KROCHMAL, A.R.; BAKKEN, G.S.: Western Diamond-backed Rattlesnakes (Crotalus atrox) Use Their Facial Pits To Mediate Thermoregulatory Behavior

Behavioral thermoregulation can impact foraging behavior, increase predation risk, and impart physiological costs. Locating thermally favorable microsites efficiently would minimize these constraints. Emitted thermal radiation is a direct indicator of an object’s surface temperature; using it as a behavioral cue would allow for efficient microsite detection. Rattlesnakes posses unique organs, called facial pits, which enable them to detect subtle fluctuations in emitted thermal radiation. We hypothesized that rattlesnakes use their facial pits to locate favorable microsites from a distance. Based on this hypothesis, we predicted that rattlesnakes could locate favorable microsites in the absence of obvious cues, and that they would lose this ability when their facial pits were temporarily disabled. We tested these predictions in a series of experiments on wild-caught Western diamond-backed rattlesnakes (Crotalus atrox). When tested in a Y-maze, snakes with functional pits located the favorable microsite more often than predicted by chance (p=0.002), while the same snakes failed to do so with blocked pits (p=0.684). We repeated the experiment in a circular arena. Once again, snakes with functional pits located the thermal refuge more often than predicted by chance (p<0.001), and were unable to do so with blocked pits (p=0.933). These data represent the first evidence suggesting rattlesnakes use facial pits to mediate behavioral thermoregulation, and the first confirmed non-predatory role of facial pits. We also examined the ecological relevance of this behavior by testing the snakes' ability to use their facial pits to evaluate semi-natural retreat sites.