Transgendered Hooded Warblers: females of this species usually have little or no black on their heads (far left), but some individuals are plumage transvestites, exhibiting a full malelike black hood and chin strap (far right). Other females exhibit a gradation of plumage patterns that fall between these two extremes (center).
Even in species where some individuals clearly are “tricked” into same-sex relations by transgendered animals, the situation is considerably more complex than this. In Common Garter Snakes, for example, some males produce a pheromone that is similar to the scent of females. These individuals are called she-males by scientists, and they attract as many male suitors as female snakes do. Most males who court she-males are apparently “deceived” into thinking they are interacting with a genetic female. However, she-males and genetic females are not identicaclass="underline" chemical analysis has shown that the pheromones of she-males, rather than being indistinguishable from those of females, are actually intermediate between those of males and females. When given a choice, most nontransvestite males prefer genetic females—demonstrating that they can distinguish between the two under the appropriate circumstances. Moreover, nontransvestite males sometimes abandon their courtship of females to pursue she-males, and up to 20 percent of males may actually prefer courting she-males rather than females when given a choice—indicating that not all individuals who interact with transgendered snakes do so entirely under “false pretenses.” Even though their pheromones resemble females’, she-males also have no trouble finding opposite-sex partners—in fact, some studies indicate that they may be more successful in mating with females than males who are not transvestite (she-males actually have more than three times as much testosterone as do males). In addition, male Garter Snakes also occasionally court each other in situations that do not appear to involve transvestism—and therefore not all same-sex interactions can be attributed to (transgender-induced) mistaken sex identification. In many other species where a subset of the population is transgendered, homosexuality does not occur at all, and transgendered individuals again have no difficulty in attracting mates of the opposite sex. This is true for female red-winged blackbirds that have malelike epaulets, female Pied Flycatchers that have the white forehead patches characteristic of males, female lesser kestrels that have male rump and tail coloration, and younger male long-tailed manakins whose plumage resembles that of females.88 If sex misrecognition were a “cause” of homosexual pairing, one would expect same-sex pairing, courtship, or mounting to be prevalent in these species as a result of “confusion” between transvestite individuals and members of the opposite sex. One would also expect transvestite individuals to be avoided by members of the opposite sex because they do not resemble “obviously” heterosexual partners. Once again, neither of these scenarios generally occurs.
Another problem with attributing homosexual interactions to mistaken sex identification is that it can (at most) account for the initial interest of one animal in another of the same sex. It cannot explain why the animal “mistaken” for the opposite sex often willingly participates in the homosexual interaction or may even initiate it. Even if homosexual pairs in Antbirds, for example, result from an initial failure on the part of a courting male to distinguish between the sexes (as has been claimed), such pairs could not persist for years unless both males were actively fostering the bond between them (or at the very least, not resisting the homosexual relationship). As scientists studying homosexual matings in Tree Swallows have pointed out, even if males mistake other males for females (which is not likely), the males they copulate with nevertheless do not resist their homosexual advances and even actively facilitate genital contact. Notably, they do not adopt the specific tactics used by birds in this species to deter unwanted sexual advances (typically displayed by females in heterosexual contexts). While male Black-crowned Night Herons may court males and females indiscriminately, their male partners are nevertheless sexually stimulated by the performance and may go on to form a homosexual pair-bond with them. In Regent Bowerbirds, “female-resembling” adolescent males may actually initiate courtship display toward adult males (the reverse of the usual scenario in cases of “mistaken” sex identification). Finally, male Greenshanks who visit other males’ territories and are “mistaken” for females actively precipitate homosexual courtship pursuits: they depart from the territory using a special swerving flight pattern that invites the other male to follow them (also used by females during heterosexual courtships). If they did not want to spark a homosexual courtship, they could simply employ any of the several strategies used by females to deter males’ advances in this species, such as leaving the territory in a direct flight path or “leapfrogging” over a pursuing male during a ground chase—yet these are not typically part of homosexual interactions.89 Thus, even if mistaken sex recognition is responsible for bringing two animals of the same sex together, it is ultimately irrelevant in explaining why those two animals often remain together to continue their interaction and bring it to its full conclusion, be it a completed courtship or mating episode, or a pair-bond lasting many years.90