Better to be bimodal: the interaction of color and odor on learning and memory

Defended prey frequently advertise to potential predators using multimodal warning displays. Signaling through more than one sensory pathway may enhance the rate of avoidance learning and the memorability of these learned avoidances. If this is so, then mimetic insects would gain more protection from mimicking a multimodal rather than a monomodal model. Day-old domestic chicks (Gallus gallus domesticus) were used to examine whether a common insect warning odor (pyrazine) enhanced learning and memorability of yellow prey, a common warning color. Pyrazine increased the rate at which the chicks learned to avoid unpalat-able yellow prey, and how well this learned avoidance was remembered after a 96-h interval. After 96 h, mimics of the multimodal prey were avoided, whereas mimics of the monomodal prey were not. In the absence of pyrazine, chicks generalized their learned avoidance of the unpalatable yellow prey to palatable green prey; however, the presence of pyrazine reduced this color gener-alization. These results suggest that much is to be gained from signaling multimodally, for both models and mimetic prey species. The presence of multimodal prey in the habitat may also advantage the predators as it allows it them to distinguish more easily between palatable and unpalatable prey. Key words: avian predators, learned avoidance, memorability, mimics, prey, pyrazine. [Behav Ecol 19:425–432 (2008)] Animals need to signal for a multitude of reasons to a rangeof different receivers. Whatever the meaning of the signal, it is important that it is noticed, recognized, and correctly interpreted (Guilford and Dawkins 1991). It is a striking fea