Intergroup calls of male pig-tailed langurs (Simias concolor)

Pig-tailed langurs (Simias concolor) were observed in the Pagai Islands and in Siberut. They lived in 1-male groups containing from one to five or more females plus their young. Adult males produced loud vocalizations of the sortGautier andGautier (1977) called “type 1 loud calls.” The pig-tailed langur's type 1 loud call (TOLC) was a series of 2 to 25 nasal barks, the loudest of which could be heard for 500 m or more in the rain forest. Exchange of TOLC's between males was the only frequent intergroup interaction. Fifty-one percent of TOLC's were emitted spontaneously, 33% occurred in response to TOLC's of other males, 13% to falling trees, 4% in response to thunder, and 1% during a fight between males of different groups. Although TOLC's occurred throughout the day, they exhibited a bimodal distribution, with a peak of calling early in the morning, and another in late afternoon. Tape-recorded TOLC's played back in the field stimulated males hearing them to emit TOLC's of their own. Barks in experimentally-elicited TOLC's were delivered at a faster rate than barks in other TOLC's were. While TOLC's mediate intergroup communication among males, field playback experiments are needed to truly elucidate their functions.