Decline in avoidance of predator chemical cues: Habituation or biorhythm shift?

Abstract

Animals for behavioral studies are often brought into captivity out of necessity or to control for experimental variables, and are often used repetitively in experiments for similar reasons. A mix of potential difficulties can be generated ranging from potential captivity effects to pseudoreplication, making interpretation difficult. Problems arising from these studies are seldom identified or reported. We have conducted long-term studies of the avoidance response of red-backed salamanders (Plethodon cinereus) to chemical cues from predatory eastern garter snakes (Thamnophis sirtalis), and have found that freshly-captured salamanders always avoid chemical cues from T. sirtalis that have recently fed on P. cinereus. In recent studies, salamanders held captive 5 months during summer and used randomly in multiple tests showed no decrease in predator avoidance behavior or activity, but a comparable group of salamanders maintained during winter showed a progressive loss of avoidance and activity. We discuss possible interpretations and suggest that the results reflect a natural decline in predator sensitivity or metabolism during winter rather than being a consequence of captivity or the outcome of habituation to predator chemical cues.