Presbytis potenziani (Bonaparte, 1856)

Russell A. Mittermeier, Anthony B. Rylands & Don E. Wilson, 2013, Cercopithecidae, Handbook of the Mammals of the World – Volume 3 Primates, Barcelona: Lynx Edicions, pp. 550-755 : 721

116.

Mentawai Langur

Presbytis potenziani

French: Langur des Mentawai / German: Mentawai-Langur / Spanish: Langur de Mentawai

Other common names: Golden-bellied Mentawai Langur, Long-tailed Langur, Mentawai Leaf Monkey

Taxonomy. Semnopithecus potenziani Bonaparte, 1856 ,

Tenasserim. Corrected to Mentawai Islands by O. Thomas in 1895, and restricted to Sipora Island by F. N. Chasen and C. B. Kloss in 1927. Amended by D. Brandon-Jones in 1993 to Pulau Pagai Utara (= North Pagai Island).

Monotypic.

Distribution. Mentawai Is (Sipora, North Pagai, and South Pagai Is, also on the islet of Sinakak off the E coast of South Pagai).

Descriptive notes. Head-body c.50 cm, tail c.58 cm; weight c.6-5 kg (males) and c.6-4 kg (females). The Mentawai Langur is jet-black above and on tail, with underside and innersides of thighs reddish-orange. Innersides of upper arms are whitish or reddish, and throat, cheeks, and chin are yellowish-white, grading backward through gray to the reddish color of underside. Brow band is whitish. Pubic region is yellowish-white in both sexes, and males have a white scrotum. Facial skin is black, becoming somewhat depigmented around the mouth. There is a small, erect,slightly forward-directed crest on crown and a ridge around chin and up to ears, where the forward-directed interramal hair stream meets the backward-directed cheek hair stream. Underparts are bright reddish-orange, with black-tipped hairs toward the midline of the chest. There may be slight differences between individuals on Sipora and the Pagaiislands.

Habitat. Primary and secondary lowland evergreen rainforest, swamps, logged forest, and (possibly) mangrove forest and cultivated areas. Mentawai forests are ever-wet rainforests, and annual rainfall is up to 4000 mm. Mentawai Langurs use all levels of the forest canopy, even occasionally coming to the ground, but they spend most of their active time in the middle canopy and resting time in the upper canopy. They are most abundant in forest logged 20 years ago and least abundant in recently logged forest.

Food and Feeding. The Mentawai Langur is highly frugivorous for a colobine, although the proportion of the diet that is fruit and seeds appears to vary with habitat. In one study in a primary forest habitat on North Pagai, fruit made up only 32% of the diet, while in a second study in secondary forest habitat, also on North Pagai, fruit and seeds contributed 70% of the diet, more than for any other species of colobine observed. Leaves can still make up a significant portion of the diet (22-55% of diet). The Mentawai Langur also eats flowers, sap, bark, and fungi, and it is one of the few primates that can eat leaves of the dipterocarp tree family.

Breeding. Mating of the Mentawai Langur is ventral-dorsal and solicited by the female about two-thirds of the time. A single infant is born every other year in July-August. Infants have white fur and pale skin and attain adultlike coat and skin color by 12-14 weeks of age. Infant “parking” (mother leaving the infant alone in a tree while she forages) has been observed.

Activity patterns. The Mentawai Languris diurnal and arboreal. Morning loud calls by adult males begin at 03:00-05:00 h. They leave sleeping trees before dawn, earlier than sympatric Kloss’s Gibbons (Hylobates klossii), perhaps to avoid feeding competition. In one study on North Pagai, observations of group movements in early mornings and late evenings suggest that Mentawai Langurs use sleeping trees in coconut groves and swamp forest outside the primary forest, and travel to the primary forest area to feed in the daytime. This movement pattern may be a way to avoid competition for sleeping trees with Kloss’s Gibbons. Group members usually stay within 30 m of each other while feeding and 10 m while resting. About 25-33% of their time is spent feeding and 45-56% resting. Only a very low percentage of time is spentin social activities (1-2%), and grooming is rarely observed.

Movements, Home range and Social organization. On North Pagai, home ranges of the Mentawai Langur are 17-40 ha. Social organization is variable; Mentawai Langurs have been observed in unimale—unifemale, unimale—multifemale groups, and multimale-multifemale groups. In areas with high densities and smaller home ranges, males defend territories from other groups, using visual displays and loud vocalizations, sometimes accompanied by adult females in duets. In areas with larger home ranges, adjacent territories may overlap, and groups tolerate each other. Adult males and sometimes females also give loud vocalizations to warn others of predators (people and pythons). Larger group sizes of Mentawai Langurs (compared with the closely related Siberut Langurs, P. siberu ) may be an adaptation to increased hunting and the need for increased vigilance. Adult males and females seem to share equal responsibility for leading group movements. Intragroup aggression is infrequent. Densities are c.1-7 groups/km?. It is sympatric with the Pagai Macaque ( Macaca pagensis ), the Pigtailed Langur ( Simias concolor ), and Kloss’s Gibbon.

Status and Conservation. CITES Appendix I. Classified as Critically Endangered on The IUCN Red List (as P. potenziani potenziani ). The Mentawai Langur is protected by Indonesian law. It is threatened by logging and hunting and is reported to be the second-most popular game species after the Pig-tailed Langur. On Siberut, where its sister taxon, the Siberut Langur, is found, local people are reported to climb up into their sleeping trees at night to shoot them; this hunting method may also be used for Mentawai Langurs. In recent years, hunting 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. Mentawai Langurs 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 of the Mentawai Langur is estimated at more than 50% over the past 40 years. In 2005, the population was thought to number only 300-1200 individuals across the three islands. It is not found in any protected areas, but was present in the proposed Betumonga Research Area, which was logged by 2003. In 2006, the following conservation actions were suggested: protection of areas in the Pagai Islands by cooperating with a logging corporation that has practiced sustainable logging technique there since 1971; 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), Kawamura & Megantara (1986), Meyer et al. (2011), Olson (1992), Sangchantr (2004), Tenaza (1987), Thomas (1895), Tilson (1976, 1980), Tilson & Tenaza (1976, 1982), Watanabe (1981), Whittaker (2006), Whittaker & Mittermeier (2008).

Figures

116. Mentawai Langur (Presbytis potenziani), 117. Siberut Langur (Presbytis siberu), 118. Maroon Langur (Presbytis rubicunda), 119. Pale-thighed Langur (Presbytis stamensus), 120. Natuna Islands Langur (Presbytis natunae), 121. Thomas's 9 Langur Presbytis. thomas (null)

Distribution. Mentawai Is (Sipora, North Pagai, and South Pagai Is, also on the islet of Sinakak off the E coast of South Pagai).