CALL VARIATION IN THE COLORADO RIVER TOAD (BUFO-ALVARIUS) - BEHAVIORAL AND PHYLOGENETIC IMPLICATIONS

We studied variation in advertisement calls, release calls, and callin g behavior in three populations of Bufo alvarius in central Arizona ov er a 3-yr period. Of advertisement call variables, pulse rate was the only variable significantly (positively) related to temperature, and n o variables were correlated with male snout-vent length. For release c alls, only pulse rate was significantly (negatively) related to temper ature, and no variables were related to male size. Mean advertisement call pulse rate was approximately 30% of average release call pulse ra te; such dramatic differences in temporal structure of advertisement a nd release calls are previously unreported in the genus Bufo. These re sults support the hypothesis that B. alvarius generates advertisement calls without passive vibrations of the arytenoid cartilages. Overall patterns of call variation in B. alvarius more closely parallel the va lliceps rather than the boreas species group. Preliminary discriminati on trials indicate that females are attracted to male advertisement ca lls. Within relatively low density choruses, some large males produced advertisement calls consistently, and active-searching behavior was s ize-related. Male advertisement calls may play an important role in ma te selection by females under some conditions, but an adequate test of this hypothesis awaits additional study.