Geographic Distribution and Habitat
The capped langur is found in Bhutan, northeast India, Bangladesh, western Myanmar, and possibly China. They live in subtropical and montane forests rich in vegetation and freshwater streams. The region is characterized by steady moderate temperature and heavy rainfall during the summer months.
There are four capped langur four subspecies:
- Blond-bellied capped langur (Trachypithecus pileatus pileatus)
- Buff-bellied capped langur (Trachypithecus pileatus brahma)
- Orange-bellied capped langur (Trachypithecus pileatus durga)
- Tenebrous capped langur (Trachypithecus pileatus tenebricus)
Size, Weight, and Lifespan
Male capped langurs are noticeably larger than their female counterparts. On average, males have a body length of 24.4 in (62 cm) from head to toe and weigh 2.8 lb (1.28 kg). Females stand at about 22 in (56 cm) tall and weigh 2.3 lb (1.05 kg).
The closest relatives of the capped langur can live to be from 25 to 30 years old.
Capped langurs can vary in appearance. The species is named for the thick hair on the top of their head that is usually black or gray. Their back is usually covered in gray, brown, or black hair. Their bellies can be anywhere from vivid orange to pale yellow.
As with most langurs, babies have wildly different coloration from adults, although the differences in capped langurs are less dramatic compared to most of their relatives. Adult capped langurs have black skin, while babies have pink skin. The baby’s hair is usually a light orange, similar to the color of an adult’s chest.
Scientists have long been perplexed by the highly noticeable langur offspring, which seem to put the young monkeys at a disadvantage when hiding from predators. However, there are two likely theories for the brightly colored babies. One theory is that they are meant to blend in with the mother’s chest while nursing. The other is that when there is danger, the group can immediately locate the babies and move to protect them.
Over half of the capped langur’s diet is made up of leaves. Because leaves are so hard to digest, capped langurs, along with all of their relatives in the colobine subfamily, have evolved sacculated stomachs. These multi-chambered stomachs contain special bacteria and enzymes that help break down cellulose, the molecules found in plant matter that give structure and strength to the cell walls of plants and provide dietary fiber. Langurs also have enlarged salivary glands to aid in digestion.
In addition to leaves, fruits make up a quarter of the capped langur’s diet. The rest of their diet features seeds, flowers, and tree bark.
Behavior and Lifestyle
Activity budgets show that these langurs spend half of the day foraging and traveling between foraging spots. About 40% of their day is spent resting and the remaining 10% is spent on play and social grooming. On a typical day, all of these activities will occur in the trees, generally in the upper canopy of the forest.
Capped langurs are extremely arboreal in nature, even to the point where they get most of their water from leaves and depressions in the forks of trees.
Capped langurs wake up at dawn and climb to the canopy, where they can bask in the sun. After basking, the females of the group will initiate foraging while the dominant male lags behind the group. The average group of capped langurs consists of around nine individuals featuring a single dominant male, a few adult females, and their offspring. Other group types include all-male bands as well as loner males. Some groups with multiple adult males and females have been observed, but they are rare.
Langur groups forage in the early morning and late afternoon with midday mostly dedicated to resting and traveling. Although capped langurs are highly social and verbose animals, they mostly stay silent while foraging. This is rather unique among arboreal (tree-dwelling) primates, who tend to stay in constant communication so they do not lose track of one another in the trees. Instead, capped langurs stay in close proximity to each other and only emit contact calls when necessary. At night, each langur retreats to his or her own tree to sleep.
Capped langurs are not known to be territorial animals. Groups will hold control over about 45 acres of territory, but these ranges often overlap with multiple groups and they do very little to defend it from intruders. The one exception to this is when a rogue male tries to steal a female from a group to start a group of his own. Dominant males are highly protective of their mating partners and offspring—much more so than their food sources.
Capped langurs have several vocalizations in their repertoire. Although they mostly are quiet during feeding, individuals will occasionally emit a “nouk” sound if anyone loses contact with the main group. Males often let off a low growl when feeding. Females and juveniles make a high-pitched distress call when fighting with other group members, while adult males have their own special growl when engaging in agonistic behavior with rival males. These monkeys also have a variety of alarm calls, play calls, and special calls for mother-infant relationships.
Adult males may make several displays when showing dominance to their group or rival groups. One such display is a “run display,” where the males will leap through the branches making as much noise as possible to make their presence known. Another display has the male standing on all four limbs with his tail curled in an effort to show his size and strength. A more general display is baring one’s teeth to intimidate a rival, a common gesture among many species of primate.
Grooming is also a common practice among langurs and is used to reinforce social bonds. Although females and juveniles will groom the males, the males usually do not return the favor.
Most mating for capped langurs occurs during the dry season between September and January, although there is sometimes mating in April and May. With a gestation period of about 200 days (or 6 to 7 months), babies are born around the beginning of the rainy season, when food is most plentiful and competition is less fierce.
Capped langurs practice allomothering, meaning that all females in the group help take care of the babies. The male’s role in parenting is usually limited to protecting the offspring. Babies are fully dependent on their families for the first two months of life before they start to show independence. They continue to nurse until they are about 10 or 12 months old, at which point they begin foraging for themselves.
These langurs reach sexual maturity around the ages of 3 or 4, with first-time mothers giving birth between 48 and 52 months of age.
Capped langurs hold niches as primary consumers in the mid and upper canopies of their forest, where they sometimes live near Phayres’ leaf monkeys. By eating fruits and seeds, capped langurs also act as seed dispersers. When langurs ingest seeds and defecate them far away from their parent tree, it allows the seeds to grow without having to compete with their parent tree for resources.
Although there has been no observed predation on capped langurs, researchers assume that jackals as well as birds of prey may be potential predators.
Capped langurs are listed as Vulnerable by the International Union for Conservation of Nature (IUCN, 2015). The IUCN states that species has declined by 30% over the past three decades and will likely continue to decline at the same rate for the foreseeable future. The major reasons for this decline habitat are destruction and human hunting them for food (bushmeat) and the pet trade.
Slash and burn agriculture, locally referred to as jhum cultivation, is responsible for much of the destruction of the capped langurs habitat. Capped langurs need a continuous and undisturbed forest to prosper. A sparse forest, where langurs are forced to cross over bare ground to get to another tree, puts the monkeys at an increased risk from ground predators such as jackals and stray dogs.
The governments of India and Bangladesh have enacted laws to protect the capped langur and the species appears in several protected areas across the two countries. The species is protected in China, where it has only recently been discovered. Myanmar also lists the langur as a protected species, but conservationists believe the protection is in name only.
- Choudhury A Distribution and current status of the capped langur Trachypithecus pileatus in India, and a review of geographic variation in its subspecies. Primate Conservation, 2014. 28 (1): 143- 157.
- Hu, Y. M., Zhou, Z. X., Huang, Z. W., Li, M., Jiang, Z. G., Wu, J. P., Liu, W. L., Jin, K., Hu, H. J. (2017). A new record of the capped langur (Trachypithecus pileatus) in China. Zoological research, 38(4), 203-205.
- Stanford, Craig B. The Capped Langur in Bangladesh: Behavioral Ecology and Reproductive Tactics. Karger, 1991.
Written by Eric Starr, February 2019