To conserve biodiversity, scientists monitor wildlife populations and their habitats. Current methods have constraints, such as the costs of ground or aerial surveys, limited resolution of freely available satellite images, and expensive high-resolution satellite images. Recently researchers started to use unmanned aerial vehicles (UAVs or drones) for wildlife and habitat monitoring. Here we tested whether we could detect nests of the critically endangered Sumatran orang-utan on imagery acquired from a camera-mounted drone to determine distribution and density. Our results show that the distribution of nests compares well between aerial and ground-based surveys and that relative density (nest/km) shows a significant correlation between these two survey types. The results also indicate that both methods can be used to detect significant differences in relative density between previously degraded reforested and enriched areas. We conclude that orang-utan nest surveys from drones are a promising survey method to determine distribution and (relative) density of Sumatran orang-utans and perhaps other ape species.