WEST JAVAN EBONY LANGUR

Trachypithecus mauritius

Geographic Distribution and Habitat
​The West Javan ebony langur (Trachypithecus mauritius) is a species of Old World monkey native to the island of Java, west of Jakarta. They are well at home in the lush forests of the island, occupying primary and secondary dry deciduous, mangrove, beach, freshwater, swamp, and hill forests.

TAXONOMY IN TRANSITION

Until recently, West Javan ebony langurs were considered to be a subspecies of the Javan langur (T. auratus). A 2008 phylogenetic study found that they were deserving of their own species designation, along with another former subspecies, the spangled ebony langur (now considered T. auratus). This taxonomical change was adopted by the IUCN in late 2020. Because this change was only recently widely adopted, most research about Javan langurs lumps West Javan ebony langurs and spangled ebony langurs together as one species. While these two species are closely related and share many of the same characteristics, we will undoubtedly discover more interesting traits that are unique to West Javan ebony langurs as more research into the species is conducted.

West Javan Ebony Langur range, IUCN 2020

Size, Weight, and Lifespan
The head and body length of West Javan ebony langurs is between 17 and 26 inches (44–65 cm), with the tail adding another 24–34 inches (61–87 cm). Based on other langur species, males likely weigh about 29 lbs (13 kg) and females about 22 lbs (10 kg). Their lifespan is about twenty years.

Appearance
As their name might suggest, West Javan ebony langurs have glossy black hair over almost their entire bodies, transitioning to dark brown on their legs and bellies. Their hair splays out in all directions around their face, giving them the appearance of having a beard, long sideburns, and bangs. Like other langurs, they have a tail that is very long compared to their body. Infants are born with bright orange coats that darken to black as they age. Females have yellow pubic patches; this, and a slight overall size difference, is the only form of sexual dimorphism that West Javan ebony langurs exhibit. 

Photo credit: Hans De Bisschop/Flickr/Creative Commons

Diet
As folivores, West Javan ebony langurs eat mainly leaves, supplemented by fruit and flowers. They have sacculated stomachs that help them to break down plant material that would otherwise be difficult to digest. This allows them to eat tough leaves that other species can’t digest, reducing competition with other species and allowing West Javan ebony langurs ample food supplies.​

Behavior and Lifestyle
​West Javan ebony langurs are diurnal and arboreal, moving quadrupedally through the trees. Based on related species, their home range size is likely about 74 acres (30 ha) on average. Adults spend more than half of their day resting (61%, according to one study), longer than most frugivorous primates, and this is likely because their special digestive system requires more rest time to completely digest food. Juvenile West Javan ebony langurs spend less time resting and feeding and more time moving than do adults.

What Does It Mean?

Allocare:
Also known as “alloparenting.” An individual other than the biological parent of an offspring that performs the functions of a parent (as by temporarily caring for an infant).

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

​Diurnal:
Active during daylight hours.

Folivore:
An animal who primarily eats leaves.

Frugivore:
An animal who feeds on fruits.

Generation time:
The average time between successive generations in a population.

​​Natal group:
The group into which an animal is born.

Polygynous:
A mating system in which one male mates and lives with multiple females.

Quadrupedal:
Using four limbs to move about. This word comes from the Latin meaning “four feet.”

Sexual dimorphism:
Distinct difference in size or appearance between the sexes of an animal in addition to difference between the reproductive organs themselves.

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.

Sympatric: 
Occurring or living in the same area; overlapping in distribution.  

Taxonomy: 
A branch of science that encompasses the description, identification, nomenclature, and classification of organisms.​

Visit the Glossary for more definitions

Daily Life and Group Dynamics
​West Javan ebony langurs typically live in groups composed of one or two males and usually five or six females, although there can be as many as 20 females in a group. There is very little competition between the males in a group, and females only mate within their group. Upon reaching maturity, males disperse from their natal group, either traveling alone or sometimes forming loose groups with other bachelor males. Overall, intragroup dynamics are very peaceful, with male aggression being rare, relationships between males and females being affectionate, and extensive cooperation occurring among females as they raise their offspring together. Females can, however, be aggressive towards females in other groups, although it has been noted that several groups of West Javan ebony langurs can forage at the same tree without significant aggression.

Fun Facts

Studies suggest that infants’ bright orange coloration is an evolved trait that helps females in a group recognize an individual that needs care. The bright colors of the baby’s hair triggers parental instincts in adults and ensures that the youngest, most vulnerable members of the group are protected and cared for.

Communication
West Javan ebony langurs communicate acoustically, with an alarm call that has been described as sounding like “ghek-ghok-ghek-ghok.” Allogrooming is common within groups and is an important behavior in forming and cementing social bonds. Aggression is expressed with a variety of vocalizations and visual cues. It is not known to what extent West Javan ebony langurs use olfactory communication.

Reproduction and Family
​West Javan ebony langurs exhibit a polygynous mating system, in which males mate with multiple females, but females mate with just one male. Because of the high ratio of females to males in a group, there is very little competition between males. Female West Javan ebony langurs reach sexual maturity at around three to four years of age. They give birth once per year, one offspring at a time. The infants are independent within about a year. The group exhibits alloparenting, with all adult females in a group caring for the offspring. The bright orange coloration of the infants helps the adults keep track of them. This color begins to fade at about three months of age and is completely gone by about six months of age. Their generation length is about 12 years.

Ecological Role
West Javan ebony langurs are sympatric with the Javan surili (Presbytis comata), another Old World monkey. Their only known predator is humans. A likely natural predator once included the Javan tiger (Panthera tigris sondaica), a population of Sunda Island tiger that was once native to Java, but sadly went extinct in the 1970s. One of the contributing factors to the extinction of this tiger population was a significant reduction in prey, which likely included the West Javan ebony langur. This sad story illustrates perfectly how the web of life is interconnected, because a population loss in one species can contribute to the extinction of another species or population.

Conservation Status and Threats
West Javan ebony langurs are considered Vulnerable by the IUCN (2015). This designation is based on an estimated population decline of more than 30% over the past 36 years (comprising three generations of West Javan ebony langurs).

Indonesia is the 4th most populous country in the world, and about 70% of Indonesians live in Java, making it the most populated island in the world. This puts an enormous amount of pressure on the natural ecosystems, and has sadly resulted in rainforest degradation, fragmentation, and deforestation. Between 2000 and 2005, an astounding 45.5% of the forest cover on the island was lost. This dramatic loss has resulted in a number of environmental problems, including flooding, droughts, and landslides, and of course has contributed to habitat loss for West Javan ebony langurs and the many other species that call Java home. Besides habitat loss, West Javan ebony langurs are also threatened with capture for the illegal pet trade and hunting.

Conservation Efforts
​West Javan ebony langurs occupy several protected areas, including Ujung Kulon National Park, Cibanteng Nature Reserve, and Cikepuh Nature Reserve.

References:​​

  • Prasetyo L. B., H. Kartodihardjo, S. Adiwibowo, B. Okarda. 2009. Cause and Prediction of Deforestation in Java Island: Spatial Modeling Approach. Journal of Integrated Field Science 6(3):130.
  •  Trisilo S. P. , K. A. Widayati, Y. Tsuji. 2021. Effect of infant pelage colour on infant caring by other group members: a case study of wild Javan lutungs (Trachypithecus auratus). Behaviour. https://doi.org/10.1163/1568539X-bja10064 
  • Zul Asri S. W., K. A. Widayati, Y. Tsuji. 2019. Age-Sex differences in the daily activity and diet of West Javan langur (Trachypithecus mauritius) in the Pangandaran Nature Reserve, West Java, Indonesia: A preliminary report. Asian Primates Journal 8(1): 2-12.
  • https://www.iucnredlist.org/species/39849/17988526
  • https://animaldiversity.org/accounts/Trachypithecus_auratus/
  • http://www.catsg.org/index.php?id=570
  • https://www.mindat.org/taxon-8081886/
  • https://www.census.gov/popclock/print.php?component=counter
  • https://animaldiversity.org/accounts/Semnopithecus_entellus/

Written by K. Clare Quinlan, March 2021