Delacour's Langur The Delacour's langur is a critically endangered species of lutung endemic to northern Vietnam. They inhabit open forest up to elevations of 328 m in terrain dominated by limestone karst and are folivorous, with about 78% of their diet consisting of foliage, although they also eat fruit, seeds, and flowers. Their fur is predominantly black, with white markings on the face and distinctive creamy-white fur over the rump and the outer thighs, while females also have a patch of pale fur in the pubic area. Like other closely related lutungs, they also have a crest of long, upright, hair over the forehead and crown. They typically measure from 57 to 62 cm in length, with a tail 82 to 88 mm long. Males weigh between 7.5 and 10.5 kg while the females are slightly smaller, weighing between 6.2 and 9.2 kg. They are diurnal, often spending the day sleeping in limestone caves, although they sleep on bare rocky surfaces if no caves are available. Despite living in forested habitats, Delacour's langurs are primarily terrestrial, only occasionally venturing into the trees. They swing by their hands when travelling through trees, and use their tails for balance when scrambling over steep rocky terrain. They live in troops of up to 30 individuals, often including a mix of males and females, although in more recent years, the typical group size seems to be much smaller, with only about 4 to 16 members each. Males defend the troop's territory from outsiders by 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, and only resort to chasing and fighting if this fails. Within the group, social bonds are maintained by grooming and play. Females give birth to a single young after a gestation period of 170 to 200 days. The young are born orange, with open eyes and strong arms. The fur begins to turn black at around four months, and the young are probably weaned at 19 to 21 months, when the mother is likely ready to breed again. Females reach sexual maturity at four years, and males at five years; the total life expectancy is around 20 years. Considered to be one of the world's most endangered primate species, they have declined in population rapidly in recent years. As of 2006, only 19 populations were known, following a dramatic decline in the total population of approximately 20% between 1999 and 2004. Since that time, we have lost two of those populations, and only those in the Van Long Nature Reserve may have enough members to remain viable. As of 2010, less than 250 animals were believed to remain in the wild, with nineteen in captivity. Classified as critically endangered by the IUCN, the primary threat to the species is hunting for traditional medicine, and loss of forest habitat through logging, unsustainable agricultural practices, and local development that is meant to serve the tourist trade.