SPRING MOVEMENTS IN THE AMERICAN TOAD, BUFO AMERICANUS

Abstract

Populations of Bufo americanus were studied in London, Ontario, from 1958 to 1962 to determine how they locate their breeding sites.Toads were capable of rapid, well-oriented movement to the breeding site, some moving at least 650 yd.Population turnover at breeding pools was high. There was a continuous influx and exodus of toads during the breeding season.Only 15% of 5937 captured toads were female. This disproportion might have resulted from later sexual maturation of females.Experiments showed that toads in breeding condition, within at least 80 yd of their breeding site, did not move at random but oriented towards the site. After translocation, individuals demonstrated homing behavior, returning over 100 yd to a particular breeding site, even when other active sites were available. Moreover, toads showed annual fidelity to a pool. Homing behavior evidently depended on familiarity with the characteristics of the breeding sites or the routes of influx to them.Experiments were performed on the significance to orientation of auditory, olfactory, hygrotactic, geotactic, and visual cues. Toad populations were capable of orienting towards a pool in the absence of a chorus, but were also able to orient towards the recording of a chorus broadcast from a position on land. Experiments involving surgery indicated that olfaction was not essential to orientation. Similarly, neither humidity nor topographic gradients appeared to be indispensable. Evidence on vision was inconclusive. Toads are probably able to utilize several characteristics of the breeding site, or its surroundings, during orientation. The relative significance of these characteristics probably depends on the nature of the environment.