Thesis

Snake Scent Application Behavior in California Ground Squirrels (Otospermophilus beecheyi)

California ground squirrels (CGS) have evolved a repertoire of mechanisms to defend against rattlesnakes and gopher snakes. A putative antipredator behavior known as snake scent application (SSA), in which a squirrel chews and rubs materials from a snake onto its body, is not yet well understood. SSA in CGS is elicited by rattlesnakes, but some unpublished reports suggest that SSA could be elicited by other snake species as well. In addition, there are uncertainties concerning the function of and motivation to perform this behavior. Here, I tested three hypotheses related to the function and nature of SSA: 1) SSA will be more often elicited by rattlesnake (the most potent predator of CGS) than gopher or garter snake sheds, and gopher snake sheds will elicit SSA more often than garter snake (not predators of CGS) sheds; 2) SSA will be more common in the spring than in the fall. This prediction is based on the assumption that SSA is primarily aimed at the protection of CGS pups, which are most vulnerable after their birth in the spring; 3) CGS will enter traps, which they normally avoid, to gain access to snake sheds less often than they will enter traps to gain access to food, but more often than they will do so for traps that contain a piece of wood. To test these hypotheses, I conducted three field experiments at locations in San Diego County where I presented snake sheds and treated traps to wild CGS. I found that rattlesnake shed elicited the only occurrences of SSA, suggesting that SSA in CGS is limited to rattlesnakes and that the benefits of SSA derive not simply from disguising one’s olfactory identity as a squirrel but, more specifically, from smelling like a rattlesnake. Although CGS exhibited SSA more in the spring than in the fall, I did not find statistical support for this difference. Finally, CGS entered traps that contained rattlesnake shed no more often than they entered traps that contained a piece of wood, implying that motivation to engage in SSA is not high, at least under the circumstances of my experiment. Based on these results, I propose future research that addresses the specific characteristics of rattlesnake sheds that elicit SSA (e.g., age and size of sheds) and the benefits of SSA for pups versus adults.

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