CAPPED LANGUR

Trachypithecus pileatus

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)
Capped langur geographic range. Map credit: IUCN, 2020

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.

Appearance
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 dorsal side 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.

Diet
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. 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.

What Does It Mean?

Activity Budget:  
A way to quantify animal behavior by observing an animal over an extended period and documenting activity. An activity budget demonstrates how much time an animal spends in various activities such as eating, resting, sleeping, and moving.

Agonistic:
Of, relating to, or being aggressive or defensive social interaction (such as fighting, fleeing, or submitting) between individuals usually of the same species.

Allomothering:
Individuals other than the biological mother of an offspring performs the functions of a mother (as by caring for an infant temporarily).

Arboreal:
Physically adapted to living primarily or exclusively in trees.

Canopy:
Beneath the emergent layer, the canopy layer is the primary layer of the forest and forms a roof over the two remaining layers (the understory and forest floor).  Most canopy trees have smooth, oval leaves that come to a point. Many animals live in this maze of leaves and branches, where food is abundant.

Cellulose:
Molecule found in plant matter that gives structure and strength to the cell walls of plants and provides dietary fiber.

Colobines:
Members of the subfamily Colobinae.
Dorsal: 

Of, on, or relating to the upper side or back of an animal, plant, or organ.

Gestation Period:
The time of pregnancy from conception until birth. 

Sacculated:
Having a series of different sections (e.g. langurs have sacculated stomachs, i.e. stomachs with three sections).

Slash and burn agriculture:
A method of unsustainable farming where farmers clear land by cutting and burning flora in order to create an empty field—a “swidden”—for cultivation. Such practices are detrimental to local ecosystems.

Subspecies:
A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.

Visit the Glossary for more definitions

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.

Fun Facts

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.

Daily Life and Group Dynamics 
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 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.

Communication
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.

Reproduction and Family
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.

Photo credit: Aparajita Datta/Creative Commons

Ecological Role
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.

Conservation Status and Threats
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.

Conservation Efforts
The governments of India and Bangladesh have enact 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.

​References:

  • https://www.arkive.org/capped-langur/trachypithecus-pileatus/
  • https://www.iucnredlist.org/species/22041/9350087
  • https://alltheworldsprimates.org/Members/Home/MasterPrimate.aspx?tid=841
  • http://www.theprimata.com/trachypithecus_pileatus/
  • 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