Optimizing field and analytical procedures for estimating densities of arboreal and threatened primates in tropical rainforest.

The application of distance sampling to primate density estimation is challenging and susceptible to estimation biases, mainly due to the difficulties of properly accounting for variation in species' detectability and of accurately sampling the spread of the social groups. We apply a hierarchical distance sampling approach to primate data, to account for a comprehensive set of environmental covariates of both detectability and abundance, and we propose a novel field routine to measure the spread of groups during transect sampling. We confirm the good potential of this approach, given we obtained refined estimates of primate density (as measured by the Akaike Information Criterion) in comparison to estimates from models without covariates.