Although songbirds rely on auditory input for normal song development, many species eventually attain adult song patterns that are thought to be maintained without reference to auditory feedback. In such species, it is believed that a central motor program for song is established when the stereotyped adult song pattern is achieved. However, we report here that in the Australian zebra finch, stereotyped song patterns gradually change in adult males following bilateral cochlear removal. By 16 weeks after surgery, deaf birds accurately reproduced only 36% of the song syllables produced prior to surgery. Moreover, on average, the phonology of over 50% of the syllables produced by deaf birds was either only slightly similar or unlike the phonology of any syllable produced prior to surgery. In contrast, control birds accurately retained over 90% of their syllables over a comparable time period and less than 5% of their syllables was unmatched or only slightly similar in phonology to previously recorded syllables. In many of the deafened birds, changes in song patterns were not evident until 6-8 weeks after surgery. These data indicate that continued auditory input is necessary to maintain the patterns of neural organization supporting learned song in zebra finches and raise questions concerning the neural sites and cellular mechanisms that mediate this feedback control.