Toads use the subsurface thermal gradient for temperature regulation underground

As ectotherms with moist, permeable skins, amphibians continually seek a physiological balance between maintaining hydration and optimizing body temperature. Laboratory studies have suggested that dehydrated and starved amphibians should select cooler temperatures to slow the rate of water loss and reduce metabolism. However, much less is known about amphibian thermoregulatory behaviour in the wild, where environmental conditions and constraints may be more variable. In seasonally cold environments, where animals must maximize growth, gamete production and/or fat storage for winter dormancy over a short active season, maintaining a high metabolic rate may be primary. We investigated the thermoregulatory behaviour of the Fowler's Toads, Anaxyrus fowleri, in the wild at their northern range limit at Long Point, Ontario. We outfitted adult toads with small temperature loggers and radio-tracked them for periods of 24 hours. Simultaneously, we also recorded air and subsurface temperatures to a depth of 18.6 cm. When active at night, toads rapidly equilibrated with ambient air temperatures. However, during the day, resting toads selected and maintained body temperatures around 30 °C during the heat of the day by adjusting the depth to which they were buried. This strongly suggests that they behaviourally thermoregulate during their resting hours to maintain a high metabolic rate without regard to the dryness of their immediate surroundings.