Sleeping site use of François' langurs (Trachypithecus francoisi) inhabiting limestone forest of Nonggang, southwest China: the importance of foraging efficiency.

The selection of sleeping sites of animals provide valuable insights into their adaptations to a changing environment. We collected data on the sleeping sites used by a group of François' langurs (Trachypithecus francoisi) from September 2005 to August 2006 at the Nonggang National Nature Reserve in southwest China. Our results showed that the langurs utilized four sleeping sites on cliffs throughout the year. They foraged in the feeding patches close to their sleeping sites, showing a multiple central place foraging strategy. Notably, two sleeping sites were predominantly used during the dry season with least available young leaves and fruits, suggesting food seasonality may have a significant impact on the sleeping sites utilization. Moreover, the langurs used the sleeping sites in the peripheral area less than expected. They repeatedly and continuously slept at the Site 1, with a frequency of 79.8% of all recorded sleeping nights, and a maximum of eight consecutive nights. In conclusion, the sleeping site choices of François' langurs are mainly influenced by dietary factors, rather than range and resource defense, predator avoidance, thermoregulation, or parasite avoidance. This study highlights the significance of food resource and foraging efficiency to karst-dwelling François' langurs when selecting sleeping sites.