Tiny Arctic Tern's Incredible Pole-to-Pole Migration Mapped for the First Time
Even Arctic terns need a break now and again. Photo by alllyballly via Flickr.
Living overseas, I find that no matter how much I miss family and friends, the thought of a trip home -- nearly 7,000 miles, two flights, and 10 time zones -- seems absolutely exhausting. (Not to mention guilt-inducing.) But the annual travel of the Arctic tern puts that of even my most frequent-flying friends to shame.The small, 3.5-ounce bird flies 43,000 miles round-trip each year, a pole-to-pole migration from Greenland to Antarctica that has been detailed for the first time by a team of scientists from Greenland, Denmark, the U.S., the U.K., and Iceland. The trip "may be the longest seasonal movement of any animal," according to the researchers, who published their findings in the Proceedings of the National Academy of Sciences (PNAS), a respected journal in the United States.
Using Light-Tracking Geolocators
To track the birds' route, team members attached small "geolocators" to the animals, the BBC reports:
The devices record light intensity. This gives an estimate of the local day length, and the times of sunrise and sunset; and from this information it is possible to work out a geographical position of the birds.... The study reveals they fly down either the African or Brazilian coasts but then return in an "S"-shaped path up the middle of the Atlantic Ocean.
The birds fuel up along the way south in the middle of the North Atlantic, feasting on fish and zooplankton in a spot where satellite imagery reveals a high level of biological productivity. "It's the last high productive area before they enter tropical waters where we know productivity is low," said Carsten Egevang of the Greenland Institute of Natural Resources.
An Energy-Efficient Route
When they return to the Arctic in the spring, the researchers discovered, the birds largely eschew the continental coasts, instead taking an S-shaped route up the middle of the Atlantic Ocean, Egevang explained:
[O]nce 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.
Via: "Arctic tern's epic journey mapped," BBC News
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