Altitudinal Ranging Pattern of Critically Endangered Cao Vit Gibbon in Karst Forest: Pinpointing the Reforestation Sites.

Cao vit gibbon (Nomascus nasutus) is one of the world's 25 most endangered primate species, with only one population of 11 groups living in a small karst forest patch along the China-Vietnam international border. Assisted habitat regeneration is underway in both China and Vietnam to conserve the species. However, the lack of crucial information on habitat use and habitat preferences of these gibbons could severely compromise the conservation outcomes. To understand gibbon habitat use patterns and guide ongoing habitat restoration, we studied the ranging behavior of two cao vit gibbon groups in Bangliang Gibbon Nature Reserve, Guangxi, China. We established vegetation plots within gibbon's habitat along the altitudinal gradient. Then quantified food distribution in different altitudinal ranges. Both groups avoided using areas above 800 m, but preferred lower areas, and they spent more time feeding in low-altitude areas compared to high-altitude areas. Our analysis revealed that the altitudinal ranging pattern was affected by both food distribution and temperature. The gibbons preferred altitudes that provided more food for their diet, and their selectivity for lower altitudes increased as temperatures dropped while they adopted an energy-conserving strategy during cold seasons. Our results suggested that gibbons prefer habitats at lower altitudes, which serve as important feeding sites and provide refuges during cold exposure. Therefore, we strongly propose prioritizing reforestation in areas below 750 m by planting important food species.