Pig-tailed langur

The pig-tailed langur (Simias concolor), monotypic in genus Simias, is a large Old World monkey, endemic to several small islands off the coast of Sumatra in Indonesia. Its face is black, its fur is black-brown and it has a relatively short tail. It is a diurnal species, feeding in the rainforest canopy on leaves, and to a lesser extent, fruit and berries. Little is known of its natural history, but it is heavily hunted, its populations have been declining rapidly and the International Union for Conservation of Nature has assessed its conservation status as being "critically endangered". It has been included on a list of the World's 25 Most Endangered Primates.

As an arboreal primate the pig-tailed langur spends most of its time in the canopy devoting the majority of its activity budget towards resting and feeding. The structure of groups is single-male, multi-female. Group sizes range from around 3 to 9 individuals depending on locations and hunting pressures. There are two subspecies of this primate, Simias concolor concolor which lives in the southern Mentawai islands, and Simias concolor siberu which lives exclusively in the northern island of Siberut. Sexual dimorphism and sexual swelling is exhibited by this species.

Population estimates from the 1980s compared to data from the 2000s show a decrease in population size. The northern island of Siberut shows a greater abundance of this species in comparison to the southern Mentawai islands. This can largely be attributed to the difference in conservation efforts as much of northern Siberut has been declared a national park whereas the southern islands have historically been devastated by commercial logging. This species is subject to hunting by local inhabitants. The reduction in forest cover has allowed for greater levels of human activity and settlement which facilitates hunting, especially in the southern islands where most areas are unprotected.

The pig-tailed langur is a large and rather heavily built Old World monkey, adapted to climbing with its long arms. Its fur is black-brown, and its hairless face is also black. It is the only monkey in the subfamily Colobinae to have a relatively short tail; the tail is only slightly furred and is only 15 cm (5.9 in) long. The short nose is pointed upward. The pig-tailed langur reaches a full grown length of approximately 50 cm (20 in) and a weight of 7 kg (15 lb).

Sexual dimorphism is exhibited by this species with adult males being larger and heavier than adult females. Sexual swelling is exhibited by this species which is rare for single male multi female groups of Colobinae monkeys.

Many researchers would like to reclassify this species into the Nasalis genus but phylogenic analyses suggest that these two groups should remain in their separate sister taxa. The Critically Endangered status of this primate gives even more reason for it to remain under the genus Simias since the grouping of these genera could affect conservation efforts.

It is an omnivore with a diet consisting of leaves, flowers, fruits and occasionally insects. The availability of these foods in this area are abundant especially in unripe and ripe fruits. Leaves are the most abundant in their diet followed by fruits.  As with all other Colobinae primates, this species is diurnal.

This primate is endemic to the Mentawai Islands, there are two subspecies, Simias concolor concolor also known as simasepsep which resides on the southern islands of Sipora, North Pagai, and South Pagai. The second subspecies is Simias concolor siberut also known as simakobou which lives only on the island of Siberut. It is a diurnal and arboreal rain forest dweller, often spending most of its time in the canopy but occasionally comes to ground. The activity budget of this primate is mostly resting and feeding with a small fraction of time devoted towards travel and social behavior. Some studies in the Siberut area show relatively low group sizes (mean group size 2.6). Other parts in Siberut show relatively high group sizes (mean group size 8.7). The reason for different group sizes is not factually known, however many researchers suggest that it could be due to anthropogenic factors such as hunting and deforestation. The pig-tailed langur has single-male, multi-female groups. The mating system of this species follows a polygynous structure although it was originally thought to be monogamous.