Northern Yellow-Cheeked Crested Gibbon, Nomascus annamensis
NORTHERN YELLOW-CHECKED CRESTED GIBBON
Nomascus annamensis
Geographic Distribution and Habitat
The northern yellow-cheeked crested gibbon, also known as the northern buffed-cheeked gibbon, lives in the tropical rainforests of Laos, Cambodia, and central Vietnam. This species inhabits broadleaf evergreen and semi-evergreen forests at elevations between 330 and 3940 feet (100–1200 m) above sea level.
Identified in 2010, the northern yellow-cheeked crested gibbon is the most recent addition to the crested gibbon genus, Nomascus. Once upon a time, all crested gibbons were believed to be the same species, dubbed Nomascus concolor. Further research has slowly challenged this classification, and ultimately proved it inaccurate. Modernized methods and technological advances for gathering and analyzing genetic, morphological, and auditory data have helped us reveal the six distinct crested gibbon species known to today, one of which is the northern yellow-cheeked crested gibbon. Today, Nomascus concolor only refers to the black crested gibbon found in northern Vietnam, northwestern Laos, and southwestern China.
Before 2010, there was thought to be only one species of yellow-cheeked gibbon, Nomascus gabriellae. After the 2010 discovery of Nomascus annamensis, the geographic distribution of this species was split in two. The species in the southern part of the former distribution area kept their original scientific name while the novel species in the northern part was given a shiny new one, Nomascus annamensis. Their common names have also been given qualifiers that match where they live in relation to each other, one to the south and one to the north.
Size, Weight, and Lifespan
When it comes to size, northern yellow-cheeked crested gibbons show very little sexual dimorphism. Males weigh 15 pounds (7 kg) on average and measure roughly 18 inches (46.2 cm), head and body. The average weight of a female northern yellow-cheeked gibbon is currently unknown, but measuring a little over 17 inches (43.8 cm) on average, it’s safe to assume they don’t weigh much less than the average male.
While their lifespan has not been studied, some species of gibbons are known to live upwards of 30 years in the wild.
Appearance
Gibbons look similar to monkeys, but they are actually apes. Just like other apes such as bonobos, chimps, gorillas, and orangutans, they lack tails. However, compared to these “great apes,” gibbons are remarkably small, which is necessary since they spend their entire lives in the canopy. The only other apes who spend a significant amount of time in trees are orangutans.
Northern yellow-cheeked gibbons, like other crested gibbon species, exhibit striking variations in appearance based on sex and age. Infants are all born a whitish, buffy color. They remain this color until, at about six months, their coats turn black. Males retain their black color for the rest of their lives. Females transition back to a lighter pelage as they enter adulthood but with a more orange hue than when they were young.
Adult male northern yellow-cheeked gibbons appear stark black except for the brownish tinge on their chest. Illuminated by a ray of sun, their hidden silver strands of hair peppering their coats begin to glimmer. Only males sport this species’ signature cheek patches. The colors of these patches vary by individual, appearing golden for some and buffy for others. Reaching less than halfway up to their ears, they have a rounded shape and connect under their chins. Crested gibbons are notoriously difficult to identify in the wild, which is precisely the reason why researchers have historically had trouble classifying them. Looking at males’ cheek pouches is the most effective way to distinguish northern yellow-cheeked gibbons from other crested gibbons using the naked eye.
Adult female crested gibbons are essentially indistinguishable from each other regardless of their species. This is also true of northern yellow-cheeked gibbons. All have lighter coats and tend to sport a black crest on the top of their head, though its shape and position varies by individual. Some females also exhibit darker fur on their chests.
Diet
Northern yellow-cheeked crested gibbons have a strong preference for fruit. But many gibbon species vary their diet seasonally, relying on less tasty but still nutritious options during the dry season when fruit grows scarce. Leaves, young shoots, and flowers are some other staples of their diet, but insects, bird eggs, and lizards may also make it onto their menu.
Northern yellow cheeked gibbons may even occasionally eat other mammals. One piece of anecdotal evidence describes one female eating a Finlayson’s squirrel and sharing it with her family. Another claims seeing an adult chowing down on a baby pig-tailed macaque. If true, it is not clear if such meals are acquired by passive coincidence or through active hunting.
Behavior and Lifestyle
Gibbons are arboreal (tree-dwelling), living high in the canopy. Here, they have everything they need to live happy and healthy lives while staying out of the way of predators. They rarely, if ever, venture to the lower levels of the forest.
Northern yellow-cheeked gibbons are diurnal and notoriously early-risers. Each morning, beginning at around sunrise, male and female pairs sing to each other. The lilting and haunting arias they exchange can be heard for up to a kilometer. These are not only useful for locating each other after a night sleeping apart, but they also help the pair establish their territory, letting any nearby gibbons know where they are and not to come too close.
Many gibbon species practice both early-to-wake and early-to-bed lifestyles, keeping active only for as long as the sun is up. When the sun is up, they are quite busy. Though they take breaks after meals, when they are not feeding, they are likely traveling to find food or socializing. Adults stay alert, keeping watch for threats while little ones play.
Gibbons are territorial. Unless they are trying to find a mate, gibbons tend to socialize with their immediate family members only. All others are considered outsiders and are chased away. Grooming and singing together both act as important ways of reinforcing their strong familial bonds.
Gibbons’ primary form of locomotion is known as brachiating. Hanging from a branch by one arm, they swing their body forward to grasp the next, continuing in this alternating pattern until they reach their goal. While all apes brachiate, gibbons are the true virtuosos of this method. Not only do they navigate the canopy with style and grace, they can also reach speeds of up to 35 mph (56 km/h)! While brachiation is their go-to, gibbons improvise their movements as they go, leaping great distances and falling from great heights in order to reach the next tree. They even frequently walk in a bipedal fashion along a branch, moving swiftly and holding their arms out for balance. Due to this technique, gibbons actually walk upright more than any other wild ape.
Gibbons are the virtuosos of brachiation because they have evolved a special set of physiological adaptations not found in other ape species. Firstly, their wrists are composed of ball and socket joints. These not only allow for specialized, biaxial, movement but significantly reduce the amount of energy required by the upper arms and torso and even minimize stress in their shoulders. Additionally, the joints in their shoulders can rotate a full 360 degrees, greatly increasing their range of motion and overall dexterity. Long arms help them to bridge the distances between branches with ease while their hook-shaped hands ensure a firm and consistent grasp. Gibbons’ thumbs are shorter than other apes, keeping them useful for grooming without getting in the way during brachiation. Of course, all these traits wouldn’t be nearly as useful had gibbons not also evolved such well-developed cerebellums. This section of the brain helps to coordinate movements and regulate muscle activity, giving gibbons exceptional balance, poise, and spatial perception.
A young gibbon is not a natural acrobat, however. Young gibbons must develop their bodies and skills for several years before they are ready to take on the canopy completely on their own. Playtime is the perfect chance to practice. Since it happens so high off the ground, gibbon play is considered some of the riskiest in the world. One slip-up during a game of chase could easily mean the end of a young gibbon’s life. As a result, gibbon parents (both Mom and Dad) pay careful attention to their young while still giving them the space to practice and try out new moves.
Gibbons are learners. They aren’t born knowing how to survive in their habitat but develop the necessary knowledge and skills as they age, like being able to identify which foods are edible (and tasty) and which animals are predators. To learn this information, little ones rely on their parents to show them, a phenomenon some researchers argue qualifies as cultural transmission.
Because they are often mistaken for monkeys and receive less attention than their better-known great ape relatives, gibbons are sometimes referred to as “the forgotten apes.”
Gibbons sing in regional dialects, which is why researchers are able to use auditory data to identify different species.
Gibbons live in small nuclear families consisting of a mother and father and up to four of their offspring. Mom and Dad both take on the responsibilities of caring for their young, and family members develop close bonds with one another as they feed, play, groom, and sleep together.
A family of northern yellow-cheeked gibbons wakes just before dawn when their canopy home catches the sun but the forest below remains dark. They spent the night in separate trees, and Mom and Dad exchange songs to find each other. Their lilting calls help the pair re-establish their special bond and also act as a warning for strange gibbons to stay away.
The family members spend their morning bonding and breakfasting high in the canopy. Throughout the day they rest and travel to find more food. By nightfall, the family chooses one or two trees in which to sleep.
Gibbons are well-known for their loud, far-reaching and acoustically complex vocalizations, often referred to by researchers as “songs.” While the characteristics of such songs vary from species to species, their functions seem to be mostly universal: helping family members reconnect, as well as warning unfamiliar gibbons to keep away.
Mating pairs of northern yellow-cheeked gibbons sing each morning when the sun first hits the top of the trees. The male and female take turns in a haphazard call-and-response pattern that gradually overwhelms the competing songs of insects and birds in the still-dark jungle below.
The repertoire of calls these apes produce is distinctive to their sex. The female’s consists of a series of high-pitched and haunting notes that successively increase in pitch, volume, and speed, an auditory experience that resembles an approaching ambulance siren. At climax, her call suddenly shatters into a staccato chirp of notes that fall in pitch and bend in timbre. The male’s call is also a series of notes, each as high-pitched and haunting as the female’s, that lilt upwards in tone until they flatten into a squeak. He may also make loud booming calls that seem to shake the whole jungle around him.
Gibbons are not born instinctively knowing how to sing. It takes years of practice to perfect these highly specialized calls. Young gibbons begin by trying to mimic their parents, making a lot of mistakes at first. After a few years, they start to get the hang of it and learn each section of the duet in the order it’s sung. This process may look different in species, however. In some, it’s been observed that young males originally only practice their mother’s song. Some researchers presume this prevents them from accidentally triggering their father’s territorial defenses. Northern yellow-cheeked gibbons only begin to make the call of a male as subadults, making them with greater frequency and for longer durations the closer they get to adulthood when they finally say good-bye to their natal group.
Like so many other social primates, northern yellow-cheeked gibbons use a wide variety of facial gestures and body language to communicate. Family members also groom each other as a way of reinforcing their bonds.
The full complexity and meaning of gibbon vocalizations and other modes of communication are paramount for their conservation and will only become clearer with more research.
Gibbons establish monogamous male-female relationships that form the foundation for gibbons’ chief social unit: the nuclear family. While these relationships generally last throughout their lives, they may occasionally end in separation. There is also evidence that pairs are exclusive when it comes to mating. So, while gibbons can be considered socially monogamous, it is no longer assumed that they are sexually monogamous. However complicated their relationships may be, the family unit creates an important structure for a young gibbon’s life as each parent invests their time and energy in their young’s survival and success.
Research exploring the reproductive habits of this newly identified species has yet to be conducted. For now, we can use some of what we already know about the southern yellow-cheeked crested gibbons to fill in the blanks about their northern yellow-cheeked crested cousins.
After mating, a female northern yellow-cheeked gibbon is pregnant for around seven months. Her newborn is tiny and, at first, relies on her completely. Being beige in color himself, the little guy blends almost seamlessly into his mother’s light-colored fur. He nurses for a number of months before venturing away from his mother’s warm and comforting embrace to try his first attempts at navigating his canopy home. He begins to watch what his parents do, noting what they eat as well as what forest creatures to be wary of. He also mimics their songs, practicing for the day when he’ll also have a duet partner. Gradually, he gains the knowledge and skills to survive in the wild. Between seven and eight, after reaching sexual maturity, he leaves his family in hopes of starting one of his own.
Females lead similar lives but may leave the group sooner and are usually between seven and eight years of age when they give birth for the first time. Because raising their young is so taxing, both gibbon parents help out, and mothers wait until their current offspring can take care of themselves at least a little before having another. At any given time, a gibbon family typically consists of two parents, a juvenile, and an infant.
All gibbons play critical roles as seed dispersers. When northern yellow-cheeked gibbons eat their beloved fruits, the seeds pass through their digestive systems intact. They then drop to the ground in their feces miles away from where they were eaten. Through this process, the forest is constantly being regenerated, and the biodiversity of forests is preserved.
The northern yellow-cheeked crested gibbon is classified as Endangered by the International Union for Conservation of Nature (IUCN, 2015), appearing on the IUCN Red List of Threatened Species, and populations are currently in decline.
As arboreal apes, northern yellow-cheeked gibbons face a host of threats in the wild with habitat loss being one of the most worrisome. According to Global Forest Watch, Vietnam lost at least 16% of its natural forests in the last 20 years due to human activity and, if trends continue, may lose up to 60% in the next 20 years. In the same amount of time, Cambodia has lost 25% and is predicted to lose up to 70% by 2045. In Laos, 16% and 52% respectively.
While the complete destruction of their forest homes threatens gibbons, even seemingly minor changes to their environment have immediate and adverse effects on their well-being. Because they are strictly arboreal, gibbons rely on continuous canopy cover to navigate. Gibbons keep large ranges and travel significant distances to find food or mate. When their habitats are fragmented, it limits their ability to move about freely. Even the building of a one-lane road can create a gap too difficult for gibbons to cross. Facing such an obstacle, a gibbon must choose to either risk making a hazardous leap or venturing to the ground where they are vulnerable to predators and, in the case of a road, oncoming traffic. Additionally, the forest floor is home to a host of bacteria not found in the canopy that can make gibbons sick and even kill them.
As the gaps in their forests widen, gibbon populations become confined to these fragments, and family groups are pushed closer together. Competition for space and resources increases, ensuring more territorial disputes become physical. Under these conditions, some gibbons are bound to perish.
Those gibbons who survive are left in an unfortunate situation. As fragmentation limits gibbon-to-gibbon contact, gene flow slows to a halt, forming genetic bottlenecks. A lack of genetic diversity causes huge problems for primates. In only a few generations, once healthy gibbon populations may become vulnerable to diseases and parasites, or develop birth defects that are passed on to the next generations indefinitely. All of these changes severely decrease the chances that new generations live long enough to ever procreate.
Northern yellow-cheeked gibbons are regularly hunted and killed in Vietnam, Cambodia, and Laos for their meat or to be used in traditional medicines. Humans also capture young gibbons to keep or sell them as pets. Poachers are only interested in baby gibbons and 100% of the time have to kill the mother, and often the father as well, to get one.
As pets, gibbons not only suffer mentally and physically but also miss out on learning how to be a natural gibbon in the wild. Gibbon parents put a great deal of time and energy towards helping their young develop. Therefore, it is extremely difficult for an orphaned or kidnapped gibbon to recover after being separated from his or her parents. Even when gibbons survive capture and confinement, their rehabilitation is a long and time-consuming process, with no guarantee they will be released back into the wild.
In Vietnam, Cambodia, and Laos gibbons are frequently poached from the wild and used to entertain tourists at zoos and hotels. Tourists usually just see a cute animal and are not confronted with the gibbon’s troubling past nor do they ever witness its daily sufferings.
The same sort of problem is rampant across social media platforms where uninformed users are confronted with pictures and videos of gibbons and other primates kept in captivity as pets. Posters of such material are careful to curate their posts so their followers conveniently never see the daily cruelty and misery their captees endure behind the scenes. While this phenomenon often seems trivial to some, studies show that media depicting primates as “cute” sends the message that they make suitable pets, priming people to accept and spread this sort of material. Others may even decide they want to get a primate of their own, fueling their trafficking and ensuring more gibbons are harmed. Unlike cats and dogs, who were naturally domesticated by humans over long periods of time, primates never make suitable pets and belong in the wild.
The difficulty researchers still have when it comes to classifying crested gibbons and knowing the range and distribution of each species causes problems for people rehabilitating gibbons, as they need to be able to easily identify a gibbon’s species and know where an appropriate place to stage a release will be. Additionally, it affects what gibbons they can socialize with as well as what foods rehabilitators should give, or not give, to the gibbons in their care. Inaccurate classifications and distribution cause issues for other conservationists as well. Species like the northern yellow-cheeked gibbon, which were once thought to have a larger distribution than they actually do, may end up seeming like less of a priority than they really are as a consequence of inaccurate survey data.
Last but not least, there is the issue of inconsistent enforcement. While protections exist for northern yellow-cheeked gibbons and their habitat, the follow-through on enforcing them is not always consistent. This undermines not only the protections but all efforts to conserve gibbon populations in the wild.
The northern yellow-cheeked crested gibbon is listed in Appendix I 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. Though its recent identification means it is not yet listed specifically in any local legislation, it is presumed to be legally protected in Vietnam, Cambodia, and Laos and is found in several protected areas within all three countries.
Since poached gibbons are often trafficked to regions well outside their native ranges, the existence of any and all gibbon rehabilitation centers have the potential to help gibbon species everywhere, and a number of conservation projects to protect gibbons have already been established in Vietnam. In Cuc Phuong National Park, for example, the Endangered Primate Rescue Center is busy “working to ensure the future of Vietnam’s primates”—as the slogan on their website proclaims. The center works to rehabilitate Vietnam’s gibbons and educates locals and tourists about the importance of gibbon conservation.
The Dao Tien Primate Center (DTPC) was established at Cat Tien National Park in 2008. The center rescues and rehabilitates primate species local to the area, including the pygmy slow loris, the black-shanked douc, and the silvered langur. Since its founding, however, the center has become a champion for southern yellow-cheeked gibbon conservation in particular. Though it is outside the distribution zone of northern yellow-cheeked gibbons, the center does have a few northern yellow-cheeked gibbons in its care. Staff work to educate local populations and tourists about the importance of gibbon conservation through tours of their center and early morning hikes into the jungle to view gibbons in the wild.
The author of this page had the privilege of visiting the Dao Tien Primate Center in 2018. He had to wake up at 4:30 in the morning, strap on special “leech socks,” and bike two miles to wait in the dark for a ferry to carry his group into Cat Tien National Park, where they rendezvoused with one of the park rangers. He led them about a mile into the pitch-black jungle where they sat at the foot of a giant tree and waited, listening to the otherworldly dawn chorus of birds and insects singing all around them. Then, soon after the sun began to paint the tips of the canopy above gold, the first southern yellow-cheeked crested gibbons started dueting nearby and we took off to find them. Upon seeing the family of four (Mom, Dad, juvenile, and baby) eating high above them, the author was changed forever (an experience that ultimately led him to write for NEPC).
A number of other conservation initiatives are ongoing for this species in both Cambodia and Laos. In southern Laos, the World Wildlife Fund has spearheaded a project focused on the Central Annamites, which lists northern yellow-cheeked crested gibbons as a species of priority for protection and monitoring in the region. In Cambodia, at Venu Sai-Siem Pang National Park, Conservation International manages patrols and other means of protecting the northern yellow-cheeked gibbons found there and funding and promoting their conservation efforts by selling wild gibbon viewings. In the adjacent Virachey National Park, another project by Fauna and Flora International is doing research and helping to protect populations.
While all these centers and initiatives are doing amazing work, there is still a need for more action if we want to turn the tide for the northern yellow-cheeked crested gibbon.
- https://alltheworldsprimates.org
- https://www.iucnredlist.org/species/120659170/120659179
- https://www.iucnredlist.org/species/128073282/17968950
- https://www.eprc.asia/northern-yellow-cheeked-gibbon/
- https://www.speciesconservation.org/case-studies-projects/northern-yellow-cheeked-gibbon/11961
- https://www.researchgate.net/publication/324730192_Nutritional_composition_of_the_diet_of_the_northern_yellow-cheeked_crested_gibbon_Nomascus_annamensis_in_northeastern_Cambodia
- https://static1.1.sqspcdn.com/static/f/1200343/27576027/1495890816413/VJP_2_5_pp83-88.pdf?token=pERhlSIiwZbtDRwCbQkvxOnid98%3D
Written by Zach Lussier, August 2023