How Sea Turtles Find Their Way

Robert Beason has studied the navigation secrets of migratory birds including the bobolink and quails. Rather than testing his birds in a tank, Beason has outfitted planetariums with magnetic fields to see how birds would respond.

"As you change the field, the bird immediately changes direction in flight," said Beason.

Beason has also looked into what mechanisms in birds might help them sense their location inside a magnetic field and has located a particular receptor nerve that may be responsible for cuing the birds' navigation system.

Lohmann says no parallel studies have been done in loggerhead turtles because they're an endangered species so "we can't cut open their brains to investigate." But one possibility, he says, is the turtles may host magnetic particles of an oxide of iron, called magnetite, in their heads. These particles could act like compass needles and cue specific navigating receptors in the turtles' brains. Another idea is that magnetic fields set off a complex set of chemical reactions in the turtles' eyes that affect how the turtles see and orient themselves.

One thing Lohmann is certain of is that these turtles inherit their keen magnetic sense of direction at birth since they start their long journeys soon after hatching. Furthermore, it seems that colonies of loggerhead turtles are born with magnetic maps that are specifically calibrated to their homeland. That means that colonies of loggerhead turtles originating from the coasts of Florida could not find their way if displaced to the coasts of Japan or Australia, where other colonies live.

Since populations of loggerheads are severely endangered in Japan, that could be valuable information for ecologists.

"If the Japanese loggerhead becomes extinct, we couldn't reestablish populations by bringing in other turtles from other regions," says Lohmann. "These turtles inherit their maps at birth and would be lost starting from any other place than home."

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