WHITE-CHEEKED MACAQUE

Macaca leucogenys

Geographic Distribution and Habitat
A birdwatching group from northeast India, composed of wildlife photographers and biologists, affirmed the discovery of the white-cheeked macaque (Macaca leucogenys) while visiting Mêdog county in southeastern Tibet in March 2015. It was in the Anjaw district of Arunachal Pradesh (a region claimed by India, China, and Taiwan with a related history of political conflicts) where a troop of white-cheeked macaques surprised the unsuspecting birders. As happenstance would have it, this new species was heralded just days earlier in the American Journal of Primatology with an account from a team of Chinese researchers who had set up camera traps in four Tibetan gorges. After reviewing many months of collected camera trap images (more than 700!), along with direct observations and photographs, the Chinese team were convinced they were looking at a “new monkey.”

Later scientific testing, including physical measurements and molecular diagnosis through DNA extracted from four collected skin specimens, would confirm the white-cheeked macaque as a distinct, previously unknown primate species and as one of the most important zoological discoveries of the decade.

At present, Mêdog county is the only known range of white-cheeked macaques. But wildlife researchers speculate that the species’ geographic distribution may extend to neighboring counties in China and regions of southeastern Tibet that are controlled by India.

Mêdog county is known for its network of diverse ecosystems and rich biodiversity. Arunachal Pradesh—known as the “land of dawn-lit mountains” and home to white-cheeked-macaques—is situated at the junction of the Eastern Himalayas and Indo-Burma regions.

This area is defined by alluvial, low-lying grasslands (created by river sediment), subtropical broadleaf forests (jungles), and alpine meadows that rise above the tree line at a wide altitudinal range, from 492 to 19,685 ft (150–6,000 m) above sea level. These newly recognized “whiskered” macaques take advantage of their varied habitat, residing within tropical forests at 4,577 ft (1,395 m), within primary and secondary evergreen broadleaf forests at 6,562 ft (2,000 m), and within mixed broadleaf-conifer forests at 8,858 ft (2,700 m).

A white-cheeked macaque geographic range map is not yet available. This is the 2020 IUCN range map for a similar species, the Arunachal macaque, for perspective regarding where in the world white-cheeked macaques live.

Size, Weight, and Lifespan
Macaques are medium- to large-sized monkeys with a body length ranging from 1.25 to 2.3 ft (38–71 cm) for adults, depending on the species. Tail length also varies with species, ranging from a stub to very long. Males are much heavier than females, an example of sexual dimorphism. An adult male macaque can weigh from 11 lb to nearly 40 lb (5–18 kg), compared to an adult female’s weight of 4.4 lb to nearly 29 lb (2–13 kg).

True to their genus (Macaca), white-cheeked macaques are robust, heavy-bodied monkeys. Nature has fitted them with a comparatively short tail that bends downward in some individuals. They are larger than Assam macaques (M. assamensis), whom they resemble, but are similar in size to Tibetan macaques (Macaca thibetana).

Lifespan has not been reported for this species.

Appearance
Long white whiskers that extend from the cheeks and chin give this new monkey its common name. Their whiskers begin growing as the monkeys reach adulthood, and their facial skin darkens. By the time white-cheeked macaques are fully mature, their faces—and even their ears—are covered by a furry, densely whiskered jungle. Only the dark-skinned muzzle and pinkish eyelids escape this hirsute encroachment. As a finishing touch, Nature has painted a thin, dark stripe of fur beginning at the outer corner of each eye, or from the monkey’s upper cheek, and extended it to each ear.

As with other macaques, the coloring of their fur coat (pelage) varies. Shades of light to dark brown and dark chocolate cloak their sturdy bodies. In most individuals, fur coloring of their gloriously unkempt ventrum (underside) is lighter than the even mantle of fur covering their dorsum (the back). The white-cheeked macaque’s short, hairless tail begs for no attention. A thick, hairy ruff is worn like a muffler around the neck and is a distinguishing feature of the species.

Males have another distinguishing feature: their penis. Unlike the arrow-shaped penis and white scrotums of sympatric macaque species, particularly their “lookalike cousin,” the Assam macaque, the penis of white-cheeked macaques is rounded and their scrotum is dark and hairy. This distinction of genitalia helped convince wildlife researchers that they were looking at a new species. Prudence prevailed, thankfully, in giving these primates their common name of white-cheeked macaque.

Photo credit: Dibyendu Ash/Creative Commons

What Does It Mean?

Alarm call:
Specific calls that individuals in a troop make to warn other members of their group of imminent danger—such as predators.

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

Arthropod:
An invertebrate animal (one with no spine) having an external skeleton, a segmented body, and jointed appendages. Includes insects, spiders, and crustaceans, and myriapods.

Genus (plural, genera):
A biological classification, or ranking, of living beings that includes a group(s) of species that are structurally similar or “related” to one another through evolution.

Hirsute:
Covered by hair. Extremely hairy.

Invertebrate:
An animal without a backbone (spine), including arthropods, mollusks, myriapods (including earthworms, leeches, millipedes, and centipedes), sea anemones, and corals.

Primary forest:
Also termed old-growth forest, virgin forest, or primeval forest—a forest that has attained great age without significant disturbance and thereby exhibits unique ecological features and might be classified as a climax community, an ecological community in which populations of plants or animals remain stable and exist in balance with each other and their environment.

Secondary forest:
A forest that has regrown after a major disturbance, such as fire or timber harvest, but has not yet reached the mature state of primary forest.

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

Species:
A group of living organisms (animals) consisting of similar individuals capable of exchanging genes or interbreeding. The species is the principal natural taxonomic unit, ranking below a genus.

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

Terrestrial:
Living on the ground.

Visit the Glossary for more definitions

Diet
These primates are known to forage in a wide range of habitats; however, their dietary preferences have not been reported. More is known about the diets of the four sympatric species of macaques who live in the region.

Rhesus macaques (M. mulatta) are omnivores and consume a large number of plants, roots, seeds, bark, and fruit along with insects, eggs, and chicks. The bulk of their diet, however, comes from human handouts and from raiding farm crops.

Tibetan macaques (M. thibetana) are omnivores with strong vegetarian tendencies. They prefer fruits and leaves, and sometimes eat bamboo or grass. Birds and snakes are on their menu only occasionally.

Assam macaques (M. assamensis) are omnivores who eat fruits, leaves, grasses, invertebrates, and grains (the last item is a testament to their skill as crop raiders).

Arunachal macaques (M. munzala) are largely herbivores (adhering to a mostly vegetarian diet), eating leaves, fruits, flower, stems, and—during winter months—tree bark. They supplement their diet with the occasional small invertebrate and—for vital minerals including calcium, sodium, and iron—they eat mud. (The practice of eating mud, dirt, or clay is scientifically known as geophagy).

So, what conclusions can be made, if any, about the diet of white-cheeked macaques? While the food preferences of the aforementioned sympatric species might suggest that the whiskered ones share a common diet, certain factors must be considered. For example, are these other macaques diurnal or nocturnal? (Do they forage at the same time of day or night as white-cheeked macaques?) Do they prefer one plant to another or one part of a plant to another—having different plant preferences than white-cheeked macaques? These, and other, factors can play a role in shared food resources and in “neighborly” (or live-and-let-live) encounters between the species.

Certainly, Mêdog county offers a plethora of plant life—more than 3,000 species—from which white-cheeked macaques can make their dietary selections. Over 1,000 species of hexapods (six-legged arthropods) also live here, more than enough to supplement any monkey’s diet.

It is likely that white-cheeked macaques are primarily herbivores. Ultimately, however, documented scientific findings are needed to confirm the white-cheeked macaque’s precise food preferences.

Behavior and Lifestyle
Little is known about the behavior and lifestyle of white-cheeked macaques. Because the region where they live had remained isolated for so long—it wasn’t until 2013 that a highway was built, linking Mêdog county with the rest of China and beyond—these elusive monkeys had managed to go undetected.

Is it possible that by looking at similar macaque species, we can gain clues or insights? Scientists have placed white-cheeked macaques in the sinica group, whose members include Assam macaquesTibetan macaques (M. thibetana)toque macaques (M. sinica); and bonnet macaques (M. radiata). But some scientists dispute this placement, citing a specific anatomical difference: the white-cheeked macaque’s rounded penis. All other males in the sinica group are endowed with an arrow-shaped penis.

Furthermore, deep genetic research shows that white-cheeked macaques diverged 2.5 million years ago from their closest relatives: bonnet macaques, who are endemic to southern India; and from Arunachal macaques, a sympatric species.

What we know for certain about white-cheeked macaques is from those two independent groups of intrepid explorers: the team of Chinese wildlife researchers, credited in 2015 with discovering the species, and the bird-watching group from India who affirmed the species’ discovery shortly thereafter.

Fun Facts

Wildlife researchers recognize at least 23 species of macaques. Except for Barbary macaques (Macaca sylvanus), who reside on the Rock of Gibraltar along North Africa’s Barbary coast, all of these species live in Asia.

Daily Life and Group Dynamics 
White-cheeked macaques live in multi-male, multi-female groups (known as “troops” in the primate world) comprising a pair of breeding adults and their young. In October 2013, the Chinese researchers encountered six groups of macaques over a six-day period. Five of the groups were foraging or resting in the forest. Members of the sixth group, comprising two adult males and four adult females, were observed foraging along a riverbank. Eventually, a couple began to mate. Later in the day, researchers spotted (and photographed) two juveniles and another adult.

Fast forward to November 2014, when the Indian bird-watching group entered the forest in Arunachal Pradesh. To their delight, they encountered a family of six monkeys, yet to be identified as white-cheeked macaques. The monkeys, two males and four females, were grooming one another, resting, foraging, and playing along a riverbank. The birders’ patience rewarded them with an intimate moment: the adult couple began mating.

In reviewing extensive camera trap footage, the Chinese researchers noted that the most images of these monkeys were captured between 12 p.m. and 7 p.m.; fewer were captured between 7 a.m. and 12 p.m.; and no white-cheeked macaques were photographed at night. These finding suggest a mostly diurnal species, one who perhaps likes to sleep late.

Camera trap footage also captured white-cheeked macaques sitting upright on a bough of a tree, standing upright on the forest floor, moving quadrupedally (on all four limbs) along a riverbank, and sitting in a tree amongst thin branches, as if contemplating moving forward by grasping branch to branch. These behaviors suggest a species that is both terrestrial and arboreal. Sleeping sites have not been reported.

Communication
Adult white-cheeked macaques emit high-pitched alarm calls that carry a distance of 0.62–1.24 mi (1–2 km). The monkeys sound these urgent calls when frightened by human interlopers (or researchers, depending on perspective of nonhuman primate vs. human primate). Having lived an isolated, natural life in the jungle for so long, white-cheeked macaques are not accustomed to human company.

Although their complete vocal repertoire has not been reported, all previously studied macaques share the following call types: alarm call, coogrowlnon-tonal screamgreeting calltonal screamsqueakfood callfemale and male copulation callbark, and loud call.

Mutual grooming sessions appear to encompass a significant part of white-cheeked macaques’ days and are important in establishing familial bonds with one another.

Reproduction and Family
Little data is available about the reproductive and family life of this still fairly newly discovered primate species. For clues, we might think to look at the Arunachal macaque, the white-cheeked macaque’s closets relative and a sympatric species. Alas, not a lot is known about the reproductive life of this primate, either. Inferences about the Arunachal macaque, first described in 2005, are drawn from closely related macaque species. We know that the gestation period (pregnancy) for other macaque species varies between 150 and 190 days. All macaques give birth to one or two offspring at time, so this is likely true for white-cheeked macaques as well.

However, we can assume that the breeding season for white-cheeked macaques includes the months of October and November. Both the Chinese researchers and the Indian birdwatchers, respectively, witnessed a pair of adult white-cheeked macaques mating during these months. The winter season in Arunachal Pradesh is from October to March, so it’s likely that this is the breeding season for the species. Cooler winter temperatures, 41–59° F (515°C), are more amenable for getting cozy than the summer months (April to June) when 95° F days are common. Monsoon season (July to September) may hold the least appeal for getting romantic. (We might also assume that these monkeys find a riverbank to be a romantic setting.)

Beyond calendar deductions and amateur, lighthearted scientific conjecture, only additional wildlife surveys will provide important insight into the reproductive life of white-cheeked macaques.

We do have some insight into family life. Camera trap images suggest that these monkeys take parenting seriously. Many photographs depict parents tending to their young. Mothers appear to show particular affection for their infants, whom they allow to clamber up mom’s body.

Photo credit: Cheng Li/ Creative Commons

Ecological Role
As (presumed) herbivores, white-cheeked macaques disperse the seeds of the plants they have consumed via their feces, helping to regenerate new growth in their forested habitat. Apart from this integral ecological contribution, they are citizens of the earth in their own right.

Conservation Status and Threats
“Not Evaluated” usually applies to recently described species, like the white-cheeked macaque. Given the dearth of information about this newly named species, the International Union for Conservation of Nature (IUCN) has not yet assessed their population numbers or the threats to those populations. But this categorization does not mean that these whiskered monkeys are safe. Without extensive study, white-cheeked macaques are not afforded the protections that better-studied species garner. We could lose these monkeys before we even know enough about them to save them.

Illegal hunting (poaching) by local tribes and habitat loss due to the construction of hydropower stations in Mêdog are threatening the lives of these monkeys. Of these two threats, the hydropower stations are the more ominous. Conservationists fear that extensive tracts of riverfront forest (white-cheeked macaque habitat) will be flooded and forever lost; new roads will lead to an influx in the human population and in human settlements—and lead to an increase in the bushmeat trade by providing hunters with easier access to the macaques.

Even the chief engineer for the geological survey team associated with the project has warned, “Tibet’s ecology is extremely vulnerable, and would be very hard to restore if damaged.”

Conservation Efforts
​Wildlife researchers recognize the discovery of the white-cheeked macaque as an alarm call for the conservation of the species, along with the conservation and protection of other species (those already discovered and yet to be discovered) in this biodiverse region. They urge additional wildlife surveys and studies and call for environmental protection in southeastern Tibet.

​References:

  • ​Cheng Li, Chao Zhao and Peng-Fei Fan. “White-cheeked Macaque (Macaca leucogenys): A New Macaque Species from Modog [sic], Southeastern Tibet.” American Journal of Primatology. Published online March 25, 2015; DOI: 10.1002/ajp.22394.
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  • https://www.sciencedirect.com/science/article/abs/pii/S1055790316302731
  • https://link.springer.com/chapter/10.1007/978-3-030-27920-2_7
  • https://www.conservationindia.org/gallery/white-cheeked-macaque-a-new-primate-species-for-india
  • https://www.thehindu.com/news/national/other-states/Rare-primate-sighted-in-Arunachal-Pradesh/article14251759.ece
  • https://www.hindustantimes.com/india/meet-the-white-cheeked-macaque-new-primate-species-seen-in-arunachal/story-EprW77zDOmk3jtuAYCidxO/ 
  • http://www.sci-news.com/biology/science-white-cheeked-macaque-macaca-leucogenysmacaca-leucogenys-tibet-02705/  
  • https://www.newscientist.com/article/dn27317-new-monkey-species-revealed-thanks-to-distinctive-penis
  • https://news.mongabay.com/2015/04/scientists-find-new-monkey-with-unique-penis
  • https://www.techtimes.com/articles/45632/20150412/scientists-discover-new-species-of-macaque-and-heres-whats-unique-about-them.htm
  • http://novataxa.blogspot.com/2015/04/macaca-leucogenys/   http://www.bbc.com/earth/story/20150408-amazing-images-reveal-new-macaque
  • https://en.wikipedia.org/wiki/Arunachal_Pradesh
  • https://www.yalaadventure.com/tibet
  • https://www.chinadialogue.net/article/show/single/en/4055-A-new-era-for-Tibet-s-rivers​

Written by Kathleen Downey, May 2020