Mating behaviors of the proboscis monkey ( Nasalis larvatus )

The mating behaviors of the proboscis monkey were observed in a riverine forest along a tributary of the Kinabatangan River, Sabah, Malaysia, for a period of 30 months. Solicitation for copulation was initiated frequently by males and occasionally by females. Most copulations involved only one mount; however, some multiple‐mount copulations were observed and a maximum of six mounts per copulation were recorded. The mean duration of mounts was about 27 sec. Nonsexual mounts (female–female, female–juvenile/infant, juvenile–juvenile, and juvenile–infant) were also observed. Female–female mounts occurred shortly after failed solicitations toward males were observed. Harassment by juveniles and/or infants was observed during copulation; however, these harassments apparently did not interfere with copulation. Sexual swelling was evident in 77.4% of copulating females, with copulating subadult females showing the most distinct swelling. Am. J. Primatol. 68:832–837, 2006. © 2006 Wiley‐Liss, Inc.