Distribution and Ecology of the Most Tropical of the High-Elevation Montane Colobines: The Ebony Langur on Java

Abstract

Several species of colobines are known to inhabit high elevation regions, more so in Asia than in Africa. In Asia, three species of snub-nosed monkeys are found in the mountains of southern China, up to elevations of 2,300–4,700 m.a.s.l. and snub-nosed monkeys and several langur species are found in the Himalayas up to elevations of 3,000–4,000 m.a.s.l. By and large confined to temperate regions, these primates may make use of high-elevation habitats especially during the summer months, migrating down to lower elevations in winter. In addition to these species, the ebony langur Trachypithecus auratus, from the tropical island of Java, also occurs in high-elevation forests. Situated close to the equator, Java experiences small climatic differences over the years, but the variation between closely situated sites differing in altitude is large, with lower temperatures, different rainfall patterns and larger absolute differences between minimum and maximum temperatures at higher attitudes. On the highest mountains on Java, i.e. those between 2,500 and 3,676 m.a.s.l., the minimum monthly average temperature drops to just above 0 °C. Furthermore, depending on the local topography, frost does occur regularly, from altitudes of 1,600 m.a.s.l. upwards. Hence, in some respects these areas are more reminiscent of temperate than of tropical regions. Based on surveys conducted on 15 mountain complexes >2,500 m.a.s.l., I give an overview of the occurrence of ebony langurs in these high altitude forests. My results show that ebony langurs do indeed occur on the higher parts of all but one of the high-altitude mountain complexes, regularly >2,500 m.a.s.l. and up to 3,500 m.a.s.l. In contrast to several other high-altitude colobines, I found no evidence of (seasonal) altitudinal migration. The resident populations of ebony langurs occur in gnarled forest and data from the literature suggest that the amount of fruit available to them is appreciable smaller than in the lowlands—it is therefore suggested that these populations are amongst the most folivorous on Java. Data from 40 sites in 27 forest areas show that maximum group sizes are significantly related to altitude and seasonality in rainfall, such that the largest groups are found in highly seasonal deciduous lowland forest and the smallest groups in high-altitude rainforest. While at lower elevations groups contain one or occasionally two adult males, in the mountains smaller group sizes do not allow for two adult males groups to occur.