Why Do Birds Suddenly Appear?

Missing for months, colorful flocks of flycatchers, warblers, orioles and black-headed grosbeaks are once again abundant in the Bay Area. And they've navigated with such precision -- despite lengthy journeys with no maps -- that they return to the same park, the same yard or even the same tree.

Did they hear their way home?
That's the idea behind a new theory by U.S. Geological Survey geophysicist Jon Hagstrum, whose research suggests that birds navigate by using Earth's low-frequency sound waves to identify the "address" of home.
"They are imprinting on the characteristic sound" of where they live, he told a crowd this week at a lecture at USGS headquarters in Menlo Park. "The terrain has characteristic frequencies. I think that is the sound they are listening to."
Birds may even perceive the world as a vast sonic environment, hearing many frequencies bouncing off different landmarks, such as mountains and buildings, generated by the Earth's movement.

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