DistributionRead full entry
Until 2007, this species was thought to be endemic to the upper Rio Mayo valley or Alto Mayo (Hershkovitz 1990). However, a recent study by Bveda-Penalba et al. 2009, undertaken over six months at 96 localities, revealed that its distribution extends much further to the south of the Department of San Martin, extending into the Bajo Mayo and Huallaga Central, almost reaching the Rio Huallabamba (known locally as the rio Huayabamba). This area is heavily deforested, and to date only one area was found where a viable population might live, although further research is needed to confirm this.
Mark (2003) and DeLuycker (2006) suggested that the species altitudinal range may be restricted to below 1,000 m. The study undertaken by Bveda-Penalba et al. (2009) registered the species between 252 and 1,053 metres asl. Results from research undertaken in the Proyecto Mono Tocn show that at least 60% of the species original habitat has already been lost.
There is an urgent need for additional surveys of all potential habitats in San Martin, and larger tracts of forest. Mark (2003) notes that subpopulations near the banks of the Rio Mayo differ in colour from those in the Aguaruna territory in the north-east. DeLuycker (2006) reported a marked difference in pelage colour between a group she studied in a fragment near Moyobamba and those photographed by Noel Rowe. During surveys, attention should be given to the distributions of the different colour morphs (Mark 2003). Bveda-Penalba et al. (2009) detected little difference in colour in individuals of the Alto Mayo, they argue that pelage colour varies depending on the lighting conditions. Some darker animals appeared much lighter when their bodies were turned in a different direction, making it difficult to determine differences in colour between Alto Mayo populations and the same was true for the quantity of white hair on the face. However, animals in the southern part of San Martin appear to be somewhat greyer than animals near Alto Mayo and usually do not have a a white mask (Tello-Alvarado J. C. pers comm). Bveda-Penalba et al. (2009) claim that the species lives in sympatry with another, undescribed species of Callicebus in the southern part of its range. Recent research carried out by the same team suggests it is just a morphological variation of C. oenanthe (A.J. Bveda-Penalba pers. comm).