The Slithering Dead: Does locomotor performance affect post-capture death feigning in dice snakes (Natrix tessellata, Laurenti 1768)?

Abstract

Functional constraints between different types of antipredator behavior should be common, especially if they are on the opposite sides of the behavioral spectrum such as flight and post-capture immobility. We examined a potential compromise between post-capture immobility displays and sprint speed in dice snakes (Natrix tessellata), using a field-based approach. We sampled snakes (N=238) from two populations: from a dense island population free of mammal predators, and from a less dense mainland population, preyed upon by both bird and mammal predators. We explored the effects of sexual maturity, temperature, body size, presence of palpable food in the gut and injuries on the occurrence and duration of post-capture immobility as well as sprint speed. Our results confirm the existence of functional constraints between locomotor performance and post-capture immobility in dice snakes. Faster dice snakes start escaping promptly after release, while slower individuals utilize more passive antipredator behaviors such as death feigning. Local adaptations seem to have great influence on behavioral compromise, since the mammal-free island population exhibited a higher incidence of post-capture immobility and a significantly lower sprint speed, compared to the less dense mainland population. Additionally, immature individuals tended to avoid death feigning and their post-capture immobility lasted shorter compared to adult individuals. It remains to be seen how individuals adjust their behavior to accomodate locomotor constraints, and in which specific phases of the predator-prey interaction these adjustments occur.