Factors limiting song acquisition in adult zebra finches

Song learning takes place in two separate or partially overlapping periods, a sensory phase in which a tutor song is memorized and a sensorimotor phase in which a copy of the model is produced. The stage of song development where song becomes stable and stereotyped is called crystallization. Adult birds usually do not learn new song in many species including the zebra finch. However, it is not known whether song crystallization as such or aging impedes adult learning. Exposure to loud noises prevents birds from developing and crystallizing their song, because they cannot control their voice by auditory feedback. Zebra finches even without previous experience of hearing or singing a song failed to learn a song model provided in adulthood. Thus, neither the absence of a tutor song nor the lack of song crystallization enables new song learning in adulthood, but age per se limits the ability or motivation to learn song.