Distribution and conservation of the proboscis monkey ( Nasalis larvatus) in Kalimantan, Indonesia

Abstract

The proboscis monkey Nasalis larvatus is endemic to the island of Borneo. A review of the species' distribution reveals that it occurs throughout Kalimantan, the Indonesian part of Borneo, from the coastal areas to the headwaters of probably all major rivers. Proboscis monkeys are more widely distributed than has been thought previously, and were never confined to the coastal and downstream areas of rivers on the island of Borneo (including what is now Sabah, Sarawak, Brunei and Kalimantan) as has been assumed in some primate literature. Proboscis monkey habitat, i.e. riverine and coastal forest, is the most threatened of all vegetation types in Borneo, owing to conversion into agricultural land and logging. Another threat to their survival is hunting. The combination of these threats has reduced populations of N. larvatus in Sabah, Sarawak and East Kalimantan, and based on this it is expected that other populations elsewhere in Borneo are likewise threatened. Our study shows the present low efficiency of conservation programmes in Kalimantan, which adds to the problem of protecting N. larvatus. For the survival of the species the populations in Kalimantan are still of great significance, as they are considerably larger than those in Sabah, Sarawak, and Brunei. We therefore recommend the protection of some of the largest populations in order to ensure the long-term survival of the species.