50 Shades of Clay: Rattlesnake Coloration Affects Detection by Predators

Harmel, Mallory malloryharmel@gmail.com Crowell, Hayley Taylor, Emily N. College of Sciences and Mathematics California State University at San Luis Obispo San Luis Obispo, CA USA

Crypsis, or the ability of an animal to avoid detection by other animals, is strongly related to the organism’s coloration. Southern Pacific Rattlesnakes (Crotalus oreganus helleri) vary in coloration within and among populations, suggesting selection on coloration within specific habitats and environments. The purpose of this study was to investigate the effect of coloration on likelihood of being attacked by a predator, on latency to attack, and to observe where on the snake body predators tend to attack. Clay snake models representing four commonly observed color morphs of rattlesnakes (light, dark, intermediate color with white pattern, intermediate color with dark cream pattern) were placed in grassy and wooded habitats at a reserve in central coastal California, and marks made on the models by predators’ teeth, beaks, and claws were quantified. We found that model type was a significant predictor of the overall number of attack marks, with dark colored snakes being attacked significantly more often than light-colored snakes. The latency to attack did not differ significantly among model types. Model type was related to where on the models the marks were made although the location of the marks on the models was not significantly different. Using open platform color analysis programs our data show that coloration can play a large role in crypsis, and suggest that dark-colored rattlesnakes, which have the most contrast with the golden-colored grasses and therefore have the lowest crypsis, are most at risk from predation.