DOES DIGESTION AFFECT THERMOREGULATION IN FREE-RANGING TIMBER RATTLESNAKES (CROTALUS HORRIDUS)?

Abstract

Increasing body temperature (Tb) during digestion can facilitate localized biochemical reactions and consequently increase passage rate of food through the digestive tract in terrestrial ectotherms. Snakes, particularly infrequent feeders, may benefit from an increase in digestion rate, because they typically feed on relatively large prey, which substantially increases their body mass. There is considerable evidence, particularly from laboratory studies, that postprandial thermophily can be attained through behavioral thermoregulation. However, there are compelling reasons, such as increased predation risk, that some snake species may not choose warmer Tbs during digestion. This study examines thermoregulation, before and after feeding, in free-ranging telemetered timber rattlesnakes (Crotalus horridus), an infrequently-feeding snake in central Tennessee. Crotalus horridus were observed feeding naturally or offered large food items (laboratory rats weighing 30-50% of snake body mass). Continuous Tbs of 11 C. horridus were recorded during feeding events and indicated that limited postprandial thermophily occurred, but is unlikely to be biologically relevant. Additionally, the thermal microhabitats selected by C. horridus immediately prior to digestion, during digestion, and after digestion did not differ. This lack of increased thermal selection is counter to the hypothesis of postprandial thermophily, which is generally assumed for most snakes. Because C. horridus is an ambush predator, it may sacrifice warmer Tbs to conserve energy and/or to avoid detection. Additionally, the climate in central Tennessee may be adequately warm to facilitate digestion without the need for selection of specific sites.