Animal’s migration is something that always amazes me, especially when the trip involves travelling for thousands of miles. This little creature actually travels from the Arctic to Antarctica, and vice versa at the end of the winter. Every year!
The Arctic tern's extraordinary pole-to-pole migration has been detailed by an international team of scientists.
The researchers fitted the birds with tiny tracking devices to see precisely which routes the animals took on their 70,000km (43,000 miles) round trip.
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Starting in August and September, this small bird - which weighs little more than 100g (3.5oz) - will head away from Greenland with the intention of getting to the Weddell Sea, on the shores of Antarctica.
It will spend about four or five months in the deep south before heading back to the far north, arriving home in May or June.
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The birds then head south along the coast of western Europe and western Africa before making a choice, either to continue hugging Africa or sweep across the Atlantic from the Cape Verde Islands to continue the journey along the Brazilian coast.
About half the birds that were tracked decided to take the South American path. It is not clear why, but the researchers believe wind might make either route seem favourable to the terns.
After spending their northern winter months in Antarctic waters, the terns then fly back towards the Arctic.
But rather than retracing their southward flight paths, the birds follow a gigantic "S" pattern up the middle of the Atlantic Ocean.
"This is completely new knowledge," Mr Egevang told BBC News.
"They make a detour of several thousand km but once we start comparing the route to the prevailing wind system, it makes perfect sense - moving in a counter-clockwise direction in the Southern Hemisphere, and clockwise in the Northern Hemisphere.
"It's just more energy-efficient for them to do that even though they are travelling several thousand more km than if they flew in a straight line."
Spellbinding.
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