- Preuss’s red colobus is found in two populations in West Africa — roughly 3,000 individuals in the Korup–Cross River forest block and none confirmed in the Yabassi Key Biodiversity Area for more than a decade — and faces intense pressure from hunting and habitat loss.
- The Bangka slow loris, restricted to Bangka Island in Indonesia has not been systematically studied for decades and has suffered extensive habitat loss from mining and forest conversion.
- Proper field studies and conservation approaches used for other slow loris species could provide a road map for assessing and protecting the Bangka slow loris.
- For Preuss’s red colobus, a regional action plan is advancing in Nigeria, where monitoring and community outreach are underway, but implementation in Cameroon has been hampered by ongoing civil unrest around Korup National Park.
Between Nigeria’s Cross River and Cameroon’s Sanaga River lies one of West Africa’s largest remaining blocks of intact rainforest. Noisy groups of Preuss’s red colobus monkeys (Piliocolobus preussi) move through this forest’s canopy in bands 20-to-60-strong, feeding mainly on the young leaves of just a few tree species, including Lecomtedoxa klaineana (known locally as oguomo) and Xylopia aethiopica (“grains of Selim”). The leaf-heavy diet of these social monkeys helps shape forest structure, and declines in their numbers often foreshadow wider losses of wildlife across the forest.
Half a world away, a very different primate lurks in the trees on the small, relatively isolated Indonesian island of Bangka. Readily identified by its pale facial mask, the Bangka slow loris (Nycticebus bancanus) is arboreal, nocturnal, and venomous, with large eyes and deliberate movements. Not much formal scientific knowledge has been gathered about this species since it was first described in 1937, but local conservationists have rehabilitated and released several dozen of the animals over the past decade.
Both species feature on the “Primates in Peril”, a roll call of the world’s 25 most endangered primates, a call for careful, focused conservation action. The future prospects for either primate illustrates how a threatened species’ survival may depend on very specific conditions: the health and protection of a single small island, or a particular forest type, or a few key plant species within that forest can make the difference between persistence and disappearance.
Protecting species means protecting habitat
Ekwoge Abwe, country director of the Cameroon Biodiversity Association, told Mongabay there are two main populations of Preuss’s red colobus. The larger group, around 3,000 individuals in total, occurs along the Cameroon-Nigeria border, spanning Korup National Park in Cameroon and the adjoining Cross River National Park.
The second population occurs in the Yabassi Key Biodiversity Area in southwestern Cameroon, including the Ebo, Makombe and Ndokbou forests. Despite regular surveys in Ebo, no sightings have been made of the species here or in the Yabassi Key Biodiversity Area as a whole for more than a decade, Abwe added.
 Preuss’s red colobus, Korup National Park. Images © Astaras via Wikicommons (CC BY 4.0) . |
Hunting is the most immediate threat to Preuss’s red colobus. Unlike many monkeys that flee when alarmed, these monkeys freeze — a natural antipredator response that makes them unfortunately easy targets for hunters supplying a thriving bushmeat trade in Cameroon and southeastern Nigeria where these monkeys are found.
Habitat loss compounds these pressures, Abwe said. “[Preuss’s red colobus] feeds on the young leaves of a small handful of tree species that are themselves targeted by loggers, including Lophira alata [azobe],” he said.
Logging concessions are a particular problem in Ebo Forest and the Yabassi Key Biodiversity Area. Conversion of forests to plantations is also a threat, as large-scale industrial oil palm plantations expand into P. preussi’s range. In Cameroon, the Ebo–Makombe–Ndokbou forest complex faces pressure from logging and industrial plantations along its edges, while the nearby Korup National Park is buffered by farmland and oil palm concessions. Across the border in Nigeria, poorly marked boundaries in the Oban division of Cross River National Park (CRNP) have allowed agriculture and illegal logging to encroach on forest habitat, putting remaining red colobus groups at risk.
Habitat loss is also the defining threat for the Bangka slow loris.
“It has an extremely limited range, and Bangka Island has experienced extreme forest loss largely due to mining,” said Anna Nekaris, a conservation biologist at Anglia Ruskin University in the U.K. and a leading expert on lorises. The species has not been systematically studied for decades, and any remaining subpopulations are likely highly fragmented.
Their extreme rarity accentuates the vulnerability of lorises generally, Nekaris said. “The number of [individuals of] other primate species, which have far less restrictions biogeographically in terms of their locomotion and even the flexibility of their ecology, make [it] shocking that there are so many macaques, langurs and gibbons but so few slow lorises.”
Targeted conservation efforts
Conservationists need more information about both species. Further surveys are required to confirm where Preuss’s red colobus is still present across its fragmented range, and to better assess threats in the two national parks in Cameroon and Nigeria and their surrounding areas, Abwe said.
The implementation of the 2021-2026 Red Colobus Action Plan (ReCAP) has progressed differently in the two countries where the species persists. In Nigeria, many of the recommended measures are already underway in Cross River National Park, said Inaoyom Sunday Imong, the country director for the Wildlife Conservation Society.
“We monitor the status of red colobus, other large mammals, and human activities in CRNP through data collected from monthly ranger patrols,” he told Mongabay. “We also implement education and sensitization programs that highlight wildlife laws and the importance of Preuss’s red colobus and its habitat in communities around CRNP, including through school conservation clubs, field trips, community meetings, and a radio program.”
Collaboration between WCS, the National Park Service of Nigeria, the Cross River State Forestry Commission, oil palm companies and local communities has made major gains in limiting industrial agriculture in Preuss’s red colobus habitat in Nigeria, Imong said. “As a result of these efforts, no new concessions have been given and development of existing ones has halted.”
But in Cameroon, civil unrest in the English-speaking southwest regions since 2016 has hindered ReCAP’s implementation in Korup National Park and surrounding areas, Abwe said. Outreach work in Ebo Forest continues, following the plan’s recommendations and focusing on threatened species including great apes and Preuss’s red colobus, Abwe added.
Barely studied since it was first described for science nearly a century ago, the Bangka slow loris badly needs fresh research and fieldwork, Nekaris said. “The local team [needs] proper support to get to know exactly the status of [the Bangka slow loris] there and ideally also study their behaviour in the wild for the very first time”.
A conservation road map for the Bangka slow loris could draw on successful approaches used for other loris species. “Our work on Javan slow loris [Nycticebus javanicus] is a perfect model,” Nekaris said, explaining how research on the species has guided both its captive management and field translocations. Similar lessons come from studies of the Tioman slow loris (Nycticebus coucang insularis), a subspecies of the Sunda slow loris (Nycticebus coucang) but which may itself represent a full species, pending further study, Nekaris added.
Genetic studies across the range of lorises are another key research priority, including on small islands. Slow lorises have diversified far more than expected, and that very diversity now puts them at greater risk. “The more we know, I feel sadly certain the more complexity and threat will be revealed,” Nekaris said.
“Listing a species in ‘Primates in Peril’ is a critical call to action, amplifying awareness and galvanizing conservation efforts by targeting governments, donors, and NGOs,” said Leandro Jerusalinsky, a deputy chair of the IUCN’s Primate Specialist Group, when the most recent list was published in July 2025.
Banner image: A Bangka slow loris (Nycticebus bancanus). Image by denny_skeep_setiawan via iNaturalist (CC BY-NC-ND 4.0).
New list of primates in peril aims to focus attention and inspire action
Citations:
Fonkwo, S. N., Mbida, M., Angwafor, T. E., & Ebua, V. B. (2015). Activity budget of Preuss’s red colobus (Procolobus preussi) in Korup National Park, South-West region, Cameroon. International Journal of Biological and Chemical Sciences, 9(4), 1799-1808. doi:10.4314/ijbcs.v9i4.6
Linder, J. M., Astaras, C., Oates, J. F., Abanyam, P. A., Abwe, E. E., Betobe, E. N., … Ormsby, L. J. (2021). Population status of the critically endangered Preuss’s red colobus monkey (Piliocolobus preussi Matschie 1900) and recommendations for its conservation. International Journal of Primatology, 42(2), 262-282. doi:10.1007/s10764-021-00202-w
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