The Dusky leaf monkey is a lovely little primate with a unique appearance. The overall coloration of its fur is dark gray, though brownish fur may occur in certain subspecies. The animal exhibits large, white colored patches, surrounding its eyes and looking like sporting eyeglasses. Additionally, the monkey has a white colored circle around its mouth. This color pattern is supplemented by a light head crown and a creamy white stomach patch. The Dusky leaf monkeys are known to live up to 25 years in captivity. There is no information on the life expectancy of this species in the wild, although it's believed to be less than that of captive individuals.
Dusky leaf monkeys are distributed across the Malay Peninsula, where they are known to occur in southern Myanmar and some parts of Thailand. The natural range of these primates also includes the islands of Langkawi, Penang, and Perhentian Besar. They are arboreal animals. Within their range, Dusky leaf monkeys can be found in various habitats, generally preferring dense forests with an abundance of tall trees.
Dusky leaf monkeys are social animals, travelling in groups of 5 - 20 individuals, typically consisting of one or more mature males as well as two or more mature females. Mature males of these groups spend their time keeping watch for potential predators, holding the group united and patrolling the home range of the community. As diurnal animals, these monkeys are active during the daytime hours. During most of their active, the primates remain in the tree canopy, at heights of over 35 meters. When travelling between trees, they climb, leap and walk along tree branches, using all of their four legs. With the arrival of the night, dusky leaf monkeys move to their roosts, located in the trees. The communication system of dusky leaf monkeys includes a complex system of vocalizations. The most commonly used calls are snorts, hoots, murmurs and squeaks, through which group members associate with each other.
Dusky leaf monkeys are herbivores (folivores), they generally feed upon young leaves, fruits, shoots and seedlings. Those in captivity supplement this diet by sweet potato shoots, lettuce, cabbage, kangkong, green beans, maize, carrots, soft fruits as well as occasional insects.
Dusky leaf monkeys have a polygynous mating system. Males compete for their mating rights. As a general rule, the largest, strongest and most aggressive male will breed with the females. Breeding occurs periodically during the year. Gestation period is about 145 days, yielding a single young. Females produce offspring at intervals of 2 years, typically in January-March, although some may give birth in the summer months. During the first 20 days after birth, the infant is almost constantly with its mother. At around 1 year old, the baby begins climbing, venturing away from its mother and taking solid food. Individuals of both sexes reach sexual maturity at 3 - 4 years old.
Dusky leaf monkeys are currently hunted for their meat throughout their range. These animals also suffer from loss and degradation of their natural range because of urbanization, agriculture as well expansion of oil palm plantations. Additionally, population in Peninsular Malaysia is threatened by a high level of road-kill.
The IUCN Red List and other sources don’t provide the number of the Dusky leaf monkeys’ total population. This species’ numbers today are decreasing today, and the animals are classified as Near Threatened (NT) on the IUCN Red List.
Dusky leaf monkeys benefit the local ecosystem by their leaf-based diet, due to which these primates act as key seed dispersers of their range. Furthermore, they are, in turn, an important prey species for many predators of the area.