Songbirds nesting across the valleys of Western Ghats are witnessing genetic change in their species, which could mean creation of new species. The most common songbirds in India are bulbul, mynah, sparrows and koel.

Though it is popularly believed that climate change has a role to play in it, a study by the National Center of Biological Sciences reveals that the elevation of valleys in the mountain range is also leading to such changes.

The study, which includes 23 songbirds in the Shola forests, spread over Karnataka, Tamil Nadu and Kerala, has found out that species divergence has been happening because of the depth and width of the valley. Climate change, however, is also a contributing factor in creating many specialist species and further climate change triggered by human behaviour will lead to more genetic modifications in birds.

Deeper valleys affect many more species than shallow ones as birds get isolated in deeper valleys for a much longer time, according to the study.

Of all the songbirds, the study included specialist birds found only at the mountain tops of Western Ghats. These birds live by eating insects and fruits, and help control pests across many habitats.

“I have studied high elevation songbirds in the Western Ghats for many years and always wondered if valleys in the mountain range function as barriers for these mountain top species? Are there some valleys that many species are not able to cross?" asked V.V. Robin, the corresponding author of the study published in the Proceedings of the Royal Society B, a biological research journal.

The inference from this study, he said, has provided a framework that can be generalized for how biodiversity is generated in mountains. Four researchers from the centre found out that 10 of the 23 species did not cross the 40-kilometre-wide Palghat Gap, a divide in the Western Ghats, for several thousand years, with some specialist species isolated for up to 5 million years. For the species stuck without modifications on mountain tops, sky islands and valleys are barriers.

The bigger the valley, the larger the impact it has on divergence. And for bird populations that are “genetically diverged", this could lead to formation of species. “This makes Palghat Gap the most important divide in the southern Western Ghats, and efforts and conservation units, considering this finding, (are) on either side of this gap. The smaller Shenkottah and Chaliyar valleys affect fewer species. Studying all the birds—the entire community—helps us understand a generalizable effect of mountains across species," said researcher Uma Ramakrishnan.

The sky island birds, found in mountain ranges separated by valleys, can be traced to special habitats such as Shola and are found only on mountain tops. “Historically, when climate changed, lets say it became cooler and wetter, the Shola habitat would have moved further down the mountain. As it moves further down into the valley, it can end up connecting Shola with different mountains. As this climate change reverses and becomes drier, the cool-wet habitat would move further up the mountain, isolating the habitats on the mountains by the drier valleys (as it is today). This process driven by climate, creates divergences in species. What is important to note is that mountains themselves remained stable while the climate moved the habitat up and down connecting and breaking up habitats and ultimately affecting species like these birds that are tied to these habitats," Robin said.

The study has also shown that there was no one single big climatic event that affected all the birds. In fact, there were multiple such climate events that may have affected different species. The study collated genetic data collected by over 350 individuals over three years.

“We now understand how biodiversity is created in the Western Ghats. The role of valleys, mountains and climate is now clear too. We hope to study more landscapes, such as Andamans and Eastern Ghats, and are particularly waiting for the forest departments of Karnataka and Andamans to see the value of such studies," said Robin.

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