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This story is brought to you by BirdNote, a show that airs daily on public radio stations nationwide.

Some cloudless night in September—when the air is clear—take a seat outside. Turn your binoculars to the sky. With patience and a bit of luck, you may see birds flying across the yellow face of the moon.

September is peak migration time for millions of songbirds, heading south from temperate North America to more tropical latitudes. Most migrate at night—orioles, warblers, sparrows, and tanagers. Nocturnal migrants of the same species call as they fly, enabling flock-mates to stick together. Many of these flight calls are distinctive, enabling those with an excellent ear—or good recording gear—to identify them as they pass. 

Like many nocturnal travelers, the Swainson’s Thrush avoids predators by flying at night, because hawks migrate during the day. But mostly, night migration’s attractive because the cooler, more stable air makes flight more efficient and prevents overheating. Meaning that even a tiny bird like a warbler—that weighs around a third of an ounce—can cover as much as 200 miles in a night. 

Your moon vigil may reveal only a few dozen such birds on the move, but researchers along the Gulf of Mexico have tracked more than a million birds headed to Central America on one busy night.

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Swainson's Thrushes Calling Slightly Before Sunrise, used courtesy of "BIRD CALLS and SONGS."
Recordings and sonograms of the .
Music, Olivier Messiaen's Turangalila Symphony, sixth movement, "Jardin du Sommeil d'amour."
BirdNote's theme music was composed and played by Nancy Rumbel and John Kessler.
Producer: John Kessler
Executive Producer: Dominic Black

Written by Bob Sundstrom

© 2014 Tune In to Nature.org   September 2014 / September 2015   Narrator: Mary McCann