The captain of an ice-breaker has few problems navigating during the polar summer. The 24-hour sunlight pro-vides constant illumination of the surroundings. When storms whip up, the captain can turn to a suite of global-positioning devices, which pinpoint the ship's location to a matter of metres. Yet all this electronic sophistication is put to shame by the migratory birds wheeling overhead, which navigate thousands of kilometres using nothing more than what is in their heads. This summer, the ice-breaker Oden tracked migrating birds as they left the Arctic through the Bering Strait, the narrow waterway between Alaska and Siberia. More than 50 polar scientists had gathered as part of a wide-ranging project called Beringia 2005. Among them were Thomas Alerstam of Lund University in Sweden and his research team. They were there to shed light on one of ornithology's greatest mysteries: how do birds navigate during their annual migration?
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