WHITE-HEADED BLACK LANGUR

Trachypithecus leucocephalus

Geographic Distribution and Habitat
Home to the white-headed black langur, or more simply known as the white-headed langur (Trachypithecus leucocephalus) is the Guangxi Zhuang Autonomous Region (GZAR) of southern China, bordering Vietnam and the Gulf of Tonkin. Demarcating the species’s narrow geographic range is the Zuojiang River in the north and northwest; the Mingjiang River in the south and southwest; and the Shiwan Mountains in the southeast. These leaf-eating monkeys are found in the counties of Chongzuo, Fusui, Ningming, and Longzhou. Forested limestone ridges, cliffs, crevices, fissures, caves, and underground streams define the rugged karst landscape that provides the species’s habitat and highly specialized ecological niche.

Total distribution area is only 50 mi (80 km), fragmented by farmland, sugarcane fields, human settlements, and human infrastructure.

Average yearly rainfall in the region is 39.4 in (1000 mm); average daily temperature is 72 °F (22.1 °C), with a high of 103 °F (39.5 °C), and a low of 31 °F (-0.5 °C).

TAXONOMY IN TRANSITION

The white-headed black langur’s path to full species status is rutted with taxonomic potholes. It started out classified under the genus Presbytis before being moved to its current genus, Trachypithecus. For more than 40 years, it was thought to be a subspecies of Francois’s langur (Trachypithecus francoisi). Then scientists decided that this monkey is actually a subspecies of the Cát Bà langur (Trachypithecus policocephalus) of Vietnam—until further study disabused the researchers of this notion. While these two primates are closely related, their geographic ranges do not overlap. Furthermore, they have distinct color and pattern differences in their pelage. Today, according to the IUCN, both the white-headed black langur and the Cát Bà langur are each a distinct, monotypic species. Not all scientists are happy with this reclassification, though. Reluctant to give up the francoisi connection, some scientists assert that the previous subspecies classification of Trachypithecus f. leucocephalus—“child” of the “parent” species Francois’s langur—is correct. Giving fodder to this persisting taxonomic kerfuffle is the white-headed black langurs’ practice of interbreeding with Francois’s langurs, resulting in hybrid births.

White-headed black langur range, IUCN 2020

Size, Weight, and Lifespan
Long limbs and a slender build typify this Old World primate. Males are slightly taller and carry a bit more girth than the females.

Head-to-body length for adult males is 1.9–2.3 ft (57.9–68.9 cm), with an average length of 2.1 ft (63.4 cm). Tail length adds another 2.7–2.9 ft (83.5–89 cm), with an average length of 2.8 ft (86.3 cm). Fully grown males weigh between 17.4 and 21.2 lb (7.9–9.6 kg), with an average weight of 19.4 lb (8.8 kg).

Head-to-body length for adult females is 1.7–2 ft (52.7–61.9 cm), with an average length of 1.9 ft (57.3 cm). Tail length adds another 2.4–2.8 ft (72.6–86 cm), with an average length of 2.6 ft (79.2 cm). Fully grown females weigh between 15 and 21.4 lb (6.8–9.7 kg), with an average weight of 17.2 lb (7.8 kg).

Lifespan in the wild for white-headed black langurs is not documented. However, the average lifespan for the genus Trachypithecus is 25 years.

Appearance
As its common name suggests, a shock of white fur covers the head of this primate. Hairs stand straight up from the crown for a crazy hairdo reminiscent of the “Is that hair gel?” scene from the romantic comedy There’s Something About Mary, starring Cameron Diaz and Ben Stiller. (Google it!) More white strands of hair jut out wildly from the sides of the head, framing a dark-colored hairless face characterized by dark eyes, a modest downturned nose, and narrow lips. Dark ears sit scrunched on either side of the head. White chin whiskers meld into a white ruff that is stopped by a thick fur coat that covers the monkey’s entire body, including its long limbs, in a blackish hue. The fur is long and coarse. Black fur covers half to three-quarters the total length of its long tail before giving way to white hairs. Hands are black, and feet are mostly black with a few gray strands interspersed. Mother Nature’s color scheme for these rare primates allows them to blend with their karst, limestone habitat.

At birth, white-headed black langurs would appear to be a completely different species of monkey, for Mother Nature has completely cloaked these infants in a bright, puffy, golden-orange fur coat. (Some wildlife biologists have conjectured that this brightly colored coat helps mothers to better keep track of and care for their babies.) At about one year old, the infants’ pelage begins to resemble that of the adults, first turning to gray before becoming black. The final furry punctuation mark into adulthood is the crazy white hairdo.

It’s worth noting that both Francois’s langur and Cát Bà langur infants are also cloaked in bright, puffy golden-orange fur coats.

Characteristic of Old World monkeys, the rumps of white-headed black langurs are fitted with thick, calloused pads known as “ischial callosities” that provide some comfort to the monkeys while they sit.

What Does It Mean?

Anthropogenic:
Environmental disturbance or environmental pollution originating in human activity.

Birth interval:
Refers to refers to how soon after a prior pregnancy a female becomes pregnant or gives birth again.

Ecosystem:
A biological community of interacting organisms and their physical environment.

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.

Monotypic:
Having only one type or representative, especially (of a genus) containing only one species.

Pelage:
The fur, hair, or wool of a mammal.

Relict:
Something, or someone, who survives or remains or is left over after the loss of others; a relic.

Visit the Glossary for more definitions

Diet
White-headed black langurs are primarily folivorous, meaning they eat lots and lots of leaves—comprising up to 90 percent of their diet! Fruits, shoots, flowers, and tree bark supplement their meal plan. Overall, the monkeys consume 109 plant species, with the rainy season providing the greatest dietary diversity. To wash down all that plant matter, they drink water that has pooled on leaf surfaces or from rock crevices. Rock licking is common in the species. Further digestive assistance is provided by evolutionary adaptations.

White-headed black langurs are fitted with large salivary glands that break down plant cellulose, lubricate the passage of food, and keep the digestive system moist. A complex, multichambered stomach (characteristic of colobine monkeys) allows for bacterial fermentation, converting plant cellulose to nutrients and neutralizing any potential toxins. The extreme concentration of fiber and tannic acids in the monkeys’ diet would be poisonous to many other species (including humans), who lack this biological capability.

Behavior and Lifestyle
These leaf-eating primates are active during daylight hours (making them diurnal) and are most active in the hours of dawn and dusk (making them crepuscular). They are both terrestrial (spending time on the ground, in particular, the karst landscape) and arboreal (spending time in the trees).

After waking each morning, the monkeys spend a bit of time socializing with one another before heading out to forage, an activity that occupies most of their day. When not munching on leaves, white-headed black langurs engage in play or may take a nap. During the winter months, they are known to sunbathe on limestone surfaces. The monkeys travel quadrupedally (on all four limbs) using their long, nonprehensile tail for balance. They also climb and leap to get to where they are going (these monkeys are great leapers!). On rare occasions, they engage in brachiation (swinging from tree limb to tree limb using only their arms) or suspensory activity (using one arm to hang from a tree limb). As a species, white-headed black langurs are characterized as being highly alert to occurrences in their environment. To that point, researchers have observed a heightened level of vigilance in white-headed black langurs prior to the monkeys entering a sleeping site.

At the end of each day, the monkeys retire as a group. While they might choose a tall tree as an overnight sleeping site, they prefer caves or crevices. Or they might choose a cliff edge. While sleeping on a cliff might seem precarious, there is logic to this decision. Attacks from would-be predators are less likely. Should a predator attempt an attack, the monkeys’ comfort and familiarity with their karst landscape better allows them to escape. Their greatest threat (after humans) are large birds of prey, including the crested serpent eagle. Proximity of food sources is another consideration when choosing a sleeping site. A group typically uses the same sleeping site for up to three nights before moving on to another.

Fun Facts

​Or myth! Legend is that long ago in southern China, poor villagers—unable to provide food to their children—abandoned their children deep in the forest with the hope that the young ones might survive by eating fruits and leaves. Many years later, when the villagers’ food reserves improved, they returned to the forest to reclaim their children. What they found shocked them. Their offspring had been transformed by the forested environment. White headdresses, fur coats, and tails now characterized their once-human forms. And . . . the children refused to return home with their parents. White-headed black langurs are said to be the descendants of these mythical forest children.

Daily Life and Group Dynamics 
White-headed black langurs live in groups (known as “troops”) of 9 to 12 individuals; group size varies according to habitat quality. Typical composition includes an alpha adult male and his harem (usually several females) and their offspring. Some groups have a second adult male.

Young males, those who leave their birth (or natal) group upon reaching sexual maturity, sometimes live in bachelor (or all-male) groups, until they are able to find a new group, take it over by deposing the troop’s alpha male, and successfully instill themselves in the role. Infanticide is a common occurrence after troop takeovers, with the newly self-appointed male leader killing all the babies of the nursing females. The primary objective of this violent act, however, is biological—intended to induce ovulation in the females and improve the new alpha male’s chances of passing on his genes by siring infants of his own.

Females usually remain with their natal group. However, if their troop has been overtaken by an outsider male, they might try to find a more hospitable troop, especially if the male interloper has killed their babies.

Apart from a troop’s takeover and possible infanticide, aggression is rare within white-headed black langur troops, so hierarchical order is not overt. Nevertheless, members abide by a loose hierarchy with the alpha male foremost, followed by the most dominant female, then by subordinate females. Tacit understanding and acceptance of this organizational structure is evident during meal time. Males get to eat first. Should a subordinate female start munching her dinner before an alpha female has had a bite, the alpha female is likely to grab away the upstart’s food.

Researchers have reported an occurrence within a group of two adult males (an alpha and a “second in command”), where the males joined together to chase away males from an outside troop. As a thank you, maybe (?), the alpha permitted his “lieutenant” to copulate with members of his harem and to eat alongside him.

Home range for the species is 39.5–116 ac (16–47 ha), with an average size of 75.4 ac (30.5 ha).

Other animals who live in China’s Guangxi Zhuang Autonomous Region include black crested gibbons, cloud leopards, and pangolins. But the region’s karst limestone habitat is an ecological niche, hospitable to specially adapted creatures like the white-headed black langur and its close cousin, the Francois’s langur.

Communication
Not much information is available about how white-headed black langurs communication with one another verbally. It might be that, like some other colobine monkeys in the genus Trachypithecus, they are more the silent type. Still, a few vocalizations have been documented, attributed to a troop’s alpha male.

To draw his troop members together in a protective huddle, he emits a “ka, ka” call. To alert members to possible danger, he emits a loud and repetitive “a, a” call. Variations of this call include “a, a, a,” which gives members a chance to escape hostile outsiders, and an irregular, woeful-sounding “a, a” call emitted by an alpha male who has been dethroned by an outsider male.

The monkeys’ play sessions allow us to conjecture that tactile communication is a part of their daily life. Unmentioned in researchers’ notes are family grooming sessions. However, grooming is seen in all nonhuman primates, though the action may be performed differently among species. Performed on one another, the pastime helps to instill social bonds.

Reproduction and Family
White-headed black langurs breed throughout the year, with most births occurring during the dry, cold months of November through March. Quality of habitat impacts the species’s birth rate, with higher quality habitats favoring successful reproduction. At about 34 months of age, and after a pregnancy of 214 to 224 days, a female gives birth to a single infant. Mortality for infants younger than 20 months of age is 15.8 percent. The species’ birth interval is 18 to 24 months.

Infants are dependent on their mothers until 19 to 21 months of age, at which time they are considered fully weaned. Researchers attribute this lengthy weaning period (significantly longer than other Asian colobines) to habitat degradation and fragmentation.

Ecological Role
While they are not the forest regenerators like their frugivorous (primarily fruit-eating), scatological seed-dispersing primate cousins, folivorous white-headed black langurs help to “prune” their habitat through their heavy consumption of leaves. They are important citizens in their own right, contributing to the diversity of the ecosystem in which they live.

Conservation Status and Threats
The white-headed black langur is classified as Critically Endangered by the International Union for Conservation of Nature (IUCN, November 2015), appearing on the IUCN’s Red List of Threatened Species. This ignoble classification means that the langurs are only one step away from extinction in the wild. In the last three generations of the species (36 years), the population has declined nearly 85 percent. In 2015, the IUCN estimated only 250 adult individuals remaining in the wild, with no subpopulation having more than 25 adult individuals. Today’s total population hovers at just over 1,300 white-headed black langurs (a marked improvement, but still precarious), with most of these individuals residing in Chongzuo.

The late 1980s fueled the steady demise of the species. Poaching was rampant, and impoverished locals, looking to subsidize their paltry income, shot and killed the monkeys. They then sold the corpses to the medicine industry, where the monkeys’ dismembered and disemboweled bodies were processed to become ingredients in traditional remedies. Or, poachers sold the monkeys for their flesh, known as “bushmeat.” Additionally, farmers who were worried about potential damage to their crops set steel-jaw leghold traps to capture, then kill, the monkeys.

Habitat loss continues to be a major threat to the species’s survival. More than 80 percent of its total range has been lost through anthropogenic (human-caused) disturbances. Cleared for agricultural use and charcoal production, pristine forestland is set afire, in what is known as “slash and burn” farming. These uncontrolled forest fires spread readily and destroy white-headed black langur habitat. Trees are also routinely felled to clear the land for human use.

Forced to live in isolated, fragmented habitat patches, the monkeys are vulnerable to “inbreeding depression.” The term refers to a reduced biological fitness level in a population, resulting from breeding with related individuals. Harmful genetic alterations in offspring leave individuals susceptible to certain diseases and disorders—and can threaten a species’ survival.

Hybridization of the white-headed black langur, caused by the deliberate release of Francois’s langur, poses an additional threat.

Conservation Efforts
White-headed black langurs are listed in Appendix II of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival. The species is also classified as a category I under China’s Wild Animal Protection Law.

Protected areas where populations of white-headed black langurs reside include the Fusui and Chongzuo and Nature Reserves, in their respective counties. About 90 percent of the total population lives in the Chongzuo reserve, with each family occupying a cluster of limestone hills. Chongzuo’s population has experienced a surge from only 300 individuals at the end of the 1980s to more than 1,300 (including 130 subgroups) by the year 2020. An increased presence of ranger patrols in the reserve discourages poachers from violating the law and killing the monkeys. Technology, in the form of infrared cameras and drones, helps to better monitor the population.

Other protective actions under way are strict enforcement of conservation policies that include increased restrictions on land use and the regulation of cattle grazing and tree clearing; the creation of nature awareness programs for local citizens—beginning with children—that foster an understanding and appreciation of these Critical Endangered primates and their importance in the ecosystem; academic exchanges that bring young conservationists from across the globe to learn about the species in their karst habitat; and continued research on wild populations.

An imperative, scientists stress, in the conservation of this species is a deeper understanding of the correlation between the species’s low genetic diversity and population isolation caused by highly fragmented habitat patches. They cite the species’s two relict populations of Fusui and Chongzuo, separated from the other by 31 mi (50 km), as urgent examples.

Strategies to counteract genetic isolation (and deter inbreeding depression) include the creation of corridors that allow white-headed langurs to move freely and safely between habitats. With access to nonrelated mating partners, gene flow improves as does the species’ outlook for survival. The first such biological corridor was created in 2019 in the Chongzuo Reserve.

Finally, programs that help local people to enjoy a quality of life by earning a living that does not involve killing the monkeys cannot be overlooked. A poacher can earn $50 for each langur killed, a significant amount considering that the annual average per capita income in the region is less than $350. So incentives and real-life alternatives for livelihoods are necessary.

References:

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  • https://en.wikipedia.org/wiki/Ningming_County
  • https://en.wikipedia.org/wiki/Longzhou_County

Written by Kathleen Downey, August 2021