potti, J.