In the south and west of its range it appears to have an unusual distribution. It is absent from the Jiparaná-Marmoré interfluvium (between the Rios Mamoré, Madeira and Jiparaná and Serra dos Pacaás Novos in the south), and from areas of terra firme forest south of Serra dos Pacaás Novos; as such, it is excluded from almost two-thirds of the state of Rondônia (Ferrari and Lopes 1992; Ferrari et al. 1999). Unexpectedly, it occurs further south in transitional, savanna-like forest (Ferrari et al. 1999), extending south as far as the east bank of the Rio Guaporé in extreme southern Rondônia, on the border with Bolivia (Wallace et al. 1996). Ferrari and colleagues (1999) suggest that ecological factors, rather than physical barriers, limit the distribution of Chiropotes albinasus in this area, possibly linked to competition with the region's other pitheciine species, Pithecia irrorata.