BLACK-CRESTED SUMATRAN LANGUR
Geographic Distribution and Habitat
Black-crested Sumatran langurs (Presbytis melalophos), also called mitered leaf monkeys, yellow-handed mitered langurs, or Sumatran surilis, are tree-dwelling primates from southwestern Sumatra—Indonesia’s largest island. They can also be found on Pulau Pini, a small island in the Batu Archipelago off the northwestern coast of Sumatra.
These monkeys are found in tropical and subtropical primary and secondary forests, rubber plantations, bush areas, and lowlands. They use all levels of the forest canopy and travel between 984–4,461 feet (300–1,360 m) a day.
The first taxonomic classification for the black-crested Sumatran langur, Presbytis melalophos, was in 1821. For many years thereafter, they were commonly referred to as “mitred leaf monkeys” or “mitered leaf monkeys.”
Until around 2015, the species was classified as having several subspecies including the black and white langur (Presbytis melalophos bicolor), the mitered langur (Presbytis melalophos mitrata), and the black Sumatran langur (Presbytis melalophos sumatranus).
Because of differences in color variants, geographic locations, and DNA analysis, scientists have reclassified them each as unique species, now called the bicolored langur (Presbytis bicolor), the southern mitered langur (Presbytis mitrata), and the black Sumatran langur (Presbytis sumatranus).
Size, Weight, and Lifespan
Black-crested Sumatran langurs have slender bodies, long limbs, and even longer tails. Their head-to-body length averages between 16.5–23 inches (42–59 cm), and their tails grow anywhere from 21–32 inches (53–81 cm).
Like many other primates, males typically weigh more than females. Average weights are between 13 and 16 pounds (5.8–7.4 kg).
There have been reports of wild black-crested Sumatran langurs living 20 years in captivity. However, their average lifespan in the wild is 16 years. The shorter wild lifespan is due to many threats, such as habitat loss and hunting.
The black-crested Sumatran langur’s distinctive appearance is defined by bare rings around their eyes (like “bags” under our eyes), poorly developed brow ridges, prominent nasal bones, pale lips, and a tufted crest of hair on the crown of their head (hence their name).
Newborn black-crested Sumatran langurs have white fur coats with a dark stripe extending down their back, tail, and shoulders, forming a cross-shaped pattern. As they mature, their fur coats become brownish-red, pale orange, or blackish-gray and white, with lighter coloring on the stomach, chest, and limbs. Their brow is typically red, orange, or white and their faces are light to dark gray.
Black-crested Sumatran langurs have wizened facial features, and their very distinct look is often compared to that of an old woman—so much so that the species’ scientific name (presbytis) comes from the Greek word for “old woman.” Similarly, as found in their alternate common names, a “mitre” is the word for a headband worn by women in ancient Greece.
Black-crested Sumatran langurs are folivorous (leaf-eaters). Because of their green diet, langurs have a specialized stomach that helps them digest tough leaves and other plant materials.
They enjoy a variety of over 197 tree species and 55 different plants, plus fruits and seeds when available. Some of their favorite foods include brown-woolly figs, common figs, jackfruit, red cedar, and chaste trees.
In protected areas, including the Bukit Sebelah Protection Forest, they are more strictly folivorous, choosing to eat leaves more often than other options.
Behavior and Lifestyle
Black-crested Sumatran langurs live in tropical and subtropical dry forests in groups of 12 to 18. As diurnal and arboreal monkeys, they primarily spend their daily activities in the trees. They use their long limbs and slender bodies to swiftly leap and brachiate (swing) throughout the forest canopy. Their hands are slim and long and they have strong fingers and opposable thumbs to help them grip tree branches. On the forest floor, they can walk and run on all fours (quadrupedally).
A black-crested Sumatran langur’s day is spent resting, foraging, and eating. They also make time for group socialization to reinforce social bonds.
Home ranges average between 45 and 98 feet (14–30 m). They don’t stray too far from home, with average daily travels between 984 and 4,461 feet (300–1,360 m). While foraging, they have to be on alert for predators like snakes and birds of prey.
Black-crested Sumatran langurs live in groups of 12 to 18 individuals, including a single adult male and a harem of females. Some groups may also include several lower-ranking males who are responsible for detecting threats. Adult males may sometimes live alone or form temporary all-male groups.
Like other langurs, black-crested Sumatran langurs are territorial. They signal their territories to other monkeys with loud, distinct vocalizations. The smaller their home range, the more aggressive they’ll become when defending their territory. Males are typically the defenders and aggressors as females are typically not involved in group conflicts and display little dominance.
Black-crested Sumatran langurs communicate through vocalizations, body language, grooming, and physical aggression. One of the ways they are distinguished from similar species is their “monophasic call,” which has a single phrase that is delivered at a fast rate and at a low frequency.
A troop’s males, who are in charge of detecting potential threats to the group, jump and make distinct alarm calls to mark the group’s territory. When predators, like birds of prey or snakes, are near, they will emit loud cries and leap about to chase the predator away from the group. At night, males in neighboring groups serenade the forest by singing together in a chorus.
Little is known about the black-crested Sumatran langur’s reproduction habits. We do know that they are polygynous, which means that males mate with more than one female at a time.
We also know that females give birth to one baby at a time, with gestation lasting between 155 to 226 days (5–7 months). Twins are rare but have been recorded. Allomothering, the practice of group childcare, is rare. It is unclear how much of a role males play in child care.
Looking at similar species, we can possibly glean insights into the black-crested Sumatran langur. With the maroon leaf monkey (Presbytis rubicunda), for example, females reach sexual maturity between the ages of 3 and 4 and males at age 4. Infants nurse from their mothers for the first year and stay close by for at least two years.
Black-crested Sumatran langurs are vital to the health of their ecosystems. Because of their leaf-heavy diet, they prune the forest trees and bushes, which helps rejuvenate new plant growth. And since their diet also includes fruits and seeds, their feces help replenish their environment.
These monkeys are also a source of food for predators like snakes and birds of prey.
The black-crested Sumatran langurs is listed as Endangered by the International Union of Conservation of Nature (IUCN, 2015), appearing on the IUCN Red List of Threatened Species.
The exact population of this species is unknown. Although black-crested Sumatran langurs are somewhat adaptable to forest conversions, they face significant threats to their habitats. Forest loss in the area has exceeded 70% in the last 30 years, and their population has declined by another 50% in three generations (36 years).
Indonesia is the world’s largest supplier and consumer of palm oil, and the black-crested Sumatran langur’s habitats are threatened by the conversion of forestland into palm oil plantations. This has led to a significant decrease in the monkeys’ population. They are also trapped for the illegal pet trade and hunted for meat.
Black-crested Sumatran langurs are listed in Appendix II of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival.
Black-crested Sumatran langurs are protected by Indonesian national law. They also inhabit five protected areas: Berbak National Park, Bukit Barisan National Park, Bukit Sebelah Protection Forest, Kerinci-Seblat National Park, and Way Kambas National Park.
With the rampant forest destruction throughout Sumatra, black-crested Sumatran langurs and other animal species need further protections to conserve their habitats and save their populations.
Written by Maria DiCesare, June 2023