ABSTRACT

The alarm calls of many vertebrates encode predator-specific information such as the type of predator or the urgency of the threat. When an alarm call is only produced in a specific context and elicits specific behaviors from the recipients it is referred to as functionally referential. The pervasiveness of functionally referential alarm calls across bird species, however, remains to be established. In this study, we first classified Northern Mockingbird (Mimus polyglottos) alarm calls and then assessed if parental birds produced different alarm calls for different predators or nestling stage. To classify alarm calls we first isolated parental calls that preceded nest predation events from mockingbird nest camera footage and analyzed them using Raven Pro. Using a PCA analysis, we identified 9 different alarm calls based on 19 different predation events that resulted in 494 alarm calls given. To determine if the alarm calls were predator- or nest stage-specific we conducted a multinomial logistic regression. One call was given exclusively in association with snakes and 2 were given almost entirely in association with cats. In response to American Crows (Corvus brachyrhynchos), mockingbirds mainly produced a fourth alarm call, which was also frequently associated with Cooper's Hawks (Accipiter cooperii). The remaining 5 alarm calls were associated with Cooper's Hawks. While we have strong preliminary evidence for predator-specific alarm calls in nesting Northern Mockingbirds, many of these calls are also given in other contexts, such as in intraspecific interactions, which would exclude them from being considered functionally referential. These results highlight the challenges of categorizing alarm calls as functionally referential and the need to further integrate functional reference with context-dependent communication.

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