The ring-tailed lemur (Lemur catta) is a group-living strepsirhine primate endemic to Madagascar that has a complex vocal repertoire including affiliative moan and hmm calls. Past research has suggested that both vocalisations may be contact calls, and we assessed their usage in addition to examining the effect of individual differences and social factors on male calling behaviour. We tested three hypotheses: the group cohesion, preferred companion and individual differences hypotheses. From March to July 2010, 565h of focal animal data were collected on 31 males aged 1year at the Beza Mahafaly Special Reserve, Madagascar. Focal males were observed for 30min, with vocalisations, allogrooming and agonistic interactions noted using one-zero sampling, and general behaviour, nearest neighbour identity and distance noted using instantaneous point sampling, all at 2.5min intervals. We found support for the group cohesion hypothesis for both vocalisations, and support for the preferred companion and individual differences hypotheses for the hmm but not the moan vocalisation. Moan and hmm calls maintained the distance between a male and his nearest neighbour, and were made at higher rates during behaviours which may lead to separation from conspecifics, such as travel and vigilance. Males made hmm calls at higher rates when they were low-ranking, and/or when the nearest neighbour of a male or a preferred companion of either sex. Low-ranking males may hmm call to maintain proximity to specific individuals within social groups who will show them increased tolerance, with the hmm signalling peaceful intent. Ring-tailed lemurs are one of the best living models of gregarious primate ancestors, and gaining a better knowledge of the function and range of usage of their contact calls informs our understanding of the evolution of primate cognition.
