The Many Songs of the Sholakili

It is a fine June morning the first time I hear it. A faint, rhythmic melody emerges from deep within the dense greenery, on the edge of Bombay Shola. This is my first visit to Kodaikanal and my untrained ears have no way of discerning it from the other myriad bird sounds and vehicle noises surrounding me. Rajneesh, one of the interns working at the Shola Sky Islands field station in Kodaikanal (a Kodaikanal International School and IISER Tirupati initiative), helpfully hands over his sound recorder’s earphones and points the mic towards the source. Now I hear it crystal clear. A high-pitched melody of lilting notes. We look through the understorey of the forests but don’t see any movement. Rajneesh records the song and we move along to the next patch. Try as we might, we see no sign of the White-bellied Sholakili. But I am satisfied—I am now acquainted with this bird, which I later learn has one of the most complex birdsongs known to the human ear. 

A tiny bird, barely weighing 20–25gm, the Sholakili has more than 500 notes in its repertoire. And, like most other shola birds, it lives only in the shola forests found across the Western Ghats. If you’ve ever visited Kodaikanal, chances are you’ve heard the Sholakili’s song, especially in the early mornings and evenings, and more so during its breeding season between April and July. ‘We often see the bird in the forests of Pallangi-Kombai and Bombay Shola. It is very swift—so small and quick in its movements!’ says R Serapandi, a birder and volunteer with the Solaikuruvi group, which cleans the local sholas. 

Sholakili are quite common in the shola patches outside town, ones that you drive by after the Silver Cascade falls. Within town, Bombay Shola and home gardens around it are your best bet. ‘Bombay Shola is our most visited field site. We usually get up just before dawn and set out to start recording birdsong,’ remarks Chiti Arvind, a few hours later. It has just finished raining, and we’re huddled in the breezy portico of the field station on the Kodaikanal International School (KIS) campus. Just a few steps away from Bombay Shola, this lab is the centre of many ongoing ecological research studies in and around the Kodaikanal sholas. Chiti is one of the PhD students here, studying the Sholakili’s song.

How the Sholakili came to be

The shola ecosystem is a geographic marvel. Found in the higher altitudes of the southern parts of the Western Ghats, this mosaic of dense stunted forests and vast grasslands was formed over millennia. The mountaintops are like islands in the sky, separated by deep valleys often filled with clouds. These valleys sometimes create a barrier, preventing animals from moving between the mountaintops. Over centuries, as these sky islands and the species within them became isolated from one another, they evolved to become different species altogether. The White-bellied Sholakili is one such bird.

‘When I started studying this bird, it was not very well known. It was largely found only in the high-elevation forests. We started by studying its genetics and its demography, and over the years it branched out to various other aspects,’ VV Robin tells me, over the phone. An ornithologist from IISER Tirupati, he set up the Kodaikanal Shola Sky Islands field station in 2016. His research on the Sholakili began way back in 2000, when he conducted surveys as a prelude to his PhD thesis. 

At the time, the bird was thought to be related to the shortwings, and was called the White-bellied shortwing (scientifically Brachypteryx major). But males and females in the genus Brachypteryx usually have prominent physical differences between them (known as sexual dimorphism). Male and female White-bellied shortwings, however, look similar—slate blue to grey feathers, a white belly and a white brow above their eyes. It was then moved to the genus Myiomela, which includes robins, but the decision was still hotly debated. It wasn’t until 2017 that the bird’s taxonomy was resolved. 

An extensive study using genetic samples and morphological and birdsong data, conducted by Robin and several others, revealed that its closest relatives are actually Old World flycatchers from the genera Niltava, Cyornis and Eumyias, which are found in the Himalayas. As its genetic data is distinct from these, an entirely new genus was coined—Sholicola, combining the words ‘shola’ and ‘cola’ (meaning ‘dweller’ in Latin). Its common name became Sholakili (‘kili’ meaning ‘bird’ in Malayalam).

How this tiny bird, with its closest relatives up in the Himalayas, ended up in the Western Ghats is answered by a popular hypothesis: the Satpura hypothesis. Up until around 11 million years ago, the Satpura Range in central peninsular India formed a band of wet forest that connected those of the Himalayas and the Western Ghats. However, changing climate conditions caused these forests in northwestern and central India to dry up, effectively cutting off this vital corridor between the Himalaya and Western Ghats, causing them to become two separate wet forest regions. 

The now-isolated population of the (then-believed-to-be) shortwings in the Western Ghats evolved differently from their Himalayan sisters. Eventually, they had to contend with other challenges: geographical gaps along the length of the Western Ghats that had formed over successive ice ages. One of the major gaps, the Palghat Gap, forms a wide 40km chasm between the Nilgiris Plateau (above) and the Anamalai-Palani Plateau (below). Unable to disperse across this gap, the birds on either side diverged into two populations and, approximately five million years ago, evolved into different species—the Nilgiri Sholakili (Sholicola major) and the White-bellied Sholakili (S. albiventris). The Nilgiri Sholakili has pale rufous feathers surrounding the white belly and a less prominent white brow. 

Farther south, the Shencotta Gap forms a narrower 7km gap between the Highwavys Plateau in the north and the Peppara Plateau in the south. In Peppara resides another new species of the Sholakili, the Ashambu Sholakili  (S. ashambuensis), named after the Ashambu Hills, where it lives. It is slightly smaller and paler, with a larger white belly patch than its white-bellied sisters, from whom it is believed to have diverged about two million years ago. 

A new genus and the discovery of an entirely new species was an astonishing revelation. But the surprises didn’t end here. During their research, besides the birds’ genetic and physical differences, one thing stood out to the researchers: the incredible complexity of the  Sholakili’s song. 

What’s in a song? 

For birds, songs are the main form of communication. They call to establish territories, attract mates and warn other birds of danger. The diverse songbirds of the shola sky islands have their own unique vocalisations. Some are repetitive, like those of the Black-and-orange flycatcher, Nilgiri flycatcher, Indian white-eye and Grey-headed canary-flycatcher. Some, like the Palani laughingthrush and the Indian scimitar babbler, sing in paired duets—one initiates the first call, which is closely followed by the call of the second bird. Some birds remain out of sight in the thick forest understorey, but their calls are hard to miss, such as that of the Sholakili.

A few years ago, Robin and a few other researchers compared the songs of three different Sholakili populations. One was from the Nilgiri Plateau in Ooty (the Nilgiri Sholakili, which had separated five million years ago across the Palghat Gap), the other two were the White-bellied Sholakili from two different ends of the same Annamalai-Palani Plateau: Grass Hills near Valparai on the west and Kodaikanal on the east, which had been separated due to deforestation 100-odd years ago. The team recorded songs from 23 individuals and characterised 572 songs according to 13 parameters. Significant differences were found between the songs of the Ooty population and the other two southern populations—not unexpected, as they are genetically distinct populations. With the Ooty birds, certain notes were short and repetitive, and songs fairly simple. The Valparai Grass Hills and Kodaikanal populations, however, had longer and more variable notes. 

What was surprising was that even these two populations had differences between their songs, despite their being the same species genetically, on the same sky island, only separated by a mere century. The Grass Hills Sholakili’s songs had a series of marginally overlapping, alternating high and low-frequency notes, with fewer repetitive notes; this pattern was not observed in the Kodaikanal Sholakili, which had higher repetitive notes (though not as much as the Ooty population).

‘Bird songs are just like human languages—different populations exhibit different dialects, and populations that do not interact frequently tend to have different dialects. Just like human populations living in different valleys have different dialects,’ explains Robin. ‘That there are differences even within populations of the same landscape indicates how they could possibly be affected by disrupted forest connectivity.’

The Shola Sky Island Lab is now conducting more research on the Sholakili’s song complexity. ‘I’m doing a finer-scale sampling of the populations across the Annamalai-Palani Plateau. We know that the birds on the east and those on the west have different song signatures. It will now be interesting to see where this gradient falls, or if there is a gradient at all in the song,’ says Chiti. 

‘At the moment, what we have is a correlation with disruption in forest connectivity—but I am increasingly doubtful that this is the driver for this difference,’ says Robin. ‘The real answer may come only after Chiti’s research, in about three years.’

But it hasn’t been an easy journey. ‘The dilemma is that there is no unified metric to measure song complexity across multiple species. To add to this, the White-bellied Sholakili has a vast repertoire of notes. It doesn’t have a stereotypical call like other birds,’ Chiti says.

Last year, they innovated a formula to quantify song complexity. Led by researcher Suyash Sawant, Viral Joshi, Robin and Chiti developed a metric. ‘A song is a series of notes separated by an interval of time. In the spectrogram, each note has a different shape, called the spectro-temporal shape. For this metric, we tried to see how different these notes are from each other and compare them across songs of the Sholakili. For each song, we generated a complexity score, known as the Note Variability Index, which captures variation time, frequency and other spectral features of notes,’ explains Chiti. They then compared the complexity score of the White-bellied Sholakili with other bird species known to have complex songs. The Sholakili beat the others. 

‘The only drawback of this metric is that it doesn’t take into account the order of the notes. But we are working to improve it,’ she adds. 

The lab also has a long-term monitoring-and-banding programme. Since 2018, they have tagged several birds with coloured bands. One of the first, and the lab’s most common visitor, is called Yellow. ‘We are still recording his calls! We found another individual in its territory and gave it the colour combination Black-White-Green. We initially thought it was a female but later found it to be a male, just like Yellow,’ Chiti says.

Since Sholakili males and females are not visually distinguishable from each other, molecular sexing techniques need to be carried out. This must make the lab’s already complex research even more challenging. ‘Actually, it’s great, because we are recording blind. Traditionally, it was believed that in songbirds, it’s usually the male that sings. But more research of late has revealed that female song is quite common in several species. I’m not sure about the Sholakili yet, but it will be really cool if we discover females have a song too!’ Chiti says. 

Through these recordings, they hope to decipher if the songs change throughout the year according to seasons, if neighbours share songs, if song complexity is linked to individual fitness (either reproductive or immunological), and if there are other advantages. There is still much to be explored.

Change is the only constant

In the ever-transforming shola landscape and climate, life too is in constant evolution. Just like the White-bellied Sholakili’s adaptive radiations (when species adapt to changes in the environment) into three species, the Palani laughingthrush, which incidentally was first described in 1869 in Kodaikanal, radiated into four species. Similar evolutions have occurred across groups of frogs, insects, snakes and more unknowns. 

In just the past 20-odd years, studies have been able to uncover such vast ecological mysteries. The shola sky islands are often likened to ‘live’ labs, places where ‘evolution in action’ can be observed right in front of our eyes—if you know where to look. And yet, as more species are discovered and re-discovered, their precious shola habitats are being fragmented by development and commercial crop plantations or being invaded by exotic species planted in colonial times. Now, in addition to natural geographical barriers, animals have to contend with anthropogenic barriers, like forest fragmentation. Above all, the threats of climate change loom; the consequences this could have on this fragile landscape are yet to be documented.   

‘Most species on these mountaintops are poorly studied, and we know very little about them. Much of science  builds on natural history observations, and this is severely limited from the Palani Hills,’ says Robin. He points out that some of these factors can be explored more intricately now, thanks to citizen science data platforms, like E-bird. ‘We encourage tourists and locals in Kodaikanal to report their bird sightings on E-bird. Shola birds are common in backyards, especially where there are thick shrubs and bushes. They even nest in small crevices in old buildings,’ he says.

As for my brief tryst with the Sholakili, I wonder if I will get a chance to see one before I leave. Chiti offers some tips. ‘With time and practice, your eyes get tuned to the height they’re usually found in, and your ears to their song. It becomes easier to spot them. They’re not really that shy; they’re quite bold birds,’ she says.

By the time I walk out of the Shola Sky Island field station, the rain has slowed to a drizzle. The drenched trees of Bombay Shola beckon, just a few steps away from the gates. Walking towards them, I strain my ears to pick out the song of this ancient bird that existed before Homo sapiens even came to be. But all I can hear is the steady drip-drip of water falling from the leaves onto the soil. Perhaps if I come tomorrow, I can hear the Sholakili sing again, as I hope it will for centuries after I’m gone.