We present the first population estimate for the Natuna leaf monkey Presbytis natunae, endemic to the island of Bunguran, Indonesia, based on a 2-month survey. Bunguran has a land area of only 1,605 km2 and was until 1980 largely covered in primary forest. At present primary forest exists only in small patches within a matrix of logged forest, which covers nearly 70% of the island. Natuna leaf monkeys are confined to forest and have a preference for primary lowland forest patches. Groups average 3.5 ± SD 2.0 individuals and occur in a density of 2.3 ± SD 1.1 groups per km2. Extrapolation of the density estimates to the entire island indicates that <10,000 individuals remain in two subpopulations. On Bunguran these monkeys make popular pets and the species is threatened in part by the demand for captive individuals but mostly by continuing degradation and reduction of forest. An assessment of the species following IUCN threat criteria indicates that it should be categorized as Vulnerable. We make a number of recommendations for the conservation of the species, most importantly the implementation by the district government of Natuna of two strict conservation areas on the island, and the maintaining of a larger area of sustainably used natural forest.
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