The illegal wildlife trade in Vietnam has depleted some forests so drastically that scientists call the result “empty forest syndrome,” where almost nothing sings or crawls or rustles the branches.

“There’s a beautiful, vibrant tropical forest around you, but no animals in it,” said Andrew Tilker, a scientist with Global Wildlife Conservation and doctoral student at the Leibniz Institute for Zoo and Wildlife Research in Berlin. “It’s an eerie feeling.”

Within this emptiness, Mr. Tilker and a team of researchers went looking for a small, deer-like mammal called the silver-backed chevrotain, which scientists hadn’t seen any evidence of in nearly 30 years. But, the team reported Monday in Nature Ecology & Evolution, there’s at least one pocket of forest where the mammal is alive and well, for now.

With its Search for Lost Species initiative, Global Wildlife Conservation aims to highlight species, like the silver-backed chevrotain, that are “lost” to science, but not necessarily extinct. Scientists have only recorded five silver-backed chevrotain specimens. All of them were already dead. The first four appeared in 1910, and the final specimen, killed by a hunter, turned up in 1990.