An international team of scientists has discovered a new species of bird living in northern India and China, dubbed the Himalayan forest thrust and noted for its musical song.

The researchers first suspected they'd found a new species because birds in the forests sang a much more musical tune than similar birds on the rocky Himalayan peaks.

Previously, both had been thought to be one species known as the plain-backed thrush.

Further investigation found genetic and physical differences confirming the forest thrush to be a separate, distinct species.

The high-mountain dwellers have now been renamed the alpine thrush, while the new Himalayan thrush has been given the scientific name Zoothera salimali.

"There aren't too many new birds to be found in the world," says Per Alström of Uppsala University in Sweden, lead author of a study on the new species appearing in the journal Avian Research. "So it's exciting when you find a new one."

The researchers began to suspect they were dealing with two different species when they compared the songs of the forest and mountaintop varieties.

The song of birds living at lower levels in mixed and coniferous forests was pleasingly musical, while birds in the same region but living higher up on rocky terrain above the tree line sang tunes the researchers found to be harsh, scratchy and rather unmusical.

"It was an exciting moment when the penny dropped, and we realized that the two different song types from plain-backed thrushes that we first heard in northeast India in 2009, and which were associated with different habitats at different elevations, were given by two different species," says Alström.

The suspicion of a new species was confirmed by further research comparing birds in the wild in India and China with specimens held in numerous museums around the world.

DNA analysis in particular showed the two species, forest and alpine, have been breeding separately for several million years, the researchers reported.

They may have begun as one species but they evolved differently to meet the different demands of living in the forests and on the mountain peaks, they suggest.

"The alpine thrush has longer legs and a longer tail, proportionately, than the forest bird, which I'm sure are adaptations to its habitat," says Alström, "because longer legs are more useful in open habitats than in forest."

It is rare to find a new bird species anymore, the researchers point out, and the Himalayan forest thrush is only the fourth new species identified in India since 1949.

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