Behavioral (Predator-Prey) Interactions of Captive Grasshopper Mice (Onychomys torridus) and Horned Lizards (Phrynosoma cornutum and P. modestum)

Abstract

-In predatory attacks by Onychomys torridus 20% of the 30-min encounters involving Phrynosoma cornutum were fatal, whereas 43% of those with Phrynosoma modestum were fatal. When the trials of juvenile P. cornutum were combined with those of adult P. modestum, which are similar in size, large horned lizards (adult P. cornutum) suffered 0% mortality whereas small lizards (adult P. modestum plus juvenile P. cornutum) experienced significantly higher mortality, 55%. Horned lizard antipredator behaviors involved displays that increase apparent size, aggressive attacks that intimidate, and the absence of flight responses that might elicit Onychomys attack behavior. Lizard mortality was mainly attributable to attacks involving chewing of the cranium around the orbit. Adult Phrynosoma cornutum possess sufficient armament around the eyes and parietal region to successfully defend against such attacks. Also their tough dorsal skin hinders laceration by the mice. In contrast, P. modestum and juvenile P. cornutum were easy prey for 0. torridus.