The Advantage of a Big Head: Swallowing Performance in Adders, Vipera berus

For gape-limited predators such as snakes, maximum ingestible prey size is likely to influence the encounter rate of potential prey items and therefore presumably foraging success and fitness. In this study an attempt is made to measure the adaptive significance of head size variation in the adder Vipera berus. We examined the effect of individual variation in snake head length on swallowing performance, i.e. maximum ingestible prey mass, by providing captive snakes with different-sized prey and recording success and failure at swallowing. It was found that maximum ingested prey mass increased with snake snout-vent and head length. More importantly, when controlling for snout-vent length differences using multiple regression, ingestible prey mass increased with relative head length