The southern yellow-cheeked crested gibbon, also known as the red-cheeked gibbon, inhabits the tropical rain-forests of southern Vietnam and southeastern Cambodia.

These primates thrive in tall evergreen and semi-evergreen forests, though they can also be found in mixed bamboo and woodland habitats.

Previously, it was believed that the southern yellow-cheeked crested gibbon had a wider range, extending into central Vietnam, Cambodia, and even Laos. However, a 2010 discovery revealed that a separate population in the north is actually a distinct species, the northern yellow-cheeked crested gibbon. This finding has led to a redefinition of the southern yellow-cheeked gibbon's range, which is now known to be more limited than once thought.

Size, Weight, and Lifespan

Both males and females typically weigh between 11 and 26 pounds (5–12 kg). Males are generally around 18 to 20 inches (45–50 cm) long from head to body, while females are slightly smaller, measuring between 18 and 19 inches (46–48 cm). Though their lifespan has not been extensively studied, some species of gibbons can live for more than 30 years in the wild.

Appearance

While gibbons may resemble monkeys at first glance, they are actually apes, like bonobos, chimpanzees, gorillas, and orangutans. Unlike these great apes, gibbons are much smaller and, unlike monkeys, lack tails. Their compact size is an adaptation for an entirely arboreal lifestyle, as they live in the forest canopy. In fact, gibbons are among the few apes, alongside orangutans, that spend most of their time in trees.

Southern yellow-cheeked gibbons, like other crested gibbons, exhibit notable variations in appearance depending on gender and age. Infants are born with a soft, buffy yellow coat, which gradually darkens to black by around six months of age. Males maintain their black fur throughout their lives, while females undergo a transformation and develop a yellowish pelage as they reach adulthood.

Mature males are easily recognizable by their characteristic yellow cheek patches, which may appear orange or reddish in some individuals. They may also develop a subtle rusty-red hue on their chest. Mature females may retain a small tuft of black fur on the crest of their heads and, in some cases, have slightly darker chest fur.

Due to these variations, crested gibbons can be difficult to identify in the wild, and this challenge has historically complicated efforts to classify them. Female gibbons from different species often look strikingly similar, making the males’ distinct cheek patches the most reliable way to differentiate between species.

Diet

Southern yellow-cheeked gibbons have a strong preference for fruit, particularly figs, which make up about 39% of their feeding time. The remaining 43% is devoted to consuming other fruits. However, figs and other fruits are not available year-round, so their diet varies seasonally. During the drier months, they turn to a broader range of foods, including mature and young leaves, flowers, plant parts, vines, insects, bird eggs, and various epiphytes.

Behavior and Lifestyle

As arboreal creatures, southern yellow-cheeked gibbons live high in the forest canopy, where they find everything they need to stay safe from predators. These gibbons rarely descend to the forest floor, remaining largely out of sight of any potential threats.

Southern yellow-cheeked gibbons are diurnal and are known for being early risers. At sunrise each day, male and female pairs begin their morning vocalizations, exchanging haunting, melodic songs that can be heard from over half a mile (up to a kilometer) away. These calls serve multiple purposes: they help the gibbons locate each other after a night apart, and they also serve as territorial markers, warning other gibbons to stay clear of their home range.

Locomotion and Physical Adaptations

Gibbons are expert brachiators, using their arms to swing through the trees with remarkable speed and agility. This form of locomotion involves hanging from a branch with one arm and swinging forward to grab the next, continuing this motion as they move through the canopy.

While all apes brachiate, gibbons are the undisputed masters of this skill, reaching speeds of up to 35 mph (56 km/h). In addition to brachiation, gibbons are known to leap great distances and occasionally fall from heights to reach the next tree. They can also walk bipedally along branches, balancing with their arms outstretched.

Development and Learning

They must spend several years developing both their physical strength and their coordination before they are fully capable of navigating the canopy. Playtime is crucial during this period, offering the young gibbons a chance to practice their skills. However, gibbon play can be perilous due to the height from which they play—one wrong move could result in a fatal fall. As such, both parents carefully supervise their young while still allowing them the freedom to practice.