Morphological mimicry and its potential for deterring bird predators.

Abstract

Mimicry can impact a species' survival and fitness by increasing the species' ability to deter predators. Coloration is an integral component of mimicry, yet morphology may also influence mimicry success. Although bird predators are able to discern shapes and can associate palatability with prey shape, little is known about the deterrence of predators if the prey is exclusively a morphological mimic. To examine a mimic's potential to deter bird predators based soley on morphology, we presented free-foraging birds visiting a feeder with two types of artificial prey: white unpalatable worms and white palatable spheres. We observed the birds' preference for the two shapes over a seven day period. After the first day, the birds showed a significant preference for the palatable spheres overall, eating twice as many spheres as worms during this time period. The birds were able to distinguish between mimic shapes and to correlate palatability with shape, demonstrating that morphology could be an important element in mimicry. If morphology contributes significantly to the success of mimicry, shape mimicry may be a more common occurrence than previously considered.