Does aposematic coloration of prey facilitate acquisition of feeding avoidance by the American crow (Corvus brachyrhynchos)?

Abstract

Warning (aposematic) coloration generally involves highly conspicuous colors, which are usually displayed by different prey species in characteristic patterns. The key function of warning coloration is to advertise prey unpalatability to potential predators as well as to facilitate avoidance learning. Many studies have examined the effect of conspicuousness of prey compared to cryptic prey on avoidance learning by predators. However, no previous studies examined the effect of warning coloration of prey compared to conspicuous and cryptic coloration of prey on avoidance learning in wild-ranging birds. Therefore, this problem was the central theme of my experimental study in which I used the American crow as a predator and chicken eggs of the three coloration patterns with palatable or unpalatable contents as prey. I hypothesized that avoidance of unpalatable eggs would be acquired through learning rather than being genetically determined. Further, I predicted that crows would learn faster to avoid eggs with warning coloration than those with either conspicuous or cryptic coloration. Finally, I predicted that avoidance of originally unpalatable eggs should persist longer during the subsequent control trials (contents of all eggs made palatable) for eggs with warning coloration compared to eggs with conspicuous or cryptic coloration patterns. To test these predictions, I trained crows in several series of trials to avoid potential food by offering them an opportunity to learn to associate unpalatability of prey (eggs) with selected coloration patterns (conspicuous, cryptic, and warning coloration). My results indicated that the American crow did not exhibit an innate avoidance of eggs with warning coloration. I also found that crows did not learn faster to avoid unpalatable prey with warning coloration compared to prey with conspicuous or cryptic coloration. (Abstract shortened by UMI.)