Cao-Vit Gibbon, Nomascus nasutus

CAO-VIT GIBBON

Nomascus nasutus

Geographic Distribution and Habitat

The cao-vit gibbon (Nomascus nasutus) is a small ape native to Southeast Asia. Also called the cao-vit black crested gibbon or the eastern black crested gibbon, they are found in just one forest along the Vietnam–China border. Their habitat spans about 31 square miles (82 square kilometers) in the karst limestone mountains where Jingxi County, Guangxi (China) meets Trung Khanh District, Cao Bang (Vietnam).

They were once widespread across the lower montane forests east of the Red River in southern China and northern Vietnam. By the 1960s, they were thought extinct—a casualty of hunting, deforestation, and expanding agriculture. In 2002, a small population was rediscovered in Trung Khanh, Vietnam; and four years later, the population was confirmed to extend into neighboring Guangxi, China.

Most cao-vit gibbons inhabit the Vietnamese forest, with a few groups residing in the Chinese forest. Their limited range is hemmed by villages, farms, and roads, where logging, crop cultivation, and livestock grazing (still permitted in China, though banned in Vietnam) have degraded much of the valleys.

The core of their habitat is monsoon rainforest surrounded by secondary forest on sharp limestone peaks that rise 1,300–3,100 feet (400–950 meters). This karst terrain is uncommon habitat for gibbons and makes tracking them difficult. Most observations are made from karst peaks rather than within the forest itself.

The region has a humid subtropical monsoon climate, with hot, rainy summers (May–October) and cool, dry winters (November–April). Annual rainfall varies widely, from 47–113 inches (1,200–2,900 millimeters). Temperatures average around 84°F (29°C) in July and drop to about 46°F (8°C) in January, with occasional frost at higher elevations.

TAXONOMIC NOTES

The cao-vit gibbon (Nomascus nasutus) belongs to the family Hylobatidae—the gibbons, or “lesser apes.” This term refers partly to their smaller size compared to the great apes (family Hominidae), to whom they are most closely related. The great apes include chimpanzees (Pan), gorillas (Gorilla), orangutans (Pongo), and humans (Homo sapiens).

Taxonomy for gibbons has undergone several revisions based on new understandings about their physical traits and vocalizations. They diverged from the great apes around 16–20 million years ago and have since radiated into four major genera: Hylobates (dwarf gibbons), Hoolock (hoolock gibbons), Symphalangus (the siamang), and Nomascus (crested gibbons).

Cao-vit gibbons are crested gibbons, named for the distinctive fluffy hair crests adorning males. This group includes six other species: black crested gibbon (N. concolor), Hainan gibbon (N. hainanus), northern buffed-cheeked gibbon (N.annamensis), northern white-cheeked gibbon (N. leucogenys), southern white-cheeked gibbon (N. siki), and yellow-cheeked gibbon (N. gabriellae). 

Until the early 2000s, all crested gibbons were classified as a single species, Hylobates concolor, based on their similar appearance, vocal behaviors, and geographic range in Southeast Asian tropical forests. The differences they exhibited in appearance and behavior were attributed to minor local variation, making them subspecies.

Advances in mitochondrial DNA sequencing and acoustic analysis in the 1990s and early 2000s identified consistent genetic lineages and vocal “fingerprints” too significant to be explained by regional variation alone. This discovery led experts to recognize several new species and move all crested gibbons into a new genus, Nomascus. The cao-vit gibbon was formally classified as its own species in 2010. Now seen as monotypic (having no subspecies), it is considered one of the most genetically unique members of its genus.

Cao-Vit gibbon range, IUCN 2025

Size, Weight, and Lifespan

Cao-vit gibbons are small-bodied apes that weigh around 12 to 17 pounds (5.5 to 7.7 kilograms) when fully grown. Both males and females typically measure between 18 and 25 inches (45 to 64 centimeters) from head to rump. Unlike monkeys, apes don’t have tails.

Most gibbon species live 30-35 years in the wild, and captive individuals can reach 45 years. We aren’t certain how long cao-vit gibbons live in either condition. There are no cao-vit gibbons in captivity, and long-term lifespan tracking in the wild is incomplete. Researchers must infer lifespan by analogy to better-studied white-cheeked and black crested gibbons, which places the cao-vit gibbon roughly in the 30-35 year range.

Appearance

Cao-vit gibbons have compact, wiry bodies and small hairless faces. Hidden in their dark masks are large, forward-facing eyes with dark brown irises that provide the depth perception for judging distances between branches. Their classic catarrhine nose sits flat to the face with narrow, downward-facing nostrils close together—a feature reflecting their reduced reliance on scent.

At first glance, a gibbon family can appear to be three different species due to the coat color differences between sexes and age classes. Whereas other crested gibbon species are born blonde, cao-vit gibbon babies are all-black. As they mature, males retain their black to very dark brown fur coloration into adulthood. Males also develop a faint brownish patch on the chest and a small crest of hair on the crown. Females undergo the most drastic transformation, becoming warm golden-apricot adults with a sharp black crown patch that stretches back from the forehead. Their dark faces are framed by pale, almost halo-like rings of fur.

The most memorable feature is their extraordinarily long arms—the longest of any primate relative to body size. Stretching 1.5 times longer than their legs, they can reach up to 36 inches (90 cm) from shoulder to fingertip. That extra length gives them the span they need to swing through the treetops at breakneck speeds, covering impressive distances without ever touching the ground. Hook-like hands with elongated fingers and much shorter, low-set thumbs let them dangle securely from branches. Their feet, equipped with opposable big toes that work like thumbs, give cao-vit gibbons four grasping appendages instead of two, helping them cling to vertical supports or carry food while maintaining grip on branches.

Photo credit: ©Zhao Cao. Seeking permissions.
Diet

Cao-vit gibbons are primarily frugivores, with ripe fruit making up about 52% of their diet. They’re known to eat over 100 species of plants and plant parts, showcasing remarkable dietary flexibility that helps them survive in the rugged karst landscape they call home.

Karst forests produce less variety and abundance of fruit than the lowland habitats other gibbon species enjoy. The thin, rocky soil erodes easily and can’t hold water well, making plant growth slow and recovery even slower. Fruit trees, when they grow at all, are scattered across cliffs and rocky slopes.

Faced with sparse and dispersed resources, cao-vit gibbons anchor their diet around a few dependable tree species such as glabrous fig (Ficus glaberrima) and Hooker’s fig (Ficus hookeriana), along with paper mulberry (Broussonetia papyrifera), which provides both fruit and edible leaves across seasons. They supplement these fig staples with young leaves and buds (37%), flowers (3%), and animal matter, including spiders, stick insects, cicadas, grasshoppers, and worms (6%).

Although cao-vit gibbons can pivot to other foods when they need to, they are not generalists, and their gut design rules out many options when fruit becomes scarce. They evolved simple, single-chambered stomachs and short colons built to rapidly move soft, easily processed foods through their system. That’s why they are selective about the fallback items they consume, and they don’t simply switch to whatever grows abundantly, which tends to be mature leaves. Mature leaves contain higher levels of cellulose and tannins that require slow fermentation in the multi-chambered stomachs of leaf-eaters like their neighbors, the Francois langurs (Trachypithecus francoisi). 

Even their 32 teeth match the mission. At the front of their mouths are procumbent, shovel-shaped incisors that are great at handling soft, high-moisture plant parts, fruit skins, buds, and tender leaves. Sharp canines set behind the incisors are more for display and defense, and less for eating.  Rounded molars and shallow cusps in the back of their mouths are adapted for mashing pulp rather than heavy-duty grinding or shearing abrasive foliage.

Behavior and Lifestyle

Cao-vit gibbons are arboreal apes that navigate their degraded karst landscape by climbing, bridging, leaping, and using a special type of swinging called brachiation. This arm-over-arm movement beneath branches resembles children on monkey bars, but with far more fluidity and speed. Gibbons brachiate at speeds approaching 35 miles per hour (56 kilometers per hour), sometimes soaring nearly 30 feet (9 meters) between trees.

As a gibbon swings, he or she reaches forward with one arm, hooks it over a branch, and lets their body swing like a pendulum. Just before losing momentum, they release the rear hand and grab the next branch with the opposite arm, keeping a steady rhythm. Their shoulder joints are extremely flexible, with shoulder blades (scapulae) positioned to allow full rotation, letting them swing freely without strain. This form of movement costs less energy than climbing and helps gibbons stay in the trees, where they can efficiently maintain their territories, find food, and avoid predators. 

The karst forest canopy averages just 34 feet (10.5 meters)—the lowest recorded for any gibbon species—and is often discontinuous. These factors sometimes force cao-vit gibbons to descend partway down one tree and climb up another nearby. Ground travel is incredibly dangerous and exhausting for them. Although gibbons can walk upright for brief bursts, this ability evolved mainly to help them balance on narrow branches rather than traverse open, flat ground. With long forelimbs, short legs, and narrow hips, gibbons are unsteady and extremely vulnerable on the ground, especially in the jagged, uneven limestone terrain. This extreme dependence on trees explains why the species’ survival hinges on canopy connectivity. If gaps get too wide due to logging or habitat loss, the gibbons can’t safely cross, fragmenting their population and cutting them off from food sources and mates.

Cao-vit gibbons are diurnal, beginning each day at dawn with loud territorial duets between mated pairs. Groups spend 36-50% of their waking hours feeding (depending on season), with the remainder divided among grooming (20%), foraging (17%), traveling (11%), calling (8%), resting (4%), and playing (1%). When temperatures drop, they rest more and sleep huddled together for warmth. 

Because karst forest is patchy and strongly seasonal, foraging and travel times can vary based on the time of year, quality of the habitat, and group size. When the trees hang heavy with ripe clusters, the gibbons stay close to core feeding areas. In leaner months, adults lead the group further to track fallback foods.

One hour before sunset, groups make their way to sleeping trees, favoring tall species, such as Burmese almondwood (Chukrasia tabularis) and Chinese hackberry (Celtis sinensis), growing on slopes near ridges between 2,300 and 3,000 feet (700–910 meters). Unlike some primates that sleep near feeding trees to conserve energy, cao-vit gibbons deliberately sleep far from feeding areas, probably to avoid predators.

As night falls, they settle on the highest, exposed branches that grow free of lianas. These rope-like vines drape and twist around trunks and limbs, offering night predators easy climbing routes to ambush sleeping gibbons. They also shift unpredictably among dozens of sleeping sites, abandoning trees where raptors like crested serpent eagles (Spilornis cheela) have been lingering.

Cao-vit gibbons face few natural enemies today. In theory, clouded leopards (Neofelis nebulosa), golden cats (Catopuma temminckii), or large raptors could prey on them, as happens with other gibbon species in Southeast Asia. Yet no one has documented a cao-vit gibbon being taken by these or any other predator aside from humans. Their rarity, speed, and almost exclusively arboreal lifestyle make them difficult targets. 

Daily Life and Group Dynamics

While most gibbon species form monogamous pairs, Cao-vit gibbons live in stable groups that often include one adult male and two breeding females, along with their dependent offspring. On average, these groups are around 4-6 individuals.

These arrangements work because cao-vit gibbons have weak or absent dominance hierarchies, making them different from harems some other primates form. There’s no evidence of reproductive suppression, one female being favored over another. The male grooms both females, co-forages, and may even help carry or play with infants. Adult females groom one another regularly and even groom each other’s offspring, suggesting their relationships are built on cooperation rather than competition. 

This challenges conventional wisdom about primate social structure, where multiple breeding females in one group typically leads to conflict. The harsh karst forest environment might explain this unusual flexibility. With food scattered thinly across the terrain, larger cooperative groups may have survival advantages that outweigh the typical costs of sharing scant resources. 

Home ranges span 70 to 147 hectares, with groups traveling about 1.2 kilometers daily. These territories are defended vocally, not physically, though neighboring groups may have overlapping ranges (sometimes up to 95%) without regular direct confrontation. Groups maintain core areas they use most intensively and typically avoid one another through careful timing and acoustic signaling. 

To minimize the risk of inbreeding in small, isolated populations, both males and females disperse from their natal (birth) groups, typically between 3 and 5 years old. Males typically become solitary wanderers until they can establish new groups by attracting females or joining existing ones, whereas females might move directly into a new group.

Field studies of cao-vit gibbons have recorded male takeovers, but they’re rarely violent and typically occur when the resident male dies or disappears. It’s a known pattern in other primates that a new male removes the old male’s offspring to make the females ready to mate again sooner. Although a relatively peaceful species, when a new cao-vit gibbon male replaces the old one, infants sometimes go missing shortly after. The timing suggests that infanticide probably occurs. 

As the only primates specializing in the uppermost canopy layer, cao-vit gibbons rarely encounter some of the species they live alongside in their range. The François’ langur (Trachypithecus francoisi), an arboreal leaf-eating monkey, shares the upper canopy in some parts of the reserve but typically doesn’t live high in the forest strata. Other sympatric species include stump-tailed macaques (Macaca arctoides), the southern serow (Capricornis sumatraensis), various squirrels, civets, and a diversity of forest birds and reptiles.

Communication

Gibbons have fewer and less complex mimetic muscles, meaning they’re less capable of facial expression than great apes. Instead, cao-vit gibbons communicate through posture, movement, and most of all, sound. Vocalization is so advanced in gibbons, some researchers suggest their evolutionary investment went toward laryngeal and vocal tract development rather than facial expressivity.

Often called the “singing apes,” between 5:00 and 7:00 a.m., cao-vit gibbons climb high into the canopy to unleash synchronized song duets. The air is still in the early morning, absent of wind and ambient noise that would otherwise keep their calls from traveling far in the valleys and peaks of the karst forest.

Males contribute four distinct sounds: beginning with reverberant “booms”, followed by short, rapid “aa” notes. They culminate in intricate modulated phrases that spiral upward in pitch, often exceeding 5 kHz. Such high, clear tones resist distortion from the rugged terrain, making them ideal for long-range communication. Females add their signature “great call,” a structured vocal pattern that builds in intensity, speed, and pitch before cascading into repetitive syllables that researchers transcribe as “wa-wa-wa.”

These songs are thought to serve several purposes: to reinforce pair-bonds, signal fertility, and possibly to deter would-be trespassers. A gibbon may sing more frequently along a boundary to broadcast their occupancy to neighboring groups.

Each gibbon has their own unique voice or vocal fingerprint that is innate, or untaught. This is unusual, especially for primates, as many animals learn their songs by listening to their parents or other adults. Gibbon songs are genetically encoded behaviors rather than learned traditions. In fact, gibbon hybrids raised by one parent don’t copy that parent’s calls. In time, they develop their own distinctive, blended vocal style that reflects both species.

Females also dance. It’s a quiet performance that is slow, deliberate, and done just a few meters in front of an adult male. She moves one body part at a time, with clear pauses between small, mechanical gestures that almost resemble a human robot dance. These dances are believed to be a courtship and bonding behavior: a quiet, physical way to say “I’m here, I’m available, and I’m paying attention to you.” Notably, not all females dance or dance with the same frequency.

Reproduction and Family

Cao-vit gibbons practice polygyny, where one male mates with multiple females who typically mate only with him. Both males and females reach sexual maturity around 6 to 8 years of age.

When ready to mate, a solitary male might sing repeatedly near an existing group or dispersing female, trying to catch her attention over time. Studies on closely related gibbons suggest that how well potential partners coordinate rhythm, pitch, and timing in duets may influence whether they bond and eventually mate. Better-matched duets likely reflect stronger social and possibly genetic compatibility.

For cao-vit gibbons, explicit gestation data isn’t available, but it’s reasonable to infer from relative gibbons that females have a gestation period of about seven months, after which a single infant is born. Newborn gibbons have a strong grasp reflex that lets them cling tightly to their mother’s belly or chest as she moves through the canopy. This frees up the mother’s hands for locomotion while keeping the infant secure.

Nursing continues for 18 to 20 months, after which young gibbons begin weaning gradually. Most mothers don’t give birth again until their previous infant is mostly independent at 2 years old, spacing births about 23–38 months apart. Both parents participate in nurturing their young, but mothers provide the bulk of care. Fathers may help by carrying older infants and defending the family, and the other female may groom the other’s offspring.

Photo credit: ©Zhao Chao. Seeking permissions.
Ecological Role

The subtropical forest straddling the Sino-Vietnamese border is astonishingly diverse, despite its undulating karst topography and limestone bedrock. Within the transboundary reserves where cao-vit gibbons reside, surveys have recorded hundreds of tree species, plus dozens of ferns and other plants. But what seems like a thriving, verdant jungle is actually one of the most fragile ecosystems on Earth. Karst forests grow in shallow soil, limited nutrients, and constant erosion. Many seedlings never make it. 

This makes the gibbon’s role as a seed disperser especially important. They consume a variety of fruit and are large enough to swallow seeds that birds, bats, and rodents can’t handle. Trees like the Indochinese walnut (Dracontomelon dao), figs (Ficus), incense trees (Canarium), stone oaks (Lithocarpus), and rose apples (Syzygium) all depend on large animals like gibbons to carry their seeds away from the parent tree. These seeds are typically defecated 100 to 200 meters (328–656 feet) from the source. Gibbons often defecate from tree branches, allowing seeds to fall into pockets of soil, light, and space that are hard to reach by other means. The fact that they travel widely through the treetops also increases the chance that seeds land in one of the rare locations suitable for germination.

Without this daily movement, many trees would struggle to spread, and the forest would gradually lose its ability to sustain itself.

Conservation Status and Threats

The International Union for Conservation of Nature lists the cao-vit gibbon as Critically Endangered (IUCN, 2020), appearing on the IUCN Red List of Threatened Species.

The species received this classification due to its extremely small global population, habitat fragmentation, and confinement to a single, vulnerable forest area on the China–Vietnam border.

When last formally assessed by the IUCN, the population was estimated at fewer than 150 individuals. However, a 2021 survey using more precise detection methods revised the number to just 74 individuals, living in 11 family groups. Though their numbers are alarmingly lower than initially believed, the lower count doesn’t signal that their numbers are dwindling. Since their rediscovery, researchers have observed the formation of new family groups, suggesting the species is achieving slow but steady growth. Still, cao-vit gibbons face an onslaught of threats that make their future far from certain. 

The primary threat to the cao-vit gibbon is habitat degradation, driven by decades of unregulated logging, agricultural expansion, fuelwood collection, and grazing, particularly in valleys and lower slopes. Surrounding villages continue to encroach, reducing the canopy’s connectivity, which is critical for the species’ arboreal movement and daily survival. On the Chinese side of the border, continued livestock grazing within protected zones undermines efforts to restore the forest’s quality. 

While hunting is not currently considered a widespread threat, isolated poaching events for unspecified purposes have been reported. These, along with human disturbances and ongoing land-use conflicts, continue to pose localized but serious risks to the gibbons. The gibbon’s confinement to a single location further exposes them to stochastic events such as wildfires, disease outbreaks, and extreme weather, any of which could be catastrophic.

Conservation Efforts

The cao-vit gibbon is listed in Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (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.

Appendix I includes species threatened with extinction. Trade in specimens of these species is permitted only in exceptional circumstances (e.g., for scientific research). This listing prohibits all commercial international trade of this animal.

Vietnam categorizes cao-vit gibbons as a Group IB species under Decree No. 06/2019/ND-CP, which bans all hunting, capturing, trading, transporting, or commercial use. The species is further protected under the Biodiversity Law (2008) and the Forest Protection and Development Law (2004). Violations are serious criminal offenses under the 2015 Penal Code (amended 2017), with penalties including fines of up to 2 billion VND (approx. $85,000 USD ) and prison terms of six months to 12 years.

Under China’s Wildlife Protection Law, cao-vit gibbons receive the highest level of legal protection as a Class I Protected Animal. Local forestry and wildlife agencies must monitor, report, and prevent any disturbance to the species or their habitat. 

Both countries have established conservation areas to protect the species. Vietnam created the Cao Vit Gibbon Conservation Area (CVGCA) in 2007, protecting roughly 7,570 hectares of forest. China established the Bangliang National Nature Reserve in 2003, covering 6,000 hectares, and upgraded it to a national-level reserve in 2007. Because the forest spans the border, the gibbons move between the two countries, and the population is considered transboundary. Recent estimates suggest that around 36 individuals live in Bangliang, with the rest likely concentrated on the Vietnamese side.

While both China and Vietnam have legal protections on paper, their differences in capacity to enforce them is evident in the condition of the forest on their respective side of the border. Compared to Vietnam, China is a much wealthier nation and has been able to allocate far more funding to conservation. Bangliang has more rangers, better equipment, such as camera traps and GPS tracking, and stricter enforcement of its laws. China’s State Forestry and Grassland Administration, which manages Bangliang, upholds the grazing ban, and violations result in fines or confiscation of livestock. More importantly, the Chinese government provides subsidies to local villagers in exchange for compliance with conservation rules. These payments reduce reliance on forest resources by offering families a reliable alternative source of income. 

Vietnam’s strong laws, by contrast, are inconsistently enforced by the Vietnam Forestry Administration and provincial authorities. The conservation area sits in remote, mountainous terrain that’s difficult to patrol, and rangers are not given proper equipment to effectively manage the area. Their staff are stretched thin, underfunded, and often reluctant to prosecute local villagers who depend on the forest to survive. Families, therefore, still engage in activities that fragment the forest, like fuel collection.  

The most promising conservation work focuses on giving local communities alternatives to livelihoods that damage the forest. In Vietnamese villages, programs have introduced efficient cooking stoves that use less firewood and created jobs in beekeeping, tree-planting, and guiding eco-tourists. Unfortunately, the scale of these programs is small, and most households near the conservation area still rely on the very activities that undermine forest regeneration. Without stronger, better-funded programs to actually replace lost income, many conservation rules end up unenforceable, because locals simply have no other choice.

Several conservation groups work alongside local governments to find solutions that protect gibbons while helping people earn a living. In Vietnam, Fauna & Flora International (FFI) has led efforts since the species was rediscovered, with additional contributions from PanNature, the Wildlife Conservation Society (WCS), and academic institutions like Hanoi University of Science. On the Chinese side, the Kadoorie Farm and Botanic Garden, based in Hong Kong, has been a key player in funding, research, and capacity-building efforts within the Bangliang National Nature Reserve. They are supported by efforts by other organizations, including World Wide Fund for Nature and the Gibbon Conservation Alliance.

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Written by Alyssa Hanes, Sep 2025