Song retuning with tutor model by adult zebra finches.

Songbirds first memorize a tutor song in youth and develop their own song after the remembered model. As birds sexually mature, their song becomes crystallized and refractory to further tutoring. Here, we show that the song syllables of adult zebra finches gradually drift from their once crystallized forms, when individual birds are kept in auditory isolation or in company of cage mates singing different song syllables. Furthermore, when birds with drifted syllables are tutored with the same model again, they amend the fine structure of their syllables towards the model. In contrast, retutoring does not affect syllable sequences that differ from those of the original tutor.