Migration Marvel

A new study proves that the Arctic tern makes the longest yearly migration in the world

February 03, 2010

An international team of scientists has officially crowned the Arctic tern the king of long-distance migration. Every year, the tiny bird flies nearly 45,000 miles on its trip from the northern tip of Greenland to the shores of Antarctica and back again. That's equal to 60 trips around the Earth in the bird's lifetime.

"This is a mind-boggling achievement for a bird of just over 100 grams [about 3.5 ounces]," says Carsten Egevang of the Greenland Institute of Natural Resources. He was one of the main scientists on the tern study.

Tracking Terns

Scientists have known for years that the bitty bird, which weighs as much as a stick of butter, made a lengthy migration. But scientists could never before prove that it was the longest in the world. The instruments used to follow large animals, such as geese, penguins and seals, were too big for the terns to carry.

The development of tiny tracking devices has allowed scientists from Greenland, Denmark, the United States, Great Britain and Iceland to map the Arctic tern's massive pole-to-pole migration. Scientists attached devices called geolocators to the legs of 50 birds in Greenland and 20 in Iceland. The geolocators are about the size of a small paperclip. They helped to track the birds' flight.

What a Trip!

What did the scientists learn? The terns make a month-long stop in the middle of the North Atlantic Ocean to feed on small fish and shrimp-like animals called krill. As they continue their journey south, half of the birds fly down the coast of Africa. The others fly across the Atlantic Ocean and down the coast of South America. The two groups meet in Antarctica.

The scientists were surprised to find that the birds did not take the shortest route back to their breeding grounds in Greenland. Instead, they flew in an S-shaped pattern over the Atlantic, adding 1,000 miles to their journey. Ian Stenhouse, a scientist on the study, says that the birds follow wind systems to help them on their return trip.

"They get a lift from the wind," Stenhouse told TFK, "and this allows them to make the return journey in about half the time they spent going south."

But the biggest discovery of all was how far these birds actually travel each year. Scientists had estimated the round-trip to be about 20,000 miles. The new tracking instruments showed that the Arctic tern travels twice that distance.


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