Macaques have a reputation for being very sociable animals which often live in large groups (6). The Siberut macaque has a smaller than average group size, but can still be found in groups of around 5 to 25 individuals (9), which may include a number of adult males and females (7). Smaller subgroups are formed for foraging in the day and sleeping at night (2). The Siberut macaque can also form mixed-species groups with the Mentawai langur (Presbytis potenziani) (9).
Siberut macaques have an interesting way of maintaining positive interactions with each other, using a ‘bared teeth’ display to show their peaceful and friendly intentions. This involves opening the mouth and retracting the lips, showing the teeth (12).
The Siberut macaque primarily eats fruit (2) (7), and like the Pagai Island macaque it may potentially raid gardens and coconut groves in search of a meal (10) (11). In addition to fruit, the Siberut macaque also eats some arthropods, including termites, ants and spiders, as well as mushrooms, leaves, shoots and flowers. It has also been reported to catch and eat freshwater crabs and shrimps (2) (7).
This species forages for most of the day and sleeps in tall trees at night, sometimes within its subgroups. The groups do not generally use the same tree twice (2). The Siberut macaque is semi-terrestrial, spending much of its time on the ground (7), and if alarmed it will typically drop from the trees and flee across the forest floor (2). Groups spend a relatively large part of each day travelling in search of food (7). Once a food source is located, the Siberut macaque often eats rapidly, transferring large quantities of food to its cheek pouches to be eaten later (2).
In general, macaques breed seasonally, with mating taking place during a fairly limited period (6). In the Siberut macaque, births have been recorded between March and April, between September and October, and in January and July (7). As in other macaque species, female Siberut macaques are likely to show their receptiveness by displaying their swollen and reddened genitals to the males of the group. After a gestation period of five to six months, macaques give birth to a single infant. The infant clings to the female’s belly as soon as it is born, and develops a close relationship with its mother until adulthood or, if it is a male, until it reaches sexual maturity and leaves the group (6).
Potential predators of the Siberut macaque include eagles and large snakes (2).