ANTANANARIVO — For more than six decades, the International Primatological Society (IPS) has brought scientists, conservationists and educators from around the world together every two years to exchange ideas and drive primate research and conservation. The 30th IPS Congress welcomed nearly 800 participants from around the world to Madagascar, the “Land of Lemurs.” It’s a long-standing tradition of the congress to publish a list of the world’s 25 most threatened primates to draw attention to species at particularly high risk and inspire action to protect them.

Drawn up as a collaboration between the IPS, the Primate Specialist Group of the IUCN, the global wildlife conservation authority; and conservation NGO Re:wild, this recurring initiative highlights that more than two in five of the world’s primates were classified as endangered or critically endangered on the IUCN Red List in 2023. Multiple criteria are considered when nominating the most threatened 25, among them geographic and taxonomic representation, uniqueness, and the potential conservation impact of being listed.

“Listing a species in ‘Primates in Peril’ is a critical call to action,” said Leandro Jerusalinsky, deputy chair of the IUCN’s Primate Specialist Group Neotropics section, “amplifying awareness and galvanizing conservation efforts by targeting governments, donors, and NGOs.”

Inza Koné, president of the African Primatological Society, explained some of the thinking behind this year’s list: “Piliocolobus preussi [Preuss’s red colobus], the most threatened red colobus, was added to represent red colobus monkeys. It replaced Piliocolobus epieni [Niger Delta red colobus] from the previous edition, which has since benefited from increased attention and new population discoveries — a truly positive result.”

The greater bamboo lemur (Prolemur simus) has featured on several successive lists of the 25 most threatened primates, which has helped attract attention and funding, said Josia Razafindramanana, representative of the IUCN Primate Specialist Group’s Madagascar section. “It helped advance habitat protection and research, with many organizations actively involved in conservation efforts.”

Inclusion on the list led to the creation of a new protected area aimed at securing habitat for the pied tamarin (Saguinus bicolor), according to Jerusalinsky. Other exports pointed to targeted conservation strategies — such as the Red Colobus Action Plan and the Asian Langur Action Plan — as examples of how the list has translated into meaningful action.

In contrast, the red-bellied monkey (Cercopithecus erythrogaster) remains at grave risk, but has nonetheless been displaced by the Roloway guenon (Cercopithecus roloway), fewer than 200 of which are thought to remain the swamp forests of Tanoé-Ehy, on the border between Côte d’Ivoire and Ghana, threatened by hunting and the destruction of their habitat by mining and agriculture.

There was a “very long debate” when it came to picking a representative from the biggest of the primates, the gorilla, according to Koné. In the end, Grauer’s gorilla (Gorilla beringei graueri), endemic to the conflict-ridden eastern Democratic Republic of Congo, took the place of the Cross River gorilla (Gorilla gorilla diehli) on the latest list. “We wanted to send a strong political message, as Grauer’s gorilla is particularly threatened in the conflict zone,” Koné said. “Despite war, we have to pay attention on our nature heritage.”

The 2025-2027 list was officially presented during a dedicated session at this year’s congress, followed by a public debate where participants advocated for the inclusion of certain species, challenged others, and proposed alternatives.

Razafindramanana underlined the particular significance of five of the lemur species placed on the list this year – each of the quintet is an umbrella species, the protection of which will also help to preserve the wider landscape they live in. “All of Madagascar’s ecosystems are represented,” she said. There’s the Lac Alaotra gentle lemur (Hapalemur alaotrensis) from the east, and the mongoose lemur (Eulemur mongoz) in the west, both restricted to tiny ranges; Verreaux’s sifaka (Propithecus verreauxi) in the south, which has experienced a 50% population decline; and the indri (Indri indri), which, although widespread, “has low population recovery and serves as a flagship species,” Razafindramanana said.

She told Mongabay that the fifth species, the black-and-white ruffed lemur (Varecia variegata), was included both to represent the Varecia genus of ruffed lemurs and because of escalating hunting pressure.

Andie Ang, deputy chair of the IUCN Primate Specialist Group’s Asian section, highlighted the selection of the island-endemic Bangka slow loris (Nycticebus bancanus) to the list. “[It’s] a small, nocturnal animal found only on small islands in Indonesia. People do not really think about it, and it could disappear very quickly,” she told Mongabay. “We put [it] on the list to shine light on the species, to attract funding. Due to the lack of attention and threats, it can go extinct very quickly.”

The Western hoolock gibbon (Hoolock hoolock), from mainland Southeast Asia, was also listed in an attempt to catalyze greater research and conservation efforts and to encourage transboundary collaboration, Ang said. “We want people — local communities, governments, media — to talk about these species, to learn about them.”

Jerusalinsky spoke to Mongabay about the specific threats facing three newly listed species from the Neotropics, or tropical regions of the Western Hemisphere. Habitat fragmentation poses one of the most serious threats in South and Central America, putting species at risk and weakening their populations. Jerusalinsky cited the case of Coimbra’s titi monkey (Callicebus coimbrai), which “survives in the Northeastern Atlantic Forest [of Brazil] with no condition to maintain viable populations in the long term.” In Bolivia, the Beni titi monkey (Plecturocebus modestus) “faces substantial inbreeding levels,” he added.

On top of that, climate change impacts pose an emerging threat: the Mexican mantled howler monkey (Alouatta palliata mexicana) has experienced an unprecedented die-off in recent years, probably related to heat strikes, Jerusalinsky said.

The study of nonhuman primates offers deep insights into our own evolution, health and societies. While many primate species are under severe threat, and there have been no recorded sightings of species like Miss Waldron’s red colobus (Piliocolobus waldroni) or the Bangka slow loris in decades, there were no formal primate extinctions declared in the 20th century — and none yet in the 21st, said Russell Mittermeier, chair of the IUCN Primate Specialist Group at the launch of the list. Extending this record, he told the congress, and safeguarding the rich diversity of the world’s primates, is the core mission of the Primate Specialist Group.

Primates in peril

Banner image: Greater bamboo lemur (Prolemur simus), Ranomofana National Park, Madagascar. Image by Goran Bength (CC BY-NC-ND 2.5)

Citation:
Estrada, A., Garber, P. A., Rylands, A. B., Roos, C., Fernandez-Duque, E., Di Fiore, A., … Li, B. (2017). Impending extinction crisis of the world’s primates: Why primates matter. Science Advances, 3(1), e1600946. doi:10.1126/sciadv.1600946

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AnimalsBiodiversityConservationEndangered SpeciesExtinctionLemursMonkeysPrimatesWildlifeWildlife ConservationAfricaAsiaCameroonCentral AfricaMadagascarWest Africa

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