The Nilgiri Blue Robin (Sholicola major) is a member of the genus Sholicola which is restricted to the Western Ghats region. Part of the Family Muscicapidae (the Old World Flycatchers), it is very closely related to the White-Bellied Blue Robin (Sholicola albiventris). A third species – the Ashambu Blue Robin (Sholicola ashambuensis) was described in 2017. The genus name (which translates as ‘Shola Dwellers’ in Latin) is a reference to their habitat. These diminutive birds are said to be proof of the evolutionary and biological significance of the Western Ghats.
Extensive studies of Sholicola species have shown that the mountains of the region acted as sky islands. The term ‘sky island’ is applied to high altitude ecosystems that are isolated from similar tracts by lowlands with totally different climatic and ecological characteristics. This makes them like islands in the sea. Species on these sky islands are cut off from others by the lowlands below. As a result they are confined to their highland habitats, evolving in isolation and giving rise to new species over time.
This makes sky islands rich in terms of biodiversity with a large number of endemic species (species that are found nowhere else) and relict organisms (organisms that have gone extinct in surrounding areas but held on in the isolated, high mountains and plateaus which have conditions favourable for their survival). One can think of the Western Ghats as a lush, green island soaring above the hot, dry landscape of the Deccan Plateau. A bit like the islands of western Indonesia – Sumatra, Java and Borneo.
These islands were once connected to the Malay Peninsula (when sea levels were very low due to the world’s water being trapped in polar ice caps and alpine glaciers of the Ice Age). At that point of time, the wildlife of both Southeast Asia and western Indonesia had much in common. However, as the Earth warmed up, the ice caps and glaciers melted, sea levels rose and Sumatra, Java and Borneo became islands. Over tens of thousands of years, their plants and animals evolved in isolation, giving rise to new species and forming communities distinct from those on the mainland, and from each other.
The same is said to have happened in the Western Ghats. But instead of changes in sea levels, the process of connection, isolation and evolution was driven by fluctuations in temperature and rainfall. This is where the genus Sholicola comes into the picture. Its closest relatives (flycatchers of the genera Niltava, Cyornis and Eumyias are not to be found in the Deccan but thousands of kilometers north and east, in the Himalayas and Southeast Asia.
It is believed that during the first half of the Miocene Epoch (that lasted from 23 to 5 million yeas ago), the world was a much warmer and wetter place. Lush forests covered not only Southeast Asia, the Himalayan foothills and Western Ghats but also the Satpura Range of Central India. This meant that species adapted to the luxuriant forests of Southeast Asia and Himalayas could make their way into South India.
Evolutionary biologists believe that many plant and animal species made their way from Southeast Asia to the Western Ghats in this manner. Some might have even made their way further south to Sri Lanka. This idea is known as the ‘Satpura Hypothesis’. Among the travellers were ancestors of the Sholicola species of Old World Flycatchers. Once they had settled in this region, the climate began to change, around 11 million years ago. It became colder and drier, and the lush forests began to recede up the mountains, breaking up into smaller and smaller patches.
Eventually, the belt of wet, mountain forests connecting the Himalayas to the Western Ghats disappeared completely. North and South India were no longer bridged by the Satpura Range. The Sholicola were now isolated. Over the millennia, the forests of the Western Ghats assumed a unique character of their own. The Sholas represent the latest and most fragmented remnants of those ancient forests. And as these sky islands grew further apart, ancestral species evolved into multiple lineages. That is how the Western Ghats ended up with three Blue Robins. More about that later.
Illustration: The image above, sourced from Wikimedia Commons, is a photograph of the Nilgiri Blue Robin. It was uploaded by Nilnetrus.
- Breathtaking ‘Sky Islands’ Showcase Evolution in Action (by Shaena Montanari, dated August 11, 2017), National Geographic
- Music to the Ears: New species of Songbird Found (by E Manoj, dated January 25, 2017), The Hindu
- Two New Genera of Songbirds represent Endemic Radiations from the Shola Sky Islands of the Western Ghats, India (dated January 23, 2017), BMC Evolutionary Biology
- How Two Songbirds in the Western Ghats Evolved Into Multiple New Species (by Janaki Lenin, dated February 3, 2017), The Wire