Ashy Red Colobus, Piliocolobus tephrosceles
ASHY RED COLOBUS
Piliocolobus tephrosceles
Geographic Distribution and Habitat
The ashy red colobus (Piliocolobus tephrosceles), also known as the Ugandan red colobus, lives in small, separate areas of western Uganda and western Tanzania. Fragmented populations live in Biharamulo Forest Reserve near Lake Victoria; Gombe National Park; Mahale Mountains National Park; and parts of Ufipa Plateau—all of which are in Tanzania. But of the estimated 25,000 ashy red colobuses, the vast majority (around 20,000) now live inside Kibale National Park in Uganda. Many populations that lived in other forests have been wiped out.
Ashy red colobus monkeys can be found in a wide variety of forest environments, from riverine and old-growth lowland forests to montane rainforests. They’ve been spotted as high as 7,900 feet (2407 m) above sea level, higher than where other red colobus species are found. Ashy red colobuses also live in forests used for logging—as long as there is sufficient food—and in dry savanna habitats. Kibale National Park, where the majority of them live, is primarily old-growth moist evergreen forest.
The ashy red colobus was only declared a distinct species in 2001. Prior to that, it was considered a subspecies of the Tana River red colobus (Piliocolobus rufomitratus).
Size, Weight, and Lifespan
Male ashy red colobus monkeys are considerably larger than the females. Males weigh around 23 pounds (10.5 kg) on average, whereas females weigh an average of 16 pounds (7.5 kg). The males are also longer, with a head-body length of 17 to 26 inches (45-67 cm) and tails from 25 to 28 inches (65-72 cm) in length. Females are 19 to 22 inches long (49-58 cm) from head to body, with tails 24 to 26 inches (62-68 cm) long.
Ashy red colobuses can live around 15-20 years, but the average is around 13.7 years for females and 10.5 years for males.
Appearance
Ashy red colobus monkeys have rusty red fur, like a flat cap, on the top of their heads. Their faces and backs are dark. The fronts of their bodies are lighter, including white or grey fur under their chins and on their bellies. Their long tails are dark brown. Babies are born with completely black faces.
Ashy red colobuses’ hands, like those of other colobus monkeys, are almost absent thumbs. Since colobus monkeys are the most arboreal of Africa’s monkeys, their hands are adapted for rapidly swinging from branch to branch. Long, flexible, hook-like fingers easily grasp branches and facilitate a type of locomotion called brachiation or, more correctly, semibrachiation since they also climb and walk quadrupedally (on all fours). Thumbs might impede their acrobatics. So, what remains is a vestigial thumb—a small non-functioning nub of a thumb. Their feet, on the other hand, are quite long, helping them jump great distances. Their long tails help them balance while they move through the canopy.
Diet
Ashy red colobuses are folivores, meaning they primarily eat leaves. They particularly like young leaves, but they will also eat mature leaves, bark, flowers, and sometimes fruit. They seem to respond and adapt quickly to new food sources. For example, they’ve been observed eating leaves from Eucalyptus trees—a non-native tree first planted on plantations in the 1960s.
Because they eat food that takes so long to digest, they spend a lot of time resting. Ashy red colobuses have high-cusped molar teeth to help them chew leaves, as well as enlarged salivary glands that produce enzymes that help break down plant tissues.
Similar to cows, ashy red colobuses have large multi-chamber stomachs that actually ferment food before digestion continues. They have a special microbiome that supports their digestion—a community of bacteria and microorganisms that break down plant cell walls and ferment leaves. This fermentation process produces gas. As a result, they often burp!
Behavior and Lifestyle
Ashy red colobuses are arboreal, spending almost all their lives in the trees. Groups that live in forests tend to forage in the understory and sometimes even venture to the ground for food. Groups that live in savanna habitats are not generally seen at ground level.
Ashy red colobuses are diurnal, but they spend a lot of the day resting in the tree canopy after finishing meals. They’re most active in the early morning and late in the day. Large groups will split into smaller parties during foraging, reuniting later in the day.
Their natural predators include chimpanzees, crowned eagles, and leopards. When the group is under attack, they gather closer together. Males make noise and fight to protect the group.
Thanks to their long tails, large feet, and short thumbs, ashy red colobus monkeys can leap up to 50 feet (15 m) as they move from tree to tree!
Ashy red colobuses have even been spotted eating charcoal, which may help their digestion.
Group size varies considerably. Smaller group sizes are found in areas where the species is in decline. In Kibale National Park, group sizes have increased since 1970—researchers recorded groups of around 71 individuals in Kibale National Park in 2018. Groups in Ufipa Plateau averaged 25 individuals. In Biharamulo in northwest Tanzania, researchers found small groups with an average of only 15 individuals. However, their tendency to split into smaller groups to find food makes it difficult to accurately determine group sizes.
A study comparing forest-dwelling ashy red colobuses with their savanna-dwelling cousins showed some interesting differences. The two groups socialized with each other about 5 percent of the time. The forest group lived in a smaller area overall. The savanna group had a much larger home range, traveling longer distances each day. They moved between forested areas by leaping from tree to tree along narrow routes—not by walking on the ground. If those tree routes are cut down for logging, populations would likely be cut off from the rest of their normal habitat.
Males tend to stay with their birth group, while females are free to move to different groups. Groups have more females than males.
Ashy red colobuses are often found with other monkey species. They associate with grey-cheeked mangabeys, blue monkeys, and mantled guerezas. In Kibale, they’re seen with red-tailed monkeys most often. These mixed groups seem to give the monkeys a greater sense of safety—when they are with other species, ashy red colobuses are less alert for predators.
Ashy red colobuses have complex vocalizations. The density of their forest habitats appears to be a key factor in shaping the characteristics of their vocal communication, particularly for long-distance interactions. They use alarm calls when predators are spotted. Females vocalize most often to indicate their readiness to mate. They have also learned and respond to the alarm calls of other monkeys in the area.
Ashy red colobuses also use body language and behaviors like poking and biting one another to communicate or initiate play. They also engage in grooming behaviors, especially the female ashy red colobuses, who groom males, other females, and younger members of their group.
Ashy red colobuses reach sexual maturity at around 5 years old. Unlike with other colobus monkeys, female ashy red colobuses develop noticeable swellings on their behinds that signal their readiness to mate. However, these swellings can also occur when the females are not in estrus, and therefore not ready to conceive. The timing of these swellings, as well as the tendency of females to mate with more than one male, may be in aid of something called “paternity confusion.” Because males will kill infants that they know are not their own young, infants with unclear paternity are more likely to survive.
Female ashy red colobuses initiate breeding by making vocalizations and displays. Pregnancy lasts five to six months, and then a female will give birth to one infant. The infants stay with their mothers for nearly a year, and unlike with some other colobus species, alloparenting is not a common practice. With no one in the group helping with infant care, females are unlikely to have another infant during that first year. Therefore, the species is slow to reproduce. Infants have more time to stay with their mothers, plus lots of time to play. Indeed, young ashy red colobuses spend as much as a quarter of their time playing with others—a significantly higher rate than many other primate species.
Ashy red colobus monkeys are key pollinators and also disperse seeds because they eat flowers, nectar, and fruit. They also represent a “canary in the coal mine” for habitat health. Where red colobus monkey populations are in decline, the habitat is at risk overall.
The ashy red colobus is classified as Endangered by the International Union for Conservation of Nature (IUCN, 2019), appearing on the IUCN Red List of Threatened Species. Estimates show their population may have declined by 50 percent.
Habitat loss is a major factor in this decline. The ashy red colobus is already completely gone from several forests due to habitat loss, and populations outside protected areas are in decline. Habitat loss is often caused by logging or clearing land for farming and livestock, but can also be from charcoal production and forest fires. There is some local hunting for meat and skins, but it’s not common.
Another factor in the species’ decline is their vulnerability to predators, particularly chimpanzees. As the population has consolidated into protected lands, no longer able to spread out, it only grows more vulnerable to these predators. Surveys showed 40 percent of the population decline in Gombe National Park, for example, was from chimpanzees.
The ashy red colobus 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. They’re also listed as Class B species in the African Convention on the Conservation of Nature.
Over 90 percent of the ashy red colobuses live in protected areas, primarily Kibale National Park and Gombe National Park. The population inside Kibale is fairly stable, indicating that protected lands may be key to ensuring the species’ survival, but even inside the protected areas, there is still some logging and hunting, and some areas of their habitat are used for illegal marijuana cultivation.
The Ngogo Chimpanzee Project, a long-term project in Kibale National Park, employs local Ugandans to patrol the park and remove snares set by poachers, helping to curb illegal hunting that affects chimpanzees and red colobus monkeys.
The IUCN released a conservation action plan for the 17 species of red colobus monkeys in 2021. The plan recommended increased patrols and training for guards in protected areas, surveys to assess populations outside of Kibale, and local community education projects. Since then, the Red Colobus Network has carried out surveys in the Ufipa Plateau and engaged in education campaigns in schools and with village leaders in Tanzania. Approximately $500,000 has been raised for projects to conserve red colobus monkeys since the plan’s release, but further action is needed to curb habitat loss and to protect the species.
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Written by Courtney Daniels, Aug 2025