Age at deafening affects the stability of learned song in adult male zebra finches.

Male zebra finches (Taeniopygia guttata) master the imitation of a song model 80-90 d after hatching and retain it with little change for the rest of their lives. Acquisition and maintenance of this imitation require intact hearing. A previous report showed that male zebra finches deafened as adults start to lose some of the acoustic and temporal features of their song a few weeks after deafening and that by 16 weeks the learned song is severely degraded (Nordeen and Nordeen, 1992). However, this previous study noted no correlation between the age at deafening and the subsequent timing and extent of song loss. We deafened adult male zebra finches ranging in age from 81 d to 6 years. The song of birds deafened at the younger ages (81-175 d) deteriorated severely after a few weeks, and within that age bracket, the older the bird was at deafening, the longer it took for this degradation to occur and the slower the subsequent process of song deterioration. The song of birds deafened at 2 years and older showed little change during the first 51 weeks after deafening but was grossly altered by 100 weeks. We suggest (1) that this age effect could be independent of experience or (2) that each time a bird sings, a little bit of learning-motor engrainment-occurs, adding to memory duration in a cumulative manner.