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Cuckoo's Epic Migration

When a common cuckoo took off from Mongolia last June no one expected him to make a 26,000km round trip to southern Africa.

When Onon, as his taggers christened him, took off above the rolling hills of the Khurkh valley in Mongolia last this time last year, researchers had no idea if they would see him again. Along with one oriental cuckoo and three other common cuckoos, each fitted with a tiny tracking device, he was about to embark on an epic journey to southern Africa.

Onon has not only amazed conservationists, but gripped social media across the globe. As coronavirus lockdowns brought the world to a virtual standstill, fans followed online updates from the Mongolia Cuckoo Project, watching in awe as Onon cruised across oceans and made 27 border crossings in 16 countries.

“It’s an amazingly long migration,” says Dr Chris Hewson, senior research ecologist at the British Trust for Ornithology, who said Onon’s 26,000km round trip was one of the longest journeys recorded by any land bird.

Onon's round trip is, of course, no match for the world record holder: the Arctic Tern. By far the longest migration known in the animal kingdom, this medium-sized bird travels 90,000km (55,923 miles) from pole to pole every year — from Greenland in the North to the Weddell Sea in the South. Remarkably, Arctic Terns can live up to 30 years, which means if one adds up the distance they traverse in a lifetime, their total journey is equivalent to going to the moon and back more than three times.

Be that as it may, the good news is that Onon made it back to Mongolia at the end of May this year, having become a media celebrity in India, Kenya and Sweden. Back in Mongolia, he appeared on television and made newspaper headlines. Researchers are now studying data from his journey for clues about why cuckoos travel as far as they do, and how they might be affected by global warming.

Hewson, who worked on the project with the Wildlife Science and Conservation Center of Mongolia, admits he did not believe cuckoos were such proficient migrators. “Although they’ve got nice long wings, when they’re flying around the breeding site they look slightly ungainly compared to the other birds,” he says. In fact, cuckoos such as Onon, which migrate in search of caterpillars, their favourite food, travel remarkably fast, he adds. Using tailwinds, they can motor for more than 1,000km a day for a week.

Caterpillars are most common in places that are sunny and wet and so, in summer, there are plenty in the Khurkh valley, in the south-east of the Khentii mountain range. As the weather changes they go to India for monsoon season, and then, as the wind changes, to east Africa. It’s not an easy journey.

The four other birds that set off at the same time as Onon did not make it back. Their fate is unknown – their trackers may have failed or they may have died. One of them, Bayan, is thought to have died in Yunnan province, China, after flying 7,200km in just seven days from Somalia.

Back in the lush hills and wheat fields of the Khurkh valley, Onon is getting on with life. “He has no time to waste as he needs to set up his territory, defend it from competing males and mate with as many females as possible!” the Mongolia Cuckoo Project has informed his fans.

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