Southern Mitered Langur, Presbytis mitrata
SOUTHERN MITERED LANGUR
Presbytis mitrata
Geographic Distribution and Habitat
Southern mitered langurs, also known as mitered langurs or depigmented mitered langurs, are native to Indonesia’s largest island: Sumatra. More specifically, they inhabit the southeastern regions of the island, staying east of the Barisan Range, extending from the Batang Hari River to the upper Musi River drainage, as well as further south into Lampung Province. They prefer primary and secondary lowland rainforests; lowland rainforests are characterized by areas at or near sea level, usually found in regions near the equator with warm temperatures, high humidity, and consistent rainfall—all true for Sumatra! Southern mitered langurs are very adaptable and have been known to remain in some areas despite major changes to the habitat, mostly from human interference. They can live in all levels of the forest canopy but typically favor the understory.
This langur species was originally considered a subspecies of the black-crested Sumatran surili (Presbytis melalophos), as categorized in 1821. This taxonomic umbrella also included the bicolored langur and the black Sumatran langur. However, more recently, scientists recognized the significant geographic variations, color disparities, and unique DNA profiles, and reclassified the southern mitered langurs (Presbytis mitrata) as a distinct species. The bicolored langur (Presbytis bicolor) and the black Sumatran langur (Presbytis sumatranus) also earned their status as a unique species during this time. Currently, the southern mitered langur stands as a monotypic species, meaning there are no recognized subspecies.
Size, Weight, and Lifespan
Male southern mitered langurs tend to be slightly bigger than females, in both size and weight. While female southern mitered langurs have a head-body length ranging from 16.5-22 inches (42-56 cm) and weigh around 11-17.5 pounds (5-8kg), males can reach a height of 22.5 inches (57 cm) and weigh almost 20 pounds (9kg). Their tail length surpasses their head-body length, ranging from 25-32 inches (64-82 cm) in males and 24.5-32 inches (62-82 cm) in females.
There have not been many reports of the lifespan of southern mitered langurs but a similar species, the black-crested Sumatran langur (with which they share many similarities), is known to live around 16 years in the wild. These species can typically live longer in captivity, to around 20 years, due to their protection from threats like hunting and habitat loss.
Appearance
Southern mitered langurs are striking-looking monkeys who, with their fringe of frizzy fur, almost appear to have just been struck by lightning! Showcasing a diverse array of colors across their upper body, different monkeys within the species can range from a dark chocolate brown to a lighter auburn-yellow to even a muted ashy silver. Their coat colors vary from location to location. In general, most species have a blackish overlay, as well as big, rounded black eyes. Their bellies usually range from a rich yellow-beige to more of a stark white color, with this complexion extending onto their limbs. Their tails are long and skinny with the same color fur as their bodies, and sometimes can be nearly double the length of the body! Typically black in the face, these langurs can have semi-circles of pink flesh both above and below their eyes, giving them the appearance of having puffy eyes. Their mouths typically turn downwards, making them look slightly disappointed—maybe we can turn that frown upside down if we start doing a better job protecting them and their natural habitats!
Diet
A true herbivore, the southern mitered langur’s diet consists of leaves (both young and mature), unripe fruits (often figs), flowers, and seeds. Studies suggest that all primates in the southern region of Sumatra rely on flowers during periods with low fruit abundance. These leaf-eating monkeys are outfitted with large, multichambered sacculated stomachs—similar to those of cows. This specialized stomach, with the help of essential, symbiotic gut bacteria (microflora), efficiently breaks down cellulose fibers in the surilis’ leaf-laden diet. Large salivary glands and elongated intestines lend their assistance in the overall digestive process.
Behavior and Lifestyle
Southern mitered langurs are diurnal, with a majority of their activity taking place during the daytime, and arboreal, primarily living in trees. Though there is no information about the group size preferences for this species specifically, other langurs in Sumatra are known to have group sizes of 12 to 18.
With lanky, athletic bodies and strong fingers, southern mitered langurs leap gracefully from branch to branch via an arm-swinging method called brachiation. Their thumbs are shortened and their fingers are long and curved to facilitate this specialized mode of travel. Their opposable big toes assist with gripping while sitting, walking, or clinging to branches. When they aren’t swinging through the forest canopy, they walk or run on all fours.
Not overly averse to human interference and infrastructure, some of these langurs have been observed living in rubber plantations!
Southern mitered langurs weren’t considered to be a distinct species until 2015!
Southern mitered langurs typically inhabit home ranges spanning from approximately 34.5-73 acres (14 to 29.5 ha). The smaller their home range, the more aggressive their behavior to protect it. Generally, the males are the defenders and primary aggressors, while females display little dominant behavior traits. Within these areas, they travel distances ranging from about 985-4450 feet (300-1360 m) each day. This movement within their territory likely involves foraging for food, social interactions, and other aspects of their daily routine. Daily movement distances may be influenced by factors such as food availability, terrain, and social dynamics within the group.
Because of their diet and specialized digestive processes, these langurs have to spend the majority of their day foraging—most likely in smaller groups—to make up for the large amount of calories they burn through their intricate digestive process. They tend to utilize the cooler morning hours to find food, then rest in the afternoon to allow their bodies to fully digest what they’ve eaten.
As dense forest monkeys, the southern mitered langur has to rely on vocal communication quite a bit, both for within their family groups and for protection from unwanted visitors. Langurs are known for their aggressive, territorial behavior, and are not afraid to use loud, piercing vocal sounds or booming calls to signal their presence and territories to neighboring animals. These sounds typically come from the males (females tend to steer away from dominant behavior) and can be heard from several hundred feet away (over 100 meters). Aside from the loud vocal calls, these langurs are known to communicate through grunts as well.
All monkeys of the genus Presbytis share many similarities, including their forms of communication. Others use body postures to communicate non-verbally and we can assume the same for this species. For example, there have been observations of male Javan surilis (Presbytis comata) using menacing body postures to further intimidate and defend themselves from intruders. Also, the maroon leaf monkey (Presbytis rubicunda) uses certain tail movements and positions to convey various emotions like irritation, fear, anger, and elation. It is likely that the southern mitered langur also adopts these forms of non-verbal communication.
Lastly, as with most primates, allogrooming (grooming one another) is a major form of tactile communication for these monkeys, helping to form alliances within groups and strengthen bonds.
Little research or information about the reproduction and family dynamics of southern mitered langurs is available, but there are other comparable species from which we can assume share similar behaviors. It is likely that, like the black-crested Sumatran langur, the southern mitered langur is polygynous, meaning one male mates with multiple females within a troop. In polygynous groups, females tend to remain within their natal groups (the troop into which they were born). Males leave their natal troops upon reaching sexual maturity to lead new groups. Females reach sexual maturity around age 3-4, while males typically do so at 4 years.
Once pregnant, the gestational period lasts around 5-7 months. For the most part, females give birth to one infant at a time (twins can occur, though rare). Mothers provide childcare, carrying, feeding, grooming, and protecting their infants until they reach the age of 2.
The presence of southern mitered langurs is necessary for the health and function of the natural ecosystem in southeastern Sumatra. With their plant-heavy diet, trees rely on them to be their gardeners and benefit greatly from the pruning provided while they forage. Furthermore, when these monkeys eat the native fruit, they help spread the seeds through the leftovers that they drop (as well as their own droppings if ya know what we mean). Lastly, though unfortunate for the southern mitered langurs themselves, their smaller size makes them prey for many of the larger predators in the area, like the Sumatran tigers, Malayan sun bears, dholes, and Sunda clouded leopards.
The southern mitered langur is classified as Vulnerable by the International Union for Conservation of Nature (IUCN, 2022), appearing on the IUCN’s Red List of Threatened Species.
One of their primary threats is habitat loss, particularly from oil palm plantations. Luckily, the species is decently tolerant of forest conversion and shows patterns of remaining in areas with new human infrastructure. Unfortunately, many of the other vital organisms to the ecosystem are not as adaptable, so the entire ecosystem suffers as a whole from these interferences. Another major threat to the southern mitered langur is illegal hunting and trapping for the pet trade.
Southern mitered langurs are listed in Appendix II of the Convention on International Trade in Endangered Species (CITES), a global pact among nations aimed at safeguarding the survival of wild animals and plants by regulating international trade in their specimens to prevent any threat to their existence.
They are also protected by Indonesia and safeguarded in Bukit Barisan Selatan National Park and Way Kambas National Park in Sumatra.
While some conservation efforts are in place, much more is needed to ensure the health and stability of all the primate species of Sumatra.
- https://www.gbif.org/species/134108886
- https://www.gbif.org/species/7717621
- https://zenodo.org/records/6863400
- https://core.ac.uk/download/pdf/345095054.pdf
- https://neprimateconservancy.org/black-crested-sumatran-langur/
- https://neprimateconservancy.org/maroon-leaf-monkey/
- https://neprimateconservancy.org/javan-surili/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8932565/
- https://cites.org/sites/default/files/documents/E-CoP19-Inf-74.pdf
- https://www.iucnredlist.org/species/39811/17954271
Written by Hannah Broadland, April 2024