The Behavioural Contexts of Red Langur (Presbytis rubicunda) Loud Calls in the Wehea Forest, East Kalimantan, Indonesia.

Researchers hypothesize that male loud calls play several roles in primate societies including in the context of intergroup spacing and spatial coordination. Field studies examining the behavioural correlates of vocalizations are essential to evaluate the function of these calls. This preliminary study, from July 2011 to January 2012, explores the behavioural contexts and correlates of male loud calls in a habituated group of red langurs (Presbytis rubicunda) in the Wehea Forest, East Kalimantan, Indonesia. In analysing 418 h of data collection, we find a total of 87 vocal behaviours, including bouts of multiple calls in rapid succession (i.e. calling events) and individual loud calls. In this sample, most vocal behaviour takes place in the morning with 59% of calling events occurring before 8.00 h. The mean rate of calling events is 0.12 events/h, and the mean rate of individual loud calls is 0.20 calls/h. The mean number of calling events per day is 1.31 (range: 0-4), and the mean number of individual loud calls per day is 2.81 (range: 0-13). The rate of calling events is highest in the context of intragroup conflict, followed by intergroup encounters, predator threat, group travel, and the highest number of individual loud calls occurred during intergroup encounters. Although these results are preliminary, they suggest that adult male loud calls among red langurs at Wehea may play a role in both intergroup spacing and social coordination, supporting the hypothesis that these calls can serve different functions.