Behavioral Modification of Evaporative Water Loss by a Puerto Rican Frog

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Abstract
Leptodactylid frogs (Eleutherodactylus coqui Thomas) reduce rates of evaporative water loss threefold by adjusting their postures and activities in response to changing conditions of availability of water during their nocturnal activity periods. Frogs that do not make these adjustments experience a potentially lethal loss of body water on a rainless night. Dehydration of a frog's body tissues increases its resting metabolic rate and lowers its maximum rate of aerobic metabolism. Water is reabsorbed from urine in the bladder to maintain tissue water content on dry nights. Use of water—conserving postures precludes vocalization by male frogs and response to calling males by females. Frogs in water—conserving postures feed less readily than active frogs. Frogs in the forest canopy experience higher rates of evaporative water loss than those in the understory, but there are more anthropods in the canopy, and leaf surfaces are twice as likely to be wet by rain. Despite these potential benefits of activity in the forest canopy, most frogs remain in understory vegetation. In that microhabitat their behavioral and physiological adjustments permit them to occupy their normal perches despite wide fluctuations in hydric conditions.