We studied a zone of sympatry between Alouatta seniculus and Alouatta palliata on the left bank of the Atrato River (Chocó). We located 110 groups of Alouatta, consisting of 81 groups of A. palliata and 29 groups of A. seniculus, recorded between 12 – 300 m a.s.l. Alouatta seniculus was associated principally with arracachal and panganal vegetation of alluvial soils alongside the Atrato River below 50 m altitude, and A. palliata was associated with upland vegetation of gallery forest, primary forest and secondary forest (20–300 m a.s.l.). The average number of animals per group of A. seniculus was 5.59 (range 2–7 individuals) while the average for A. palliata was 6.76 (range 2–18 individuals). No phenotypic evidence of hybridization was detected in contrast to other studies of hybridization of Alouatta. The condition of many of the forests in this study suggests the necessity of a conservation program in order to protect this unique zone of sympatry between the two species.

Here we report on the discovery of a new population of red uakaris in the mountains of northern San Martin, north-eastern Peru. This population is isolated from the other known uakari populations in the eastern lowlands, which raises questions concerning their taxonomic status and biogeographical history. This follows a recent range extension of this taxon west of the Ucayali River. Previously, the Peruvian red uakari (Cacajao calvus ucayalii) was only known in Peru from the lowlands between the Amazon, Ucayali and Yavarí Rivers.

Intestinal parasite diversity was evaluated in two groups of free-ranging Callicebus modestus from the José Ballivián Province of the Beni Department, Bolivia. During 10 months (September 2010 to June 2011) fecal samples were collected from an adult pair (group A), and a second group (group B) living in a less fragmented area than group A composed by an adult pair, a juvenile female and an infant male. Immature structures from parasites belonging to the Strongylida and Spirurida orders and the Strongyloides and Bertiella genera were detected through coproparasitology. Eggs from Strongyloides spp. were the most prevalent along the study (present in 9 of 10 months), followed by Strongylida eggs (present in 6 of 10 months). Immature structures of parasites from the Spirurida order and the genera Bertiella were only observed at the end of the rainy season. None of the monitored individuals presented evidence of health problems related to the presence of parasites, however, the presence of Bertiella spp. eggs is relevant for its public health implications.

Large-bodied game species are in decline in tropical forests worldwide due to unsustainable extraction levels by hunters, which can result in cascading effects on vertebrate community structure. In this study, we examine the density responses of primate populations to different levels of hunting pressure in the Madre de Dios river basin, Peru. Across three surveyed sites, both small- and mid-sized primates exhibited population-level density compensation in response to the extirpation of sympatric large primates. Small primate density at one heavily hunted site was 5x that of a comparable nonhunted site, while the highest density of mid-sized primates was recorded at mid-level hunting pressure. Primate response to hunting pressure appears to be influenced by reproductive rate, with strong interspecific variability. High reproductive rate, infrequent extraction, and the relaxation of competitive interactions with extirpated large primates appear to facilitate increasing density of the smallest-bodied species. Evidence from elsewhere in the Madre de Dios basin suggests that large primates are particularly slow to recover from past hunting pressure, with continuing recovery even in sites that have not been hunted for several decades. These variable density responses to hunting pressure alter inter-specific and community dynamics, with potentially expansive short- and long-term ecosystem-level effects.

This study consists of an update on the knowledge of the geographical distribution and population data of the saddle-back tamarin (Saguinus weddelli) in the area lying east of the Madeira River in Rondônia. A literature review were conducted as well as a series of expeditions in the municipalities of Cacoal, Machadinho D'Oeste, Nova Brasilândia D'Oeste, Chupinguaia, São Francisco do Guaporé and Costa Marques. The results indicated the existence of 39 sites where S. weddelli was recorded in the study area, 31 obtained from the literature and eight resulting from fieldwork. One of the new records is located beyond the known geographic range of the species, representing an extension of such a range. Although this taxon is not considered endangered, its status in the study area deserves attention, since high rates of deforestation in this region have been recorded during the past 40 years.