Silvered leaf monkey  (Trachypithecus cristatus)

Classified as Near Threatened (NT) on the IUCN Red List (1) and listed on Appendix II of CITES (4).

The silvered leaf monkey is easily recognisable due to its dark, silver-tipped fur and dark-skinned face (5). This extremely agile animal has long limbs (5) and, like other leaf monkeys, the tail is considerably longer than the body. Despite its disproportionate size, the tail is not prehensile, and therefore the predominant purpose of the tail of the silvered leaf monkey is not to grasp or hold objects, but to provide balance (5) (6) (7). The latter part of the scientific name, cristatus, comes from the Latin word ‘crista’ meaning crest or tuft (6), referring to the pointed crest of fur on top of its head (6) (8).

Male and female silvered leaf monkeys are almost identical in appearance, the only differences being that the male is much larger than the female, and the female may have irregular white patches on the inside of the flanks (5) (6) (7). Newborn silvered leaf monkeys differ considerably, as they have conspicuous bright orange fur with white hands, feet and face. The skin changes to black within days of birth, whereas the orange fur changes to the adult colour after three to five months (5).

This species occurs in Malaysia, Indonesia and Brunei Darussalam (1). There are two subspecies: Trachypithecus cristatus cristatus occurs in Indonesia (including Kalimantan and Sumatra), Malaysia (Sabah, Sarawak and the western coast of peninsular Malaysia) and Brunei, whereas Trachypithecus cristatus vigilans occurs only on Sirhassen in the Natuna Islands, Indonesia (1) (9).

The silvered leaf monkey inhabits a diverse range of forest types, including riverine, mangrove, swamp and coastal forests. It can occur in both primary and secondary forest (6) (10).

The silvered leaf monkey is a largely arboreal species, but may spend time foraging on the ground. It feeds predominantly on leaves, preferring the youngest shoots, but also consumes fruits, seeds, flowers and buds (2) (11). Leaf monkeys have a number of adaptations that allow them to deal with this leafy diet. The large, sacculated stomach, like that of ruminants (such as cattle and deer), contains bacteria that can break down cellulose, and the large size of the stomach means it can hold a great volume of food, which is necessary as leaves are nutritionally poor (9) (11).

The silvered leaf monkey generally lives in groups of no more than ten individuals, although groups containing up to thirty individuals have been known (2). Each group usually consists of a single male, who defends and mates with multiple females, although all-male groups do occur as well (6).

The silvered leaf monkey typically breeds once every year, and although this can take place at any time of the year, there is a peak in births between December and May, when there is an abundance of food (6). The gestation period is six months, and typically just a single offspring is born, although twins do occasionally occur (12). The offspring is born well developed, with open eyes and strong forearms, allowing it to cling to its mother (5) (6). Females commonly care for the young of other females in the group (5) (6) (7), and adult males are also known to care for immature group members (13). Once fully matured, the juvenile monkeys generally disperse from the group in which they were born (5). The female silvered leaf monkey reaches sexual maturity at four years of age, whereas the average male does not reach sexual maturity until four and a half years old (12).

In parts of its range, the silvered leaf monkey is still hunted as a source of meat and for the pet trade. However, the greatest threat to this species, and indeed to most of the mammals endemic to Indonesia and Malaysia, is habitat loss caused by an ever-increasing human presence. The disappearance of suitable lowland habitat due to land clearance (especially for oil palm plantations) and forest fires present a major threat to this monkey (1).

The silvered leaf monkey is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning that any international trade in this species should be carefully monitored (4). It is also known to occur in at least four protected areas: Bukit Barisan Selatan National Park and Gunung Leuser National Park in Indonesia, and Bako National Park and Taman Negara National Park in Malaysia (1).

View information on this species at the UNEP World Conservation Monitoring Centre.

To find out more about wildlife conservation in Indonesia and Malaysia see:

• Wildlife Conservation Society:
  http://www.wcsmalaysia.org
• The Nature Conservancy:
  http://www.nature.org/wherewework/asiapacific/indonesia

To learn more about the conservation of primates see:

• IUCN/SSC Primate Specialist Group:
  http://www.primate-sg.org
• Conservation International:
  http://www.conservation.org/learn/biodiversity/species/profiles/more_primates