Noises in the Dark: Vocal Communication in Lepilemur ruficaudatus and Other Nocturnal Pair-Living Primates

Although the number of pair-living species is higher in nocturnal than in diurnal primates, less is known about the communicative function of their vocalizations. One striking feature of vocal communication in diurnal pair-living primates is that partners exchange vocalizations in coordinated duets. Several functions have been attributed to duets, including mate attraction, advertizing and strengthening the pair bond, and territorial defense. To assess whether these functions can also be attributed to vocalizations of pair-living nocturnal primates, we studied the communicative function of vocalizations of red-tailed sportive lemurs (Lepilemur ruficaudatus). Social interactions between partners were equally often accompanied by vocal exchanges or not. Half of these vocal interactions included mutual but not coordinated exchanges of vocalizations between partners. In addition, playback experiments with vocalizations of the respective partner did not elicit vocal responses. Thus, exchanges of vocalizations might function to regulate spacing and interactions within pairs rather than to advertize or strengthen pair bonds. Since Lepilemur ruficaudatus interacted more often vocally with partners than with neighbors, and also vocalized when alone, we conclude that calling serves to signal an animal’s presence in its territory and to regulate spacing among conspecifics. Because vocalizations seem to serve in territorial defense in most nocturnal pair-living primates, cohesiveness between partners may have been the initial driving force behind the evolution of duets.