Miniature tracking devices have revealed the epic 30,000km (18,640 miles) migration of the diminutive northern wheatear.
The birds, which weigh just 25g (0.8oz), travel from sub-Saharan Africa to their Arctic breeding grounds.
"Scaled for body size," the scientists report, "this is the one of the longest round-trip migratory journeys of any bird in the world.
The team reports its findings in the Royal Society journal Biology Letters.
"Think of something smaller than a robin, but a little larger than a finch raising young in the Arctic tundra and then a few months later foraging for food in Africa for the winter," said one of the lead researchers, Prof Ryan Norris from the University of Guelph in Ontario, Canada.
The species is of particular interest to scientists, because it has one of the largest ranges of any songbird in the world; with breeding grounds in the eastern Canadian Arctic, across Greenland, Eurasia and into Alaska.
Prior to this work though, it was not clear where the birds spent the winter.
Heiko Schmaljohann, from the Institute of Avian Research in Wilhelmshaven, Germany, was a member of the team that carried out this study.
He and his colleagues visited the wheatears' breeding grounds in Alaska and Canada and fitted 46 birds with the satellite tracking devices.
"The [trackers] weigh 1.4g, including a harness that loops around the birds' legs," he told BBC Nature.
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End Quote Heiko Schmaljohann Institute of Avian ResearchWe totally underestimated the flight capability of birds in terms of migration?
These data loggers recorded the bird's position twice a day for 90 days. Four trackers that the team managed to retrieve revealed that individual wheatears spent the winter in northern parts of sub-Saharan Africa.
The Alaskan birds travelled almost 15,000km (9,000 miles) each way - crossing Siberia and the Arabian Desert, and travelling, on average, 290km per day.
"This is the longest recorded migration for a songbird as far as we know," said Dr Schmaljohann.
Although the Canadian birds did not travel as far - approximately 3,500km - they had to cross the northern Atlantic Ocean.
"That's a very big barrier for a small songbird," Dr Schmaljohann explained.
Henry McGhie, a zoologist and head of collections at Manchester Museum described the birds' journey as "very impressive".
"We do see Greenland wheatears in the UK on migration, usually on the coast," he said.
"The amazing thing [about this study] is that it gives us a glimpse into the extraordinary lives of these tiny birds.
"When we see them, they're in the middle of a journey they do twice every year. When you think of the challenges they must face, you wonder how on earth they do it."
Dr Schmaljohann added: "[In the past] we totally underestimated the flight capability of birds in terms of migration.
"It seems that bird migration is limited by the size of the Earth. If the planet was larger, they would probably migrate even further."
Source: http://www.bbc.co.uk/nature/17027565
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