Persistent Females and Compliant Males Coordinate Alarm Calling in Diana Monkeys

Abstract

Sexual dimorphisms in animal vocal behavior have been successfully explained by sexual selection theory (e.g., mammals [1-5]; birds [6, 7]; anurans [8, 9]), but this does not usually include alarm calls, which are thought to be the product of kin or individual selection (e.g., [10, 11]). Here, we present the results of playback experiments with wild Diana monkeys, a species with highly dimorphic predator-specific alarms, to investigate the communication strategies of males and females during predator encounters. First, we simulated predator presence by broadcasting vocalizations of their main predators, leopards or eagles. We found that males only produced predator-specific alarms after the females had produced theirs, in response to which the females ceased alarm calling. In a second experiment, we created congruent and incongruent situations, so that the calls of a predator were followed by playbacks of male or female alarms with a matching or mismatching referent. For congruent conditions, results were the same as in the first experiment. For incongruent conditions, however, the males always gave predator-specific alarms that referentially matched the females' calls, regardless of the previously displayed predator. In contrast, females always gave predator-specific alarms that matched the predator type, regardless of their own male's subsequent calls. Moreover, the females persistently continued to alarm call until their own male produced calls with the matching referent. Results show that males and females attend to the informational content of each other's alarm calls but prioritize them differently relative to an experienced external event, a likely reflection of different underlying selection pressures.