SUBSTRATE CHOICE AND PREDATION RISK IN NEWLY METAMORPHOSED AMERICAN TOADS BUFO-AMERICANUS - AN EXPERIMENTAL-ANALYSIS

Substrate choice by newly metamorphosed American toads (Bufo americanus) and success of eastern gar-ter snakes (Thamnophis sirtalis) hunting juvenile toads on different substrates were analyzed in two experiments. Five substrates were used: (1) plain sand, (2) dark colored top soil, (3) sand with vegetation, (4) sand with holes and (5) sand with gravel. Toads chose the latter four substrates over the first substrate in the absence of predators, and snakes were significantly more successful hunting toads on the first substrate. There were no differences in capture rates among the substrates that toads preferred, and snakes showed no significant substrate preferences in the experimental arenas. Plots recorded in the field around the perimeter of a breeding pond showed that the density of toads was related to the density of vegetation and the soil color. These results suggest that predation risk is a factor leading to substrate choice in newly metamorphosed toads.