Seasonal and Daily Activity Patterns and Thermoregulation in the Southwestern Speckled Rattlesnake (Crotalus mitchelli pyrrhus) and the Colorado Desert Sidewinder (Crotalus cerastes laterorepens)

Crotalus cerastes was predominantly nocturnal, while C. mitchelli was mainly diurnal in the spring and fall and nocturnal during the summer months from June to September. The normal activity range of C. mitchelli (18.8-39.3 C) was narrower than that of C. cerastes (13.6-40.8 C). The overall preferred body temperature (April to December) of C. mitchelli (31.2 C) was significantly higher than that of C. cerastes (25.8 C). By being active at different times of the day during some months of the year, competition between these two species is reduced.