To hold or not to hold? The effects of prey type and size on the predatory strategy of a venomous snake

The dangerous prey hypothesis predicts that when predators can discriminate between harmless and dangerous prey, they should alter their predatory behavior according to the risk. Venomous snakes, which rely on an envenomating strike to kill prey, often feed on potentially dangerous prey such as rodents, and have the choice between two alternative strategies following a bite: they either hold onto prey until it is incapacitated, or release it immediately, relying on scent trailing to find the bitten prey. In this study, we combined observational and experimental data collected in the field in South Africa to test the hypothesis that prey type and size affected the predatory strategy of a venomous snake, the puff adder (Bitis arietans; Viperidae). Relative prey size, but not prey type, affected the snake's strategy: puff adders typically struck and held prey of small size (e.g., toads, small adult mice and shrews), but often struck and released larger prey (e.g., large adult mice and rats), presumably because retaliatory bites from the latter ones are more dangerous. Hence, puff adders discriminated according to prey size and adjusted their predatory strategy consequently. Contrary to the common belief that viperid snakes typically strike and release prey, our findings agree with empirical evidence found in the literature, that is, puff adders generally alter their predatory tactics based on prey size. Although a few laboratory studies have examined the theme of the present paper in other venomous snakes, our research was conducted in a natural setting and thus provides a better understanding of the factors used by predators to choose between alternative hunting strategies.