Hose’s Langur

Presbytis hosei, commonly known as Hose’s langur or Hose’s leaf monkey, is a small arboreal primate belonging to the family Cercopithecidae. Endemic to the island of Borneo, its range is confined to the lowland and hill forests of Sabah and Sarawak in Malaysia and the adjacent provinces of Kalimantan, Indonesia. The species inhabits primary dipterocarp forest, secondary growth, and forest edges up to 1,200 m elevation, preferring dense canopy layers where its slender limbs and long tail aid agile movement. Adults display a grey‑brown dorsal pelage with a distinctive white cheek stripe and a blackish face; the ventral side is lighter, and the tail is longer than the body, often exceeding 60 cm. Hose’s langur is diurnal and primarily folivorous, feeding on young leaves, shoots, and occasional fruits. The International Union for Conservation of Nature (IUCN) classifies the species as Vulnerable, reflecting a declining population estimated at fewer than 10,000 mature individuals. Habitat loss from logging, conversion to oil‑palm plantations, and hunting for meat and the pet trade are the principal threats. Conservation actions include protected‑area designation, forest‑restoration projects, and community‑based monitoring, but continued habitat fragmentation threatens the long‑term viability of remaining populations.

Hose’s langur lives in small, multimale–multifemale troops typically comprising 5–15 individuals, though larger aggregations are observed at abundant feeding sites. The groups maintain a loose home range of 5–15 km², defended through scent marking and occasional vocal displays. Activity peaks in the early morning and late afternoon; the monkeys spend most of the day foraging in the upper canopy, descending only briefly to move between trees. Social bonds are reinforced by grooming, which accounts for up to 20 % of daily activity. Communication includes a repertoire of soft whistles, alarm calls, and loud barks used to signal predator presence. Territorial boundaries are fluid, and neighboring groups may tolerate overlap, especially where food resources are plentiful.

The diet of Hose’s langur is dominated by young leaves and leaf buds, classifying it as a strict folivore. Preferred plant families include Dipterocarpaceae, Myrtaceae, and Rubiaceae, with a particular affinity for the tender shoots of Shorea and Garcinia species. Fruits and seeds are consumed opportunistically, especially during periods of leaf scarcity, and occasional insects supplement protein intake. Individuals can ingest up to 30 % of their body weight in foliage daily, selecting leaves with high nitrogen and low tannin content. Specialized stomach chambers host symbiotic microbes that ferment cellulose, enabling efficient extraction of nutrients from fibrous material. Feeding typically occurs in the upper canopy, where the monkeys move silently between branches, minimizing competition with ground‑dwelling herbivores.

Hose’s langur reaches sexual maturity at about 3 years for females and 4 years for males. Breeding occurs year‑round, with a slight peak during the rainy season when food is abundant. Gestation lasts approximately 165 days, after which a single infant is born, weighing around 300 g. Newborns cling to the mother’s belly for the first 2–3 weeks before transitioning to dorsal riding. Maternal care is intensive; the mother nurses the infant for 5–6 months and continues to carry it for up to a year. Juveniles achieve independence at 2–3 years but often remain within the natal group as subordinate members. Interbirth intervals average 18–24 months, reflecting the species’ relatively slow reproductive rate.

The IUCN lists Hose’s langur as Vulnerable, with the population estimated at fewer than 10,000 mature individuals and declining at an estimated rate of 20 % over the past three generations. Primary threats are habitat loss and fragmentation driven by commercial logging, conversion of forest to oil‑palm and rubber plantations, and infrastructure development. Hunting for bushmeat and the illegal pet trade add direct mortality pressure, especially in remote villages. Small, isolated subpopulations suffer from reduced genetic diversity, increasing susceptibility to disease. Conservation measures include the establishment of protected areas such as Kinabalu Park and Danum Valley, enforcement of anti‑logging regulations, and community outreach programs that promote sustainable livelihoods. Ongoing population monitoring and habitat corridors are essential to mitigate fragmentation.

• Hose’s langur has a specialized stomach that ferments cellulose, similar to ruminants.
• It prefers young leaves that contain higher protein and lower toxins than mature foliage.
• The species is named after the Dutch naturalist G. J. P. J. van der Hoeve, who collected the type specimen.
• Unlike many primates, Hose’s langur rarely descends to the forest floor, spending >90% of its time in the canopy.
• Its vocal repertoire includes a unique “purring” call used during close social interactions.