When a little bird, not much larger than a tennis ball,
plunged into a net that Robin V. Vijayan had strung up along a jungle path, he
felt what a big game hunter bagging his first trophy must feel. A dot of blood
taken from this blue-black, pear-shaped bird, found exclusively in the upper
reaches of the Western Ghats, would spark a series of questions that would
magically turn these mountains into islands.
This chain of mountains that stretches 1,600 kilometres along the length of India’s west coast would, on closer inspection, pixellate into a patchwork of closely related yet distinct ecological refuges. Mountaintop forests a few dozen kilometres apart—harbouring birds and plants that resembled each other—would turn out to be separated by millions of years of evolution.
The Western Ghats is for thousands of species of plants, birds, amphibians and insects what Africa is to human evolution. It is a UNESCO World Heritage Site, one of the world’s eight biodiversity “hotspots”. This range that starts near the border of Gujarat and Maharashtra, running down through Karnataka, Tamil Nadu and Kerala, has over 5,000 species of flowering plants, and 139 mammal, 508 bird and 179 amphibian species.
Yet most species of the Ghats remain unstudied, and biologists believe there are thousands of others waiting to be discovered. Very little was known about Vijayan’s quarry, the white-bellied shortwing. That was part of the attraction for Vijayan, who works at the National Centre for Biological Sciences (NCBS) in Bangalore. He had just finished a project on the “flocking” behaviour of birds, but he says he wanted to do “something more basic, ground up”. Behavioural studies, while interesting, “were only as interesting as the questions you ask”, he says. And there was always a slight doubt that you weren’t asking the right questions.
Instead he wanted to chart his own path, looking at a species from scratch—starting with its distribution, using the patterns that emerged as the stepping stone to further questions and exploration.
The shortwing was the perfect challenge. It was endemic to the Ghats, but reports from the field were frustratingly contradictory. Of the five extant species of shortwings, all except the white-bellied shortwing lived in the Himalayas. Ornithologists Salim Ali and Dillon Ripley were almost melancholy in their description of the bird as “a shy retiring species, affecting deep shades”. They claimed the bird was common, yet the Birdlife International (2001) database listed fewer than 100 sightings between 1881 and 2000.
Many birdwatchers warned Vijayan that he’d never see or hear the bird.
he shortwing lives almost exclusively in high-altitude sholas, mosaics of stunted evergreen forests and grasslands found above 1,400 metres in the Ghats. This explains its rare sighting.
In this landscape of endless rolling hills—a habitat that looks like it was shaped from sloppily-poured batter—forests nestle in mountain folds, separated by grasslands that drape themselves over ridges. But this appearance of size is deceptive. Shola forests exist in small patches, some smaller than a hectare.
Two surveys—traversing 553 kilometres of trails along the length of the Ghats, from Goa in the north to Kerala, through 14 wildlife sanctuaries and six national parks—resulted in over 200 sightings. The shortwing, it appeared, was not common, but not rare either. It was a matter of looking in the right place.
“In the bargain”, says Vijayan, “I got to see every corner and ecological landscape of the Ghats.”
Under the gnarled, wind-carved canopy of forests is a world that drips ferns, orchids and mosses onto dense undergrowth that carpets the forest floor. Small streams often flow along the edges of these patches, where the forest gives way to grassland.
This miniature landscape teems with life—nearly a third of the country’s plant species, half its reptiles and three quarters of amphibians are founds in these forests. Even the grasslands house dozens of fire- and frost-resistant species of grass.
The Western Ghat sky island system is one of a handful of such systems scattered across the globe. The system has greater biological diversity. The high-elevation parts are much older than other systems, making it a far more interesting laboratory to study differences in species.
The shortwing, Vijayan discovered, lives in the dense undergrowth of these forests, feeding on insects; rarely venturing above a height of a few metres. It was occasionally spotted at the edge of the grasslands, near streams where it collected moss to build its nest. However for the most part, it was painfully shy, conspicuous only by its shrill, twanging call during the breeding season.
The shortwing was almost invisible in the dense undergrowth of its natural habitat. The only way of spotting it was to capture it in mist nets, large 12-metre-long and two-metre-high nets strung up from poles, along tracks in the jungle. As it flew across these paths the bird would plunge into these delicate nets that resembled saris hung out to dry, getting trapped in the small pocket that formed as the net was depressed.
The team would check the nets every 15 minutes, extricating the captured birds, letting loose other unintended subjects. It was a painstaking procedure that could not be done either when it was too hot—since that would put the birds at risk—or when it was raining, since birds invariably turned turtle as they fell into the nets, and rain would wet their non-insulated under-feathers.
Once extricated, a single drop of blood—“a diabetic sample”, according to Vijayan—would be taken, the bird measured, and then set free within 10 minutes. But such was the resistance of the Tamil Nadu forest department to this (well-established) process that it took Vijayan two-and-a-half years to get permission to capture two birds each in Kodaikanal and the Nilgiris.
The survey had shown the shortwing to exist sporadically across the Ghats. Though it seemed common in the sholas, there were few sightings between 1,000-1,500 metres and, despite repeated searches, Vijayan’s team couldn’t find any below that.
The shortwing, it appeared, could not survive at lower altitudes.
However not all sections of the Ghats are connected by ridges or ranges that are above 1,000 metres in altitude (in some places the altitude dips as low as 300 metres). There are also geological gaps in the Ghats that date back to the formation of the Western Ghats about 80 million years ago.
These, in effect, divided the shortwing distribution across the Ghats into four populations that seemed to have no interaction with each other. They were islands of birds, in the sky. Some of these were only a few dozen kilometres from each other: short distances even for a tiny bird like the shortwing.
Yet these geographical gaps are for many birds species found in the Ghats what swathes of ocean are to mammals—unbridgeable.
he Western Ghat sky island system is one of a handful of such systems scattered across the globe. The most studied include the Madrean sky island system in the US, a collection of tiny enclaves of pine-oak forests found in parts of Arizona, southwestern New Mexico, and extending into northwestern Mexico. In these forests, a variety of species of squirrels, woodpeckers, jays, and one species of parrot are found in isolated clusters. The Eastern Arc sky islands in Africa—a chain of 13 sky islands spread over a 650-kilometre mountain arc in Tanzania and Kenya—are known for their floral pockets.
The Western Ghats system, however, has greater biological diversity. The high-elevation parts of the Ghats are also much older than those of other systems, making it a far more interesting laboratory to study differences in species.
How did this unique pattern come about: how did birds that were thought to be of one species end up on these nearby islands? When did it evolve? Are these populations genetically different?
The sky island project, a research initiative that Vijayan started, was an effort to answer these questions. It involved biologists who have specialised in areas like bird song, taxonomy, genetics and avian evolution. These collaborators joined the project for different segments, all of which have been coordinated by Vijayan.
As it grew, the project became more ambitious, involving engineers and software programmers. The funding has come from a variety of sources, including the Council of Scientific and Industrial Research (CSIR), the Ministry of Environment and Forests (MoEF), NCBS, and National Geographic.
The first step involved the genetic sampling of 33 shortwings from these different populations. This involved long treks and days spent camping in the forests, living occasionally in caves.
The team would set out at 4.30 a.m., finding their way by torchlight, for locations where unopened mist nets had been set up the previous day. The nets would be opened at the crack of dawn. For next six hours, the team would check them, four times every hour. Then they’d break for lunch, before setting up the nets again between 1-5 p.m. in the afternoon.
By the time they got back to their camps with their precious blood samples, it would be night. In the lab, DNA from these blood samples was processed to isolate particular sequences (mitchondrial DNA, or mDNA)—the low mutation rates of which means that it takes thousands of years for changes to show up in them. This slow mutation rate means that these sequences can be used to investigate differences that could have cropped up over millions of years.
Mutation rates of mDNA, have been studied for different bird species, and been found to be constant over millions of years across several species. This sequence can therefore serve as a “molecular clock” to determine when bird species have diverged.
Another sequence, commonly known as the barcoding gene, is used as a standard to identify taxonomically different species. Based on data from 260 bird species, it has been estimated that the barcoding genes of bird species differ from each other by at least 7.9 per cent. Conversely, this is the threshold for species to be classified as different.
The samples indicated that there were genetic differences between these isolated populations, separated by low altitude areas (or geological gaps) in the Ghats. The biggest difference was between the populations on either side of the Palghat Gap, a 40 kilometre-long break in the Ghats in Kerala. The barcoding genes of these populations differed by over nine per cent—far higher than the standard of 7.9 per cent.
These two populations were in effect, different subspecies—the rufous-bellied shortwing north of the Gap, and the white-bellied shortwing south of it.
An analysis of accumulated mutations in mDNA indicated that these populations had a common ancestor five million years ago, i.e. when they diverged. The oldest ancestor of modern humans had, in contrast, set foot on earth 2.3 million years ago.
A two per cent genetic difference across the Shencottah Gap, a 7.5-kilometre gap that lies further south, showed that this split had occurred 1.5 million years ago. It divided the Grasshills, Kodaikanal and High-Wavies sky island complex north of the gap from Peppara, south of it. North of the Palghat Gap, the shortwing populations on two islands—the Baba Budan Hills in Karnataka and the Nilgiris in Tamil Nadu—seem to have diverged 18,000-20,000 years ago.
What divided what was once, five million years ago, a single shortwing population?
Vijayan noticed that these times—5 million, 1.5 million, and 18,000-20,000 years ago—coincided with known periods of glaciation (or ice ages). These spells of intense cold at the higher latitudes were periods of drought in the tropics. During each of these glacial periods, forests that covered the Western Ghats retreated up into the climatically more stable upper reaches of the mountains. With this, birds like the shortwing took flight.
When the climate thawed, some of these forests and species re-connected, but others, like the shortwing, did not.
In the waning and waxing of these successive ice ages, the bubble encompassing the once contiguous population contracted and split into two, then expanded, then split again and again, till the population islands that exist today came into being. As the bird became specialised to living at higher altitudes, it got sequestered, unable to cross the geological and low altitude gaps that separated it from its kin.
The result is a demographic that is determined by geological gaps rather than distances—populations hundreds of kilometres apart connected by a land-bridge over 1,000 metres are similar, but those across a tiny geological gap have not inter-bred in millions of years.
As shown in the DNA analysis, the lack of inter-breeding in turn meant that these populations also started drifting genetically from each other.
ijayan’s shortwing findings have been bolstered by a similar evolutionary pattern detected in African songbirds, like the starred robin, that live on mountain highlands.
Genetic differences have manifested themselves in the plumage and song. They are starkest across the Palghat Gap, since these populations have had the most time to evolve apart. The southern species, as its name suggests, has a white belly while the northern population’s is rusty. Its songs are longer and have more variable notes compared to the northern, whose songs are shorter and more repetitive.
Song differences between the southern islands are slighter. The Kodaikanal and Grasshills sky islands were created just a few hundred years ago by the deforestation of areas between them. According to Chetana Purushotham, an ecologist who helped analyse these songs, this short span has been enough to let differences in low- and high-frequency notes creep into them.
The question that now confronted Vijayan was: what prevented the shortwing from venturing out of these islands? He doesn’t have a definitive answer, but suspects the extreme specialisation of this species is responsible. It, like the Nilgiri laughingthrush—a distinguished, professorial-looking bird, with white eyebrows and plumage that resembles a light tweed coat—is a forest specialist.
The shola sky islands are the result of the superimposition of many layers of patchiness. The first layer is created by historical climate change, the one on top of it by fragmentation due to human interference, and the final one is defined by the habits of birds which confine them to parts of the sholas.
“It requires dense undergrowth that harbours particular insects, needs to be close to a stream from where it can gather moss for its nest, and rarely ventures out into open areas,” he says. This extreme finicky-ness has, Vijayan suspects, restricted its movement.
The shortwing, however, is just one of many species of birds, like the Nilgiri laughingthrush, black-and-orange flycatcher, Nilgiri flycatcher, Nilgiri wood pigeon, etc., that are endemic to forests.
Some of them—like the laughingthrush, whose habitat largely overlaps that of the shortwing—exhibit even greater divergences, both genetically, in song and appearance. This bird is thought to exist as four species (though this is debated) across different geological gaps in the Ghats.
Of late Vijayan has been trying to replicate what he’s done for the shortwing with the Nilgiri pipit, a tiny, sparrow-like bird that is found only in shola grasslands. Unlike the shortwing that was thought to be rare, the pipit was thought to be common. The truth, however, turned out to be the opposite.
The pipit was commonly reported. But when Vijayan’s team searched the Ghats, they only managed to locate them on two mountaintops. Samples in museums were also from these locations. “It soon became obvious,” Vijayan says, “that most of the sightings were misidentifications.”
The two populations of this bird—one in the Nilgiris, north of the Palghat Gap, and other in the Anamalais, south of it—were found in grasslands above an altitude of 1,900 metres. Within these grasslands, it only lived in the marshes, where it bred; its habitat was even more restricted than that of the shortwing.
Blood samples indicated that these populations were also genetically different. Yet, this extreme localisation demanded another explanation. Vijayan stumbled upon the work of a researcher who had unearthed British forest maps from 1847. These, when compared to forest maps from 1992, revealed a shocking fact. During this period, the grassland habitat of the pipit had plunged by 85 per cent, shrinking from almost 30,000 hectares to 4,700 hectares.
In many areas, shola forests were spared, but the grasslands—an integral part of this ecosystem—were regarded as wasteland. Some were converted to tea plantations, while others were turned into timber plantations of wattle, acacia and eucalyptus, destroying the habitat of the pipit and other grassland species.
The historical and climate-induced “patchiness” in this bird’s distribution had been exacerbated by human interference. Similar processes have been at play for the shortwing, where deforestation during the last century (as in the case of the ranges between Grasshills and Kodaikanal) has divided populations, creating new islands.
he shola sky islands are the result of the superimposition of many layers of patchiness, as Vijayan likes to put it. The first layer is created by historical climate change, the one on top of it by fragmentation due to human interference, and the final one is defined by the habits of birds which confine them to parts of the sholas.
This segues into the next question: how do different species respond to these factors, these genetic barriers? What makes one species more vulnerable to a certain set of changes?
In an effort to find an answer, Vijayan collaborated with Sushma Reddy of Loyola University, Chicago, who has been working on the evolution and divergence in birds. They are exploring the evolutionary history of 24 birds, some of which—like the Nilgiri wood pigeon and the black-and-orange flycatcher—are endemic species. Others, like the white-bellied flycatcher and the dark-fronted babbler, are confined largely to the Western Ghats but within them are also found at low altitudes. The last group, which includes the red-whiskered bulbul and the pied bushchat, live in the sholas but are also common around the country.
This wide array of species will allow them to compare responses, and look at species diversification within a broader framework. Vijayan says, “We’re moving from looking at particular species to asking the general question—how do birds of the sholas respond to changes in their environment?”
Vijayan and Reddy have taken 1,000 blood samples from these species. This is a challenging task in itself, since it involved sampling “at least four individuals of each species from every mountain top”.
The results of this study are due to be published in a few months, but Vijayan reveals that they have found that large genetic variations seem to cluster into four major areas. These are demarcated by river valleys—that of the Kaveri, the Chaliyar, and a now extinct river that once flowed through the Palghat Gap.
A detailed analysis of these results, examining the effects of past climate change and deforestation, will serve as a template to predict the effect of future climate change and environmental degradation on shola species. This will shape conservation strategies and determine, for example, where forest corridors should be established.
This study will also hopefully indicate which species can be used as bellwethers for shola ecosystems.
he sky island project has so far only been looking at birds, but sholas are home to thousands of other species of plants and insects that have been subject to the same evolutionary forces. They too have been funnelled by genetic bottlenecks into separate shola sky islands.
Plant species found in the Nilgiri and Palani hills on either side of the Palghat Gap exhibit the greatest genetic divergence according to Robert Stewart of the Vattakanal Conservation Trust, who has been working on documenting and conserving them.
Fifteen species of Syzygium trees, a genus to which the jamun tree belongs, are found in the highlands of the Nilgiris. However, of these, only three have managed to bridge the 100-kilometre gap that separates the Nilgiris from the Palni Hills; another species, Syzygium caryophyllum, has failed to make the opposite journey. Similar disparities exist for other plants and trees.
“Sholas have a marked individuality regarding ‘dominant’ (plant) species,” says Stewart. This, he suspects, is determined by which species manages to get there after a glacial period.
In a study published in scientific journal PLOS ONE in 2013, Sandhya Sekar and Praveen Karanth outlined the sky island effect for a butterfly known commonly as the red-disc bushbrown. This butterfly, with prominent discs on its wings that give it a slightly ghoulish appearance, is a shola grassland specialist.
They first compared the genetic diversity of this species to one that was much more continuously distributed in lower elevations. Not surprisingly, they found that it showed far greater differences in gene flow.
A detailed analysis of samples taken from the Anamalai sky island complex however showed that there was a genetic break in the butterflies’ population. Butterflies from Kodaikanal and Munnar (in this complex), though only 40 kilometres apart and connected by continuous mountain habitat, exhibited marked differences.
The genetic barrier in this case, it transpired, was the dry terrain between the two areas. Being adapted to high rainfall and low temperatures, the butterfly just couldn’t navigate it.
Another area that the sky island team has been focusing on is an automated birdcall monitoring and recognition system. When functional, the system will use a series of wireless recorders and transmitters (that use the mobile phone network that exists around shola forests) to record and relay birdcalls to a software programme which is designed to match birdcalls to species. This will allow them to investigate song variation in the sky island birds, as well as monitor bird populations and their movements.
To create it, Vijayan has been working with Anil Prabhakar of the Indian Institute of Technology, Chennai; Samira Agnihotri, a researcher at the Indian Institute of Science, Bangalore; and Tarsh Thekaekara of The Shola Trust, a conservation NGO.
Prabhakar, an amateur birdwatcher, says that 10 experimental recording stations are operational in the Ghats. Funds have been a limitation, but the team is hoping to get a grant soon.“It is designed to help people like me, who find it difficult to identify birds visually, to interact with professional birders,” he jokes.
The recognition software has proved far more challenging. The algorithm recognises birdsong on the basis of parameters like note length, frequency modulation, etc. But in order to do, this it needs to be “trained” with sample songs. That, according to Prabhakar, requires 10 instances of each song variant of a species. It’s a gargantuan task, given the wide variation in songs across sky islands and the difficulty in getting clear recordings. It has taken the team a year to get enough data to train the programme to recognise seven species.
Agnihotri, who joined the project recently, has worked extensively on adapting human speech recognition software to track mimicry in the racket-tailed drongo. “Creating a programme to recognise the call of a single species is easy,” she says. The challenge lies in creating a multi-species song recognition programme since it requires more detailed song definitions for each species.
Prabhakar believes that recognition accuracy can be increased if the geographical information like the location of the bird, the altitude at which it was recorded is included in the algorithm. But this is something they are yet to incorporate. Even for species where the team has adequate recordings, the songs need to be identified or “tagged”, a process that can take many hours.
Scaling up the project requires speeding up the song recording process. In an attempt to do that, the sky island team has decided to enlist the help of “citizen scientists”—school children, amateur birders and staff at various NGOs—to record bird songs on their mobile phones and upload them to a site, along with data that identifies the bird.
A comprehensive monitoring system for the Western Ghats, Thekaekara estimates, will require nearly 500 recording stations. But it’s essential since current monitoring is based largely on expert opinion, which can be subjective and geographically limited.
A decade into the project the questions and goals only seem to be multiplying. That is a measure of the project’s success. The years have had their ups and downs. “The most difficult part has been convincing state forest departments who’re primarily interested in numbers —an obsession that comes from working with large mammals—that there is value in doing this research,” says Vijayan.
There have been moments of trepidation while “mist netting” birds, when sambar deer, tigers and elephants have very nearly strayed into their nets. “Elephants, I realised,” Vijayan remarks, “are incredible creatures.”
He recounts an incident when a herd found their path obstructed by a set of nets that they proceeded to tear, also bending the poles. As luck would have it, the herd came across another set of nets a few kilometres away. These nets were unopened and rolled up into strings (strung between the poles), one and half meters above the ground. This time, the nets were intact, but there was large drag marks in the mud, “where these giants had squatted under the nets, scraping the wet mud with their bellies as they made their way across”.
“When we started we didn’t even know whether the shortwing existed,” Vijayan laughs, “today we’ve almost come to the point where we’re discussing cultural differences within their populations.”