Delacour's Lutung

Delacour's langur is endemic to Vietnam, where it is found only in an area around 6,000 km2 (2,300 sq mi) in the capital Hanoi and provinces of Ninh Bình, Hà Nam, Hòa Bình, Thanh Hóa in the north of the country. The largest surviving population is thought to live in Van Long Nature Reserve in Ninh Bình, where the it inhabits open forest up to elevations of 328 m (1,076 ft) in terrain dominated by limestone karst.

Delacour's langurs are diurnal, spending daylight hours exploring their home range and often sleeping on open rock surfaces or in limestone caves at night. They are folivorous, with about 78% of the diet reportedly consisting of foliage, although they also eat fruit, seeds, and flowers. The monkeys have been reported to eat leaves from a wide range of different plant species, indicating that their apparent dependence on limestone habitats is not related to their diet. In previous decades, Delacour's langurs were reported to live in troops of up to 30 individuals, often including a mix of males and females, although single-male groups are more common, and some small all-male groups have also been reported. In more recent years, the typical group size seems to be much smaller, with only about four to 16 members each. Males defend the troop's territory from outsiders, often standing watch on rocky outcrops. When potential rivals are spotted, the males in a troop initially try to intimidate them with loud hoots and visual displays, resorting to chasing and fighting if this fails. Within the group, social bonds are maintained by grooming and play. Despite living in forested habitats, Delacour's langurs are primarily terrestrial, only occasionally venturing into the trees. …