Black Crested Gibbon, Nomascus concolor
BLACK CRESTED GIBBON
Nomascus concolor
Geographic Distribution and Habitat
Black crested gibbons are mainly found in the Yunnan region of China. There is a small population of them in northern Vietnam, between the Black and Red rivers, and in western Laos. They live in mid-mountainous forests, usually above an elevation of 4,921 feet (1,500 m), which can range from evergreen forests to deciduous forests in which the leaves are shed during dry seasons. They prefer primary forests, which are old-growth forests that are largely untouched by humans but have adapted to secondary or more disturbed forests. They tend to avoid grassland and open areas, making them highly vulnerable to logging activities.
Black crested gibbon taxonomy has seen some revisions over the past 20 years. They were initially classified as 4 subspecies based on their slight appearance differences and geographical distribution. They were thought to be separated by barriers such as the Mekong river that runs across East Asia. But now we know that two of these subspecies were just variants of the most widely distributed black crested gibbon, Nomascus concolor concolor, sometimes referred to as the Tonkin black crested gibbon. The second subspecies, Nomascus concolor lu, or the Laotian black crested gibbon, occurs in an isolated population in Northwestern Laos.
Size, Weight, and Lifespan
Black crested gibbons are small apes with a body length of 1.4–1.7 feet (43-54 cm) and weight of 15–22 pounds (7–10 kg). Their lifespan in the wild is between 25–30 years. One captive black crested gibbon was recorded to have a lifespan of 46 years. Though the quality of a captive primate’s life is questionable, their lifespan is usually longer because of the lack of predators and the availability of food.
Appearance
Gibbons have dark shiny eyes that look piercingly through their small hairless face that is surrounded in thick fur. They have a flat nose with long nostrils that they can flare or narrow in order to keep out debris as they swing quickly though the forest. Their mouths appear small and slightly down-turned but open up into a neat “O” shape to make their signature loud whooping calls.
They have incredibly long arms, almost twice as long as their body! Swinging from branch to branch using these long arms makes it easier for the gibbons to travel long distances through the forest canopy. It is definitely a trait that Tarzan would envy.
The difference in appearance between females and males is striking. Adult males are almost completely black, with a cone or crest of fur on their head. Adult females are beige-gold in color with a black patch of fur on the crown of their heads. The visible differences between males and females mean that they are sexually dimorphic and, because the difference is mainly in their coloring, this trait is to referred as being sexually dichromatic.
Newborns are completely buff or beige-colored, matching the color of their mother’s chest and belly. This camouflages them from predators and they cling to their mothers. As they become juveniles, their fur darkens to black. Male juveniles and subadults remain black as they mature into adults. Female juveniles lighten up as they sexually mature and eventually become the pale gold color of adult females.
Photo credit: ©@huangmingpan/ iNaturalist/Creative Commons
Diet
Gibbons are highly energetic apes. Imagine toddlers running around a park, screaming and swinging on monkey bars at a blinding pace. They need to eat high energy foods to maintain their activity level. Gibbons desire fruits that are high in sugar (like figs), which are perfect for satisfying their nutritional needs. However, fruits are seasonal and not always available. So, gibbons switch their diet to leaves and sometimes even eat insects or mammals during colder seasons or in harsh habitats. They tend to eat younger and softer leaves that are easier to chew and digest. These leaves have higher amounts of protein and lower amounts of toxins than mature leaves. Gibbons have also shown a preference for flowers when they are in season.
Some biologists have observed that gibbons tend to eat fruits early in the morning and late in the evening. One theory for this is that the quick energy boost from the sugar in the morning helps them actively swing through the forest to look for more food. Mid-morning they eat more protein-rich leaves, which slowly release energy and can sustain them for the rest of the day. An evening meal of fruits gives gibbons a surge of energy to keep warm during the cool nights.
Behavior and Lifestyle
Gibbons are arboreal and extremely agile as they move through the forest canopy. They are most famous for swinging in large arcs from branch to branch using their long arms, a behavior called brachiation. Using this motion gibbons can travel at speeds of 34 miles per hour (56 km/hr)!
Gibbons can also walk bipedally (on two legs) quite well, with their long arms lifted overhead for balance. Although they can and do walk bipedally on tree branches, like acrobats walking a high wire, they use this method primarily when walking on the ground, though they do not spend much time there.
They are diurnal and most active during the day, between dawn and dusk. They are territorial, especially the males. Males use vocalizations to deter “floating” or non-paired males from coming close to their families. Females are less territorial and more tolerant of other females and older offspring that have left their natal troops.
Black crested gibbons are sexually dichromatic, with adult males being completely black and adult females being gold-beige in color.
All infants (males and females) are born pale gold, they become black as juveniles, and subadult females become golden again as they sexually mature.
They sing duets—loud songs that are started by males with responses from females in the family troop.
Males and females, and in some cases even individuals, can be distinguished from their calls.
They move in a characteristic swinging movement called brachiation which can carry them long distances between trees, at a speed of 34 mph!
Soon after sunrise, gibbons leave their sleep sites and males start vocalizing to let neighboring troops know that they are present and active that morning. On any day, they spend 40% of their time sleeping, 35% feeding, 19% traveling, 2% singing, and 1% playing. During the summers, when it is hot and fruiting season is at its peak, gibbons travel further away to reach a food patch that has a lot of sugar-rich foods. Feeding sessions are most energetic during the cooler mornings and late afternoons, and the hot middays are for resting.
In the winter, it can get cold in the montane forests of East Asia and the gibbons conserve energy by traveling less and resting more. There are also fewer fruits available in winter, which means there are fewer food-patches to travel to. So, throughout the year, their travel distances can vary between 0.1 and 1.9 miles (300–3,144 m) per day. The widely distributed foods and the extreme seasonal temperature differences mean that, over the course of a year, gibbons travel long distances and have large home ranges, often greater than 250 acres (100 hectares).
Before sunset, gibbons find suitable sleeping sites in tall trees among the thick foliage of the canopy. They prefer sleeping sites that are closer to food sources and protected against predators and high winds. During the winter, family members huddle for warmth. In summer, the family sleeps in smaller groups (such as fathers and sons, or mothers and infants) in a more spread-out sleeping site. They tend to choose different sleep sites every night, and this may be done to prevent predators from predicting the gibbons’ nightly presence. This behavior could also be a strategy to reduce reinfection from parasites that get shed during sleep.
Gibbon troops are centered around a monogamous pair of adults (one male and one female) or a polygynous system (one male with 2–3 adult females), and the resulting offspring. Gibbons can be aggressively territorial against intruding troops but, within the family, interactions are mostly peaceful. Family members forage together and help take care of juveniles. Sometimes adults aggressively force older, sexually mature offspring out of the troop.
Females tend to be more tolerant and less prone to confrontations. Females that are transitioning between their natal troop and forming their own mating pair have been seen feeding with established families. These “floating” females may be intruders, but they are often tolerated, particularly by females in the family, when food is abundant.
Research on the social dynamics of black crested gibbons is limited. We know that family members groom each other, a behavior called allogrooming, which strengthens bonds between individuals and establishes hierarchy. In polygynous gibbons, females seem to groom the male more and he does not return the favor as much.
Black crested gibbons, like other gibbons, make loud calls, referred to as songs, to communicate with each other. You can distinguish adult males and females by their songs. Researchers use this method to track the movements of a group. The songs are also used to count members as a group and to estimate gibbon populations, similar to how researchers might count birds using bird calls.
Gibbons create these songs by making “phrases” of sounds that build on each other. The result is a call with complex song structures. The phrases depend on the singer, and with males it can be quite individualistic. Just like you may be able to recognize different popular singers by their voices, researchers can distinguish different males by their songs. Interestingly, neighboring troops make sure their songs are significantly different, so there is no confusion about who is singing, even when they are singing at the same time.
One form of these loud calls is a “duet” between males and females. Males climb a tall tree and start a duet call by making sounds that repeat and become louder. As the male song becomes louder, he adds more sounds to make a complex musical phrase, which triggers a slightly calmer song from females. These are called “great calls.” Other family members may join the duet call leading to a loud symphony of calls that draws the attention of neighboring troops. Interestingly, these songs do not seem to trigger a response call from non-family members.
While researchers do not know the exact purpose of these loud calls, it seems likely that there is more than one use for highlighting the presence of the troop to the rest of the forest. Some of the functions of these calls can include territorial defense, where the louder calls indicate larger troops with better defense capabilities.
Males usually select singing trees around the best food patches. So, this supports the idea of a troop defending valuable food resources from competitors. Duet bouts between mates also strengthen the bonds between pairs and advertise that strong bond to other gibbons. The social bonding effect of duetting could result in a lower chance of a female leaving a bonded pair or it could deter an unmated male from approaching a mated female.
Other than singing, gibbons also use quieter grunting and trilling sounds to communicate with family members. These sounds may also be accompanied by facial and hand gestures. These forms of communication are usually done when they are close to each other. Unless they are physically close to one another, the dense forest limits direct visual contact between members. Vocal communication is, therefore, the most effective way for gibbons to get the attention of other gibbons and transmit their message successfully.
For decades, all gibbons were classified as monogamous (one male mating with one female for their whole lives) because most observations consisted of troops with single male-female pairs. However, the black crested gibbon was one of the exceptions to this observation where troops with one adult male and multiple adult females were observed. Recent studies have suggested that polygynous (one male, many females) grouping is not uncommon in wild black crested gibbons. Males in these troops will mate with all the adult females within that troop, but not at the same time. So, females are usually not at the same stage of pregnancy at the same time. Studies of troops from different habitats suggest that social systems in black crested gibbons are flexible and dependent on the amount of food available to sustain more members in a troop and the ability of the habitat to improve the reproductive success of males (or how many offspring they can father). As a result, a family can consist of 2–3 adults, 1 infant, and 2 older siblings.
Parental care and infant development are long, which may account for their long lifespans. Females are usually pregnant for 7–8 months with one offspring at a time. Mothers tend to become pregnant again 2–3 years after the birth of a child. Gibbons have low birth rates and take a long time to recover from any reduction in their population.
Infants are born completely buff or white-colored, and they cling to their mother’s belly for protection as their mother swings effortlessly through the forest. The infant feeds on mother’s milk until they are about two years old. During this time, the infant’s fur color slowly darkens to a blackish color by the time they are a year old (regardless of sex). As a light-colored gibbon, the infant can hide in their mother’s pale gold fur and be virtually invisible to predators or other gibbons. The darker fur of juveniles gives the young gibbons some more camouflage to blend into the dark shadows of the forest canopy as they learn to navigate their new environment away from their mother’s protection. At the age of two, young gibbons are also taken care of by adult males and siblings.
Once females reach sexual maturity (about 8 years old), their black fur darkens to a pale golden color, though some dark patches remain on the backs and they retain a strip of black fur on top of the head.
Sexually mature offspring (both males and females) are encouraged to leave the natal troop. In some cases, parents are openly aggressive to their older offspring, particularly males, forcing them to leave the troop. When the offspring are adults, they must find a mate and establish a territory elsewhere. This behavior prevents overcrowding and allows gibbons to survive in habitats where desired foods like fruits cannot be found consistently throughout the habitat and throughout the year.
Photo credit: © Ran Dai/iNaturalist/Creative Commons
Gibbons are major seed dispersers in their mountainous forest habitat. When gibbons eat fruit, they tend to consume the seeds without destroying them. Studies have found seeds that are completely intact in their feces. This means that these seeds that are deposited on the ground with their own supply of fertilizer have a higher chance of developing into plants. Forest regeneration is a long-term benefit of having a thriving gibbon population.
Gibbons affect the horizontal and vertical movement of nutrients through the habitat. They eat fruits in one part of the forest and defecate in another, allowing the fruiting tree to spread its seed further than it ever could on its own. This moves nutrients along the horizontal length of the forest that can feed other living things (insects, fungi, mammals, etc.) far from the source tree. Gibbons also drop fruits, leaves, and flowers from tree heights down to the forest floor where they can be consumed by insects and small mammals, or become decomposed by fungus and bacteria to fertilize the soil. This vertical transfer of nutrients allows animals living closer to the forest floor to access foods they normally would not be able to get to.
As a consumer that can adapt their diet to consume leaves, insects, and the occasional small mammal, gibbons affect different parts of the intricate food web in their habitat. Their ability to thrive in the harsh, cold environments of high-altitude forests, and their influence on forest regeneration and nutrient transfer provide an ecological chain reaction for other species to thrive as well.
The International Union for Conservation of Nature lists black crested gibbons as Critically Endangered (IUCN, 2015), appearing on the IUCN Red List of Threatened Species.
The largest population of black crested gibbons (about 1,300 individuals) is in the Yunnan region in China. Less than 100 can be found in Vietnam.
The major loss of habitat from 1950–1970 led to a rapid decline in the black-crested gibbon population in China. These gibbons require large trees in old-growth forests that have been stable for many generations. Unfortunately, these forests are slow to develop and take a long time to regenerate after a disturbance. Therefore, historical and current human activities such as logging and deforestation for agriculture have long-lasting negative effects on black crested gibbon populations. While these gibbons have adapted to moving through newer forests that have been altered by human developments, their distribution in these habitats tends to be patchy.
Some communities hunt gibbons for bush meat and use their body parts for traditional medicines. They are, therefore, particularly vulnerable in habitats that border human developments. In some places, black crested gibbons have been hunted to local extinction.
The black 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. This provides them with the highest level of protection to prevent the trafficking and export of these gibbons
In Vietnam and China, most of the gibbon habitat is under the protection of national parks and laws, which prevents further logging activities and hunting in these regions
The State Forestry Bureau of China declared the black crested gibbon as a biodiversity conservation flagship species (an ambassador to highlight the importance of conservation in that area). This gave them species national protection, which resulted in a reduction in the hunting of gibbons in China. In some habitats in Yunnan, increases in gibbon numbers have been recorded as a result of this national effort.
In Lao PDR, the Nam Kan National Protected Area has the smallest population of black crested gibbons. This region is protected by an ecotourism project that works with local people to educate tourists about gibbon ecology and conservation. Additionally, the project funds forest patrols to control wildlife poaching in the area.
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Written by Acima Cherian, October 2023