The transvestite serpent: why do male garter snakes court (some) other males?

In large mating aggregations of red-sided garter snakes, Thamnophis sirtali s parietalis, in Manitoba, male courtship is directed not only to females, but also to other males with female-like skin lipids ('she-males'). We show that 'she-maleness' is an intrinsic property of:a male rather than an arte fact of lipid transfer from females, and that male-male courtship is very c ommon in the field. She-males were distinctive in terms of appearance (they were heavier than other males and more often covered with mud), behaviour (they were inactive and rarely courted females) and performance (they were slow crawlers, ineffective courters and easily outcompeted by other males i n mating trials). 'She-maleness' was not a characteristic of a particular s ubset of males, as envisaged in previous. work; instead, it was a transitor y phase that most (perhaps all) male snakes passed through soon after they first-emerged from the winter den. Recently emerged males spent their first day or two relatively inactive, while restoring physiological functions (i ncluding locomotor performance and courtship ability). Experimental applica tion of female skin lipids on to males dramatically decreased courtship lev els of the recipient snakes. Thus, recently emerged males may derive two ki nds of benefit from mimicking female skin lipids. First, female mimicry 'sw itches off' the male's own (energetically expensive) courtship at a time wh en that courtship would be unproductive. Second, it may disadvantage his ri vals by distracting:them from females, and increasing their energy expendit ure. (C) 2000 The Association for the Study of Animal Behaviour.