Several new species of bird have been discovered in the Himalayas on the border between India and China. They were first identified by researchers when a difference in the songs of various thrushes, thought to be the same species, was noted. The new study, published in the journal Avian Research, details the serendipitous discovery.

The plain-backed thrush, Zoothera mollissima, was long thought to occupy a large habitat across the northern regions of the Indian subcontinent, particularly in the dramatic Himalayan mountain range. Also found in Bhutan, Thailand, Myanmar and Vietnam, it has been thoroughly studied by ornithologists and definitively categorized.

However, an expedition to the forests of the Himalayas has effectively changed the way researchers see the evolution of thrushes in the entire region. The discovery dates back to 1999, when Professor Per Alström, a researcher at Uppsala University in Sweden, was trekking in the area.

“We noted that there were two different groups of what was previously called the plain-backed thrush, that occurred at different elevations, in different habitats,” Alström told BBC News. The first group of birds, found far above the tree line in the mountains, had a rather unpleasant birdsong: It was harsh and somewhat coarse-sounding.

The set of thrushes found lower down, mostly within the thick forests, sang a far more tuneful sound. At a glance, the researchers could not find any immediately obvious differences in plumage or body shape. But only a limited number of observations had been made of the lower-living thrush, so further expeditions were conducted, and a comprehensive study on regional thrushes was undertaken. Specimens of various thrushes from around the world, including examples from 15 different museums, were also analyzed.

^{The three new species of thrush. (A) the alpine thrush, Z. mollissima; (B) the Himalayan forest thrush, Z. salimalii; (C) the Sichuan forest thrush, Z. griseiceps. Alström et al./Avian Research}

Detailed DNA analysis revealed what the songs had suggested: There are two completely different species of plain-backed thrush in the Himalayas. In addition, it revealed they had diverged from a common ancestor several million years ago.

The mountain-dwelling variety, now known as the alpine thrush, was what was originally classified as the plain-backed thrush. It has longer legs and a longer tail (proportionally) than the forest-dwelling equivalent, both of which are more useful for navigation in open environments. As this was the “original,” it will get to keep the Z. mollissima scientific name. The forest variety will now be called Zoothera salimalii.

As luck would have it, the researchers also stumbled across a third, new, closely related thrush species. The Sichuan forest thrush, found within nearby China, was previously considered a sub-species of the plain-backed thrush.

However, with an even more musically pleasant song than its Himalayan cousins, and with a distinctly different genetic signature, it was considered deserving of its own species designation: Zoothera griseiceps. So out of one original species, three discoveries have been made.

Discovering new birds is indeed a rare thing in the modern world, with this new research representing the fourth species of bird discovery in India since its independence in 1947. In the last 15 years, roughly five new species have been discovered annually, primarily in the dense forests of South America.