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Scientists track long-distance migration of Arctic tern

LOS ANGELES - Of all migrating birds, the Arctic tern flies the farthest - braving cold, wind, storms, predators and starvation to travel from as far as upper Greenland to the shores of Antarctica.

But little has been known about how these birds, weighing less than 125 grams, make their grueling journey. Now, for the first time, scientists using tiny geo-locating devices have tracked the terns' migration, and discovered some surprising details.

The tern can fly about 44,000 miles, nearly twice the distance scientists had generally predicted - and some can fly more than 50,000 miles in a year. "Over the course of its life, it's flying to the moon three times and back," said study co-author Iain J. Stenhouse, an ornithologist who worked for the National Audubon Society for five years.

Scientists had guessed at the routes the terns took, but had not been able to definitively test those hypotheses before now.

"We see them when they're breeding . . . but the rest of the year we have no idea where these birds are," said Bridget J. Stutchbury, a professor at York University, Toronto, who runs a behavioral and conservation ecology lab. Stutchbury was not involved in the study.

Stenhouse and lead author Carsten Egevang, of the Greenland Institute of Natural Resources, found that the southbound trek is a relatively straight shot down the Atlantic. But the way north is much longer, curving in an "S" shape and potentially adding more than 1,000 miles to the journey. Yet, the northbound birds were making the trip home much faster.

Flying north, the scientists realized, the birds were using the same trade winds merchants used centuries ago to speed their journey. Flying south, the terns made a weeks-long stop right after starting out - delaying the journey to fuel up in the food-rich North Atlantic waters.

The study, published online Monday in the journal Proceedings of the National Academy of Sciences, was made possible by new technology.

More traditional tracking devices are equipped to regularly transmit information via satellite - which requires a heavy battery. The new geo-locators are small and more energy efficient. Instead of sending out signals, the 1.4-gram devices keep track of light levels. This allows scientists to pinpoint the birds' location on a given day. - Los Angeles Times

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