Parental alarm calls and nestling response of the Northern Mockingbird

Background/Question/Methods

Vocalizations are an important form of animal communication that can be used to communicate numerous types of information. Alarm calls in particular typically act to alert kin to nearby predators. It has been shown that birds, among other taxa, give specific alarm calls that allow the recipient to extract information indicating the type of predator presenting the danger. In this study, we first classified adult Northern Mockingbird (Mimus polyglottos) alarm calls at the nest and then assessed if these alarm calls were specific to different predator types. Given the mockingbird’s flexible vocal capacity and aggressive nest defense, we predicted that the parent mockingbirds would encode predator-specific information in their alarm calls. To classify alarm calls we first isolated parental alarm calls during predation events from videos that were placed at the nests of mockingbirds and analyzed them using Raven Pro. Then to determine if the alarm calls were predator specific we calculated the average proportion of each call type given towards each predator type. We also compared the proportion of call types given to the time of day of the predation event, the nest stage, and study site. 

Results/Conclusions

We classified eight different alarm calls produced by the Northern Mockingbird during nest predation events. This is an additional four calls to those that have previously been reported. Previous studies only observed mockingbird behavior during the morning and afternoon thus any nocturnal predation events and accompanying calls would have been missed. Furthermore these alarm calls appear to be predator specific. Composition of the calls differed for each predator type and mockingbirds typically gave only one alarm call for each predator type, excluding hawks and cats. Soft chucks were given in response to snake predators, chats and chat burst in response to cat predators, screams in response to crows, and all calls excluding chucks and chats, were given in response to hawk predators. Time of predation event, nest stage, and site were also associated with different alarm calls. However, these differences do not appear to be the result of one of these alternative variables but rather are supportive of our hypothesis for predator specificity.