Presbytis siberu

117. Siberut Langur Presbytis siberu French: Langur de Siberut / German: Siberut-Langur / Spanish: Langur de Siberut Other common names: Siberut Leaf Monkey, Sombre-bellied Mentawai Island Langur, Sombre-bellied Mentawai Langur Taxonomy. Semnopithecus potenziani siberu Chasen & Kloss, 1928, Siberut Island, Indonesia. P. siberu is a separate species from P. potenziani on the basis of genetic divergence. Monotypic. Distribution. Mentawai Is (Siberut I). Descriptive notes. Head-body 48-50 cm, tail 58-64 cm; weight c.6-5 kg (males) and c.6-4 kg (females). Thereislittle sexual dimorphism in the Siberut Langur. Ischial callosities are connected in males but separated in females. Adults are predominantly black, with whitish tufts of hair around their faces, atop their heads, around their necks, and on their pubic region in both sexes. Chest, abdomen, and inner sides of thighs are reddish-brown or reddish-orange. Males have a white scrotum. Facialskin is black, becoming somewhat lighter around the mouth. There is a small, erect, slightly forward-directed crest on crown. Coloration is similar to the Mentawai Langur (Presbytis potenziani), but underparts of the Siberut Langur are darker and white pubic patch is more sharply demarcated. Habitat. Primary and secondary lowland evergreen rainforest, swamps, logged forests, and (possibly) mangrove forest and cultivated areas. Mentawai forests are ever-wet rainforests, and annual rainfall is up to 4000 mm. Most oftheir active time is spent in the middle canopy and they rest in the upper canopy. Food and Feeding. The diet of the Siberut Langur has not been studied, but it is probably similar to that of the Mentawai Langur, which is highly frugivorous for a colobine, but also highly folivorous. Breeding. Infants have white fur and pale skin but attain adultlike coat and skin color by 12-14 weeks of age. Activity patterns. The Siberut Langur is diurnal and arboreal. Morning loud calls by adult males begin at 03:00-05:00 h. They leave their sleeping trees before dawn, earlier than sympatric Kloss’s Gibbons (Hylobates klossii), perhaps to avoid feeding competition. Group members usually stay within 30 m of each other while feeding and 10 m while resting. About 25-33% oftheir time is spent feeding and 45-56% resting. Only a very low proportion of time is spent in social activities (1-2%), and grooming is rarely observed. Movements, Home range and Social organization. Home ranges of Siberut Langurs are 11-5-22 ha, somewhat smaller than is typical of the Mentawai Langur. Only unimale—unifemale groups have been observed, unlike the variable social organization observed in the Mentawai Langur. In areas with high population densities and smaller home ranges, males may defend territories from other groups, using visual displays and loud vocalizations, sometimes accompanied by adult females in duets. Adult males and sometimes females also give loud vocalizations to warn others of predators (people and pythons). Adult males and females seem to share equal responsibility for leading group movements. Intragroup aggression is infrequent. A population density of 8-2 ind/km?® was reported at a site in northern Siberut. The Siberut Langur is sympatric with the Siberut Macaque (Macaca siberu), the Pig-tailed Langur (Simias concolor), and Kloss’s Gibbon. Status and Conservation. CITES Appendix I. Classified as Endangered on The IUCN Red Last (as P. potenziani siberu). The Siberut Langur is protected by Indonesian law, but its new species designation may not yet be recognized. It is threatened by logging and hunting and is reported to be the second-most popular game animal among Mentawai huntersafter the Pig-tailed Langur. Local people climb up into sleeping trees at night to shoot them. In recent years, hunting pressure has intensified because of increased access to remote areas due to logging roads and tracks and the replacement of bows and arrows with rifles. Local rituals and taboos that formerly regulated hunting have been lost because of the Christian religion. They are occasionally kept as pets but do not thrive in captivity. Other threats include oil palm plantations, forest clearing, and product extraction by local people. Population decline is estimated at more than 50% over the past 40 years. In 2006, the population was estimated at 1600-9500 individuals. The Siberut Langur occurs in only one protected area, Siberut National Park. It is also found in Peleonan Forest in northern Siberut, which, as of 2011, is protected on a short-term basis by local agreements to exclude the area from logging concessions. In 2006, the following conservation actions were suggested: increased protection for Siberut National Park, which currently lacks enforcement; formal protection of Peleonan Forest in northern Siberut, which has unusually large primate populations and is easily accessible for research; conservation education, especially regarding hunting; and the development of alternative economic models for the local people to reduce the likelihood of them selling off their lands to logging companies. Bibliography. Brandon-Jones (1993), Chasen & Kloss (1927), Fuentes (1996), Meyer et al. (2011), Sangchantr (2004), Thomas (1895), Tilson (1976, 1980), Tilson & Tenaza (1976, 1982), Waltert et al. (2008), Watanabe (1981), Whittaker (2006), Whittaker & Mittermeier (2008).Published as part of Russell A. Mittermeier, Anthony B. Rylands & Don E. Wilson, 2013, Cercopithecidae, pp. 550-755 in Handbook of the Mammals of the World – Volume 3 Primates, Barcelona :Lynx Edicions on pages 721-722, DOI: 10.5281/zenodo.686706