The black-headed night monkey, Aotus nigriceps, has one of the largest distribution ranges of the 11 night monkey species found across Central and South America. Yet, only three studies have focused on their ecology, describing considerable variation in habitat, group composition, and population density. Therefore, we analyzed habitat use, group composition, population density, and diet of 14 groups at two field sites in southeastern Peru. All sampled groups were found in secondary tropical rainforest, often dominated by native bamboo species. Half of the observed sleeping sites were in bamboo stands, though groups also emerged from cane thickets and lianas. This contrasts with other Aotus studies which have found groups living in tree cavities and lianas. Population density estimates for both sites were 19 and 50 individuals per km2, outside the range previously reported for A. nigriceps (31−34 individuals per km2). We recovered seeds of 12 species from fecal samples over the course of two field seasons, belonging mainly to Cecropiaceae, Piperaceae and Moraceae. Our results suggest that the black-headed night monkey in Peru can survive and even thrive in secondary forest, feeding extensively on pioneer species, occupying a range of forest types, all while living near human settlements.
We would like to thank the Amazonian Conservation Association (ACA), Villa Carmen Biological Station, and 24Manu Learning Center (CREES) staff for hosting us, clearing trails, and providing valuable insight into location and 25 behavior of groups. We are indebted to students and staff from the School for Field Studies who assisted with data 26 collection and logistics. We carried out data collection in accordance with the legal requirements of Peru, and with 27 permission of the Amazon Conservation Association and CREES. 28
Abstract 29Quantitative acoustic analysis has been used to decipher individual differences, population structure, and taxonomic 30 diversity in numerous primate species. We previously described three distinct call types in wild Aotus nigriceps, and 31 now assess acoustic differences in two of these call types between social groups and spatially distinct populations. 32Acoustic parameters for both analyzed call types exhibited significant variability between groups. Similarly, 33 geographically distant field sites were acoustically distinct from one another. Several groups also used a variation of 34 a common call: a triplet Ch Ch instead of a duplicate. Other groups made use of ultrasonic frequencies which have 35 not previously been reported in Aotus. Our results suggest that Aotus nigriceps exhibits substantial acoustic 36 variability across sites that could potentially be useful for taxonomic classification, although additional 37 geographically distant populations still need to be sampled. The possibility of individual signatures also exists and 38 will require recording vocalizations from known individuals. 39
The study of wild black-headed night monkey (Aotus nigriceps) ecology is limited to a single field station, despite the species being found across a vast distributional range in the Amazon.We studied several aspects of their ecology, specifically habitat use, group size, population density, and diet. All sampled groups were found in secondary tropical rainforest, often dominated by either native bamboo or cane species. Sleeping sites were often in bamboo stands, though groups were also found in cane thickets and lianas. This is in contrast to other Aotus studies which have found groups living in tree cavities and lianas. Population density estimates varied between field sites (19 and 50 individuals per km 2 ), but both were consistent with other Aotus studies (31-40 individuals per km 2 ). And, twelve seed species were recovered from fecal samples over the course of two field seasons, dominated primarily by Cecropiaceae, Piperaceae and Moraceae. Our results suggest that the black-headed night monkey can survive and even
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