Variation in hearing within a wild population of beluga whales (Delphinapterus leucas)

Abstract

Documenting hearing abilities is vital to understanding a species' acoustic ecology and for predicting the impacts of increasing anthropogenic noise. Cetaceans use sound for essential biological functions such as foraging, navigation and communication; hearing is considered to be their primary sensory modality. Yet, we know little regarding the hearing of most, if not all, cetacean populations, which limits our understanding of their sensory ecology, population level variability and the potential impacts of increasing anthropogenic noise. We obtained audiograms (5.6-150 kHz) of 26 wild beluga whales to measure hearing thresholds during capture-release events in Bristol Bay, AK, USA, using auditory evoked potential methods. The goal was to establish the baseline population audiogram, incidences of hearing loss and general variability in wild beluga whales. In general, belugas showed sensitive hearing with low thresholds (<80 dB) from 16 to 100 kHz, and most individuals (76%) responded to at least 120 kHz. Despite belugas often showing sensitive hearing, thresholds were usually above or approached the low ambient noise levels measured in the area, suggesting that a quiet environment may be associated with hearing sensitivity and that hearing thresholds in the most sensitive animals may have been masked. Although this is just one wild population, the success of the method suggests that it should be applied to other populations and species to better assess potential differences. Bristol Bay beluga audiograms showed substantial (30-70 dB) variation among individuals; this variation increased at higher frequencies. Differences among individual belugas reflect that testing multiple individuals of a population is necessary to best describe maximum sensitivity and population variance. The results of this study quadruple the number of individual beluga whales for which audiograms have been conducted and provide the first auditory data for a population of healthy wild odontocetes.

Field-based hearing measurements of two seabird species

“…(e.g. Mooney et al, 2018;Norman et al, 2012) to assess how hearing abilities may be associated with certain habitats, individual condition, relatedness and chronic stress. By combining hearing data with the acoustic environment around the birds and the frequency content and intensity of their communication sounds, we can address how changes in background noise levels may lead to masking and shorter communication ranges.…”

Combining Cochlear Analysis and Auditory Evoked Potentials in a Beluga Whale With High-Frequency Hearing Loss

“…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 μPa 2 /Hz) for the pool in which Aurora and Qila were tested are shown with a dotted line.…”

“…Following click-evoked ABR testing, hearing thresholds as a function of frequency (AEP audiograms) were measured for both belugas. The thresholds for Aurora, Qila, and 26 wild belugas previously tested using similar AEP methods ( 25 ) are shown in Figure 1b . This large sample size from Mooney et al ( 25 ) bounds nearly all other AEP thresholds reported for belugas ( 17 , 26 , 27 ), and thus they are used to provide a reference to the normal values for this species and method [but see ( 28 – 32 ) for behavioral thresholds].…”

“…The thresholds for Aurora, Qila, and 26 wild belugas previously tested using similar AEP methods ( 25 ) are shown in Figure 1b . This large sample size from Mooney et al ( 25 ) bounds nearly all other AEP thresholds reported for belugas ( 17 , 26 , 27 ), and thus they are used to provide a reference to the normal values for this species and method [but see ( 28 – 32 ) for behavioral thresholds]. Aurora's thresholds were comparable to those for belugas from Mooney et al ( 25 ) at all examined frequencies (blue and gray traces in Figure 1b ).…”

“…This large sample size from Mooney et al ( 25 ) bounds nearly all other AEP thresholds reported for belugas ( 17 , 26 , 27 ), and thus they are used to provide a reference to the normal values for this species and method [but see ( 28 – 32 ) for behavioral thresholds]. Aurora's thresholds were comparable to those for belugas from Mooney et al ( 25 ) at all examined frequencies (blue and gray traces in Figure 1b ). The hearing sensitivity of Qila was reduced relative to the other belugas (red in Figure 1b ), and no frequency-specific AEPs could be detected above 90 kHz.…”