Interspecific Communication: Gaining Information from Heterospecific Alarm Calls

Many birds and mammals give alarm calls when they detect predators or other threats, and these calls have been used as classic models for understanding signal design. Here we consider signal design and usage, and how individuals acquire and use information from the alarm calls of other species. Alarm calls often encode detailed information on danger, such as the type of predator, its current behavior, size, or proximity. Alarm calls are sometimes very similar among species or can share generic acoustic features, and both help to explain recognition of heterospecific alarms. However, alarm calls can vary greatly among species, and taxonomically widespread eavesdropping also requires learning the association between calls and danger. Once heterospecifics eavesdrop on alarm calls, there is potentially selection on callers to modify their alarm calls or usage. If callers benefit from eavesdroppers’ responses to their alarm calls, they may be selected to enhance signal efficacy, leading to interspecific communication and mutual benefit. Alternatively, callers can be selected to manipulate eavesdroppers, using deceptive signaling, including mimicry, causing the eavesdropper to suffer a cost. If callers suffer a cost from eavesdroppers’ responses, their signaling can be modified to make eavesdropping harder, leading to cue denial. Overall, alarm signals provide an insight into the evolution of signal design, and the complex flow of information within and among species in natural communities.