Hide or die when the winds bring wings: predator avoidance by activity shift in a mountain snake

Abstract

Background Understanding predator-prey relationships is fundamental in many areas of ecology and conservation. Basking time often increases the risk of predation and one way to minimise this risk is to reduce activity time and to stay within a refuge. However, this implies costs of lost opportunities for foraging, reproduction, and thermoregulation. We aimed to determine the main potential and actual predators of Vipera graeca, to estimate the incidence and the age and sex distribution of predation events based on body injuries to infer predation pressure, and to assess whether and how the activity of V. graeca individuals is modified by predation pressure. Results We observed n = 12 raptor bird species foraging at the study sites, and we determined Circaetus gallicus, Falco tinnunculus and Corvus cornix as predators of V. graeca. We found injuries and wounds on 12.5% of studied individuals (n = 319). The presence-absence of injuries were significantly positively influenced by estimated age of vipers, and were more frequent on females than on males, while interaction of age and sex showed a significant negative effect. The overlap between the activity of raptors showed significantly smaller overlap with observed viper activity than with potential viper activity. Conclusion The time being active on the surface by the snakes has cost: the incidence of predation-related injuries increased with age, were more frequent in females than in males and they occurred earlier in age for females than for males. The vipers show a shift in the bimodal activity time-frame by being active earlier in the morning and later in the afternoon than could be expected based on thermal conditions suggesting that there is no maximalization to exploit the whole time frame available to reach the preferred body temperature in a cold environment.