Fig. 10.

Results of a deafening operation done in two steps. A, The left cochlea was removed when the bird was 86 d old. B, The right cochlea was removed at 231 d of age, which falls between the age ranges of the middle-aged and old birds shown in Figure 5. The time after each surgery is shown for each recording. Notice that there were no song changes after the first operation but song degraded after the second operation at a rate intermediate between what would have been expected from the middle-aged and old birds shown in Figure 5. (This bird is represented on the graph in Fig. 6 where its age at deafening, 231 d, corresponds to that when the second cochlea was removed.) This bird's long call appears at the end of the song motif. Although the long call was unaffected by the first operation, it too had deteriorated by 60 weeks after removal of the second cochlea. Theasterisk at the bottom inA marks the long call of an unseen female zebra finch used to elicit long-call responses from the male. This bird's single cochlea permitted him to hear, process, and respond to this female's long call at 16 weeks after surgery.