Respiratory cooling in rattlesnakes

We used infrared thermography to study respiratory cooling in the rattlesnakes (Viperidae: Crotalinae) and to partition the effects of air temperature, humidity, and activity levels on head-body temperature differences. We observed a single, cooled region centered around the mouth and nasal capsule that extended across the pit membrane at air temperatures above 20 °C. Both head and body temperatures of rattlesnakes increased linearly with air temperature. Head-body temperature differentials also increased with air temperature, but declined significantly at higher relative humidities. Rattling rattlesnakes exhibited significantly greater head-body temperature differentials than did resting rattlesnakes. We suggest that respiratory cooling may provide a thermal buffer for the thermoreceptive pit organs at high air temperatures, but caution that this adaptive hypothesis must be tested with direct neural or behavioral assays.