The Arctic songbird weighs less than an ounce and is not much longer than a pen, but the northern wheatear is astounding researchers who've discovered it makes an annual migration halfway around the world to Africa.
The journey to Africa the tiny bird takes every spring and fall is one of the longest seasonal migrations in the world, Postmedia News reports.
Scientists published a study of the wheatear's migration in the latest issue of Biology Letters, the journal of Britain's Royal Society.
"The northern wheatear [Oenanthe oenanthe] is a small [approx. 25 grams], insectivorous migrant with one of the largest ranges of any songbird in the world, breeding from the eastern Canadian Arctic across Greenland, Eurasia and into Alaska," the study says.
The paper says researchers found the bird follows two routes to Africa. One population in Alaska flies about 14,600 kilometres every year through Russia, Kazakhstan and the Arabian Desert to spent the winter in eastern Africa. It takes about three months in the fall but only 55 days in the spring because of favourable winds.
A population in the Canadian Arctic crosses the North Atlantic Ocean from Baffin Island to Britain—about 3,400 kilometres over four days—before flying south to the coast of Mauritania in West Africa, a total journey of 7,400 kilometres.
Postmedia reported that while the Canadian group's journey is shorter, researchers noted weather conditions on the Atlantic crossing are more severe.
The Canadian wheatears fatten up on insects and spiders, doubling their body mass before what researchers believe is a non-stop flight.
"Think of something smaller than an [American] 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 of the University of Guelph, in an interview with BBC News.
The bird also considers the strength of the wind before setting off, says Heiko Schmaljohann, a researcher with the Institute of Avian Research in Germany and an author of the study.
"If the birds on Baffin Island intended to depart but experienced bad weather conditions, they would just stay and wait for good weather," he said. "Otherwise they would just die."
Scientists long suspected the wheatear's epic migration pattern but electronic geolocators have become small enough to attach to the tiny bird to track its path only recently.