CAT BA LANGUR

Trachypithecus poliocephalus

Geographic Distribution and Habitat
The Cat Ba langur, or golden-headed langur, is only found on Cat Ba, the largest (110 sq m / 285 sq km) of the 367 islands that comprise the Cat Ba Archipelago in the Gulf of Tonkin, northeastern Vietnam. It is the only island in the archipelago where humans live (approximately 13,000) and where tourism has developed over the years.

The dramatic landscape of the island is characterized by limestone boulders, coral terraces, mangrove forests, lagoons, beaches, and willow swamp forests. Such variety of natural ecosystems explains why the island is home to over 1,500 species of flora and fauna, some of which do not exist anywhere else.

The Cat Ba langur is on the brink of extinction, with only 65-67 individuals remaining. They are restricted to less than 8 sq m (20 sq km) of moist tropical forest on limestone karst hills in the Cat Ba National Park, at about 440 ft (135 m) elevation.

Cat Ba langur range, IUCN 2020

Size, Weight, and Lifespan
The Cat Ba langur species is genetically related to the Chinese white-headed langur.

Males are larger than females, but not significantly so. The length of their body is approximately 19-23 in (50-60 cm) and their weight is approximately 20-26 lbs (9-12 kg), with females on the lower end and reproductive males on the upper end.

Documented deaths of old females in the last few years seem to indicate they can live up to 25 years.

Appearance
Cat Ba langurs have long, slender bodies, long limbs, and extremely long tails (32-35 in / 82-89 cm). The tail is not prehensile, but it helps the langurs keep their balance while on the move.

Their hands and feet are black. Their hands have an underdeveloped thumb and their feet have five digits with an opposable big toe.

Their body is covered with thick dark brown-to-black hair, which is longer in the back and gives them the appearance of wearing a vest. A band of pale gray hair starts on their lower back and extends to the outer thighs. Their neck and shoulders appear to be wrapped in a shawl of orange-to-yellow hair. Their head is covered by a tuft of gray yellowish hair that extends to the sides of their face and chin. Interestingly, the word “poliocephalus” in their scientific name of the species translates to “gray-headed.”

Their faces are black, with big, round, and expressive eyes, black ears, and a flat nose. Males and females share the same coloration, except for the white patch of fur on females’ inner thighs. A pair of thick calluses on their bottom acts as a seat; the male’s calluses are connected but the female’s are separate.

Infants are born a flamboyant orange and keep their bright coloring until about four months of age, although it takes several years for them to fully fade into adult coloration.

What Does It Mean?

Karst:
Formed by the dissolution of soluble stones, such as limestone and dolomite. Typical karst landscapes include caves and springs and are often spectacular looking. Aquifers in karst landscape provide large supplies of water and are therefore extremely important and should be protected to avoid water contamination.

Alloparent:
An individual other than the biological parent of an offspring performs the functions of a parent (as by temporarily caring for an infant).

Visit the Glossary for more definitions

Photo courtesy of ©Neahga Leonard, Cat Ba Langur Conservation Project. Used with permission.

Diet
Cat Ba langurs have a varied diet which consists mainly of leaves but also includes other fiber-rich food items such as shoots, flowers, bark, and fruit, many of which could be poisonous to other animals and humans. The high concentration of tannic acid in their diet is most likely helpful at keeping microbes, yeast, and viruses at bay.

No need to worry about their digestion—the langurs’ have large salivary glands to break down food and their sacculated stomach can perfectly handle the cellulose they ingest.

These langurs have been observed drinking small amounts of saltwater, an unusual trait not understood by scientists. Still they get most of their water from vegetation and pockets of trapped rainwater. It is important to note that caves within langur areas may retain running water, even long after the rains. Within the current langur areas, there are no ponds or other sources of fresh water.

Behavior and Lifestyle
Cat Ba langurs are at ease in the trees or on the ground, but their preference seems to be for steep cliffs, where humans cannot set foot.

Their primary mode of locomotion is climbing in a nearly upright position, usually across their rocky habitat. Excellent climbers and amazing jumpers, these langurs make gigantic leaps from rocks to trees and from tree to tree. Their longest jumps tend to be from high to low areas. On less steep ground, they bound a bit like a dog.

Daily Life and Group Dynamics 
Cat Ba langurs live in small groups, although this appears to be the result of the population collapse. The 4 reproductively active groups on Cat Ba island range in size from 22 individuals down to 6 individuals. Locals report that in the past, groups of up to 30 individuals were not uncommon. Each group has only one reproductively active male. Immature males stay with the group until they reach sexual maturity (4 or 5 years old), then they leave their natal group.

Like most other primate species, the Cat Ba langurs devote a great portion of their time to foraging for food, grooming, and resting. They use sheltered areas, primarily ledges and overhangs, as well as a small number of carefully selected natural caves throughout the year to sleep and seek shelter from harsh weather conditions. They rarely stay more than two nights in the same sleeping site, as they move to different feeding areas during the day.

Fun Facts

The meaning of the name Trachypithecus, in the Cat Ba langur’s Latin or scientific name, comes from the Greek words “trach,” meaning rough and “pithekos,” meaning ape.

Cat Ba means women. Legend holds that, centuries ago, three women of the Tran Dynasty were killed. Transported by the ocean, their bodies floated to Cat Ba Island. The residents built a temple for each of them and this how the island got its name! As for the langurs, it is speculated that they arrived on the island during the last ice age when sea levels were low.

In 2004, Cat Ba island was designated as UNESCO Man and the Biosphere Reserve.

Communication
The Cat Ba langurs are very quiet—maybe the result of hunting pressure selecting against vocal individuals.

There are two primary calls: a nasal/throat growling and a short coughing bark. The first is used by males to mark their territory. The second is shared by all individuals and is at the origin of the Vietnamese name “vooc,” which means “langur.” The very young animals make a high-pitched squeak that sounds like a cross between a bird call and someone twisting Styrofoam in their hands.

Reproduction and Family
Each group is usually composed of one male and a harem of females and their offspring. The reproductive rate for this species is low as females can only give birth every 2 to 3 years to a single baby. If we add the risk factor of the single male being killed, the group reproductive chances drop even more. This is mitigated somewhat by the relatively low infant mortality rate.

The langurs breed throughout the year, with the majority of births taking place near the end of the dry season. February is the peak birth month and a roughly 200-day gestation period indicates that the breeding time is toward the end of the rainy season, with August being the peak conception month.

Cat Ba langurs practice alloparenting—when infants are born, all the females in the group take an interest in the little ones.

The young learn by watching the adults and playing with each other. Once they’re old enough to venture away, the mother will sometimes hold them by the tail to keep them close by and safe. As they get a bit older and can travel from site to site on their own, she will stay close by and pause and wait if they are having trouble climbing over an obstacle.

Offspring reach sexual maturity between 4 and 6 years of age.

Photo courtesy of ©Neahga Leonard, Cat Ba Langur Conservation Project. Used with permission.

Ecological Role
Because their population is incredibly small and the territory they occupy is tiny, the Cat Ba langurs’ ecological role is minimal at present. In the past they were likely important for seed and nutrient transport. By foraging, they may have played an important part in the natural pruning of plants, thereby allowing these plants to increase their potential leaf and budding areas for flower and fruit production.

When there were still large predators on Cat Ba island—mainly large snakes and predatory birds—young langurs may have been an occasional food source for them.

Conservation Status and Threats
The Cat Ba langur is assessed as Critically Endangered (IUCN, 2015) in the International Union for Conservation of Nature’s Red List of Threatened Species and in the Vietnam Red Book. In 2016-2018, the IUCN included the Cat Ba langur in its list of the 25 most imperiled primate species. and then again in the 2018-2020 report.

The Cat Ba langur population in the 1960s was estimated to have been between 2,400 and 2,700 individuals. By the year 2000, the population had been devastated and reduced to less than 135 individuals. Today, the population counts 65-67 individuals and is slowly rising.

In late June 2020, the Cat Ba Langur Conservation Project reported the following: Early this year we had several more incidents of infanticide during male take-over attempts, so despite having 5 babies born so far we are still at 65-67 individuals, no net gain so far in 2020.

The population is still growing as we started 2019 with 60 individuals and currently have 65-67 individuals, but these animals face a lot of challenges, both from an overabundance of males (or not enough females, depending on how you look at it) and due to the ever increasing pressures of the rapidly growing tourism industry on Cat Ba.

The latter exacerbates a number of stresses the langurs are already under, making foraging, raising young, and accessing sleeping sites more difficult, as well as adding proximity stresses that can lead to violence within and between groups.

It is important that people understand that wildlife of all sorts needs a minimum of disturbance as well as peace and quiet.

Despite the many challenges faced we are happy to report that the population continues to grow, albeit slowly.

Poaching was the main reason for the rapid and drastic decline of the species. The langurs were hunted mostly for parts and bones used in folkloric “medicines” to prepare a “monkey balm” for aging men. They were also hunted for food in times of famine (even though their flesh does not taste good), and some were hunted for sport.

The local illegal pet trade also contributed to their decline, but was minor when compared to hunting.

More recently, the problem has been compounded by habitat fragmentation due to logging, agricultural use of the land, poorly regulated yet booming tourist development, and forest fires on the limestone cliffs caused by honey collectors.

Conservation Efforts
The need for local economic development—paired with the fact that the Cat Ba langur is often confused with other Vietnamese langur species—has slowed down protection efforts.

Fortunately, in November 2000, the Zoologische Gesellschaft für Arten und Populationsschutz (ZGAP) and the Allwetterzoo from Germany started a conservation program dedicated to the Cat Ba langur.

Through their tireless work with the local authorities and the communes, they successfully established Forest Protection Group and Forest Protection Clubs (the latter are managed by Dr. Neahga Leonard) that actively remove traps, free captured animals, confiscate guns, stop forest destruction, and educate the population about conservation and the importance of biodiversity. Poaching of Cat Ba langurs has stopped, and an increasing number of births have been recorded.

A hopeful sign for the future.

acknowledgement

Special thanks to Dr. Neahga Leonard, Project Director of the Cat Ba Langur Conservation Project, who kindly provided recent data about the species and offered to review and provide edits for this profile. In addition, Dr. Leonard generously allowed us to use the stunning photos supplied on this page.

Click to learn more about Cat Ba Langur Conservation Project.

References:

  • IUCN Red List
  • Karst water institute website.
  • Vietnamese Journal of Primatology – May 2007 – Tilo Nadler – Frankfurt Zoological Society, Endangered Primate Rescue Center, Vietnam
  • Ecology Asia website.
  • The Cat Ba Langur: a primate walks the razor’s edge of extinction – Mongabay news.
  • World Association of Zoos and Aquariums website​
  • Australasian Primatology publication – vol. 16 – “A Crusade to Save a Rare Species” – Ben Stocking

Written by Sylvie Abrams, March 2018. Population numbers, per the Cat Bar Langur Conservation Project, updated July 2020.