Geographic Distribution and Habitat
A team of conservation biologists exploring the Lomami Forest Basin in the Democratic Republic of Congo (DRC) in June 2007 were astounded when they came upon a most unusual looking monkey, tethered to a post, in the remote town of Opala. They had never before seen such a monkey, colloquially referred to as a “lesula” (luh-SOO-la) by the locals. Kept as a pet by the district school director’s daughter, the young female monkey had been left orphaned in the forest after hunters killed her mother.
Further exploration of Opala turned up another juvenile captive male and female lesula. Then, in December 2007, the biologists saw their first wild lesula in the Obenge region along the Lomani River. (The primate’s species name, lomamiensis, is derived from the river where the monkey was seen.)
It would be several years before genetic testing proved the lesula (Cercopithecus lomamiensis) to be a new primate species, distinct from its closest relative, the owl-faced monkey (Cercopithecus hamlyni) from whom the lesula is separated geographically by both the Lualaba (Congo) and the Lomami Rivers.
Finally, in 2012, the lesula received its overdue fanfare with loads of press coverage that heralded the species’ “discovery.” The last readily available article about this newly recognized primate was published in 2015; since then, the lesula appears to have faded from the media’s fickle limelight and retreated into its lowland tropical rainforest habitat between the DRC’s Tshuapa and Lomami Rivers. Conservationists speculate that the biogeographic barriers of these two rivers likely contributed to the lesula’s initial isolation and its evolution into a unique species.
Lesulas occupy a geographic range of about 6,564 sq m (17,000 sq km) in the DRC’s eastern central basin. They are found mostly in primary (mature) forests dominated by lush abeum trees (Gilbertiodendron dewevrei), enormous evergreens that thrive in the humid climate. The monkeys move through the forest canopy at elevations between 1,312 and 2,346 ft (400-715 m) and also travel on the ground. They are less frequently sighted in secondary (regenerating) forests close to human activity; the species has never been observed in seasonally flooded forests or in southern savanna regions.
Size, Weight, and Lifespan
A member of the guenon family, the lesula is a slender, medium-sized Old World monkey with long limbs and a long, thin tail. Males have larger bodies than females and have larger canine teeth. Lesulas are similar in size to owl-faced monkeys, but are equipped with larger incisors and molars than their “daintier” sister species.
Head-to-body length in adult males is between 18.5 and 25.6 in (47-65 cm); they weigh between 8.8 and 15.65 lb (4-7.1 kg). Head-to-body length in adult females is between 15.75 and 16.5 in (40-42 cm); they weigh between 7.71 and 8.81 lb (3.5-4 kg).
Because scientists discovered the lesula fairly recently, no accurate data is available for the species’ lifespan, either in the wild or in captivity. For its sister species, the owl-faced monkey, with whom the lesula shares several commonalities, the average lifespan in captivity is about 27 years.
Look at that face. Human-like—but guileless—pale and bare, with pinkish gray skin and eyelids, a long, narrow nose accented by a cream-colored or white stripe, and understated, thin lips. A speckled golden mane with elongated hairs encroaches, overwhelming the face and giving it the shape of an incandescent lightbulb, before meshing with a full beard. (Lesulas and owl-faced monkeys are distinguished from other species of the genus Cercopithecus by their vertical nose stripe, facial mane, and skull shape.) Super-sized eyes (bigger than those of owl-faced monkeys) sit closely together in deep sockets and appear to assess, without judgment, whatever subject is in its field of vision. Is there a soulfulness in this primate’s countenance? Maybe.
An art critic from the Guardian, one of the many publications worldwide that heralded the lesula’s discovery, compared the “soulful” portrait of a lesula to a Rembrandt painting.
The fur coats (known in science-speak as “pelage”) of adult lesulas are nuanced with gold, buff, and black flecks. Like their speckled mane, the fur on their back and chest is gold with flecks of black and buff hairs. Shoulders, forelimbs, lower belly, and abdomen are black. Hind limbs are silvery gray at the upper thigh; the lower leg is black. The base of the tail is gold, gradually darkening to a black tip.
Juvenile lesulas have pale blond fur coats and lack a prominent nose stripe. By the time they are 15 months old, their coats take on the coloring of the adult fur coats.
Adult males are easily identified by their hairless, bright blue buttocks. Their scrotum and anus are the same brilliant shade of blue. Scientists have observed that this blue brilliance quickly fades upon a male’s death, becoming a creamy white color. The bottom and genital area of the female lesula is a pale gray color.
Owl-faced monkeys are similar in appearance to lesulas, but the adults have darker gray coats. Juvenile owl-faced monkeys have yellow-brown coats. Both sexes of owl-faced monkeys have bare, blue buttocks, and mature males sport bright red and blue genitals.
Lesulas are herbivores. They eat a wide variety of fruits and vegetation and have a penchant for the leaves, ripe and unripe fruits, and flowers of the arrowroot (Marantaceae) plant family, sometimes called the “prayer-plant family.”
Behavior and Lifestyle
Lesulas are both arboreal (tree-dwelling) and terrestrial (ground-dwelling) monkeys who are active during daytime hours (making them “diurnal”). Camera trap footage from field studies suggests that the species may spend more time on the ground than in trees.
Their daytime activity includes grooming, foraging feeding, and resting. Lesulas are opportunists when it comes to foraging. They are known to eat fruits dropped to the ground by other primate species feeding in the trees above. Lesulas travel in the company of other lesulas or sometimes with other primates, including Wolf’s guenons (Cercopithecus wolfi), red-tailed guenons (Cercopithecus ascanius katangae), or red colobuses (Procolobus badius tholloni).
The lesula is one of two new species of monkey to be discovered in Africa since the sun-tailed monkey (Cercopithecus solatus) was discovered in Gabon in 1984. The second new species is the kipunji (Rungwecebus kipunji), discovered in Tanzania in 2003.
Some researchers use the common noun “lesula” to refer to both the singular and plural name of the species, much like the word “deer” refers to one or several deer.
Lesulas live in small family groups of up to five individuals.
Researchers have described lesulas as shy and quiet. These monkeys are particularly wary of encounters with humans, no doubt because they are hunted by humans. If they sense danger, lesulas will immediately flee, whether on the ground or through the forest understory, middle level, or canopy, as reported by researchers on their encounters with lesulas while conducting a field study of the species.
These same researchers came upon a wounded lesula, crouched in the crevice tree, just as a crowned eagle (Stephanoaetus coronatus) flew off. Although the eagle did not eat the lesula after this apparent attack, the young female lesula succumbed to her injuries and fell from the tree. The researchers collected her body as a specimen.
Lesulas greet the dawn with a chorus of loud “booms,” sounded in bouts of two or three calls with overlapping voices of different individuals. An all-male choir is suspected; a specialized laryngeal air sac enables the males to drop their voices to the low notes in these descending, low-frequency calls. The female lesula is equipped with a significantly smaller air sac, preventing her from emitting this distinctive call; so, no lesula chanteuses.
According to researchers, the lesula’s dawn boom chorus is the only call regularly sounded by free-ranging nonhuman animals. Lesulas might sound an occasional boom, just after dark.
The lesula male’s deep, descending boom is similar to that of the owl-faced monkey’s boom, but with a slightly different sound wave and duration.
Because of its “newness” as a primate species, the mating practices and reproductive life of the lesula is largely undocumented. Scientific speculation is based on the lesula’s sister species, the owl-faced monkey. Owl-faced monkeys share many anatomical and behavioral similarities to lesulas, so researchers conjecture that these two primate species likely share similar reproductive lives.
Like the blue bottoms of owl-faced monkeys, researchers believe that the brightness of an adult male lesula’s bare, blue bottom might serve as an indicator of his sexual maturity and as a signal to females that he is ready to mate.
Because owl-faced monkeys engage in polygynous behavior; that is, the males mate with multiple females, lesulas are likely polygynous, too. Females reproduce with a single male while rearing their young.
The breeding season of owl-faced monkeys is from May to late October or November, fluctuating slightly based on yearly regional rainfall.
After a gestation period of 5 to 6 months, a female gives birth to one offspring (twins are rare), every two years.
No specific accounts of parenting behavior in lesulas or owl-faced monkeys are available. However, the females of other guenon species, specifically members of the genus Cercopithecus, care for their young for approximately six months, the average weaning age.
Lesulas contribute to the regeneration of their forest habitat by dispersing seeds, through their feces, from the many fruits that they eat. As prey to native predators, including crowned eagles and leopards, the lesula is linked to the survival of these near-threatened species.
The International Union for Conservation of Nature assesses the lesula’s threat level as Vulnerable (IUCN, 2019). The lesula is threatened over most of its range by uncontrolled commercial bushmeat hunting. It is particularly vulnerable to snares set for duikers and bushpigs, although the monkey may not itself be targeted. Lesula population densities are lower in heavily-hunted areas relative to patrolled protected areas with similar forest habitats.
In addition, it is threatened by localized habitat loss caused by shifting agriculture affects the species’ range. Habitat loss through further expansion of subsistence shifting cultivation and commercial growing of upland rice is likely to increase in the future.
The lesula’s population size is unknown, but thought to be more than 10,000 individuals. However, populations are decreasing.
The lesula is not listed specifically by CITES, but is included in Appendix II as a member of the genus Cercopithecus. The government of Tshopo Province has designated its a protected species at provincial level; however, scientists assert that it should be considered for designation as a totally-protected species at the national level.
Most of the known lesula range is in Tshopo Province (formerly Oriental Province) in eastern-central DRC. It occurs in the Lomami National Park, where patrols protect about 20% of its known geographic range.
The lesula’s discovery highlights the importance of conservation and biodiversity in the area known as the interfluvial (an area divided by two or more river valleys) “TL2 region,” named for the Tshuapa, Lomami, and Lualaba (Congo) Rivers that flow through the landscape.
Although the TL2 region, the sole range of lesulas, is not currently under threat from habitat destruction through mining, logging, and other human-caused deforestation, humans are threatening the species’ future through bushmeat hunting.
Since 2006, the Lukuru Foundation has been actively involved in lesula conservation, thanks to the persuasive efforts of husband-and-wife scientist team John and Terese Hart. The Harts serve as lead researchers for the Lukuru Foundation’s Wildlife Research Project, focused on the remote interior of the DRC: lesula habitat. Working with local citizens, village chiefs, and government officials, the foundation works to establish protections and cultivate a next generation of conservationists by recruiting local Congolese people.
The Harts and their fellow conservationists petitioned the Congolese government and global wildlife organizations to create a protected wildlife reserve within the TL2 region. What began as an earnest undertaking in 2007, and involved great diplomacy, collaboration, and support from multiple conservation groups, was realized on July 7, 2016. On that day, Prime Minister Augustin Matata Ponyo of the Democratic Republic of the Congo officially established Parc National de la Lomami/Lomami National Park, the first national park created since 1970 and only the eighth with this designation (the highest level of protection) in the country.
In addition to lesulas, the Parc National de la Lomami is home to the Lomami River blue monkey (Cercopithecus mitis); Kasuku River Wolf’s monkey (Cercopithecus wolfi elegans); bonobo (Pan paniscus); okapi (Okapia johnstoni), DRC’s endemic forest giraffe; forest elephants (Loxodonta cyclotis); the Congo peacock (Afropavo congensis); and the extremely rare and critically endangered Dryad monkey (Cercopithecus dryas).
“The challenge now is to make the lesula an iconic species that carries the message for conservation for all of Congo’s endangered fauna,” John Hart has sagely stated.
Written by Kathleen Downey, April 2018. Conservation status updated July 2020.