A black kite, of which the black-eared kite is a subspecies, takes flight somewhere in Japan, January 2014. Photo: nubobo/Wikimedia Commons, CC BY 2.0.
Now is quite the season for bird-watchers in the tropics, as they welcome thousands of migratory birds flying towards their winter homes. These migrants journey along one of the world’s nine major flyways – the patterned routes in the sky that birds take – to reach their destinations. Over 229 species of migratory birds spend their winters in the Indian subcontinent.
One of them is the black-eared kite, a bird of prey, also called a raptor, that breeds in central-northern Asia, and spends its winter in multiple parts of South Asia, including in and around Delhi.
While some ornithologists have studied the migration of waterbirds that flap across the Himalaya to get to India, the raptors’ routes have been less known. In fact, scientists continue to be intrigued by how and where these birds cross the Himalayan barrier.
In a recent study published on September 29, scientists from the Wildlife Institute of India (WII), Dehradun, the University of Oxford and the Doñana Biological Station, Seville, tracked the migration of black-eared kites to and from Delhi, flying over nine Asian countries. The researchers tagged 19 kites – 14 adults and five pre-adults – with GPS trackers to reveal their routes. This way, the researchers found, the kites seem to cross over the Karakoram range.
“This is a remarkable study that adds tremendously to our knowledge of bird migration,” Suhel Quader, a senior scientist at the Nature Conservation Foundation, Bengaluru, told The Wire Science. “It is notable for two reasons, to my mind – the large number of individuals systematically tracked, and that this is one of the very few studies of a species other than waterbirds in India.”
Yossi Leshem, a professor of zoology at Tel Aviv University, studies the migration of soaring birds, and he said the quantitative work and separation between immature and adult birds was quite impressive.
Most notably, the researchers found that the kites used the Central Asian Flyway, a route that has been well-appreciated for some flapping birds like ducks and geese, but not for soaring birds. The kites roosted at night and travelled during the day, from 150 km to 240 km before nightfall. So in two to seven weeks, they could fly 3,300-4,800 km. The migration routes the birds took were largely similar before and after breeding.
At the start of their breeding season, these raptors travelled northwest from Delhi, crossed the Himalaya over their western portion – between Punjab and Jammu & Kashmir – and soared through or circumvented the Taklamakan desert and China’s Tian Shan mountain range, to reach their breeding grounds. These made up a large swath of land in and around the Altai mountain range, some 85-times larger than the area the birds covered in and around Delhi. It is adjacent to western Kazakhstan, southern-central Russia, western Mongolia and north-western China.
Most birds crossed over the Himalaya by the Karakoram range at over 6,500 m above sea level. Many even flew by the K2 peak – the second-highest in the world. However, the researchers found that three kites travelled even further west, through eastern Pakistan, Afghanistan, Tajikistan and Kyrgyzstan, to reach the same destination.
The researchers have reasoned that the birds took this somewhat circuitous route to avoid harsh weather and for the favourable winds. The paper describing their study noted that the south-westerly winds could displace the birds farther east. So if they had chosen to cross the Himalaya directly, along the shortest route, they might have been forced to fly continuously over mountain ranges and desert for about 1,500-2,000 km.
The researchers also recorded the spread of the breeding area and the region where black-eared kites spent the winter. Those birds that spent their post-breeding season in and around Delhi restricted themselves to a smaller area, mostly in the vicinity of rubbish dumps, abattoirs, slaughterhouses and other animal-processing facilities. But during the breeding period, they spread out over a much larger region, including over diverse habitats like farmlands, semi-arid areas and marshlands.
Curiously, the birds didn’t necessarily visit the same place every year to breed. One of the kites that the researchers had tracked for two consecutive breeding periods went to north-western China in the first year but moved about 1,100 km away, to south-central Russia, the next.
Knowing these migration patterns and ‘pitstop’ spots are crucial to conserve the species and their habitats. On a more local level, Leshem, of Tel Aviv University, said that since soaring birds use thermal currents for migration, they follow fixed paths and relatively fixed times – which poachers could anticipate. As an easy alternative, he suggested that this study and others like it could help identify such potentially problematic areas and turn them into unlikely bird-tourism, along the lines of one in the strait of Bosporus in Turkey and at Batumi in Georgia.
Rajah Jayapal, a senior principal scientist at the Salim Ali Centre for Ornithology and Natural History, Coimbatore, even singled out songbirds like the Blyth’s reed warbler, the booted warbler, the Sykes’s warbler, the greenish Warbler and the rosy starling, which breed across northern Eurasia and migrate to the Indian subcontinent in winter.
But speaking more broadly, Jayapal said the study was significant for revealing the importance of the Karakoram and other mountain-passes in the Western Himalaya as migratory passages for transcontinental migrants. “This study has given an enormous thrust to our understanding of the conservation value of the Central Asian Flyway, an underrated region for bird migration, and has brought forth key conservation issues that currently threaten the fragile Himalayan ecosystem,” he said.
In line with the study’s implications for conservation at large, Jayapal expressed concerns about the exploitation of Himalayan river systems for hydroelectric projects. According to him, development projects in river valleys and gorges running through the Greater Himalaya, like the Upper Sutlej Valley in Himachal Pradesh, degrade avian habitats and affect the birds’ ability to use that region to move or in fact live in.
And going a step further, the researchers write in their paper that the loss of habitat and urbanisation could, among other things, “affect the population health of migrants and their potential to spread infectious diseases dangerous to humans, such as avian influenza, particularly in the case of species that are urban human commensals and thus in constant close-contact with dense human populations.” Urvi Gupta, another author of the paper and who works at WII, added to The Wire Science that knowing the route could also help understand the impact of urban foraging and to monitor the transfer of pathogens and toxic substances in its path.
Nishant Kumar, one of the paper’s authors, and an ornithologist affiliated both with WII and the University of Oxford, said conservationists are often not concerned for black-eared kites because these birds are opportunistic. However, he added, what they had found about the kites could in fact be extended to other birds that use the same or similar migratory routes – and that in turn amplifies the conservation question. “So the sample size of kites” in their study “extends a lot of opportunities to conduct research that one can translate for other endangered birds,” Kumar said.
In the coming months, Gupta said she and her colleagues intend to study the migratory routes of different populations of black-eared kites that spend their winters in India, and how they interact with the small Indian kites, a sister subspecies. “It will be critical to understand how they came to share geographical areas and partition resources in rapidly urbanising socio-ecological systems within the tropical megacity of Delhi,” she said.
T. Ganesh, a senior fellow at the Suri Sehgal Centre for Biodiversity and Conservation, Bengaluru, said that in the larger context of the conservation of migratory raptors, the government should encourage and facilitate such studies in India, and that it ought to consider “signing MoUs with Uzbekistan, Kyrgyzstan, Kazakhstan and other countries that are part of the flyway” to improve regional cooperation.
Joel P. Joseph is a science writer.