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You're walking in a park when suddenly a bird bursts into song. At a spot where a pile of leaves are flying, you see it-a large, robinlike bird with orange flanks and a white belly. It's a rufus-sided towhee. It's singing a song that sounds like drink-your-tea-ee-ee-ee-ee. The bird spots you and changes its tune to dreet, dreet, tow-hee, chee-wink. Is the bird talking to you? What is it saying? Why does a towhee sing this song instead of a robin's song? Why do songbirds sing at all? For the answers, you need to look at both heredity and experience. The songs a bird sings are usually distinctive to its species. Scientists believe a bird is born with a neurological model of what its song should sound like. The baby bird learns that song by matching the sounds it hears from its father and male neighbors. Scientists call this theory the auditory template hypothesis. In this theory, song learning begins at about ten days after hatching and continues for about 40 days. Baby birds then practice their songs through the fall and winter. By spring, birds have developed a crystallized song. To communicate, birds combine songs and other vocalizations with certain behaviors and outward appearances. Males tend to sing more than females, and they sing more in the spring. Songs help proclaim territory, attract mates, and maintain a pair bond. Some birds like gulls and parrots have no songs. Instead they use complex calls to defend territory and attract mates. Oilbirds and cave swiflets use vocalizations to maneuver in the dark, a process called echolocation. The ruffed grouse and mourning dove make sounds with their wings and woodpeckers with their beaks. Most songbirds have several songs and calls. Birds in the Mimid family (the mockingbird, catbird, and brown thrasher) have very large repertoires. Scientists believe that repertoires increase with age and may indicate to females the health and experience of the male. A songbird uses its syrinx, a vocal organ in its throat, to create a song. A bird's songs can vary in pitch, tone length, number of notes, and special sounds. The two halves of the syrinx can produce songs simultaneously so a bird may sing harmonies with itself, resulting in extremely rich and complex melodies. No human voice can equal this feat.

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