快猫短视频

WITH nothing more than a simple compass and a nice breeze, turtles can
navigate their way across thousands of kilometres of featureless Atlantic
Ocean.

Each year, female green sea turtles set out from Brazil for Ascension Island,
2300 kilometres away. It鈥檚 a tiny target just 5 kilometres across, and there are
no landmarks in the open ocean to guide them. So Paolo Luschi of the University
of Pisa in Italy wondered whether the turtles were using the Earth鈥檚 magnetic
field to make a map of where they were going.

He and his colleagues released 18 turtles at various places up to 450
kilometres away from the island, and then tracked them using radio transmitters
to see how they fared. All the turtles seemed lost at first, swimming in big
circles as if carrying out a random search. But most of them got to the island
eventually, almost always approaching in a straight line from the
north-west.

Luschi says that although the turtles probably sense the Earth鈥檚 magnetic
field to tell them which way to swim when they set off from their usual starting
point, they aren鈥檛 able to use magnetic information to work out where they are
if they get lost. He thinks the turtles must be picking up sounds or smells from
the island carried in the wind, which almost always blows offshore towards the
north-west.

But turtle expert Ken Lohmann of the University of North Carolina, a
proponent of the magnetic map theory, is cautious about the wind idea. He says
the turtles may have got lost because they were confused by magnetic fields
produced by the tracking transmitters.