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.
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.