Black Sumatran Langur, Presbytis sumatrana
BLACK SUMATRAN LANGUR
Presbytis sumatrana
Geographic Distribution and Habitat
The black Sumatran langur is native to western and north-central Sumatra, an island in western Indonesia. There, they can be found in lowland and hill rainforests, old-growth forests, and secondary forests. Old-growth forests, also known as primary forests, are those that have developed over a long period of time without human disturbance, while secondary forests are those that have re-grown after a period of human-caused disturbance.
The black Sumatram langur was once considered a subspecies of the black-crested Sumatran langur (P. melalophos). Genetic analysis eventually confirmed the two are separate species.
Size, Weight, and Lifespan
The head-body length of male black Sumatran langurs ranges between 13-13.8 inches (33-35 cm), while that of females ranges between 13.4-15.4 inches (34-39 cm). The LOOOOONG tail ranges in length between 25.2-28.4 inches for males, and 26-33.1 inches (66-84 cm) for females. Males weigh between 10.8-15.9 pounds (4.9-7.2 kg), while females weigh between 11.2-18.7 pounds (5.1-8.5 kg). These differences in size and weight are examples of sexual dimorphism or noticeable physical differences between genders.
Their lifespan in the wild is not known, but that of the black-crested Sumatran langur is an average of 16 years.
Appearance
Much of the body of the black Sumatran langur is dark gray-brown to nearly black. This includes the backside of the tail. The hands, feet, and backside of the limbs are black in color. Contrasting all of this darkness, are the throat and stomach regions, underside of the tail, and inner portions of the limbs as far as the wrists and ankles, which are all white. The top of the head sports a gray to dark brown fluffy crest, while the facial skin is gray-blue in color. Finally, the skin around the mouth is flesh-colored, while the lips contrast with a black coloration. All of these, combined with their dark-colored eyes make them a sleek, fluffy, and gorgeous monkey.
Like that of other langur species, the tail is non-prehensile, meaning it is not used for grabbing or grasping. Rather, the tail aids in balancing while navigating through the branches of the trees.
Diet
The diet of the black Sumatran langur is not well known, but like other langurs, it is likely composed largely of young leaves, unripe fruits, flowers, mature leaves, and seeds.
Behavior and Lifestyle
The black Sumatran langur has never been studied in the wild, so very little information about their behavior, lifestyle, and other characteristics remains unknown. Much information has to be inferred based on what we know of closely related species, such as the black-crested Sumatran langur.
What is known is that the black Sumatran langur is diurnal, or most active during daylight hours, and arboreal, preferring to spend that time in the trees. Their limbs are long, which aids in their preferred methods of locomotion: hopping and brachiation. Brachiation is acrobatically swinging from tree to tree.
Looking at the sleeping habits of other members of the genus Presbytis, such as the Javan surili (P. comata), and maroon leaf monkey (P. rubicunda), it’s likely that the black Sumatran langur does not construct sleeping nests, and instead, sleeps within the branches of trees.
Predators of the black Sumatran langur likely include snakes and birds of prey, and maybe even the Sumatran clouded leopard. Predator avoidance strategies are not known, but other members of their genus have been observed emitting loud calls and leaping around to chase the predator away from the group.
Distinguished and cute: The black Sumatran langur has a short nose and poorly-developed eyebrow ridges and can be distinguished from other members of their genus by narrow infraorbitals (the area below the eye socket) and long nostrils.
Once again, due to the lack of studies regarding the black Sumatran langur, little is known regarding their daily life and group dynamics and must be inferred from other closely related species.
What is known is that they live in one male multi-female groups consisting of a single male and five to seven adult females, and their immature offspring.
If we look at the black-crested Sumatran langur, their days are spent resting, foraging, and eating. They also make time for group socialization in order 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). Like other langurs, black Sumatran langurs are likely territorial. Looking once again at the black-crested Sumatran langur, they signal their territories to other monkeys with loud, distinct vocalizations. The smaller their home range, the more aggressive they 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.
Information regarding communication among the black Sumatram langur is lacking, and once again, must be inferred from other closely related species.
Black-crested Sumatran langurs communicate through vocalizations, body language, grooming, and physical aggression. A group’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 are nearby, 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. That must be quite the choir to hear at night!
If we also look at the maroon leaf monkey, they use grunts and calls to express emotions to other members of the group or warn them of danger. Males will use a booming call to warn other members of the group of danger or intimidate rival groups. These calls can be heard several hundred feet away (over 100 m). These calls are usually a short series of “ka-ka-ka” sounds and, depending on vocal inflection, they can mean different things. Their vocalizations are a testament to their lineage, as many members of the genus Presbytis sound incredibly similar.
The maroon leaf monkey’s tail is an important communication tool as well. Depending on the movement and positioning of the tail, they can convey all sorts of emotions, including excitement, annoyance, alarm, fear, and aggression.
The role of allogrooming is vital in many primate groups, and maroon leaf monkeys are no exception to this. This method of grooming one another is an important form of communication within the group, conveying friendship or alliance, or strengthening familial ties. The absence of grooming can indicate tension between individuals. It is also important for their health, as grooming helps to remove parasites.
Unsurprisingly, due to the lack of studies on the species, information on the reproduction and family habits of the black Sumatran langur is unknown and needs to be inferred from information on other species.
If we look at the black-crested Sumatran langur, they are polygynous, which means that males mate with more than one female at a time. 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 among black-crested Sumatran langurs, and allomothering, the practice of group childcare, is rare. It is unclear how much of a role males play in child care.
Looking once more at the maroon leaf monkey, females reach sexual maturity between the ages of three and four years, and males at age four. Infants nurse from their mothers for the first year and stay close by for at least two years.
As a portion of their diet likely consists of fruit and seeds, the black Sumatran langur aids in the regeneration of the forest habitat by dispersing seeds through their feces as they travel. They additionally may play a role in pollination. Like bees and butterflies, they collect pollen from flowers while consuming them. They then deposit the pollen on each flower they visit, thereby pollinating the plants. Finally, as a prey species, they also play a role in feeding local predators within their habitat.
The International Union for Conservation of Nature lists the black Sumatran langur as Endangered (IUCN, 2015), appearing on the IUCN Red List of Threatened Species.
The main threats to the black Sumatran langur are the illegal pet trade, and extensive degradation in their habitat range. More than 50% of their forest habitat has been lost over the past 30 years.
The black Sumatran langur is 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.
The black Sumatran langur is found within the protected Batang Gadis National Park.
Conservation actions needed include: properly enforced land, water, site, and area protection and management; a proper species management and recovery plan; and increased education, communications, and awareness among locals regarding the black Sumatran langur and the dangers they face.
Since the black Sumatran langur has never been studied in the wild, undoubtedly, basic biological research on the species as a whole is needed. Research on their: population size, distribution and trends, life history and ecology, harvest, use and livelihoods, and threats are critically needed. Additional research on a species/action recovery plan, an area-based management plan, and finally, monitoring of habitat and black Sumatran langur population trends are all needed should this little-studied langur stand a chance against the eventual plight towards extinction.
- https://www.bioexplorer.net/animals/mammals/monkeys/black-sumatran-langur/
- https://www.borneonaturefoundation.org/wp-content/uploads/2016/02/Ehlers-Smith-15-Ecology-and-Conservation-P.-rubicunda-Sab-PhD.pdf
- https://www.ecologyasia.com/verts/mammals/black-sumatran-langur.htm
- https://en.wikipedia.org/wiki/Black_Sumatran_langur
- https://factsanddetails.com/indonesia/Nature_Science_Animals/sub6_8d/entry-9115.html
- https://www.iucnredlist.org/species/136912/17986913
Written by Sienna Weinstein, February 2025