Thermoregulation Patterns of the Northern Pacific Rattlesnake in a Shrub-Steppe Habitat

Little is known about the thermal biology of the Northern Pacific Rattlesnake (Crotalus oreganus) native to Central Washington. Northern Pacific Rattlesnakes are both important predators to many small vertebrates and prey to many carnivores, which make them of particular interest in conservation biology. I used temperature-sensing radio-transmitters and i-button data logger implants to monitor body temperatures of four individual rattlesnakes over the course of 11 months, from June 2012 to April 2013. I also recorded air temperatures and relative humidity using portable data loggers over the same period. Rattlesnakes actively thermoregulated at times during the day. At other times, they passively accepted environmental temperatures, especially during the winter. Rattlesnakes showed a body temperature of about 22°C during the day for the summer months, which at times was 13°C less than the ground temperature, as well as a minimum temperature of about 8°C during overwintering in their hibernacula. Other times their body temperatures were within 1°C of the ground temperature. My results suggest that rattlesnakes show changes in habitats and thermal environments over the year. If they are unable to maintain an optimum body temperature at one location then they may choose to seek out more hospitable thermal environments, or risk a drop in survivorship