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Navigating by Earth's Magnetic Field

How do they know where to go?

How do birds navigate? They steer by landmarks and by the sun and stars. A keen sense of smell helps some birds chart their course. And, it turns out, migrating birds also find their way by responding to the magnetic field of the earth. Iron-rich magnetic crystals inside the upper beak of this Bobolink help the bird orient itself to Earth's magnetic north. Also, light hitting a specific protein in a bird's eye may trigger a chemical reaction that varies depending on the direction of the earth's magnetic field. And "birds may actually see Earth's magnetic field in the form of changing dark areas across one eye."

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Transcript: 

BirdNote®

Navigating by the Earth's Magnetic Field - New Discoveries

Written by Todd Peterson

This is BirdNote.
[Bobolinks singing and calling]
How do birds navigate? They steer by landmarks and by the sun and stars. A keen sense of smell helps some birds chart their course. And, it turns out, migrating birds also find their way by responding to the magnetic field of the earth. [Bobolink singing and calling]
These Bobolinks we're hearing orient themselves to earth's magnetic north with the help of iron-rich magnetic crystals inside their upper beaks. Homing pigeons also carry these magnetoreceptors, as do robins and other birds. [Whinny of American robin]
But that's not the only way birds use the earth's magnetic field to help them on their way. Light hitting a specific protein in a bird's eye may trigger a chemical reaction that varies depending on the direction of the earth's magnetic field. And "birds may actually see earth's magnetic field in the form of changing dark areas across one eye." 1 [Song of Bobolink]
This sensitivity explains why night-flying birds need to recalibrate their magnetic sense every day by the light of the setting sun. In an experiment in central Illinois, 18 thrushes were fitted with radio transmitters and exposed to a misaligned magnetic field. When released after dark, the birds headed west. Birds not exposed to the false geomagnetic field headed north. On subsequent days, however, the misdirected birds reoriented themselves to follow their true course. 2
Like to hear this show again? Come to birdnote.org. I'm Michael Stein.
                                                                           ###
Bird sounds provided by The Macaulay Library of Natural Sounds at the Cornell Lab of Ornithology, Ithaca, New York. Bobolink song and calls 47596 recorded by D.S.Herr; whinny of American Robin 105811 recorded by G.A. Keller; and song of Bobolink 12419 recorded by A.A. Allen.
Producer: John Kessler
Executive Producer: Chris Peterson
© 2012 Tune In to Nature.org    March 2012    Narrator: Michael Stein
ID# migration-12-2012-03-02   migration-12 1

"Masters of Magnetism". Ed Yong. NewScientist. 27 November 2010. Page 44. 2 "The Compass Within". Davide Castelvecchi, Scientific American. January 2012. Page 51

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