Effects of deafening on song development in American robins and black-headed grosbeaks

Robins that were either raised in acoustic isolation or deafened as young birds developed abnormal syllables in their songs. However, there were distinct differences in syllables between hand-reared intact and deaf birds. The deaf birds produced syllables with higher maximum frequencies, more irregular frequency modulations, and wider frequency ranges than intact birds. They also lacked the typical rhythm of singing and delivering syllables. Song-learning ability was demonstrated with a hand-reared Robin. Hand-raised intact Black-headed Grosbeaks produced more or less normal syllables in their songs, whereas a deaf Grosbeak developed abnormal syllables in addition to some normal ones and pattern of singing. It was concluded that in both species the ability of a bird to hear its own sounds is important in normal song development