Affiliative interactions between one-male units in a band of Sichuan snub-nosed monkeys (Rhinopithecus roxellana) living in the Qinling Mountains, China.

We studied affiliative behaviors that occurred within and between one-male units (OMUs) in a band of Sichuan snub-nosed monkeys (Rhinopithecus roxellana) living in the Qinling Mountains, China for 3 years from 2002 to 2004. During the birth season, females handling infants of other females affiliatively interacted with females in neighboring OMUs as well as with females in their own OMU. After these interactions, affiliative encounters occurred without conflict between the OMUs. In the mating season, females sometimes presented their genitals to males of other OMUs. These interactions may facilitate the maintenance of a higher level social organization, a band. Therefore, the band composed of OMUs and all male group(s) is the basic unit of social structure of this species. Almost all other Asian colobines have OMUs that either maintain distance from each other or engage in territorial defense, so these OMUs would not be expected to form a band. Contrary to these species, the 3 species of Rhinopithecus spp. inhabiting China form a band composed of OMUs, because infants and females may function as a bridge connecting OMUs.