Surili

The surilis are a group of Old World monkeys and make up the entirety of the genus Presbytis. They live in the Thai-Malay Peninsula, on Sumatra, Borneo, Java and smaller nearby islands. Besides surili, the common names for the monkeys in the genus also sometimes use the terms "langur" or "leaf monkey."

Surilis are rather small, slimly built primates. Their fur at the top is brown, grey, black, or orange, and at the lower surface whitish or greyish, sometimes also orange, with some species having fur designs at the head or at the hips. Their German name of Mützenlanguren ("capped langurs") comes from the hair on their head, which forms a tuft. They differ from the other langurs by characteristics in the shape of their head (particularly the poorly developed or absent brow ridges, and the prominent nasal bones), in the teeth, and by the size of their small thumbs. Surilis range in adult length from 40 to 60 cm (with a 50- to 85-cm-long tail) and a weight of 5 to 8 kg.

Diurnal forest dwellers, they spend nearly their entire lives in the trees. They live in groups of up to 21 animals (typically 10 or fewer animals in most species) consisting of a male, several females, and their young. A few species have been observed in monogamous pairings (particularly the Mentawai langur), although this might be a reaction to the decrease of their habitat. Lone males and all-male groups have also been reported. The groups are hierarchically developed, with intergroup communication that is both vocal and postural.

The surilis' diet consists of leaves, fruits, and seeds.

Gestation time is 5–6 months, and births are typically of single young. Newborn animals are white colored and have a black strip at the back, although some have a cross-shaped mark. By one year old, the young are weaned and at an age of 4–5 years, they are fully mature. The typical life expectancy in the wild remains poorly known for most species, but captive Sumatran surilis have lived more than 18 years.

Several species in this genus are restricted to regions with extensive habitat destruction, and are also threatened by hunting. Consequently, eight of the 11 species are rated as vulnerable or worse by IUCN, and the Sarawak surili has been referred to as "one of the rarest primates in the world." Recently, a subspecies of Hose's langur called Miller's grizzled langur, thought to be extinct, was rediscovered in the Wehea Forest on the eastern tip of Borneo island, though it remains one of the world's most endangered primates.