A team of international scientists has discovered a new species of bird with a soothing tone in northeastern India and adjacent parts of China.

The bird, described in the current issue of the journal Avian Research, has been named Himalayan forest thrush Zoothera salimalii.

The scientific name honours the great Indian ornithologist Salim Ali, in recognition of his contributions to the development of Indian ornithology and nature conservation.

The discovery process for the Himalayan forest thrush began in 2009 when it was realised that what was considered a single species, the plain-backed thrush Zoothera mollissima, was in fact two different species in northeastern India, said Pamela Rasmussen from Michigan State University in the US.

Shashank Dalvi from Bengaluru-based National Centre of Biological Sciences was also part of the research team.

What first caught scientists' attention was the plain-backed thrush in the coniferous and mixed forest had a rather musical song, whereas those found in the same area - on bare rocky ground above the treeline - had a much harsher, scratchier, unmusical song.

"It was an exciting moment when the penny dropped, and we realised 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," said lead researcher Per Alstrom of Uppsala University in Sweden.

Along with keen field observations, the scientists had to do a lot of sleuthing with museum specimens.

Investigations involving collections in several countries revealed consistent differences in plumage and structure between birds that could be assigned to either of these two species.

It was confirmed that the species breeding in the forests of the eastern Himalayas had no name.

Further analyses of plumage, structure, song, DNA and ecology from throughout the range of the plain-backed thrush revealed that a third species was present in central China.

This was already known but was treated as a subspecies of plain-backed thrush. The scientists called it Sichuan forest thrush.

The song of the Sichuan forest thrush was found to be even more musical than the song of the Himalayan forest thrush.

DNA analyses suggested that these three species have been genetically separated for several million years.