Is There an Antipredator Blood-Squirting Defense in the Bull Horned Lizard, Phrynosoma taurus?

摘要

Understanding of the phenomenon of the squirting of blood from orbital sinuses of horned lizards has been slow in unfolding since its early historic (Spanish Empire 1651 and 1767; Manaster 1997) and scientific reports (Middendorf and Sherbrooke 1992; Wallace 1871). Only infrequently do conditions during capture by humans result in blood squirting. In contrast, this defensive behavior is elicited with much greater frequency by exposure of the lizards to native canid predators such as Coyotes, Canis latrans (Sherbrooke and Mason, in press) and Kit Foxes, Vulpes macrotis; (Sherbrooke and Middendorf 2004), or a Dog (Canis familiaris) model (P. comutum: 70-100%, P. hernandesi: 50%, and P. solare: 60% of trials; Middendorf and Sherbrooke 1992; Sherbrooke and Middendorf 2001). Indeed, this defensive behavior may be elicited by only a subset of would-be predators. For example, P. comutum did not squirt blood in response to a variety of non-canid predators including Greater Roadrunner (Geococcyx califomianus), Southern Grasshopper Mouse (Onychomys torridus), Long-nosed Leopard Lizard (Gambelia wislizenii), Western Diamondback Rattlesnake (Crotalus atrox), or whipsnakes (Masticophis spp.) (Sherbrooke 1990, 1991, 2003, unpubl. data). Anecdotal field observations of human encounters with a specific species of horned lizards can be useful for determining the presence of the behavior if the results are positive, but negative reports leave doubt as to the ability of the species to squirt blood under more appropriate conditions. Nevertheless, negative records under controlled conditions are useful for comparing the relative frequency of occurrence of blood squirting among species.