Mentawai macaque (Macaca pagensis)

Mentawai macaque
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Mentawai macaque fact file

Mentawai macaque description

GenusMacaca (1)

The Mentawai macaque is one of four primates that inhabit the islands of the same name; all are considered to be threatened and in urgent need of conservation action (1). The macaques belong to the subfamily Cercopithecinae, or the ‘typical monkeys’, and are members of the most widespread primate genus (Macaca), ranging from northern Africa to Japan. In common with other macaques, the Mentawai macaque has cheek pouches into which it stuffs its food using the back of the hand (4). The fur is dark brown on the back, and pale chestnut to pale ochre on the sides of the neck, the front of the shoulders and the underside (2) (4). The legs are brown and the arms reddish brown. The tail is sparsely furred and the cheeks have relatively short whiskers. The face is hair-free, revealing black skin that frames the brown eyes (4).

Also known as
Mentawai Island macaque, Pagai Island macaque, Pagai macaque.
Macaca nemestrina pagensis.
Male head-body length: 45 - 55 cm (2)
Female head-body length: 40 – 45 cm (2)
Male tail length: 13 - 16 cm (2)
Female tail length: 10 – 13 cm (2)
Male weight: 6 – 9 kg (2)
Female weight: 4.5 – 6 kg (2)

Mentawai macaque biology

Mentawai macaque groups are flexible, but usually consist of between 5 and 25 individuals. Larger groups may split up into subunits to forage, and also to sleep. However, they are also seen contentedly foraging in mixed-species groups with the Mentawai Island leaf-monkey, Presbytis potenziani. The Mentawai macaque group tends to consist of a single adult male amongst a group of mature females and their young. Solitary males occasionally try to usurp ageing male group leaders in order to mate with the females, and meet with aggression to establish dominance (4).

Walking on all fours in the search for food, Mentawai macaques forage for the fruits of several trees, including two species of fig, and may stray from the forests to raid gardens and coconut groves. The group’s movements are coordinated by the male with a series of high-pitched cries. In the evenings, the group will always return to the forest where they seek a new sleeping tree every night to settle down with their subgroup. The group watches for predators, notably the crested serpent eagle (Spilornis deela sipora) and pythons (Python reticulatus) and any alarm will result in a short, gruff bark (4).

Females signify their fertility and willingness to mate by displaying their swollen and reddened genitals. Courtship is not elaborate since mates are usually known to each other, but females will crouch before males to initiate copulation (4). After a gestation of five to six months, a single infant is born during the night, clinging to its mother’s belly immediately. The mother eats the placenta and licks the infant clean before morning. She will retain a close bond with her daughters into adulthood and with sons until they reach sexual maturity and leave the group (6).


Mentawai macaque range

The Mentawai macaque is found only in the Mentawai islands, a chain of islands that lie 150 kilometres off the west coast of Sumatra, Indonesia. Of the four main islands of Mentawai, this species is found on North Pagai, South Pagai and Sipora (4).


Mentawai macaque habitat

The Mentawai Islands became separate from the Sumatran mainland over half a million years ago, so the tropical forests there are not as diverse as those on the mainland. The forest is characterised by extremely large buttressed trees, known as dipterocarps, as well as woody climbers and epiphytes. Smaller trees exist at the ground level but the forest floor is sparsely vegetated. The Mentawai macaque forages in the canopy layer, between 24 and 36 metres above the ground. It moves up to the tallest trees to sleep, some reaching 45 metres (5). It is accustomed to high levels of rainfall and is also found in riverine and coastal swamp forests (4).


Mentawai macaque status

The Mentawai macaque is classified as Critically Endangered (CR) on the IUCN Red List (1) and is listed on Appendix II of CITES (3).

IUCN Red List species status – Critically Endangered


Mentawai macaque threats

The forests of the Mentawai Islands survived intact far longer than the forests of the Sumatran mainland, but a recent migration of mainland Indonesians to the islands has resulted in large tracts of land being cleared for cash crops and oil palm plantations (5). Not only does this logging result in a reduced area for the macaques to live, but it also destabilises the local ecosystem, causing water levels in the forest rivers to fluctuate much more extensively than in the past. The alternating flooding and very low water levels has also caused an increase in malarial mosquitoes (7).

With logging also comes the creation of new roads and tracks, which opens up previously remote areas to hunters. The Mentawai macaque is hunted as it is considered a crop pest, and also for the pet trade. A move from traditional hunting weapons such as bows and arrows, towards modern-day rifles has resulted in an increase in hunting pressure on this highly threatened monkey (1).


Mentawai macaque conservation

The Mentawai Islands are of high conservation significance as they are home to an unusually high number of endemic species and subspecies (8) and are part of the Sundaland Biodiversity Hotspot (7). Although 18 percent of the Mentawai Islands lies within three major protected areas (5), unfortunately the Mentawai macaque is not found in any protected area (1).

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

Find out more

To learn about conservation efforts on Siberut, one of the Mentawai Islands, see:



Authenticated (22/05/06) by Matt Richardson, independent primatologist and writer.



A family of resinous trees that are found in the old world tropics.
A species or taxonomic group that is only found in one particular country or geographic area.
A plant that uses another plant, typically a tree, for its physical support, but which does not draw nourishment from it.
A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.


  1. IUCN Red List (April, 2006)
  2. Richardson, M. (2006) Pers. comm.
  3. CITES (April, 2006)
  4. The Primata (April, 2006)
  5. WWF WildWorld Report (April, 2006)
  6. Macdonald, D. (2001) The New Encyclopedia of Mammals. Oxford University Press, Oxford.
  7. Siberut Conservation Project (April, 2006)
  8. Roos, C., Ziegler, T., Hodges, J.K., Zischler, H. and Abegg, C. (2003) Molecular biology of Mentawai macaques: taxonomic and biogeographic implications. Molecular Phylogenetic Evolution, 29(1): 139 - 150.

Image credit

Mentawai macaque  
Mentawai macaque

© Daniel Heuclin /

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