Effects of Temperature, Body Size, and Hybridization on Mating Calls of Toads, Bufo a. americanus and Bufo woodhousii fowleri

Abstract

The mating calls of Bufo a. americanus and B. woodhousii fowleri studied in northern New Jersey and on Long Island, New York, consist of trains of pulses uttered at a rate of from 18 to 59 pulses/sec in americanus and 83-161 in fowleri. Pulse rate is highly dependent on body temperature, and approximately doubles with a 10? C increase. Average duration of call ranges from about 4 to 11 sec in americanus and from 1.3 to 2.5 sec in fowleri; call length is negatively correlated with temperature, but is much more variable than pulse rate. An increase in temperature probably exerts a slight, positive effect on dominant frequency, but the effect is largely obscured by individual variation. In general, increasing body size is accompanied by reduced pulse rate, increased length of call and lowered dominant frequency, but within the range of body size found in one population, the effects of differences in body size on mating calls are usually too slight to be detected readily. Limited data suggest that B. a. americanus of the northern and eastern United States produces mating calls with higher pulse rates (at a given temperature) than does B. a. charlesmithi of Oklahoma and Arkansas. The mating calls of hybrid toads have pulse rates intermediate between those of the parental species. When temperature is taken into consideration, there is no overlap in the ranges of pulse rates of 42 fowleri, 24 americanus and five hybrids recorded in one breeding pond. Pulse rate is perhaps a more sensitive criterion of hybridization than is morphology, because individuals indistinguishable morphologically from one of the parent species gave the calls of hybrids. Judging from mating calls, introgression has not measurably influenced the sympatric populations of fowleri and americanus studied.