Competing Behaviors of Thermoregulation and Ambush Foraging in the Timber Rattlesnake (Crotalus horridus horridus): A Mechanistic Assessment of Thermal Conduction

Abstract

The interaction between the biophysical environment and ectotherm morphology elicits behaviors designed to maintain internal body temperature (Tb) within a range that promotes physiological functions. The short-term requirements of mass (energy requirements) and heat balance are subject to tradeoffs imposed by the organisms current physiological (heat and mass budgets) and environmental (biophysical, demographic, social, and predation) constraints and available resources. In temperate forests, extreme temperatures are common in summer even with intermittent sun exposure due to dense canopy cover. In Spring and Fall, temperatures can range from below freezing to 35 ℃ in 24 hrs. An ambush predator like the rattlesnake requires prolonged immobility (e.g., hours or days) to be an effective predator but thermoregulatory needs still take precedence. How then would a rattlesnake thermoregulate during periods of exposure to thermal extremes while remaining motionless for long periods? In this dissertation I explored the relationship between thermoregulation and ambush foraging using fixed videography, principles of heat transfer, and operative temperature models to address my general question. I found that in this study populationC. horridus are rarely forced to make thermoregulatory movements. A combination of morphological features, thermal conduction, and positioning in the microhabitat are used to offset potentially extreme environmental temperatures throughout the active season. The results emphasize how adaptations for balancing tradeoffs between foraging and thermoregulation in a variable thermal environment help shapeC. horridus life-history traits.