RESPONSES OF GREATER ROADRUNNERS DURING ATTACKS ON SYMPATRIC VENOMOUS AND NONVENOMOUS SNAKES

Abstract

Innate avoidance responses by potential predators to color patterns of snakes have been reported. Predation that is nonrandom with respect to the phenotype of the prey species is a well-characterized mechanism of natural selection, the driving force of adaptive evolution. Using both model and live snakes, we investigated the responses of 11 naive roadrunners, Geococcyx californianus, to 3 sympatric species of venomous and nonvenomous snake (Micruroides euryxanthus, Pituophis catenifer, and Crotalus atrox). Neither model nor live coral snakes elicited overt avoidance responses from the birds. Models elicited fewer pecks than moving live snakes. A gopher snake and a rattlesnake also failed to elicit overt avoidance behaviors. However, in contrast to the coral snakes, both snakes elicited a significantly higher number of leaps and wing flips, behaviors used by roadrunners when subduing dangerous prey. We conclude that roadrunners have no overt innate reactive behaviors to color patterns of coral snakes. Roadrunners do display such behaviors to rattlesnakes and gopher snakes as if both were dangerous prey, suggesting either Batesian or Mullerian mimicry.