Assessing group size and the demographic composition of unhabituated northern muriqui (Brachyteles hypoxanthus) using non-invasive biomonitoring

Obtaining accurate population measures of endangered species is critical for effective conservation and management actions and to evaluate their success overtime. However, determining the population size and demographic composition of most canopy forest-dwelling species has proven to be challenging. Here, we apply two non-invasive biomonitoring methods, arboreal camera trap and genetic tagging of faecal samples, to estimate the population size of a critically endangered primate, the northern muriqui (Brachyteles hypoxanthus), in the Caparao National Park, Brazil. When comparing population sizes between camera trapping and genetic tagging, the genetic tagging survey estimated fewer individuals for one of the muriqui groups studied but showed slightly higher population size estimates for the other group. In terms of the cost-efficiency of both methods, arboreal camera trapping had high initial costs but was more cost-effective in the long-term. Genetic tagging on the other hand did not require expensive equipment for data collection but had higher associated expenses for laboratory consumables and data processing. We recommend the use of both methods for northern muriqui monitoring and provide suggestions for improving the implementation of these non-invasive methods for future routine monitoring. Our findings also highlight the potential of arboreal camera trapping and genetic tagging to other arboreal mammals in tropical forests.