| Auditory feedback influences the development of budgerigar vocalizations, but until now, little was known about nestling hearing. The present study tracked the development of auditory sensitivity in nestling budgerigars using the auditory brain stem response (ABR).; In Experiment 1, the ABR was recorded in adult budgerigars in response to clicks and tones. The typical budgerigar ABR waveform showed two prominent peaks occurring within 4 ms of the stimulus onset. As sound pressure levels increased, ABR peak latency decreased, and peak amplitude increased for all waves while interwave interval remained relatively constant. While ABR thresholds were higher than behavioral thresholds, the shape of the budgerigar ABR-derived audiogram closely paralleled that of the behavioral audiogram. Based on the ABR, budgerigars hear best between 1 and 5.7 kHz with best sensitivity at 2.86 kHz—the frequency corresponding to the peak frequency in budgerigar vocalizations. The latency of ABR peaks increased and amplitude decreased with increasing repetition rate, and the latency increase was greater for wave. Generally, changes in the ABR were comparable to what has been found in other vertebrates.; In experiment 2, ABRs were used to track the development of auditory sensitivity in nestling budgerigars from 5 days post hatch (P5) until P43. With 95–100 dB being the highest level available, responses could be obtained from nestlings as young as P7 but only at frequencies at or below 2 kHz. Thresholds for these frequencies were above 90 dB SPL but improved noticeably over the next 6 days. By P12, responses could be obtained for frequencies up to 4.8 kHz, with best sensitivity at 2 kHz. By P30, ABR responses could be elicited to all frequencies tested, with the shape of the ABR audiogram becoming adult-like. The average ABR audiogram was indistinguishable from that of adult budgerigars by P30.; This series of experiments shows that non-invasive ABRs can be used to assess peripheral auditory system function, including thresholds, in adult and nestling budgerigars. This is the first complete study of hearing development in a bird that uses auditory feedback to learn and modify their vocalizations throughout life. |
