Feeding behavior of crayfish snakes (Regina) : allometry, ontogeny and adaptations to an extremely specialized diet

Dietary specialists are often predicted to have specialized and stereotyped behaviors that increase the efficiency of foraging on their preferred prey, but which limit their ability to feed on nonpreferred prey. Although there is support for various aspects of this prediction, a number of studies suggest that specialists should not be characterized in such a simplified way. The purpose of this study was to describe the prey selectivity, prey handling behavior, and chemosensory behavior of crayfish snakes (Regina, Colubridae), which are extreme dietary specialists, and determine the effects of prey type, feeding experience and ontogeny.

Museum specimens and field captured snakes, together with published data, were used to determine the effect of predator and prey size on prey selectivity in each species of Regina. Snakes were videotaped feeding on different prey to determine the effects of prey type and size on prey handling behavior, its efficiency and stereotypy. Finally, snakes born in captivity were raised on different diets to determine the effect of prey availability and prey type on the ontogeny of chemosensory behavior.

This study confirmed the dietary specializations of Regina grahamii, R. septemvittata and R. alleni, and found that R. rigida, like R. alleni, includes odonate larvae in their diet as juveniles. Snake size and prey availability determines prey selection by R. alleni and R. rigida. This study also demonstrated that the relationships between dietary and behavioral specialization can be complex and depend on the characteristics of both the predator and its prey. For example, behavioral specializations in prey handling behavior were correlated with prey type rather than degree of dietary specialization. Hard crayfish required complex prey handling techniques, while soft crayfish did not. In R. alleni and R. rigida, such specialization appears to have permitted dietary expansion rather than restriction. Also, experience improved both prey handling efficiency and stereotypy irrespective of prey type consumed. As predicted the chemosensory response of each Regina species was greatest toward species characteristic prey. However, prey availability and type influenced these responses. In particular, R. septemvittata increased its chemosensory response toward hard crayfish (nonpreferred prey) when not permitted to eat soft crayfish.