A review of François' leaf monkey Trachypithecus francoisi (sensu lato) in Lao PDR

Abstract

A monkey population allied to François' leaf monkey Trachypithecus francoisi discovered in 1920 constitutes the taxon laotum, endemic to Lao PDR. The next seven decades provided very little additional information about it. Wildlife surveys in the 1990s found a large population of T. (f.) laotum in Phou Hinpoun (=Khammouan Limestone) National Protected Area (NPA) and north into southern Nam Kading NPA, and a large population in and around Hin Namno NPA of T. (f.) ebenus, known outside Lao PDR only from adjoining Vietnam. Detailed here are confirmed records of smaller and more localized populations of leaf monkeys of the T. francoisi group (sensu Groves 2001, 2005, p. 175) from two other areas (Nakai-Nam Theun NPA and a region outside the protected area system, Muang (= District of) Vilabouli, in Savannakhet province), highly plausible reports from one more site, and records of T. (f.) ebenus from southern Phou Hinpoun NPA. Animals from Nakai-Nam Theun NPA and Muang Vilabouli differ in pelage from reported forms, and further information is required to resolve their taxonomy in relation to the named forms hatinhensis and ebenus. All Lao records of the Trachypithecus francoisi group leaf monkeys are within the latitudinal band of 16°58′N (probably 16°49′N) to 18°17′N, but reports from local people suggest the possibility of occurrence north of this latitude, and perhaps (parallel with the complex's distribution in Vietnam) north to the Chinese border. Populations in large karst landscapes remain healthy but cannot be assumed to remain so, and those in smaller karst and non-calcareous ranges are highly vulnerable to hunting-induced local extinction. Many uncertainties remain concerning the species-complex in Lao PDR: its overall distribution, the number of forms present, their distribution, and their taxonomy. Undescribed forms may yet be found, most likely to the north of the known range, where threats are much higher, adding to the urgency for surveys in this region.