Figure 1.

(a) Click-evoked auditory brainstem responses (ABRs) measured for the 40-year-old beluga Aurora (blue) and 21-year-old Qila (red). ABRs from Aurora were of relatively large amplitude. In contrast, ABRs from both ears from Qila had smaller amplitude, with increased latencies of the dominant waves. (b) Auditory evoked potential audiograms measured in Aurora (left ear, blue circle) and Qila (left ear, red closed squares; right ear, red open squares), in comparison with those reported by Mooney et al. (25) for 26 belugas. Underwater ambient noise levels (power spectral density, units of 1 μPa²/Hz) for the pool in which Aurora and Qila were tested are shown with a dotted line. Note that Qila has a hearing loss which is most apparent in the high frequencies at 56 kHz and above (see table) and in the right ear (light red). Table in (b) AEP hearing thresholds (in dB re 1 μPa) for Aurora and Qila tested in March 2014. Hearing threshold was defined as the mid-point between the lowest stimulus level for which a statistically significant response was detected, and the highest level for which no AEP was detected. R, right; L, left.