Do Free-ranging Rattlesnakes Use Thermal Cues to Detect and Evaluate Prey?

Schraft, Hannes A.

Department of Biology

San Diego State University

San Diego, CA USA

Graduate Group in Ecology

Department of Neurobiology, Physiology, and Behavior

University of California at Davis

Davis CA, USA

Goodman, Colin

Environmental Science and Policy Program

University of Maryland

College Park, MD USA

Predators use sensory organs to evaluate the suitability of potential prey before attack. Rattlesnakes can use infrared radiation to detect the temperature of objects in the environment, such as the body temperature of lizards they attack from ambush. Because the locomotor performance of ectotherms such as lizards depends on temperature, it is possible that rattlesnakes could use body temperature to evaluate the potential of lizards to evade attacks. We examined this possibility by testing whether hunting rattlesnakes use infrared information to (i) detect potential prey and (ii) evaluate prey before attack. If snakes use infrared to detect prey, we would expect the thermal contrast between prey and background to be the best predictor of predatory behavior. If they also evaluate prey based on temperature, we would expect absolute prey temperature to be the best predictor of predatory behavior. We presented lizard carcasses of varying temperatures to free-ranging juvenile sidewinder rattlesnakes (Crotalus cerastes). We scored strike occurrence, strike distance, reaction occurrence, and distance at first reaction as a function of thermal contrast between lizard and background, absolute lizard temperature, and categorical light level (day vs. night). Thermal contrast and light level emerged as the most salient predictors of snake behavior. Snakes were more likely to respond to lizards and/or respond at greater distances at night and when thermal contrast was high. Absolute lizard temperature was not an important predictor of snake behavior. This supports the prey detection function of infrared sensing in snakes. Absolute lizard temperature was not an important predictor of snake behavior; thus, we did not find evidence for temperature-based prey evaluation. Infrared sensing is still poorly understood, especially in ecologically relevant contexts, and future research will test whether rattlesnakes learn to evaluate prey based on temperature with experience.