RESUMO
Reliable assessments of species' status are prerequisites for monitoring the success of conservation programmes. However, survey conditions such as terrain and inaccessibility, compounded by the low densities of many species across Southeast Asia and other parts of the world are considerable barriers to obtaining robust populations estimates. We used an occupancy-based approach and multi-model inference to generate occupancy and abundance estimates for northern white-cheeked crested gibbons Nomascus leucogenys and southern white-cheeked crested gibbons N. siki in the Nam Kading National Protected Area (NKNPA) in central Lao Peoples' Democratic Republic (hereafter Laos). We present these estimates for gibbons within the context of a strategy designed to monitor multiple species and discuss the practical challenges to obtaining sufficient data for robust population estimates to detect change in gibbon status over time. We surveyed approximately 210 km2 of habitat and estimate an abundance of 45 (SE = 17, CV = 37%) groups, giving an average site abundance of 0.21 (SE = 0.08, CV = 37%) groups per km2 . We make recommendations for ongoing gibbon monitoring and discuss the wider implications for cost effective wildlife monitoring in Laos. Am. J. Primatol. 78:462-472, 2016. © 2015 Wiley Periodicals, Inc.