To learn a song, young white-crowned sparrows don't need to hear the entire tune straight through. Hearing it in two-phrase bits will do. If the order of phrases in a pair is reversed—BA and DC instead of AB and CD for instance—the sparrows put together the song in reverse, Gary J. Rose of the University of Utah in Salt Lake City and his colleagues report in the Dec. 9, 2004 Nature. Play the same phrases without pairing them, however, and the young birds end up singing a jumble.
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