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The world's longest commute
Every year, a small grey-and-white seabird makes the longest migration of any animal on Earth. The Arctic tern weighs only about 100 grams, less than a mobile phone, but it flies from its nesting grounds in the far north to the seas around Antarctica, and then all the way back again.
Scientists have known about this journey for a long time, but until recently nobody knew exactly how far the birds travelled. In a study published in 2010, researchers fixed tiny tracking devices, each weighing less than 2 grams, to the legs of terns nesting in Greenland and Iceland. When the birds came back the following summer, the researchers removed the trackers and studied the information they had recorded.
The results surprised them. The terns did not fly in a straight line. Instead, they followed a long S-shaped route down the Atlantic Ocean, using the winds to save energy. On average, each bird travelled about 70,000 kilometres in a year. Many also stopped for around a month in the middle of the North Atlantic, where there is plenty of food, before continuing south.
Because the tern spends the northern summer in the Arctic and the southern summer near Antarctica, it experiences two summers every year. As a result, it probably sees more daylight than any other animal.
Arctic terns can live for more than thirty years. Over a whole lifetime, one bird may fly well over two million kilometres. That is roughly the same as flying to the Moon and back three times.
The terns' journey may also help scientists understand how the oceans are changing. If winds or sea temperatures change, the birds may need to change their routes or the places where they stop to feed. By following them, researchers can learn how ocean life is responding to a warming planet.
