Alert calls of male Red-winged Blackbirds: call rate and function

Abstract

Male Red-winged Blackbirds (Agelaius phoeniceus) give alert calls continuously while on their breeding territories. To investigate the possibility that their rate of calling encodes information about distance to predators or degree of danger associated with different predators, I conducted experiments in which males were presented with stuffed "predators" and human "predators," reflecting varying degrees of danger to the caller, at various distances from their territories. Males called at higher rates when stuffed predators were closer to their territories and increased their rates progressively when a person approached, which supports the hypothesis that information about distance to potential predators is contained in the call rate.