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,”
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
In many species, young may also be raised in heterosexual trios, i.e., family units with three parents in which only opposite-sex bonding is present between the adults. See chapter 5 for some examples.
18
For discussion of single parenting in animals where two (heterosexual) parents usually raise the young, as well as examples of other heterosexual parenting arrangements that deviate from the species-typical pattern, see chapter 5.
19
For additional discussion of male bias in biological studies, see chapters 3 and 5.
20
Rhesus Macaque (Altmann 1962:383; Lindburg 1971:69); Hamadryas Baboon (Abegglen 1984:63); Gelada Baboon (Bernstein 1970:94); Tasmanian Native Hen (Ridpath 1972:30); Gray-headed Flying Fox (Nelson 1965:546).
21
Pukeko (Jamieson and Craig 1987a:1251 ); Bonobo (Thompson-Handler et al. 1984:349; Kano 1992:187; Kitamura 1989:55—57); Stumptail Macaque (Chevalier-Skolnikoff 1974:101, 110); Red Deer (Hall 1983:278); Red- necked Wallaby (LaFollette 1971:96); Northern Quoll (Dempster 1995:29).
22
Pig-tailed Macaque (Oi 1990a:350—51): Galah (Rogers and McCulloch 1981); Pronghorn (Kitchen 1974:44).
23
Gorilla (Fischer and Nadler 1978:660—61; Yamagiwa 1987a:12, 1987b:37).
24
Pukeko (Jamieson and Craig 1987a:1251—52); Flamingo (C. E. King, personal communication). In Lesser Flamingos, however, the reverse appears to be true: males but not females achieve cloacal contact during their homosexual mounts (Alraun and Hewston 1997:176).
25
Japanese Macaque (Hanby 1974:838-40; Wolfe 1984:149; Fedigan 1982:143).
26
For further discussion of comparisons between animal and human homosexuality, see chapter 2.
27
These formulas are also used to estimate the number of bisexual/heterosexual trios in a population; see Conover and Aylor 1985:127 (Ring-billed Gull).
28
Kob (Buechner and Schloeth 1965); Long-tailed Hermit (Stiles and Wolf 1979). Likewise, up to 30 homosexual pairs of Herring Gulls have been counted in some locations—a relatively high number of same-sex associations to be present at one time—but in colonies that number more than 10,000 pairs, this amounts to less than I percent of the total number of pairs (Shugart 1980:426—27).
29
Same-sex courtship, sexual, pair-bonding, and /or parenting behaviors have been documented in the scientific literature in at least 167 species of mammals, 132 birds, 32 reptiles and amphibians 15 fishes, and 125 insects and other invertebrates, for a total of 471 species (see part 2 and appendix for a complete list). These figures do not include domesticated animals (at least another 19 species; see the appendix), nor species in which only sexually immature animals/juveniles engage in homosexual activities (for a survey of the latter in mammals, see Dagg 1984). For a number of reasons, this tally is likely to be an underestimate (especially for species other than mammals and birds, which are not as thoroughly covered): see chapter 3 for further discussion. It should also be pointed out that species totals may differ depending on the classificatory schema used; in some taxonomies, for example, animals that in this book are lumped together as subspecies are considered separate species (e.g., the various subspecies of Savanna Baboons, Flamingos, or Wapiti/Red Deer). This roster also excludes a wide variety of other cases in which the evidence for homosexual activities is not definitive, such as:
1. species in which homosexual activity is suspected (and sometimes included in comprehensive surveys of homosexual behavior, such as Dagg 1984) but in which the sex of participants has not yet been coin-firmed (e.g., one-horned rhinoceros [Laurie 1982:323], yellow-bellied marmot [Armitage 1962:327],
