Geographic Distribution and Habitat
The Hose’s langur (Presbytis hosei) is a small primate endemic to subtropical and tropical dry forests in Borneo, the third-largest island in the world. The island is divided among three countries: Brunei, Indonesia, and Malaysia. Hose’s langurs are found in the biodiverse forests of Brunei, Sarawak and Saba (Malaysia), and Kalimantan (Indonesia).
Also known as Hose’s leaf monkeys, gray leaf monkeys, and Hose’s surilis, they spend the majority of their time in the middle of the forest canopy.
Size, Weight, and Lifespan
Hose’s langurs are small and slim primates. For both males and females, average body length can range from 18.8 to 22 inches (48.0–55.7 cm) and tails can be up to 33 inches (84 cm) long. Males are larger than females, averaging 13.6 pounds (6,200 g) to the females’ 12.2 pounds (5570 g).
Lifespan data for the Hose’s langurs is not available, but the similar maroon langurs (Presbytis rubicunda) can live up to 20 years in the wild and over 25 years in captivity.
The small and slim Hose’s langur has a pink face with black markings, similar to how a human wearing a charcoal colored facemask might look. Their faces are framed by white, gray, or black hair. Coat colors are typically light to dark gray on the back with a white stomach and chest. Their hands and feet are black. Newborns and infants stand out with a white coat and black lines on their shoulders and back.
Hose’s langurs are primarily folivorous, with foliage making up at least 65% of their diet. They have a specialized multi-chambered sacculated stomach and enlarged salivary glands to help break down the hard-to-digest leaves.
Seeds, fruits, and flowers make up the rest of their diet. But these langurs are also dietary opportunists, and will feed on bird’s eggs when given the chance.
Behavior and Lifestyle
Hose’s langurs are diurnal and arboreal. They spend their days traveling through the trees quadrupedally, using all four limbs. The species is very territorial, especially the males who emit loud calls to warn other groups and animals to stay away.
Hose’s langurs sometimes form coalitions with maroon leaf monkeys.
Although primarily folivorous, Hose’s langurs will feed on bird’s eggs when given the chance.
Groups of Hose’s langurs typically consist of six to eight monkeys, but groups can include 12 or more. Groups are polygynous and are made up of one adult male, two or more adult females, and their offspring. Solitary individuals have also been reported, but are not as common.
Around the age of adolescence, typically three or four years old, males leave home to form their own group or take over an existing group.
Like their relatives the maroon leaf monkeys, Hose’s langurs help with habitat regeneration by way of seed dispersal throughout the forests.
The International Union for Conservation of Nature lists the Hose’s langur as Vulnerable (IUCN, 2015), appearing on the IUCN Red List of Threatened Species.
Hose’s langurs are threatened by hunting and habitat loss. They are facing habitat loss due to the development of human settlements, plantations for wood pulp and palm oil, and development of oil fields. In the areas where the Hose’s langur is not threatened by deforestation, they are heavily hunted.
Inland residents hunt Hose’s langurs for meat and bezoar stones, which are mineral deposits found in their digestive tracts. The stones are only found in certain species of monkeys, so they are rare and expensive. People buy the stones to use as good luck charms or as an agent to neutralize certain poisons.
Hose’s langurs are found in protected areas including Kutai National Park and Kayan Mentarang National Park in eastern parts of Borneo (Kalimantan). However, protections are insufficient and not strongly enforced.
The parks are severely degrading due to industrial developments, illegal settling, logging, and fires. Only 5% of Kutai National Park forest has survived. In Kayan Mentarang National Park, unenforced laws are failing to prevent Hose’s langurs from being hunted. Hose’s langurs need stronger—and enforced—protections in order to survive as a species.
Written by Maria DiCesare, October 2022