Geographic Distribution and Habitat
With a total population of just 37 individuals from six separate family groups (as reported in 2023 by Xinhua News, China), the Hainan gibbon (Nomascus hainanus) is the world’s rarest ape and is also one of the world’s rarest mammals. Also known as the Hainan black-crested gibbon, the Hainan black gibbon, and the Hainan crested gibbon, this Critically Endangered primate is found only on Hainan Island, China’s southernmost province, in the South China Sea. Home is the Bawangling Nature Reserve within Hainan Tropical Rainforest National Park in Changjiang County on the western side of Hainan Island.
Hainan gibbons were once distributed across half the country of China, according to governmental records dating back to the 17th century. While these apes had long vanished from the mainland by the late 1950s, their population on Hainan Island still numbered over two thousand individuals. But by the end of the 1970s, fewer than 10 individuals remained. Human activity—specifically, destruction of habitat and hunting—is to blame for nearly eradicating the total population.
Mountainous tropical rainforests provide these enigmatic creatures with their current habitat. The gibbons reside high in the treetops at elevations from 2,133–3,937 feet (650–1,200 meters). Ninety-five percent of their original habitat had included lowland, tropical primary forest where the gibbons resided at lower elevations. But the destruction of these lowland forests (only a small, shrinking patch of these remnant rainforests remains) forced the gibbons to take up residence in less-hospitable (with regard to resources) mountainous rainforests.
Gibbons belong to the primate family known as Hylobatidae, which is divided into four genera with at least twenty species, including Nomascus, and at least nine subspecies.
Prior to being elevated to full species status, the Hainan gibbon was considered to be either a subspecies of the Eastern black-crested gibbon (N. nasutus) from the provinces of Hòa Bình and Cao Bằng in Vietnam and from Jingxi County in Guangxi Zhuang Autonomous Region, China, or a subspecies of the black-crested gibbon (N. concolor) found in China, Laos, and northern Vietnam. But further review of molecular data, including morphology (the branch of biology that deals with the form and structure of animals and plants), along with differences in vocalizations and coat colors, led scientists to reclassify the Hainan gibbon as a distinct species.
Today, six gibbon species share the genus Nomascus with the Hainan gibbon.
- Black crested gibbon (N. concolor), with two subspecies:
- Tonkin black-crested gibbon (N. concolor concolor)
- Laotian black-crested gibbon (N. concolor lu)
Initially, scientists had identified two additional subspecies: the West Yunnan black-crested gibbon (N. concolor furvogaster) and the Central Yunnan black-crested gibbon (N. concolor jingdongensis). The current belief is that these two former alleged subspecies are actually synonymous with the nominate, or “parent”: the black-crested gibbon
- Cao-Vit gibbon (N. nasutus), also known as the Eastern black-crested gibbon
- Northern white-cheeked gibbon (N. leucogenys)
- Southern white-cheeked gibbon (N. siki)
- Northern yellow-cheeked crested gibbon (N. annamensis), known also as the northern buffed-cheeked gibbon
- Southern yellow-cheeked crested gibbon (N. gabriellae), also called red-cheeked gibbons
Size, Weight, and Lifespan
Because of their smaller size as compared to great apes (who include chimpanzees, orangutans, bonobos, and gorillas), gibbons were referred to as “lesser apes.” Another reason for this lesser distinction is that these smaller apes were thought to be of lesser intelligence than their larger relatives. (Harumph!) The preferred term now is “small apes.”
Hainan gibbons weigh between 12.8 and 22 pounds (5.8–10 kilograms), with little difference between males and females. The average weight for adult males is about 14.6 pounds (6.6 kilograms); average weight for adult females is about 14.3 pounds (6.5 kilograms).
These are slender primates, with an incredible arm span of 5.6 feet (170 cm) and long legs. Average head-to-body length for adult males is about 19.3 inches (49 cm); average head-to-body length for adult females is nearly the same at about 19 inches (48.5 cm).
Characteristic of all apes, whether great or lesser, Hainan gibbons (like all gibbons) lack a tail. This feature, or lack thereof, helps to distinguish them from their tail-twitching monkey cousins whose long tails can be prehensile or nonprehensile.
The lifespan for Hainan gibbons averages 30 to 40 years in the wild, with some wildlife biologists suggesting the species can live up to 55 years, given favorable circumstances such as lush habitat and protections.
Their silky, luxurious coats give Hainan gibbons a plush-toy resemblance. Coat coloring differs between adult males and females (a condition known as “sexual dichromatism”). Coat coloring and hairdos give these gibbons their alternative aliases.
The pelage (coat) of males is completely black. Outlandish, fluffy, golden-colored furry tussocks adorn the cheeks of some individuals. Males also sport a distinct crest on the crown of their head (like a punk-rock Mohawk hairstyle).
The coat of females is golden or a creamy buff, with a black patch on the crown of their head that tapers to the nape of the neck. Yellow whiskers spring from their black muzzle, which is outlined by a narrow ring of white facial fur.
Both male and female youngsters have creamy buff-colored coats, paler but similar to that of adult females. At about 5 years old, males develop their all-black coat while females attain a richer and creamier pelage like that of their mothers.
Hainan gibbons are primarily frugivores—that is, they eat mostly fruits. They have a penchant for figs and also enjoy lychee fruits, juicy berries, flower blossoms, seeds, bamboo shoots, and young leaves. The rare insect snack or small lizard may complement their meal plan, providing an additional source of calcium and protein. The gibbons drink water that has collected in tree hollows or leaves.
Their original primary forest habitat once provided Hainan gibbons with more than six species of edible plants. But this habitat was overtaken by pulp paper and rubber plantations. Today, these small apes rely on Banyan trees (producer of figs) and wild banana trees, available year-round, to provide them with much of their sustenance.
Behavior and Lifestyle
The species is arboreal, meaning these primates spend all their time in trees. Like other gibbon species, the bodies of Hainan gibbons are specialized for living in the forest canopy. Their most common form of locomotion is “brachiation,” whereby they propel themselves forward swinging from branch to branch using their strong forearms. Flexible shoulder and wrist joints aid their fluid movements as they soar as much as 30 feet (9 meters) between trees while reaching speeds up to 35 miles per hour. Long fingers and toes assist these forest acrobats with grabbing branches and “sticking their landing” when leaping. They have also been observed climbing and walking upright through the thick canopy; they almost never descend to the ground.
Hainan gibbons are active during daylight hours, making them a diurnal species. Waking at sunrise, they head out together for a day of foraging and feeding. Family members follow one another single file along a well-traveled trail along tree branches through the forest. Dad leads, followed by mom who carries her tiny infant, any other adults, and the couple’s older children in the rear.
Unlike some monkeys, these small ape gibbons have no cheek pouches in which they might store a snack for later eating. After picking a select ripe fruit, peeling the skin with its teeth, and removing the juicy flesh with its flexible tongue, Hainan gibbons eat slowly and deliberately, appearing to savor the epicurean experience.
Adults pause for a midday nap, selecting a comfy branch where they can rest and close their eyes. They might first engage in a grooming session. Youngsters prefer to play, somersaulting through the treetops. At sunset, the gibbons get themselves ready for bed.
Unlike great apes, gibbons do not build nests. Instead, they sleep upright on branches within the primordial rainforest; the dense forest canopy provides perfect shelter. Hard pads of skin on their bottoms, known as ischial callosities, allow them to comfortably sit for extended periods. Selecting a tree for overnight sleeping is not a frivolous activity; rather, it is a strategic and deliberate act to keep themselves safe from predators. In an effort to thwart attacks from ground predators, the gibbons select the tallest and straightest trees. To further ensure a safe night’s sleep, they’ve devised an alarm system: gibbons sleep on branches with lots of twigs that would snap beneath the feet of an approaching predator, alerting the sleeping gibbons and giving them a chance to escape.
Aerial predators include eagles and hawks. Researchers have recorded two unsuccessful hawk attacks, lasting about 15 minutes. However, the species’ foremost predator and threat to survival are humans.
The song notes of Hainan gibbon duets are specific enough to deter interbreeding with the other six “singing” gibbon species who share the Nomascus genus.
Hainan gibbons live in small family units of four to eight individuals, typically composed of an alpha male, one or two mature females, and their offspring. The alpha male acts as protector, while his female partner cares for the couple’s young offspring. Upon reaching adulthood, male gibbons are forced to leave home. They disperse into the forest, hoping to instill themselves into or form a new group as an alpha male. But with such a small total population of the species, they are rarely successful. And there’s no going home. Should they try, their parents reject them. These males end up living a solitary and likely lonely life.
Home range for this highly territorial species is between 0.39 and 1.9 square miles (1–2 square kilometers), similar to that of other gibbons in the genus Nomascus.
Other wildlife species who share Hainan Island with the gibbons include Pallas’s squirrel (Callosciurus erythraeus), also known as the red-bellied tree squirrel; the Hainan flying squirrel (Hylopetes electilis); the Hainan hare (Lepus hainanus); the Hainan moonrat (Neohylomys hainanensis); the Asiatic black bear (Ursus thibetanus), also known as moon bear; the sambar deer (Rusa unicolor); the yellow-bellied weasel (Mustela kathiah); the Eurasian otter (Lutra lutra); the crab-eating mongoose (Urva urva); the leopard cat (Prionailurus bengalensis); and a variety of birds such as the light-vented bul bul (Pycnonotus sinensis).
Hainan gibbons have been called “rainforest elves” who, upon rising each dawn, awaken the rainforest with their morning song. A bonded male and female couple engage in an elegant duet with the male taking the lead, a distinct role reversal from other gibbon species that emphasize the female voice. Nature has fitted the males with a laryngeal sac that allows them to sing elaborate notes.
The notes begin slowly, imbuing an ethereal quality, then become sharp and insistent. Both long notes and sharp notes are sounded, while females emit chattering or laugh-like vocalizations. The rest of the family acts as chorus by providing backup vocals for a harmony that reverberates throughout the forest. Song performances might last up to 20 minutes.
Hainan gibbons use song as their premier method of communication. Thus, these melodies are more than captivating musical expressions; they serve at least a twofold purpose. The gibbons sing to announce themselves as they greet each day, and they sing to warn intruders to keep away.
“Hoos” and howls are also part of the species’ vocal repertoire, and these sounds are emitted throughout the day as these lesser apes go about their business.
Most gibbon species reach sexual maturity between 6 and 8 years old. It’s possible that Hainan gibbons mature earlier. In one instance, scientists observed a 5-1/2-year-old male driven from his group by other members, a forced exile likely led by the group’s alpha male. Scientists speculate that this banishment may have had more to do with limited resources, necessary for the group’s survival, than with the young male attaining sexual maturity and needing a kick in the bottom to get him to strike out on his own.
A group’s alpha male enjoys polygynous relationships with the females in his group; that is, he gets to mate with each of them. Multiple copulations may occur during a single day. But it is the female who initiates sexual encounters, sashaying toward the male while rhythmically moving her head and limbs and performing what has been described as a robot-like dance. Or she may hang from a tree branch and expose her chest to get a male’s attention. During the act itself, she elicits soft grunts. According to scientists who’ve studied gibbon behavior, Hainan gibbons are one of only three gibbon species in which the female makes vocalizations during mating.
Typically, a bonded gibbon couple has a child within a year of being together. And after a gestation period of 20 to 24 weeks, a single infant is born. Births occur during the blooming season on Hainan Island, when fruits are plentiful. The species’ small family size and relationships with one another is likely a reproductive adaption to their decreased natural habitat. A female’s two-year birth interval, shorter than other gibbon species, is thought to be a reproductive adaptation linked to her bonded relationship with the male. However, a female’s tendency to give birth to only two offspring during her reproductive lifetime is a somber offset to any fecundity.
Infant Hainan gibbons are dependent on their mothers for their first 1.5 year of life; they remain with their families through the juvenile stage. Weaning period is not reported in the species; however, it is known that lactation depletes a great amount of energy from nursing gibbon mothers.
The Hainan gibbon is considered an “umbrella species” of Hainan Island. This distinction means that the species serves as an environmental marker for the health and stability of the island’s overall ecosystem. Alterations or disruptions in the island’s ecosystem that negatively impact the Hainan gibbon are indicative of negative impact on other species as well.
As example, the species has historically played an important role by dispersing seeds from the fruits that it eats, via its feces, throughout its forest habitat. But the continued destruction of vegetation coupled with the of the precariously low population of Hainan gibbons threatens the regeneration of native plant species and thus threatens the wildlife who depend on these plants.
The Hainan gibbon is listed as Critically Endangered (CR) by the International Union for Conservation of Nature (IUCN, November 2015), appearing on the IUCN Red List of Threatened Species. With only 37 individuals remaining—on our entire planet—it has the ignoble distinction of being the world’s most Critically Endangered ape and has appeared multiple years, most recently 2016–2018, on the listing of “Primates in Peril–World’s Top 25 Most Endangered Species.” (Endangered species are routinely dropped from this listing, not because their situation has improved, but to focus attention on other species who also have “bleak prospects of survival.”)
Anthropogenic (human) activities such as habitat destruction (slash-and-burn agriculture, clear cutting land for conversion to farmland, illegal logging, etc.), human encroachment (in the form of new settlements and related infrastructure), hunting and killing these primates for their flesh (known as bushmeat) and for their body parts for use in folkloric medicinal remedies, and the illegal pet trade have all conspired to nearly eradicate the species.
Developing rubber and commercial logging industries, the construction of roads, a human population boom (between 1950 and 2003), and a subsequent increase in human settlements have all contributed to wiping out the Hainan gibbon’s original lowland rainforest habitat. This willful destruction of habitat has also resulted in a split of gibbon populations, isolating them from one another and hindering successful reproduction in the species. A significant decline in genetic diversity (many of the remaining individuals are closely related to one another) also jeopardizes the species’ viability.
Although the current rate of habitat loss has greatly diminished from decades of reckless disregard for the species’ survival and for the biodiversity of the island, the damage has been done—and the Hainan gibbon sits on the edge of extinction.
Historically, Hainan gibbons have been hunted and killed, and their bones have been traded on the black market to be used in “traditional medicines”—none of which have been proven valid. Mass hunts between 1960 and 1980 led to the deaths of approximately 100 gibbons. These rare apes have also been killed for their flesh (bushmeat).
The low income of Hainan citizens has fueled the illegal pet trade. Mother gibbons are shot and killed and their babies are stolen. Or, if a young mother is the intended kidnap victim, her baby is left to die. It is illegal to keep a Critically Endangered species as a pet. Furthermore, wildlife species require specific needs that are not met in a domestic environment, leading to their suffering and subsequent early death.
Hainan gibbons are also vulnerable to intrinsic threats related to their habitat destruction and low population. A natural disaster, such as a major storm, could wipe out the remaining population. As example, the region experiences annual typhoons, some which can be particularly devastating.
An epidemic could also eliminate the species. And these rarest of apes are at risk of succumbing to secondary anthropogenic causes, such as harmful pollutants inflicted upon the species’ environment. Conservation biologists refer to the confluence of any of these factors as an “extinction vortex.”
The Hainan 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. It is also listed as a national first-class protected species in China, making it a crime to hunt these primates. In response to the Critically Endangered status of the Hainan gibbon, the Chinese government enacted a ban on all types of logging in or around the Bawangling Nature Reserve.
In late 2019, a bonded male and female couple was sighted by villagers about 5 miles (8 kilometers) outside their normal range within the reserve, giving hope to conservationists committed to saving these small apes from extinction. Wildlife biologists confirmed the pair’s presence by the duet that the gibbons sang.
In 2000, the Chinese government launched an innovative program that transformed former local woodcutters into forest rangers. Not only did this action improve the livelihood of these individuals and conserve wildlife habitat, it put local eyes and “hearts” in the forest . . . to observe and protect the Hainan gibbon.
While the total population increased from 7 individuals in the 1980s to 37 individuals in 2023, thanks largely to conservation efforts of local wildlife professionals supported by international conservation groups, it’s still way too early to celebrate. The species’ ravaged habitat combined with slow breeding and lack of genetic diversity means that conservationists still have a long way to go if we are to ensure this species’ survival.
The notion of captive breeding programs has been discarded as unwise and possibly perilous to the viability of the remaining individuals. Likewise, relocating Hainan gibbons to alternative habitat has been discarded as a reckless endeavor.
The Hainan Gibbon Action Plan was developed in 2003 with two main objectives: teach the newly formed monitoring team (former woodcutters, now forest rangers) effective methods to conduct population surveys; and begin a reforestation program that reconnects fragmented forest with isolated Hainan gibbon populations in Bawangling Nature Reserve. Of course, trees do not grow overnight. In the interim, conservationists have suggested constructing artificial canopy bridges to encourage the gibbons to move between forest patches.
In 2005, The Hainan Gibbon Action Plan focused on several reparative actions: dissuade illegal loggers by increasing and better equipping enforcement patrols; revert plantations into habitable forests by planting specific plant species necessary to the gibbons’ survival; and educate local residents as to the importance the Hainan gibbon as a fellow citizen of their shared ecosystem.
In the years since the action plan’s creation, several new initiatives have been implemented. Most significantly, perhaps, in January 2019, the Hainan Tropical Rainforest National Park was established. Within the park, the Bawangling Nature Reserve was created to better protect the Hainan gibbon and restore its ecosystem. The provincial government also launched a project that relocated villagers (by offering incentives and improved living amenities) from core protected Hainan gibbon areas to settlements outside the park.
In 2020, the Hainan Institute of National Parks was established as a gibbon protection and research base with a focus on long-term conservation.
Population monitoring is crucial in conserving the species. Over the years, methods have included positioning infrared cameras to capture photographs and videos of the gibbons and remote sensing and geographic information systems (GPS) to determine suitable Hainan gibbon habitat. Call playback—playing gibbon calls to attract and locate solitary Hainan gibbons—has also been implemented, but only with a small measure of success. Furthermore, scientists caution that call playback may potentially stress the gibbons and should only be used sparingly, in key locations, for short periods of time only when attempting to detect gibbon presence.
While in-person field studies remain important mainstays in observing gibbon behavior—and forest rangers play a crucial role—modern technology has recently made species monitoring more accurate. Artificial intelligence (AI) has come to the rainforest.
By providing a framework to automatically identify and classify gibbon vocalizations curated from an algorithm, captured from strategically placed audio-recording equipment connected to a wireless network, AI is being implemented to create a unique “voiceprint” for each gibbon. Scientists hope to establish a database of all individual gibbons to better protect the species and ultimately save it from extinction.
In the meantime, forest rangers remain the Hainan gibbons’ biggest local advocates, acting as ambassadors for the species. They also help these lesser apes navigate daily life. As example, rangers routinely build rope bridges that allow the gibbons to cross deep valleys, created by mudslides from the annual typhoons. After a super typhoon hit Hainan Island in 2014, creating mudslides that left gaps in the forest 98-feet (30 meters) wide, a team built a metal cable for the gibbons to use for crossing.
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Written by Kathleen Downey, 2018; updated by author October 2023.