On the Case: Solving the Mysteries of the Lost Silver-backed Chevrotain

Camera Trap Survey Reveals Miniature 'Deer' in Vietnam's Coastal Forests

Every time Vietnamese biologist An Nguyen finds a mammal in the wild that he’s never detected before, either in person or in photos taken by camera trap, he gets a new tick-tack tattoo on his left arm. While each tattoo marks a special sighting, tattoo number 50 is the result of some top-notch detective work and the determination of a team committed to solving what has been nearly a century-long scientific mystery: what ever happened to the Silver-backed Chevrotain, a small deer-like animal only confirmed scientifically once since 1907.

For every new mammal he finds in Vietnam, biologist An Nguyen adds another mark to his tattoo. (Photo courtesy of An Nguyen)

“For those of us living in Vietnam and working in wildlife conservation, the question of whether the chevrotain was still out there and if so, where, has been nagging us for years,” Nguyen said. Nguyen is an associate conservation scientist with GWC and a PhD student with the Leibniz-Institute for Zoo and Wildlife Research. “There was very little information available to point us in the right direction and we didn’t know what to expect. That we were able to find it with so few leads and in a relatively short period of time shows how a little bit of effort and willpower can go a long way in finding some of these special species lost to science.”

The rediscovery of the Silver-backed Chevrotain—also known as the Vietnamese Mouse-deer—is the first rediscovery of a mammal on GWC’s 25 most wanted lost species list. The species was described in 1910 from four individuals collected in 1907 near the southern beach city of Nha Trang. A Russian expedition in 1990 in central Vietnam collected a fifth individual. With only this information on hand, Nguyen and a team that included GWC’s Dr. Barney Long and Andrew Tilker, set out to figure out where to start.

“We had these two historical localities separated by quite some distance—one in the southern part of Vietnam and the other much further north,” says Tilker, GWC’s Asian species officer. “But we knew that many people have camera-trapped in the wet evergreen forests and hadn’t seen it, so we thought we should look at the dry forest habitat that’s really different and where not many people have looked.”

The team also started to put out some feelers to investigate potential leads. Soon after, one colleague obtained a photo of what appeared to be a young chevrotain with silvery coloration. Although the photo had been taken more than 10 years ago and was not conclusively a Silver-backed Chevrotain, the animal was reportedly found near the dry coastal forests where the 1907 individuals came from. It was this clue and the process of elimination, Tilker says, that set the successful mission on course.

Once the team had identified the general area to search, they needed to determine exactly where to look. So Nguyen and his colleagues conducted interviews with local villagers and government forest rangers who reported seeing a gray mouse deer—distinguishing the Silver-backed Chevrotain from the more common Lesser Chevrotain. With each interview, Nguyen says, he grew more optimistic that the animal the villagers were seeing in two forest areas was, indeed, the long-lost chevrotain.

Setting camera traps (Photo by Andrew Tilker, Global Wildlife Conservation).

“So the next step was to put out camera traps in one of those areas where villagers had described seeing the chevrotain,” Nguyen says. “The results were amazing. I was overjoyed when we checked the camera traps and saw photographs of a chevrotain with silver flanks. With three camera traps left in the field for five months, we were able to get 275 photos of the species. The Silver-backed Chevrotain went from being lost for at least 30 years, to found really within a matter of months. One more tick for my tattoo.”

The team then set up another 29 cameras in the same area, this time recording 1,881 photographs of the chevrotain over another five months. This month the field team will begin camera trap surveys in two additional areas, including the second area that villagers had said they saw the animal. Those cameras will run for at least three months.

But the case isn’t yet closed.

“Just because we found this species relatively easily, doesn’t mean it’s not threatened,” Tilker says. “This might represent the last population or one of a handful of populations, in which case we need to take action immediately to put conservation measures in place to ensure its survival. This is a region known to be under immense anthropogenic pressures, so we need to get ahead of the curve, instead of waiting until it’s as rare as Saola and our conservation options become more limited.”

The chevrotain is one of a number of fascinating species that live in the diverse tropical forests of Southeast Asia, where some species have only been discovered in the last few decades. This includes the antelope-like Saola (the Asian “unicorn”), which was only discovered in 1992 and that no biologist has seen in the wild. Animals in this area of the world, however, are victims of a devastating hunting technique—the use of cheap and homemade wire snares. The level of indiscriminate hunting in the region has led to widespread “empty forest syndrome” across Vietnam, pushing numerous Annamite species to the brink of extinction.

The Silver-backed Chevrotain was rediscovered in Vietnam's coastal forests. (Photo by An Nguyen)

“It’s an amazing feat to go from complete non-understanding of the Annamites 25 years ago to now having this unique question mark resolved,” says Long, GWC’s senior director of species conservation. “But now we have to focus attention on this overlooked species and put it on a trajectory to safety and recovery.”

A team is now working to determine how large—and stable—this population of Silver-backed Chevrotains is, the wider distribution of the species, and understanding the threats to its survival. If it is restricted only to the dry coastal forest, it would have the smallest distribution of any ungulate in the world. The team members will use all of the information that they gather to develop and implement a conservation action plan that strengthens enforcement and protection of the species across its range, building on the increased enforcement already put in place at the site of rediscovery.

For Nguyen, Tilker, Long and team, solving the mystery of whether the Silver-backed Chevrotain is still tiptoeing through the forests has spurred tremendous hope for its future.

“Vietnam may be one of the toughest places on the planet to work on mammal conservation,” Tilker says. “So it’s nice to have a hopeful story from Vietnam and to be a part of something positive that can help ensure that this species is never lost again, including as the result of extinction.”

This project was made possible in part by the generous support of Wroclaw Zoo, Aukland Zoo, Mohamed bin Zayed Species Conservation Fund (Project 172515989), and the Gerald Singer Deer Research Grant provided by the Sainte Croix Biodiversité. Additional support was provided by Southern Institute of Ecology and the Leibniz Institute for Zoo and Wildlife Research.

Now that we have found the Silver-backed Chevrotain, we don’t want to lose it to extinction.

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