In behavioral transvestism, an animal of one sex acts in a way that is characteristic of members of the opposite sex of that species—often fooling other members of their own species. For example, males of several species of terns imitate female food-begging gestures to steal food from other males. Behavioral transvestism does not mean animals behaving in ways that are thought to be “typically” male or female in other species. In sea horses and pipefishes, for instance, the male bears and gives birth to the young. Even though these are activities usually thought to be “female,” this is not a genuine case of transvestism because it is part of the regular behavior patterns and biology of the species (i.e., it is true for all males and no females). Female sea horses never bear young, nor are they fooled into thinking that males aren’t male because they do bear young. The same goes for initiation of courtship: in some species the female is more aggressive in initiating courtship and copulation (e.g., in greater painted-snipes), yet this could only be considered “transvestism” with reference to other species in which females do not initiate such activity.52
The question of transvestism is an important one for animal homosexuality because these two phenomena have often been confused. Many scientists have labeled all examples of animal homosexuality male or female “mimicry” since they consider any same-sex behavior to be nothing more than imitation of the opposite sex. True, many animals, when courting and mating homosexually, employ behavior patterns that the opposite sex also employs. In most cases, however, this simply involves making use of the available behavioral repertoire of the species rather than being an attempt to mimic the opposite sex. Moreover, the resemblance to “heterosexual” patterns is often partial at best, while in some species entirely distinct courtship and copulation patterns are used for homosexual activity.53
A good example of the difference between behavioral transvestism and homosexuality is in the Bighorn Sheep. In this species, males and females lead almost entirely separate lives: they live in sex-segregated herds for most of the year and come together for only a few short months during the breeding season. Among males, homosexual mounting is common, while females do not generally permit themselves to be mounted by males except when they are in heat (estrus). A small percentage of males, however, are behavioral transvestites: they remain in the female herds year-round and also mimic female behavior patterns. Significantly, such males also generally refuse to allow other males to mount them, just the way females do. Thus, among Bighorn Sheep, being mounted by a male is a typically “masculine” activity, while refusal of such mounting is a typically “feminine” behavior. Males who mimic females specifically avoid homosexuality. This is the exact opposite of the stereotypical view of male homosexuality, which is often considered to be a case of males “imitating” females. It is also a striking reminder of how important it is not to be misled by our preconceptions about human homosexuality when looking at animals.54
Transsexuality or sex change is a routine aspect of many animals’ lives, especially in invertebrates: shrimp, oysters, and sow bugs, for example, all undergo complete reversals of their sex at some stage in their lives.55 It is among coral-reef fish, however, that the most remarkable examples of transsexuality are found. More than 50 species of parrot fishes, wrasses, groupers, angelfishes, and other species are transsexual. In all such cases, the reproductive organs of the fish undergo a complete reversal. What were once fully functional ovaries, for example, become fully functional testes, and the formerly female fish is able to mate and reproduce as a male.56
The types of sex change that are found, the number and fluidity of genders, and the overall social organization of these species are so complex that a detailed terminology has been developed by scientists to describe all the variations. In some species, females turn into males (this is called protogynous sex change), while in others males become females (called protandrous sex change). In some fish, sex change is maturational; that is, it happens automatically to all individuals when they reach a certain age or size or else occurs spontaneously at different times for each individual. In other species, sex change appears to be triggered by factors in the social environment of the fish, such as the size, sex, or number of neighboring fish. In female-to-male fish species, many different gender profiles are found. In some cases, all fish are born female, and males result only from sex change (such a system is called monandric). In other cases, both genetic males (born male) and sex-changed males are found (this arrangement is called diandric). In these fishes, genetic males are sometimes referred to as primary males while sex-changed males are called secondary males. Often these two types of males differ in their coloration, behavior, and social organization so that transsexual males form a distinct and clearly visible “gender” in the population.
Homosexuality as a “masculine” activity: a male Bighorn ram mounts another ram. Males who mimic females in this species (behavioral transvestites) do not generally permit other males to mount them, unlike nontransvestite rams.
Things get even more complicated in some species. Among secondary males, some change sex before they mature as females (prematurational secondary males), while others change sex only after they live part of their adult life as females (post-maturational secondary males). Many species also have two distinct color phases: fish often begin life with a dull color and drab patterning, then change into the more brilliant hues typically associated with tropical fish as they get older. Which individuals change color, when they change, and their gender at the time of the color change can yield further variations. Many species of parrot fishes, for example, have multiple “genders” or categories of individuals based on these distinctions. In fact, in some families of fishes, transsexuality is so much the norm that biologists have coined a term to refer to those “unusual” species that don’t change sex—gonochoristic animals are those with two distinct sexes in which males always remain male and females always remain female.
As an example of how elaborate transsexuality can become in coral-reef fish, consider the striped parrot fish, a medium-sized species native to Caribbean and Atlantic waters from Bermuda to Brazil (the name refers to the fact that its teeth are fused together like a parrot’s beak).57 Striped parrot fish, like many sex-changing fishes, have both males that were born as males and males that were born as females. In fact, more than half of all males in this species used to be females. Moreover, all female striped parrot fish eventually change their sex, becoming male once they reach a certain size; the sex change can take as little as ten days to be completed. Sex-changed males have fully functional testes that used to be fully functional ovaries when the fish was female; they are able to mate and fertilize eggs the same way that genetic males do. Striped parrot fish have one of the most complex polygendered societies in the animal kingdom. There are five distinct genders, distinguished by biological sex, genetic origin, and color phase. Biological sex refers to whether the fish has ovaries (= female) or testes (= male). Genetic origin refers to whether the fish was born that sex or has changed from another sex (= transsexual). Color phase refers to the two types of coloration that striped parrot fish exhibit: initial-phase fish (so named because all fish start out with this coloration) are a drabber brown or bluish gray, while terminal-phase fish are a brilliant blue-green and orange. These three categories intersect to create the following five genders (percentages refer to what proportion of the total population, at any given time, belongs to each gender): (1) genetic females: born female, each of these initial-phase fish will eventually become a male and change color (45 percent); (2) initial-phase transsexual males: born female, these fish become male before they change into their bright colors and are fairly rare (1 percent); (3) terminal-phase transsexual males: born female, these fish become male at the same time they changed color, usually at a later age than genetic males (27 percent); (4) initial-phase genetic males: born male, most of these will change color as they get older (but won’t change sex) (14 percent); and (5) terminal-phase genetic males: born male, these fish start out as initial-phase males and change color (but not sex) at a younger age than transsexual males (13 percent).