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December 25, 2007

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It turns out that birds do actually see the magnetic field. Details are reported over at Not Exactly Rocket Science:

"When cryptochrome is struck by blue light, it shifts into an active state where it has an unpaired electron – these particles normally waltz in pairs but here, they dance solo. The same thing happens in a companion molecule called FAD. Together, cryptochrome and FAD, both with unpaired electrons, are known as a “radical pair”. Magnetic fields act upon the unpaired electrons and govern how long it takes for the radical pair to revert back to their normal, inactive state. And because cryptochrome affects the sensitivity of a bird’s retina, so do magnetic fields.

The upshot is that magnetic fields put up a filter of light or dark patches over what a bird normally sees. These patches change as the bird turns and tilts its head, providing it with a visual compass made out of contrasting shades."

There's an interesting illustration accompanying the article that sheds much light on the phenomenon.

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