Low mammal and hornbill abundance in the forests of Barito Ulu, Central Kalimantan, Indonesia

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Faunal surveys in Kalimantan have been biased towards primates in protected forests close to the coast. Relatively little has been documented on other animal species, particularly in the vast interior forests. The results of a 1996–97 census of nine large mammal and eight hornbill species in tropical lowland forest in Barito Ulu, Central Kalimantan are reported here. Pigs Sus barbatus had the highest biomass, but this was due to large numbers migrating through the study area over 4 months and the resident population is probably low. Langurs Presbytis rubicunda and hybrid gibbons Hylobates mulleri × agilis had the highest biomass of all resident species. Orang-utans Pongo pygmaeus were absent from the area during the study period and pig-tailed macaques Macaca nemestrina were rarely seen. The resident hornbill species (Anthracoceros malayanus, Anorrhinus galeritus, Buceros vigil and B. rhinoceros) had high densities compared to that reported from lowland areas, but overall hornbill density was low due to the absence of the nomadic Aceros corrugatus and A. undulatus, except during peak fruit abundance. Sun bears Helarctos malayanus, long-tailed macaques M. fascicularis, muntjacs Muntiacus spp. and mouse deer Tragulus spp. were at low densities. Density of two large squirrel species, Ratufa affinis and Sundasciurus hippiurus, was lower than has been reported in Sarawak, but the density of Prevost's squirrel Callosciurus prevostii was higher. We discuss hunting pressure, isolation, low abundance of large fruit trees, poor soils, and specific habitat preferences as possible explanations for the low mammal and hornbill density at Barito Ulu.