In November 2012, electrophysiological measurements of hearing sensitivity were conducted on Morgan and five other killer whales at Loro Parque, Tenerife (Spain). The goal of the study was to establish audiometric baseline information on Morgan relative to other whales help at Loro Parque and to determine whether Morgan suffered from hearing impairment. The six killer whales were between three months and 17 years of age. Animals of both sexes are held at this facility in four interconnected pools.
The electrophysiological measurements involved played different types of sound stimuli to the whales and measuring the resulting auditory evoked potentials (AEPs). Comparisons of hearing sensitivity across whales consist of AEPs collected following the transmission of clicks either with the whales voluntarily beached of rested at the side of the pool with the electrodes out of the water.
While click-evoked AEPs were measured in all of the other killer whales tested, no AEP responses were found in Morgan, even at the highest click level that could be tested (134 dB re 1 µPa peak-to-peak equivalent (ppe)). A click-evoked response by Morgan would be expected based on the age and size of the whale and the success at recording click-evoked AEPs in the other whales.
The lack of a click-evoked response in Morgan suggests that this killer whale suffers from a hearing deficit. The magnitude and frequency range over which the hearing deficit occurs cannot be specified with the techniques used here as the click stimulus lacks the frequency specificity necessary for frequency-specific threshold measures. Nevertheless, it can be concluded that Morgan's hearing ability is at least 20-30 dB worse than the hearing sensitivity of the other whales tested. Morgan potentially suffers from a profound hearing deficit, or even complete loss of hearing, but this cannot be determined through currently employed electrophysiological means.