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.

As part of a study of responses by red howler monkeys (Alouatta seniculus) to forest fragmentation, we studied red howlers in an extensive forest including a habitat mosaic of old-growth forest, secondary forest of different ages, and non-commercial monospecific plantations of exotic Chinese ash (Fraxinus chinensis) and pines, to produce baseline information on resource use and their role as seed dispersers. We followed three troops for six months, encompassing a dry and a wet season; in total, they fed on 48 species of trees, including fruits, leaves and flowers, but each group relied on a limited set of species available within its home range, particularly in the Moraceae and Cecropiaceae. This contrasts with lowland forest, where howlers feed on a larger variety of species. We observed no season of generalized fruit scarcity, as is the case in the lowlands. However, localized fruit scarcities in howler home ranges occurred. Howlers fed on relatively small quantities of leaves when fruit was available, and became primarily folivorous when fruit was unavailable. Howlers transported a mean of 2.3 species of seeds per fecal sample, to a mean distance of 116 m from the parent tree. More importantly, howlers are transporting seeds to ash and pine plantations, helping to enrich these habitats.

Captive Cebus paraguayanus were observed to express spontaneously a wide variety of species-specific behaviors in different zoos from Argentina. The monkeys were kept in old-style wire mesh cages with cement floors, as well as island enclosures. We collected qualitative data on nine species-specific behaviors, and all the sex-age classes analyzed expressed some of these behaviors. The results indicated that in spite of living under predictable captive conditions without environmental enrichment, Cebus paraguayanus were able to react to the incidental opportunities that were presented in these environments.