Fig. 5.

Sound-spectrographic representations of song degradation in three birds, deafened at 81 d (Young), 175 d (Middle-aged), and 2090 d (Old) after hatching. Degradation of the long call is shown for two of these birds (Young,Old). The time after deafening is indicated for each of the songs. A continuoushorizontalline is below the most complete rendering of each bird's song motif before deafening and after deafening for as long as that motif can be easily recognized. Notice that eventual degradation occurs in all three birds, but the onset, extent, and time course differs with the age at deafening. This observation, scored for all 16 birds in this experiment, is shown below (see Fig. 6). For purposes of comparison (this figure, see Fig. 6), the SSI for the last recording of the young, middle-aged, and old birds shown in this figure was 0.0, 0.6, and 2.8, respectively.