Components of a Visual Stimulus Used by Scrub Jays to Discriminate a Batesian Model

Abstract

Scrub jays [Aphelocoma coerulescens] were trained using operant conditioning procedures to avoid a model associated with punishment (food soaked in quinine dihydrochloride or no food) and to choose a palatable nonmimic which differed from the model in 3 visual components-size, color and pattern. In order to determine which components were used by the birds to recognize the model, subjects were then presented the model and 3 palatable mimics, each of which differed from the model in only 1 component and shared that component with the nonmimic. Of the 7 birds that learned to avoid the model, one did not discriminate any mimics from the model. The rest of the birds primarily used color to recognize the model, although half of the individuals which were able to distinguish between the model and mimics also used size and/or pattern, and only one bird showed Gestalt perception of the model. If these results are general in their applicability, the amount of variation shown in the predators'' responses may serve to perfect the mimicry of the palatable species in terms of all 3 visual recognition parameters, although mimetic color probably evolves first. At the same time, such variations in predator perception may allow the predator population to exploit a variable food resource more widely.