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Abstract

Garter snakes (genus Thamnophis) rely mainly on chemical cues to recognize prey, but in some of the more aquatic species visual stimuli may suffice to elicit predatory attacks. However, the only visual components known to be involved in the visual release of attacks are movement and contrast with background. We explored other visual components by presenting visual models varying only in size, shape, or path of movement to an aquatically specialized species, Thamnophis melanogaster. Snakes responded preferentially to models consistent in size with natural prey, to models having non-elongate shapes regardless of type of contour (rounded or angular), and to those following paths with vertical, rather than only horizontal, components.