Golden-Bellied Mangabey, Cercocebus chrysogaster
GOLDEN-BELLIED MANGABEY
Cercocebus chrysogaster
Geographic Distribution and Habitat
Only found in the Democratic Republic of Congo, golden-bellied mangabeys are found south of the Congo River in two separate population blocks that do not seem to have any connection to each other. Because both blocks are severely fragmented, it’s unknown how much of these ranges golden-bellied mangabeys occupy. The larger western block is mostly swamp, while the smaller eastern block is made up of much dryer forests known as terra firma. Recent studies suggest that golden-bellied mangabeys prefer to spend the majority of their time in the dry terra firma forests where they’ll forage for fruits both in the canopy and on the ground. They have very large home ranges of up to 8.3 square miles (21.5 sq km), which is much larger than the home ranges of other mangabey species. As the forests they live in are being reduced, golden-bellied mangabeys can also sometimes be found near villages and foraging along roadsides.
Not a lot is known about golden-bellied mangabeys, since up until 2001 they were thought to be a subspecies of the agile mangabey—which itself was once thought to be the same as the Tana River mangabey. Because of being lumped in with the agile mangabey, the golden-bellied mangabey has been assumed to share a lot of their characteristics. In fact, a lack of knowledge due to mistakes in their taxonomy has been a common issue for the mangabeys.
Members of the Cercocebus genus are commonly known as the white-eyelid mangabeys or semiterrestrial mangabeys to differentiate them from the more arboreal crested mangabeys (Genus: Lophocebus). While the white-eyelid and the crested mangabeys were originally thought to be closely related, as scientists have gotten better at looking at the differences between primates on the molecular level, they’ve found that the white-eyelid mangabeys are actually more closely related to mandrills (Genus: Mandrillus) than the crested mangabeys despite sharing part of their name. This makes more sense because white-eyelid mangabeys look and act a lot more like their mandrill cousins than crested mangabeys.
Size, Weight, and Lifespan
The largest of the white-eyelid mangabeys, golden-bellied mangabey males have a head-to-body length of 20–26 inches (52-66 cm), a shoulder height of 17–18 inches (42-46 cm), and weigh about 22–31 pounds (10–14 kg). Females are slightly smaller than males, making them sexually dimorphic, with a head-to-body length of 18–22 inches (45–55 cm), a shoulder height of 15-17 inches (38-42cm), and weigh between 13-22 pounds (6-10 kg). Both males and females have very long tails that can range from 20-30 inches (50-75cm).
The expected lifespan for golden-bellied mangabeys hasn’t been recorded. However, the lifespan for other species of white-eyelid mangabey has been documented at 18-30 years in the wild, so it’s very likely that golden-bellied mangabeys fall within the same range.
Appearance
As their name suggests, golden-bellied mangabeys have lush golden fur covering their chests, bellies, and even inner thighs (technically described as yellow-orange, but “golden” captures the true majesty of their appearance better). The fur on the rest of their body ranges from reddish brown to gray. Babies also have this coloring from when they’re born, essentially making them a “mini-me” of their parents. The adults have a robust build, similar to mandrills.
Like the other white-eyelid mangabeys (as the name suggests) golden-bellied mangabeys have striking pale eyelids which contrast the dark skin on the rest of their face. During aggressive interactions, they’ll flash their eyelids at each other by raising their eyebrows to emphasize their glare.
Diet
Golden-bellied mangabeys are a generalist species, meaning they’re not too picky about what they like to eat. Mostly, they enjoy feeding on fruits and nuts, such as figs and palms. They can use their large canines to crack open hard seeds and then store extra food in their cheek pouches (a little bit like hamsters). Being able to eat harder seeds and nuts that don’t decompose easily on the forest floor is a useful skill for mangabeys, as it ensures a more consistent source of food than fruits that go in and out of season. Unlike many other primate species, mangabeys are also okay with eating fruit that hasn’t quite ripened yet. For a long time, scientists believed that golden-bellied mangabeys only ate plants and insects. However, very recently, they were observed feeding on medium-sized mammals—specifically mongoose and duikers.
Behavior and Lifestyle
Considered semi-terrestrial, they prefer to spend most of their time on the ground and only take to the trees to forage for fruit, find a safe place to sleep, or take shelter from the rain. They’re most active during the day when they travel together up to 4.7 miles (7.560 km) daily, which is much farther than most other primate species and even up to four times farther than other white-eyelid mangabeys. Scientists think this large travel distance has to do with the broad distance between the golden-bellied mangabeys’ food sources. To make sure they don’t miss out on any opportunity for a meal, golden-bellied mangabeys will actually travel fastest during the middle of the day when temperatures are high and most other primate species are taking a midday nap. After sunset, they’ll settle down for the night and begin their travels again early the next morning.
When traveling through the day, the group may change direction if one of their predators is spotted. These include leopards, pythons, African golden cats, some birds of prey, and even bonobos. If a predator is seen or heard, golden-bellied mangabeys will emit alarm calls to let the rest of their group know of the danger.
Golden-bellied mangabeys are known as “Linku” by the local Nkundo people in the Lonkundo language.
Due to being an understudied species, it’s difficult to get the full picture of what a day in the life of the golden-bellied mangabey looks like. The first reports of their group structures indicated a group size of 15 individuals. However, more recent estimates suggest that groups can contain 50 or even up to 100 individuals. Groups will have multiple adult males and adult females led by a single alpha male. Once mature enough, males born into the group will leave to find a new group to live with.
Because of the high competition for food sources, encounters between two groups of golden-bellied mangabeys will result in aggression between the groups. They also share habitat with several other primates, including red-tailed monkeys, Wolf’s monkey, black mangabeys, Allen’s swamp monkey, De Brazza’s monkey, and both red and black-and-white colobus. It’s not clear how golden-bellied mangabeys behave around these other primate species as researchers haven’t had the chance to observe these interactions in the wild.
While a detailed study on golden-bellied mangabey communication has yet to be described, we have a few ideas on how they might “talk” to each other. They primarily rely on visual communication through facial expressions and vocalizations. They’re not a species known to scent-mark, but it’s still possible that they have some level of olfactory (the technical term for smell) communication that humans haven’t been able to pick up on.
A full description of the calls specific to golden-bellied mangabeys hasn’t been described yet, however, a common vocalization that many mangabeys use is known as the whoop-gobble. Only used by adult males, whoop gobbles are deep loud calls that are likely used to let the rest of the group know when other mangabey groups or predators are nearby.
Like many primate species, during aggressive interactions, golden-bellied mangabeys will direct a stare toward the recipient of their aggression that may be emphasized with raised eyebrows and/or a gaping mouth to display their teeth. During affiliative interactions such as grooming, they may smack their lips repeatedly to show appeasement, which is also a common behavior in many primate species.
Like many aspects of golden-bellied mangabeys’ behavior, our understanding of their reproduction is limited. In this case, only a few studies have been done in zoo settings, which leaves a lot of questions open about how reproductive behaviors differ in the wild. Female golden-bellied mangabeys reach sexual maturity around 4 years of age. Like other white-eyelid mangabeys, females have genital swellings at various points in their reproductive cycle. Females will display these swellings both when they are ovulating and after they become pregnant, which scientists believe is an adaptation that makes it difficult for males to determine which offspring they may have fathered. Having more males think they may have fathered a female’s offspring means more males will be likely to protect the female’s offspring. While births can happen at any time of the year, often females will give birth within the same few months of each other. Their gestation length is around 6 months, and they will only give birth to one infant at a time.
Like many primate species, golden-bellied mangabeys act as seed dispersers. Although the specific relationship between golden-bellied mangabeys and the seeds they consume has not been researched yet, scientists have shown that other seed dispersers not only help spread seeds farther than they could travel on their own, but many seeds eaten by seed dispersers have a better chance of growing after being passed or spat out by an animal. While we don’t know the specifics of the golden-bellied mangabeys’ role as seed dispersers, we do know what an incredibly important role it is. Scientists have found that parts of forests that no longer have any primates found in them have fewer saplings than forests where primates are found, meaning that without primates the forest may not be able to thrive.
The International Union for Conservation of Nature lists golden-bellied mangabeys as Endangered (IUCN, 2020), appearing on the IUCN Red List of Threatened Species.
Before 2020, they were considered “Data Deficient” due to the lack of research. Golden-bellied mangabey populations are declining, and unfortunately, they are not found in protected areas. Much of their habitat is being diminished by logging, which is pushing them more and more into human environments. As the fruiting trees they typically feed on are demolished, golden-bellied mangabeys are more likely to forage on people’s crops, which leads to them being viewed as pests. Because golden-bellied mangabeys frequently forage along the ground, they’re easy targets for retaliation from farmers. Humans will also hunt golden-bellied mangabeys and sell them for bushmeat or trade them as pets.
Golden-bellied mangabeys are listed in Appendix II 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.
No specific efforts are being made towards the conservation of golden-bellied mangabeys. However, some researchers have been calling attention to the threats to and lack of understanding of this species for years and advocated for action to reduce the species’ decline. Recently, researchers have begun studying two groups of golden-bellied mangabeys in the wild to finally gain a better understanding of them.
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Written by Lina Rademacher, April 2024