Benefit by contrast: an experiment with live aposematic prey

Aposematic prey often have a coloration that contrasts with the background. One beneficial effect of such conspicuous coloration is that it produces faster and more durable avoidance by predators. Another suggested benefit is that prey that contrast with the background are more quickly discerned and recognized as unpalatable by experienced predators. To further investigate the effects of prey contrast on predator behavior, I conducted an experiment with young chicks (Gallus gallus domesticus) as predators on live aposematic and nonaposematic prey. Birds with prior experience of both prey types were allowed into an arena with both palatable prey and aposematic prey on backgrounds that either closely matched or contrasted with the coloration of the aposematic prey. Also, the time a bird had available to decide to attack a prey was manipulated by including a competing chick or not. The experienced birds showed greater attack latencies for aposematic prey on more contrasting backgrounds, and aposematic prey were also attacked to a greater extent when on a matching background. The presence of a competitor generated similar effects, where birds in high competition attacked more and faster compared to birds subjected to lower degree of competition, but there was no interaction between competition and contrast. Thus, the experiment provides evidence that prey contrast against the background may produce better recognition and avoidance, independently of predator viewing time.