Sichuan bush warbler

A wild Sichuan bush warbler, Locustella chengi, in May 2014. (Photo: Bo Dai)

It took 20 years, but scientists have tracked down a mysterious songbird in China. And despite its elusiveness, the bird doesn't seem to be endangered — a welcome novelty for a newfound species.

Researchers first noticed the Sichuan bush warbler's song while exploring the mountains of central China in May 1992. They weren't able to find the bird itself, and it evaded discovery for the next two decades. But a new study by 16 experts finally confirms the species' identity.

"The Sichuan bush warbler is exceedingly secretive and difficult to spot as its preferred habitat is dense brush and tea plantations," Michigan State University biologist and study co-author Pamela Rasmussen says in a press release. "However, it distinguishes itself thanks to its distinctive song that consists of a low-pitched drawn-out buzz, followed by a shorter click, repeated in series."

That song was noted in 1992 by Swedish biologists Per Alström and Urban Olsson, who initially struggled so much to find the source that weren't even sure if it was a bird or a bug. "We heard a song that was unfamiliar to us coming from a dense patch of tall herbs," Alström tells the Guardian. "The song didn't sound very 'bird-like,' and as we couldn't see a trace of any bird, we were debating for a little while whether it was a bird or some insect. Although we thought it was most likely a bird."

They finally caught a few brief glimpses of the bird, which seemed to resemble the russet bush warbler. Its song was very different, though, suggesting a new species. Here's a recording:

Alström and Olsson couldn't track down the bird in '92, though, so they returned to Sweden still wondering if they'd really encountered an unknown species. Almost 20 years later, while Alström was a visiting professor at the Chinese Academy of Sciences, he learned that some Chinese biologists had also noticed this bird. They launched an expedition, and in May 2011 they found it.

This became the first specimen of the Sichuan bush warbler. Over the next three years, researchers spotted more of the birds, recorded more songs and collected more samples. Analysis of its DNA confirms it is a new species, although it's closely related to the previously known russet bush warbler. The two warblers split from a common ancestor about 850,000 years ago — which means the newfound Sichuan bush warbler is four times older than the species that just "discovered" it.

Newly identified species often turn out to be endangered, especially when they're highly dependent on a specific habitat. The Sichuan bush warbler breeds in dense vegetation at elevations between 1,000 and 2,300 meters (3,280 to 7,545 feet), and it remains unclear where it spends winters. Fortunately, though, the researchers say it's locally common "and does not appear to be under any imminent threat."

The bird's scientific name, Locustella chengi, honors the late Cheng Tso-hsin, who died in 1998 and is known as as China's greatest ornithologist. "We wanted to honor Professor Cheng Tso-hsin for his unparalleled contributions to Chinese ornithology," Rasmussen says. "Many species are named for European explorers and monarchs, but few bear the names of Asian scientists."

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Russell McLendon ( @russmclendon ) writes about humans and other wildlife.