Further notes on the distribution of endemic Bolivian titi monkeys, Callicebus modestus and Callicebus olallae

Abstract

We present information on the distribution of the endemic Bolivian primates Callicebus olallae and C. modestus based on a series of site visits in the Beni Department. Callicebus olallae was registered at four localities and C. modestus at 11 localities, and in combination with negative data and localities for other Callicebus species in the region we defined the distributional boundaries for both endemics. Mean group size was 2.7 individuals for C. olallae and 3 individuals for C. modestus. The results highlight the restricted distribution of both species, with C. olallae having one of the highest levels of primate endemism in the world and an “occurrence area” of 400 km², and considering forest fragmentation in the region, more realistically an “occupancy area” of 50 km². Although C. modestus is found in slightly larger areas (1,800 km² and 450 km² respectively) the distribution area is still extremely restricted. The restricted distributions together with ongoing forest fragmentation due to cattle ranching, unregulated ecotourism activities, and principally the scheduled improvement of the “Northern Corridor” road that passes through this region, means that both species should be considered highly endangered.