Bluffing and Waiting: Handling Effects and Post-Release Immobility in a Death-Feigning Snake (Natrix natrix)

Authors

  • Patrick T. Gregory

    1. Department of Biology, University of Victoria, Victoria, BC, Canada, and Durrell Institute of Conservation and Ecology, University of Kent, Canterbury, Kent CTZ 7NR, Kent, United Kingdom
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Patrick T. Gregory, Department of Biology, University of Victoria, PO Box 3020 STN CSC, Victoria, BC, Canada V8W 3N5.
E-mail: viper@uvic.ca

Abstract

Tonic immobility is a common response of animals to capture by a predator; in some cases, the behaviour is elaborated into death-feigning. Death-feigning is usually interpreted as a last-resort anti-predator tactic that depends on the predator ceasing or slowing its attack when the prey is apparently dead, thus buying time for the prey to escape if the predator’s attention is directed elsewhere, even momentarily. I tested the effects of different handling regimes on the expression of death-feigning in the grass snake (Natrix natrix). In one test, degree of handling had a significant effect on frequency of death-feigning in small snakes, with snakes that received more handling feigning death more often. A second test showed that different initial handling regimes also affected the probability of death-feigning in large snakes, with snakes initially held by the tail feigning death least frequently and those initially held by the head most frequently. Thus, increased apparent threat to a vulnerable part of the body is more likely to result in death-feigning. It remains to be seen whether death-feigning can reduce the threat posed by real predators, but immobility is frequently carried over into the post-release period, during which the animal presumably weighs its chances and awaits an opportunity to escape. Regardless of cause, death-feigning snakes exhibited significantly more frequent and longer post-release immobility than did non-death-feigning snakes, which typically fled immediately upon release. Overall, small snakes feigned death less frequently than adults and were more likely to flee upon release, suggesting that immobility is a riskier anti-predator defence strategy for them.

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