Alarm barks of male vervet monkeys as displays of male quality

Abstract

Research on the vocal behaviour of non-human primates is often motivated by a desire to understand the origins of semantic communication, which led to a partial separation of this research from ecological-evolutionary approaches. To bridge this gap, we returned to the textbook example of semantic communication in animals, the vervet monkey, Chlorocebus pygerythrus, alarm call system, and investigated whether male alarm barks fulfil a dual function of alarming and indicating male quality. Barks are loud calls, produced by adult males, in response to large carnivores. However, since barks occasionally occur in agonistic interactions, we investigated whether barks may also indicate male quality. We recorded natural barking events over 23 months, sampling individual male participation from 45 individuals in six free-ranging groups at the Mawana Game Reserve, KwaZulu-Natal, South Africa. We hypothesized that barking frequency is under intra-sexual selection and predicted that barking frequency would increase with male rank and the degree of male-male competition. We found that the highest-ranking males were more likely to produce barks than lower-ranking males and that the number of daily barking events increased during the mating season. We advocate studying primate communication in its evolutionary context to achieve a comprehensive understanding of call "meaning".