The influence of prey-scent stimuli on predatory behavior of the North American copperhead Agkistrodon contortrix (Serpentes: Viperidae)

Abstract

Viperid snakes strike, envenomate, and release mammalian prey to prevent being harmed by the prey; snakes must then track prey in the process of strike-induced chemosensory searching. Because rattlesnakes prefer to track and consume envenomated prey, it would seem that the scent of envenomated tissue is key to the tracking process. After striking rodents, rattlesnakes also retain a specific chemical search image of prey items. I examined this behavioral pattern in copperheads (Agkistrodon contortrix) from three US populations with documented dietary biases toward mammals (Kansas), lepidopteran larvae (Texas), and amphibians (Louisiana), respectively. Experiments were conducted to assess whether copperheads form a specific search image of nonenvenomated mouse, hornworm, and frog prey items. Additional experiments tested the relative importance of envenomated tissue to prey scent. Results indicate that copperheads do not form a specific search image of prey items. Preference for nonenvenomated prey items is in the order mouse > hornworm > frog for all three populations; therefore, the innate behavioral preference for types of prey does not match the dietary biases noted in the literature. Envenomated mice and hornworms were preferred to all nonenvenomated prey items, but most trials involving envenomated frogs did not suggest envenomated prey preference. Overall, these results suggest that when the snakes search for prey, envenomated tissue stimuli are more important to snakes than scents arising from the prey itself. Searching and consumption behaviors seem to be independent, suggesting that strike-induced chemosensory searching and consumption are more complicated behavioral processes than previously recognized.