A new species of bird has been discovered in India and China through its musical song. Zoothera salimalii, or Himalayan forest thrust, is only the fourth new species of bird to be discovered in India since 1949.

An international team of scientists from Sweden, China, the US, India and Russia began their search for the Himalayan forest thrush in 2009. They team, which published its findings in the journal Avian Research, realised what had previously been considered a single species – the plain-backed thrush Zoothera mollissima – was actually two.

Study leader Per Alström and the researchers realised the Himalayan forest thrust had a far more musical song than the plain-backed thrush, whose song is described as harsher, scratchier and unmusical.

"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 north-east India in 2009, and which were associated with different habitats at different elevations, were given by two different species," Alström said.

Subsequent field observations and research on museum specimens revealed a number of differences in plumage and structure. It was then confirmed the new species, which was found inbreeding in the forests of the eastern Himalayas, was unknown to science. The name for Zoothera salimalii honours Indian ornithologist Sálim Ali.

Pamela Rasmussen, one of the researchers, said: "At first we had no idea how or whether they differed morphologically. We were stunned to find that specimens in museums for over 150 years from the same parts of the Himalayas could readily be divided into two groups based on measurements and plumage."

A third species was then identified living in central China. The Sichuan forest thrust was already known to science but before their research, it had been thought of as a sub-species of the plain-backed thrust. This final species had an even more tuneful song than its Himalayan counterpart. DNA evidence showed all three had been genetically separated for several million years.

Alström told the BBC: "They have had separate evolutionary histories for a very long period of time - possibly the same length of time as humans and chimpanzees have been separate from one another... out of this single species, we got three different species."