Researchers at IIT Bombay discover the role of environmental resources, genes and mating in species in the development of new species in the same area, challenging the traditional view that new species can develop only in distinct geographies.

Every year, these raptors hovering Delhi’s landfills migrate across the Himalayas to Central Asia

Read time: 4 mins
30 Nov 2020
Every year, these raptors hovering Delhi’s landfills migrate across the Himalayas to Central Asia

Black-eared kite [Image credits: Dr. Nishant, Urvi, and the Black Kite Project]

Slavomir Rawicz’s controversial book, The Long Walk, is a gripping tale of how three men walked their way to freedom after a treacherous journey of over 6,500 kilometres. The story describes the trek that started in the Soviet Union, proceeded south towards the Himalayas, crossed it and reached British India. In a recent study, researchers from India, the UK, USA and Spain, have found that black-eared kites make a similar journey across the Himalayas every year, back and forth.

Black-eared kites (Milvus migrans lineatus) are raptors commonly found hovering over Delhi’s garbage dumps during the winters. The study, published in the journal Scientific Reports, shows that these birds take journeys of an astounding 3300–4800 kilometres each year across the Himalayas into Central Asia, and back. They do so in 13–47 days, covering about 150–240 kilometres per day, reaching as far as western Mongolia. 

During the winters, the number of Black kites found around Delhi is one of the world’s highest raptor concentrations recorded since 1960. Dr Nishant Kumar, a researcher at the University of Oxford, UK, and his colleagues, were curious to know how these birds moved around landfills in a megacity like Delhi. They attached a few GPS trackers to some of these landfill birds to find out.

“The telemetry study, which was started in April 2014, was not focused on studying migration. It was to see how a landfill-based bird moved in response to urban resources,” says Nishant.

“We did not classify the birds on the dump as migratory unless the Black-eared kites were exactly matching the textbook descriptions. To our surprise, most of the birds in a 10,000 strong flock were the migratory Black-eared kites,” says Urvi Gupta from the Wildlife Institute of India, who is a co-author. Over 95% of the birds seen at the Ghazipur landfill were Black-eared kites.

A flock of Black-eared kites in a landfill in Delhi [Image Credits:Dr. Nishant, Urvi, and the Black Kite Project]

When the researchers began their study, data on the migratory paths and route-patterns of these birds were mostly unknown. In fact, it was not clear whether these birds we see in the middle of Indian cities were even migratory! “The major text on Indian raptors is a book by Rishad Naoroji, where he discussed that these birds were rather associated with the high altitude areas and Bangladesh, with anecdotal reports from across the Sub-continent” explains Nishant. There began a journey of awe for the researchers too!

The study found that the Black-eared kites, after leaving Delhi, soared at heights of over 6.5 kilometres to cross the Himalayas. Then, they flew across the Taklamakan Desert and the Tian Shan mountain range in China and the Altai mountain range in Kazakhstan to reach their breeding grounds located at the intersection of Kazakhstan, Russia, China and Mongolia.

Tagged Black-eared kites took this arduous route to escape the harsh winter in their breeding grounds in Central Asia and came to Delhi.

“Migratory birds move seasonally between their breeding grounds and wintering zones. The Black-eared kites breed in Central Asia between April and August and migrate to South Asia September onwards to overwinter,” shares Urvi. 

Akin to our highways, the geographic zones used by birds for migration are known as ‘flyways’. “Flyways usually include the breeding, non-breeding and stopover sites of migratory birds, and are spread across continents and oceans,” explains Nishant. The Central Asian flyway, taken by these kites, covers Eurasia between the Arctic and the Indian Ocean. “It spans over 30 countries of North, Central and South Asia and Trans Caucasus, and their associated islands,” he explains. 

Several species of birds use the Central Asian flyway for migration. Black-eared kites thus serve as useful model species to understand the route and the habitats on the flyway. “Conservation of these habitats along the flyway is necessary to ensure safe passage to several endangered birds,” says Nishant. With rapid urbanisation, these habitats are changing—they are littered with landfills or polluted with toxins.

“It is crucial to monitor the transfer of pathogens and toxins, if any, along the route,” signs off Nishant. 

This article has been run past the researchers, whose work is covered, to ensure accuracy.