An international team of scientists, including Yale researchers, has described a new Colobus monkey species inhabiting high forest canopies in the Democratic Republic of Congo (DRC). It is just the fifth new species of African monkey discovered in the past 75 years.
The species, Colobus congoensis , is a rare and cryptic monkey largely unknown even among people living within its range. But those who are familiar with the small, black monkeys — an arboreal creature marked by distinctive orange-cream patches around their mouths and noses — call them “Likweli,” which the researchers recommend remain the species’ common name.
The identification of Likweli as distinct from other Colobus monkey species is supported by evidence drawn from its physical traits, genetics, and vocalizations.
“Our team evaluated multiple datasets that all reached the same conclusion: Likweli is a distinct species of Colobus monkey we haven’t seen before,” said Julia Arenson, a postdoctoral fellow in Yale’s Department of Anthropology and the Yale Institute for Biospheric Studies and coauthor of the study. “Discovering a primate species is exceptionally rare, especially from populations previously unknown to science.”
The documentation of the Likweli, she said, also highlights the importance of protecting the rich biodiversity of Lomami National Park, an 8,874-square-kilometer park known for its rare and endemic species.
In the past 75 years, only eight new ape and Old World monkey species from populations previously unknown to science have been discovered. Those include Lesula, a monkey species discovered in 2012 in the Congo Basin by a team that included several coauthors of the current study.
The latest discovery is described in an article published on July 15 in the journal PLOS One. For the study, Arenson and Eric Sargis, professor of anthropology in Yale’s Faculty of Arts and Sciences, collaborated with researchers from the Lukuru Wildlife Research Foundation and Lomami National Park in DRC, Florida Atlantic University, and Hunter College of the City University of New York. All research was conducted under the authorization of the Congolese Institute for Nature Conservation (ICCN), an agency of the DRC government.
John and Terese Hart, conservation biologists with the Lukuru Wildlife Research Foundation and curatorial affiliates at the Yale Peabody Museum, are coauthors of the study.
“The discovery and documentation of the Likweli never would have happened without our team of Congolese explorer naturalists,” said John Hart, the study’s lead author. “These field leaders recognized when they were in front of something they did not know. They put in the extra effort needed to document and confirm it. Their attentive fieldwork, covering hundreds of hours and thousands of kilometers of reconnaissance across trackless forest, produced some of the most remarkable information for this new find.”
From 2018 to 2022, the researchers recorded 114 observations of Likweli over a range of about 1,700 square kilometers in Lomami National Park and its buffer zone on highlands located between three tributaries of the Congo River: the Tshuapa, Lomami, and Lualaba. The monkeys, which were most frequently observed in small groups of about six individuals, are difficult to spot and photograph because they live high in dense forest canopy, the researchers noted.
“Only after 10 years of exploring the Lomami Forest did we have enough clear views and convincing photos to allow us to say that there was yet another new monkey,” said Terese Hart. “This primate was not only new – it was extremely rare and with a limited range.”
In addition, the researchers spoke with residents of 52 villages bordering or located within Likweli’s range. Residents in only eight villages reported knowledge of the species and could accurately describe it. Since people in the region typically have detailed knowledge of local flora and fauna, this supports the notion that Likweli is a cryptic species, the researchers said.
In April 2021, ICCN officers confiscated three deceased Likweli specimens from hunters within the Lomami National Park buffer zone. Those specimens — two adult females and one adult male — were acquired by the researchers with authorization from ICCN. The skins and skeletons are now housed in the Yale Peabody Museum’s mammalogy collection.
Likweli are small, long tailed, and have black coats. Long, black hairs frame their foreheads and faces. Their small size, striking orange-cream patches on their faces, and white patches on their backsides underneath their tails distinguish them from Colobus satanas , its sister species and the only other Colobus monkey with all-black coats, the researchers said. Characteristics of its teeth and skull also differ from those of Colobus satanas , according to the study.
The researchers also compared Likweli vocalizations with those of other Colobus species. They found that its roars are similar to vocalizations of its sister species ( Colobus satanas) in some ways but differ in sequence and frequency, among other aspects.
Based on a genetic analysis, the researchers estimated that the most recent common ancestor of Colobus congoensis and Colobus satanas existed between about 4.7 and 5.8 million years ago, which represents the deepest split in lineages among Colobus monkeys, further suggesting that Likweli is a distinct species.
The researchers note that the new species and its sister species, though very similar, inhabit ranges that are at least 1,200 kilometers apart, with the latter living to the west of the former.
Based on Likweli’s limited range and small population, coupled with the effects of increased hunting and human encroachment on the monkeys’ habitat, the researchers recommend that the species be designated as endangered.
“This is a rare discovery with significant conservation implications,” said Sargis, a curator of mammalogy and vertebrate paleontology at the Yale Peabody Museum and director of the Yale Institute for Biospheric Studies. “Our analyses provide strong evidence that this is a distinct new species that is endangered.
“Documenting new primate species like Likweli and Lesula illustrates the incredible biodiversity in this region and points to the importance of Lomami National Park and other conservation efforts in protecting that diversity.”
PLOS One
15-Jul-2026