Pagai Island Macaque, Macaca pagensis

The Pagai Island Macaque (Macaca pagensis), known also as the Pagai Macaque or Bokkoi, is an Old World monkey that is native to the Mentawai Islands off of the west coast of Sumatra. It is classified as Critically Endangered under the IUCN Red List because of its ever-shrinking habitat. It previously included the overall darker M. siberu as a subspecies, but this agreement is polyphyletic, leading to the two being classified as a separate species. Both were previously thought to be subspecies of M. nemestrina.

Pagai Island macaque males are usually larger than the females. The males’ body lengths range from 45 to 55 centimeters and females’ body lengths are around 40 to 45 centimeters. The tails are 13 to 16 centimeters long in the males and 10 to 13 centimeters for the females. The males are also heavier, weighing roughly 6 to 9 kilograms while the females weigh only 4.5 to 6 kilograms. Their backs feature a dark brown color, and chestnut to pale ochre on the sides of the neck, the front of the shoulders, and the undersides of this species. The legs are brown and the arms a reddish brown. The faces have no fur and are black-skinned with brown colored eyes. They feature cheek pouches to carry food while they are foraging.

Their natural habitat is rainforest, but they can also be found in riverine and coastal swamp-forests. They reside high above the forest floor in the canopy, foraging between 24 and 36 meters and might sleep as high as 45 meters. The primary food of this species’ diet is figs. They may split into splinter groups to forage for food and to sleep. They will eat alongside groups of Mentawai langurs. M. pagensis groups are made up of around 5 to 25 individuals. Usually, a group is made up of a single male with adult females and their offspring. The male decides where to go and communicates this to the rest of the group with high-pitched cries. Roaming and solitary Pagai Island macaques might challenge the dominant male for this position, leading to aggressive fights. The natural predators of this species are the crested serpent eagle and the reticulated python. When these predators are seen, the macaques will alert the rest of the group with a short and gruff bark.

The females show fertility and willingness to mate by showing their swollen and reddened genitals. The females crouch to initiate the mating. The gestation period is between 5 and 6 months. A single offspring is born during the night. The mother eats the placenta and licks the infant clean before morning. The mother and the young share a close bond into adulthood.

Image Caption: Pagai Island Macaque (Macaca pagensis), Safari Park, Cisarua, West Java, Indonesia. Credit: Sakurai Midori/Wikipedia (CC BY 3.0)