Playing dead, playing for time, or just playing around? Responses of grass snakes (Natrix natrix) to capture by human predators.
Gregory, Patrick*,1, Isaac, Leigh Anne1, Griffiths, Richard2, 1 University of Victoria, Victoria, BC, Canada2 University of Kent, Canterbury, United Kingdom
ABSTRACT- Snakes exhibit a wide diversity of apparent defensive behaviours. One of the most peculiar of these is death-feigning, which may have links with tonic immobility, a common response of animals to predators. In snakes, death-feigning has been reported in three families, wherein it is likely convergent, but it is perhaps best known and most frequently seen in the North American hognose snakes (Heterodon) and the European grass snake (Natrix natrix). During a study of the ecology of grass snakes near Canterbury, UK, we recorded incidence of death-feigning and potential correlates of this behaviour. A majority of snakes feigned death, but there was wide variation in the extent of display and the timing of its onset during handling. There was no difference in occurrence of death-feigning between the sexes, nor could we detect effects of body size, feeding status, time of season, or most other factors in field-caught snakes. Although recapture rates were low, our data suggest that death-feigning behaviour also is variable within individuals. Hatchlings were unusual in showing no sign of death-feigning behaviour and snakes with stumped tails were less likely to begin feigning death immediately upon capture than were those with intact tails; the latter suggests a possible link between incidence of injury and antipredator behaviour. However, interpretation of these results is hampered by lack of observations of encounters between snakes and their natural predators in the field. One possibility is that death-feigning is an example of protean behaviour, and hence effective because it is unpredictable to the predator.
Key words: defensive behavior, Natrix natrix, death-feigning, grass snakes
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