Stressed snakes strike first: Hormone levels and defensive behavior in free ranging cottonmouths (Agkistrodon piscivorus)
The risk of predation is widely accepted as being one of the most significant evolutionary pressures driving selection upon wildlife species. Animals can respond to potential predation with defensive behaviors, allowing them to mitigate some of the risk of encounters with predators. In this context, understanding the factors which influence defensive behaviors is critical to expanding our knowledge of organismal response to strong selection. Predation risk is often cited as a primary contributor to ecological stress, which is believed to be an important factor mediating animal behavior. The eastern cottonmouth (Agkistrodon piscivorus) is an abundant, large bodied pit viper which has a reputation for commonly exhibiting intense defensive behaviors. Both the defensive behaviors and hormonal ecology of cottonmouths have been studied extensively. However, the interaction between these is not well understood. We conducted field trials to examine how levels of the stress hormone (corticosterone) affect the defensive behavior of cottonmouths. We recorded the intensity of defensive behaviors and plasma corticosterone concentrations of cottonmouths both immediately upon first encountering the snake, and after confining it for 30 minutes.
We found that snakes with elevated levels of baseline corticosterone exhibited more intense defensive behaviors when we approached them in the field; snakes with higher levels were more likely to strike. Somewhat surprisingly, this behavior was not related to how stressed snakes were following confinement. This study suggests that baseline stress levels can be important correlates of defensive behavior, providing insight into a potential consequence of environmental stress.