Because the forest-dwelling thrush is notoriously elusive, it was, at first, difficult for scientists to learn whether there were in fact any physical differences between the two – as on the surface their plumage and anatomy are very similar. It wasn’t until several years of research, DNA analysis and painstaking comparison studies between the wild birds and specimens from 15 different museums that physical and genetic differences between the two were confirmed.
A Few Million Years of Separation
What scientists discovered from DNA analysis was that while the two different birds had come from the same ancestor, they had been breeding entirely separately for at least several million years. To put in it context, Professor Alström likened their genetic evolution and relationship to that of humans and chimpanzees.
The reasons for the split in breeding most likely occurred as an adaptation to surviving in their very different habitats – for example, the forest bird has shorter legs than the alpine bird, as longer legs are more of a physical benefit in open or mountainous habitats. Aside from the difference in leg length, the alpine species also has a longer tail.
Diverging the Species: One Becomes Three
Based on past research and comparisons, scientists agreed that the alpine species was the original Zoothera mollissima, while the “new” forest species became Zoothera salimalii. In another twist, however, during the course of fieldwork in China they discovered a third population of thrush in fact deserved reclassification from sub-species to its own species.