SEX RECOGNITION AND MATE CHOICE BY MALE WESTERN TOADS, BUFO-BOREAS

In field-based choice experiments, we examined sex recognition and mat e choice in male western toads, Bufo boreas. When given a simultaneous choice between a male and a female of equal size, males did not discr iminate between the sexes and attempted to amplex a male or a female w ith equal frequency. When a test male clasped a stimulus male, the sti mulus male uttered a release call that caused the test male to release the stimulus male. Male-male amplexus never lasted more than 3 s, but male-female amplexus was tenacious and prolonged. Furthermore, males discriminated between gravid females that differed in body size, choos ing larger gravid females over smaller ones, but they did not discrimi nate between gravid females or non-gravid females of equal size. In ch oice tests that excluded chemical cues, males jumped more frequently t owards large females than small ones. Given that females are significa ntly larger than males, selecting larger individuals as potential mate s increases the probability that males amplex with a female. (C) 1998 The Association for the Study of Animal Behaviour.