Pennant’s Red Colobus, Piliocolobus pennantii
PENNANT'S RED COLOBUS
Piliocolobus pennantii
Geographic Distribution and Habitat
Endemic to the Equatorial Guinean island of Bioki off the coast of Cameroon, the Pennant’s red colobus has one of the most restricted ranges in the primate world. “Endemic” means that it is found nowhere else on earth—the species as a whole is fully dependent on the island for survival. They are now even more restricted, relegated to only a portion of the island on the southwest side. Pennant’s red colobuses live up to an elevation of about 4,000 feet (1,200 m), favoring lowland and mid-altitude forests. These are “monsoon forests”, and they receive nearly 400 inches (1000 cm) of rain every year. For context, the rainiest state in the United States, Louisiana, receives 59 inches (150 cm) of rain annually. Pennant’s red colobus monkeys are also referred to as Pennant’s colobuses or Bioko red colobuses.
Colobus monkeys are notoriously difficult to sort out. Red colobus and olive colobus are either divided into entirely separate genera, Piliocolobus and Procolobus, or into separate subgenera under the genus Procolobus. This profile follows the classification used by the International Union for the Conservation of Nature (IUCN) and considers them an entirely separate genus, Piliocolobus.
Pennant’s red colobus was formerly considered a subspecies of the P. pennantii species, alongside Bouvier’s red colobus and the Niger Delta red colobus. In 2007, it was proposed that they be considered distinct species, and that classification has been widely adopted.
Size, Weight, and Lifespan
Pennant’s red colobus monkeys weigh about 15 to 22 lbs (7-10 kg) and measure between 21 and 25 inches (53-63 cm) from the top of their head to the base of their tail. Their tail adds another 24 to 28 inches (60-70 cm) to their overall length. Their lifespan is not well-researched, but based on other red colobus species, they can likely live to about 30 years of age in captivity, and less in the wild.
Appearance
Pennant’s red colobuses are a dark red color over their backs, legs, arms, and tail, which darkens to black towards their spine. Their bellies and the inner parts of their arms and legs are a stark white. Their heads are black on the top half, and they possess a rather impressive white beard that covers the bottom half of their faces. Red colobus monkeys all have a similar body type and color pattern, but Pennant’s red colobuses look most similar to the Niger Delta red colobus. Though they are easy to confuse, the Pennant’s red colobus has a brighter white on their belly while the Niger Delta red colobus has more of a cream color.
They have long, muscular legs that allow them to leap through the canopy, and a long tail for balancing on narrow branches. Their thumbs, like other colobines, are so small that they are barely visible. Instead, they appear to have just four fingers and a bump where their thumb should be. It is not known for sure why colobus monkeys lost their thumbs, but scientists have speculated that their thumbs may have gotten in the way of their branch swinging, so it slowly evolved to become smaller and less obtrusive. Colobines join Latin America’s spider monkeys and woolly spider monkeys (or muriquis)—who also lack thumbs—as the only primate groups to have less than five digits on each hand. As colobines are not closely related to the Latin American groups, this is an example of convergent evolution—the evolution of similar features in unrelated species as a result of similar environmental pressures.
Sexual dimorphism, or visual differences between males and females, comes in the form of size, with the males slightly larger than the females, and teeth, as males have much larger and more prominent canines than females.
Diet
As with other colobines, Pennant’s red colobuses have a special multi-chambered stomach that is capable of digesting tough, mature leaves and seeds. These are so difficult to digest that few other animals, even other primates, do so, and this special adaptation affords colobus monkeys little competition for their main food source. In addition to leaves and seeds, they likely supplement their diet with fruit and flowers. Though they may occasionally eat meat, this is likely rare. Their water consumption comes mostly from the water content found in the leaves they eat.
Behavior and Lifestyle
Unfortunately, little is known about the daily life of Pennant’s red colobuses, as their behavior has not been well-studied. However, we can glean some basics from what is known of other closely related species in the red colobus family. Pennant’s red colobus monkeys are largely arboreal, which means that they spend most of their time in trees. They can leap impressive distances using their powerful leg muscles and taking advantage of the elasticity of thin tree branches to get an extra bounce. They often rest by using their tails as a brace against tree trunks and branches. They most likely spend the majority of their day feeding and resting, and, as diurnal animals, they sleep at night.
Red colobus monkeys have been known to engage in some unusual behaviors, such as charcoal eating and suckling by young adult males. More research into this unique group of primates will likely uncover more interesting behaviors.
Pennant’s red colobuses live in groups of up to 20 individuals, though the average group size is as low as two to three individuals. However, it is important to bear in mind that humans have significantly altered their natural lifestyle, so these group compositions may not reflect what would form in natural, undisturbed conditions. Red colobus groups are typically multi-male multi-female groups, and sometimes they engage in what’s known as “fission-fusion”. In this dynamic, smaller sub-groups of a larger group break off, usually for feeding, before coming back together at the end of the day.
Red colobus monkeys are known to have very complex vocalizations. These calls often blend into one another, making them difficult to classify. Unfortunately, research into communication among Pennant’s red colobuses is sorely lacking, but, as well as vocalizations, Pennant’s red colobus likely also uses facial expressions and body postures to communicate with one another.
As with other aspects of their daily life, we know very little about the reproductive lives of Pennant’s red colobus. Most likely, all adults in a group mate freely, with both males and females mating with multiple partners. Females have significant perineal swellings, some of the largest among the red colobus monkeys. This makes it obvious to surrounding males when she is fertile, so they can take advantage of that window to mate with her. Based on similar species, their gestation length is likely between four and six months.
We know very little about parenting among Pennant’s red colobuses. Naturally, the mother nurses her baby after birth, but we do not know what role the father or other group members play in raising the young. Female red colobuses are known to leave the groups they were born into, while males are generally more likely to stay, though this is now known for certain in Pennant’s red colobus.
Red colobus have been known to live peacefully with other primates, such as chimpanzees. While there are no chimpanzees on Bioko Island, it is possible that Pennant’s red colobus monkeys live among some of the island’s other primate species, such as the black colobus and the red-eared guenon. Natural predators of Pennant’s red colobus, if they exist on Bioko Island, are not documented.
The International Union for Conservation of Nature lists the Pennant’s red colobus as Critically Endangered (IUCN, 2016) appearing on the IUCN’s Red List of Threatened Species. Their populations have plummeted by approximately 80% over three generations, and there are estimated to be fewer than 1,200 individuals remaining, leaving them extremely vulnerable to extinction. This decline is thought to be largely caused by unsustainable hunting, exacerbated by the species’ extremely small range. Sadly, Pennant’s red colobuses are not unique among their genus. Red colobuses are considered to be the most threatened group of African monkeys, as every species within the genus is threatened with extinction and 13 of the 17 red colobus species are listed as Endangered or Critically Endangered.
Unfortunately, Pennant’s red colobuses are a favored target of bushmeat hunters due to their relatively large size and untimid nature. Unsustainable levels of hunting have pushed them towards the brink of extinction. Hunting of Pennant’s red colobuses ramped up in the early 1980s when a commercial bushmeat market was created in the capital city of Malabo on the northern coast of Bioko Island. Although the hunting, sale, and consumption of primates is banned in Equatorial Guinea, it is not well enforced and hunting of primates continues nearly 20 years after the law was put into place. Gran Caldera Scientific Reserve, where all remaining Pennant’s red colobuses live, is unfortunately a “protected area” in name only. Due to a limited budget and staff, there is little effective management of the reserve, and hunting has only increased within it in recent years.
The development of roads on the island has opened up previously remote and inaccessible parts of the island to hunters and other types of disturbance, exacerbating an already dire situation. Increasing military presence within the monkeys’ range will also likely increase hunting pressure as more military personnel reside in otherwise remote areas of the island.
The Pennant’s red colobus is 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. It is also in Class B of the African Convention on the Conservation of Nature and Natural Resources, a continent-wide agreement to conserve Africa’s rich natural resources.
More effective management of the land and enforcement of laws is critical to protect the remaining populations that reside within its boundaries. Towards this end, researchers have called for a number of top-priority conservation actions, including, 1) developing and implementing a management plan for the Gran Caldera Scientific Reserve, 2) strengthening of the legal basis for protection of the reserve, 3) increasing enforcement of laws, and 4) more government involvement in conservation, particularly towards the issue of primate hunting.
For over 25 years, the Bioko Biodiversity Protection Program (BBPP), a research partnership between Drexel University in Philadelphia and the Universidad Nacional de Guinea Ecuatorial in Malabo, Equatorial Guinea, has worked to study primate populations on the island. Survey efforts in recent years have gathered data on the plight of the Pennant’s red colobus: a crucial step in addressing their downfall. In recent years, the BBPP has expanded its mission to encompass education programs and conservation action. The IUCN’s red colobus conservation action plan has also identified conservation actions to improve formal protections of Pennant’s red colobuses, including the implementation of capacity-building workshops to improve enforcement of hunting and conservations laws, the deployment of enforcement patrols throughout the Gran Caldera Scientific Reserve, and the establishment of bushmeat checkpoints to enforce hunting laws.
A United Nations Development Program Global Environmental Facility program is underway with the goal of addressing the management issues in the protected areas of Equatorial Guinea. Among other goals, the project aims to have Bioko Island recognized as a UNESCO Biosphere Reserve.
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Written by K. Clare Quinlan, January 2025