Research shows the ability to detect infrasound, or ultra-low-frequency sound waves, is the third factor allowing pigeons to navigate, in addition to their internal compass and use of the sun. Jersey Hill, near Ithaca, N.Y., is known as the "Birdmuda triangle," an area where local pigeons never return once they migrate, except for one day: Aug. 13, 1969. Researcher Jon Hagstrum used weather data and a computer model to uncover a kind of sonic shadow that deflects infrasound, effectively blocking the birds' ability to find their way. Unusual conditions on that 1969 day allowed pigeons to navigate successfully.

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