Snakes in search of sex: the relation between mate-locating ability and mating success in male garter snakes

Is a male's ability to find fertilizable females an important determinant of his mating success? We exploited unique logistical advantages offered by courting aggregations of garter snakes, Thamnophis sirtalis parietalis, in Manitoba, Canada, to ask: (1) does the order at which a male arrives at a solitary female affect either his courtship tactics or his chances of inseminating her; and (2) does a male's body size affect his probability of arriving before his rivals? Experimental trials in the field and in outdoor arenas (to control group size and arrival intervals) suggested that, in the area near the main den, being the first to find a solitary female conveys limited or no fitness benefits to a male snake. Other males were likely to arrive before the male could achieve copulation; and early arrival did not guarantee optimal positioning within the mating ball. Thus, late-arriving males were as likely to obtain copulations as were early arrivers. Male body size enhanced mating success more in early arrivers than latecomers, but did not affect arrival times. However, although mate-finding ability was unimportant for male garter snakes competing near the den, it was critical in surrounding woodland where densities of rivals were much lower.