Researchers working on the island of Borneo have discovered two tiny new populations of Miller's grizzled langurs (Presbytis hosei canicrus), one of the world's 25 most endangered primates. The species is so rare that it has probably disappeared from all of its previously known habitats, which have been almost completely logged and burned out of existence. The langur was last observed in 2008 (pdf) in an isolated patch of mangrove forest on the banks of the Baai River which flows through Borneo's Sangkulirang Peninsula, when just five of the primates were found. Those five langurs have not been seen since.

But now two teams of researchers—working independently of each other—have located two new populations of the animals in Wehea Forest, 150 kilometers inland from their previously known locations. It's a discovery that points to the possibility of additional langur populations and offers hope that the species can be saved from extinction. The news was published online January 20 in the American Journal of Primatology.

The researchers weren't looking for the langurs. Stephanie Spehar, assistant professor of anthropology at the University of Wisconsin–Oshkosh, was in Wehea studying the behavioral ecology of the area's other primates—including Bornean orangutans (Pongo pygmaeus), Bornean gibbons (Hylobates muelleri) and red langurs (Presbytis rubicunda)—when one of her students, Eric Fell, captured photos of a primate they did not recognize.

Eight kilometers away, a research team led by Brent Loken, a PhD student at Simon Fraser University in British Columbia, had set up camera traps hoping to capture images of the elusive Bornean clouded leopard (Neofelis diardi). Instead, they also found images of a primate they did not recognize.

Spehar and Loken, who each work with the local Wehea Dayak community to help preserve the forest, compared notes and concluded that they had observed the same species.

"We realized that our research groups had simultaneously discovered this rare primate, Miller's grizzled langur, in the Wehea Forest," Spehar says. "It was definitely unexpected, but the best kind of surprise for a group of primatologists and conservation biologists."

Positively identifying the langur wasn't easy. "The pictures we have are some of the only pictures that exist of this monkey and therefore confirming its identity was a bit of a challenge," Loken says. "The current description of this monkey comes from museum specimens, and the pictures that we took did not fit perfectly with the previous description of this monkey." His colleague, Stanislav Lhota of the University of South Bohemia in the Czech Republic, contacted three primatologists with extensive experience in Borneo, all of whom agreed that the teams had located the Miller's grizzled langur.

The researchers later found out that two other researchers had observed and photographed the langurs in Wehea in 2008 and 2010 but they had not been identified as this rare species. Those photos had never been published.

Spehar and Loken's teams observed the Miller's grizzled langurs in Wehea near two mineral springs in June and July 2011. They reported observing the langurs on five out of nine days; the greatest number of animals they saw was on July 11 when they spotted 11 individuals. The adults were estimated at about six to seven kilograms—"pretty big for a Bornean forest mammal," Spehar says—and were easily distinguishable from Wehea's three other langur species by their gray limbs, white underbellies, black faces and full white beards.

Unfortunately, the researchers concluded that the population density for this species in Wehea Forest is still extremely low. They explain that all of the forest's resident primate species tend to gather at mineral springs for reasons that are not yet known, so observations there do not reflect possible population density throughout the 38,000-hectare forest.

The researchers are now calling for increased efforts to protect Wehea Forest from logging and deforestation, which have already destroyed 95 percent of the langurs' previous habitats. Loken himself co-founded a nonprofit called Ethical Expeditions which helps the indigenous Wehea Dayak people fight back against deforestation.

Meanwhile, Spehar, Loken and Lhota have shifted some of the focus of their ongoing research to learn more about the Miller's grizzled langur.

Loken discusses the discovery and shows off time-lapse photographs of the Miller's grizzled langurs here:

Photo by Eric Fell