The world might be losing wilderness at a frightening rate, but there are still wild places that have surprises in store for us. And researchers working in the rainforests of the Congo have video footage to prove it. They've captured the first recordings of an extremely rare – and extremely endangered – species of monkey in a place no one expected to find it.

Lomami National Park is a 2.2 million-acre section of rainforest in the Democratic Republic of Congo. Officially established as a park only this past July, the vast patch of wilderness is invaluable to the conservation-focused Lukuru Foundation, whose international members have spent years studying African primates and the ecosystems that sustain them.

"The Congo Basin rainforest is the second-largest rainforest in the world," says Kate Detwiler of Florida Atlantic University, "and contains some of the least-known species on the planet, many of which are threatened from hunting pressure and deforestation."

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Cercopithecus dryas is listed as "Critically Endangered" by the IUCN. Image: Pablo Ayali/Flickr

Lomami is home to nearly a dozen primate species, including several monkeys and bonobos. Some years ago, Lukuru scientists even discovered a completely new species – the Lesula monkey – living in the park. And just recently, another surprise primate made an appearance: the rare Dryas monkey.

The animals are small and secretive, so there is a lot we don't yet understand about the species. But we do know this: the monkeys are considered critically endangered due to habitat loss, with possibly fewer than 200 remaining in the world. What's more, these primates have only ever been seen in the Wamba-Kokopori forest of the Congo, so it was quite a surprise to see them 400 kilometres away in Lomami.  

In 2014, Lukuru researchers exploring the area noticed the carcass of an unfamiliar monkey in the possession of a hunter in a small village near base camp. It took some investigation to identify this peculiar primate as a Dryas monkey, and then to learn that the species was actually living in Lomami. The obvious next step was to find more of them.

Canopy cameras allowed the team to capture the first footage of Lomami's Dryas monkeys. Image: Terese Hart/Flickr

"The Dryas monkey is extremely cryptic and we had to think of a creative strategy to observe them in the wild," says Detwiler.  

The research team set out to place cameras and sound recorders in the rainforest, but it wasn't enough to position them in easy-to-reach spots near the forest floor – that's not where you'd expect monkeys hang out, after all. So it fell to Detwiler's student, Daniel Alempijevic, to climb around high in the rainforest canopy to set up the equipment.

"This was an opportunity of a lifetime," Alempijevic says. "It was an incredible experience to work in the canopy of such a remote site, and to get the first camera-trap videos of an extremely rare and elusive species."

The team placed cameras at three levels in the forest: the ground, the mid-level understory and high up in the canopy. At ground level, the cameras caught bonobos and other large animals; high in the canopy they saw many birds and monkeys (there was even a climbing pangolin cameo). But it was in the vine-covered understory that they got what they were looking for: the first video footage of the local Dryas monkeys.

According to Detwiler, finding the species is only the first step. "Our goal is to document where the new Dryas populations live and develop effective methods to monitor population size over time to ensure their protection."