The effect of predator type and danger level on the mob calls of the American Crow

Abstract

Flee-inducing alarm calls often communicate information about the type of predator and the danger associated with it. Less is known about how approach-inducing mob calls encode this information. We studied the mob calls of the American Crow to determine whether these calls convey information about the predator type or the level of danger by presenting a model owl (representing an avian predator) and raccoon (representing a mammalian predator). We found that crows emit the same types of vocalizations in response to both of these predator classes. Our results, however, suggest that calls with a longer duration, higher rate, and shorter interval between caws reflect a higher degree of danger. We also found significant differences in call structure from trial to trial, possibly reflecting variations in call structure among individuals or groups. The ability to encode specific information about urgency and individual or group identity while mobbing may be particularly important for efficient coordination of group activities in species-such as the American Crow-that live in stable social groups. © 2009 by The Cooper Ornithological Society. All rights reserved.