Size-dependent misclassification of masquerading prey

Masquerading organisms appear to closely resemble inedible and generally inanimate objects, such as twigs, leaves, stones, and bird droppings. It has recently been demonstrated that masquerading prey gain protection from predation by being misclassified as inedible objects by their predators. Here, we present the first experimental test of the requirements of effective masquerade. Specifically, we explore whether masquerading prey need to be very similar in size to the model objects that they appear to resemble. Using domestic chicks as predators of twig-mimicking caterpillars, we find that matching a model object in size increases protection from predation; however, similarity of appearance without size matching still affords some protection. This study helps to explain why masquerading prey often resemble objects that are inherently variable in size (e.g., twigs, leaves, and stones) and has important implications for the evolution of masquerade as an antipredator defense.