Taste-aversion conditioning of crows to control predation on eggs.

Free-ranging crows (Corvus brachyrhynchos) that ate chicken eggs that were painted green and contained a nonlethal toxin subsequently avoided green eggs at various locations, whether or not they contained toxin. The crows also continued to eat unpainted and nontoxic chicken eggs. Illness-induced aversions among predators in nature may be a powerful determiner of the evolution of Batesian mimicry and, in human hands, serve as a practical tool for wildlife ecologists.