Biological Exuberance: Animal Homosexuality and Natural Diversity

And of course new revelations about heterosexual behavior are being made all the time: female initiation of mating activity in Orang-utans, for example, was not documented until 1980 in spite of nearly 22,000 hours of observation over the preceding 20 years (and prior extensive field studies often failed to report any heterosexual copulations). As recently as 1996, the existence of polygamous trios in the tanga’eo or Mangaia kingfisher (of the Cook Islands near New Zealand) were uncovered for the first time, and the full extent of heterosexual mating by Common Chimpanzees with animals outside their group was not understood until 1997. Multiple heterosexual matings by female Harbor Seals were not verified until 1998; even then, the behavior was never directly observed during three years of study (including continuous, 24-hour videotape surveillance of captive animals over an entire breeding season), and had to be verified indirectly through DNA testing.³⁶ If direct observation by scientists were used as the sole criterion for the existence of a behavior, we would have to conclude that many species never engage in heterosexuality (or in certain forms of heterosexuality)—yet we know this cannot be true. So the fact that homosexuality has not been seen in many animals does not necessarily mean that it is absent in those species—only that it has yet to be observed.

Ironically, many species in which heterosexuality has rarely or never been observed are ones in which homosexual activity has been recorded. No information on the heterosexual mating system of wild Emus was available prior to 1995, for example, although homosexual copulation in the same species had been observed in captivity more than 70 years earlier. Heterosexual mating has never been observed in Black-rumped Flameback Woodpeckers—although homosexual copulation has—while some studies of Nilgiri Langurs, Harbor Seals, Northern Quolls, and Gray-capped Social Weavers failed to record any instances of opposite-sex mounting, although same-sex mounting did occur. Similarly, documentation of sexual activity between male Walruses—including photographs—preceded by almost a decade comparable descriptions and photographic evidence of sexual activity between males and females. In Acorn Woodpeckers—a species that regularly engages in same-sex mounting—only 26 heterosexual copulations were recorded in over 1,400 hours of observation devoted specifically to recording opposite-sex mating. Likewise, heterosexual copulations in Australian Shelducks (a species in which females sometimes form homosexual pairs) were observed only nine times during nearly a decade of study, and on only three of these occasions was a complete behavioral sequence involved. Because of the difficulty of observing heterosexual copulation, the mating system of Killer Whales is still poorly understood and, according to one scientist, “may never be known with certainty.” Homosexual activity in the same species has already been documented, although its study is also still in its infancy.³⁷ Obviously, then, an activity can be part of the regular behavior of a species and still be completely missed by observers or documented only rarely, in spite of conscientious and in some cases exhaustive observational regimens (both in the wild and in captivity).