Presbytis thomasi

Conservation: CITES – Appendix II; IUCN – Lower Risk (nt).

Sumber: Order Primates

Distribution: Sumatra: Aceh, south to about 3 ° 50 ' N.

Sumber: Order Primates

Habitat. Primary and secondary lowland rainforest, swamp forest, lowland alluvial (riparian) forest, and fruit and rubber tree plantations. The highest densities of Thomas’s Langurs have been recorded in swamp forest, with densities somewhat lower in lowland alluvial and lowland forests. They are also found in mosaics of rubber plantations and primary hill dipterocarp forest, and they tolerate selectively logged forest. Thomas’s Langur prefers the understory. They occur at elevations of 1500 - 2400 m and in lower parts of the subalpine zones up to 3400 m in the Leuser Ecosystem. Rainfall is high where they occur (3288 - 4575 mm / year), and forests are humid throughout the year. They were studied in a forest-plantation mosaic at Bohorok (1981 - 1984) and alluvial lowland rainforest at Ketambe Research Station, Aceh (1987 - 2001).

Sumber: Cercopithecidae

Movements, Home range and Social organization. Thomas’s Langurslive in unimale — multifemale groups of 2 - 16 individuals, and they also form all-male groups. Two-male groups were recorded at Bohorok, and they were always larger (9 - 21 individuals). Both males and females disperse from their natal groups, and females also transfer among groups. Sometimes all females leave a group and transfer to another, resulting in an all-male group being left behind. Sometimes females leave a group to join a solitary male. Home ranges averaged 27 ha at Ketambe, but they were smaller at Borohok at 14 ha. The largest home range was 53 ha (at Ketambe). Home ranges tend to be larger in groups that have been stable for some years. Newly established groups have small home ranges, independent of the group’s size. At Ketambe, male group tenure was five days to 72 months, with a median of 60 months. Males are typically resident in only one mixed-sex group; establishing their residency at c ¢. 7 years old and maintaining their status until they are c. 13 years old. Daily distance traveled was smaller at Bohorok (average 683 m / day) than at Ketambe (average 1068 m / day). Thomas’s Langurs have very distinct long calls, which distinguish them from all other langurs on Sumatra, especially neighboring Black-crested Sumatran Langur (P. melalophos). These calls show age, individualism, and contextual variation. Thomas’s Langurs utter different calls depending on whether or not other individuals are present and whether or not they give alarm calls. Loud calls are uttered in the morning before leaving their sleeping trees, during encounters with other groups, and as an alarm call after spotting a predator. Males give loud calls and chase each other when groups meet; females of each group generally ignore each other. The aggressive behavior is believed to result from the male’s defense of his females rather than defense of the territory itself.