Direct Hearing Measurements in a Small Mysticete Whale, The Common Minke (Balaenoptera acutorostrata)

The hearing abilities of baleen whales have long been a mystery that has in recent decades impeded understanding of how anthropogenic noise might affect them. Because of their large size and difficulty maintaining them under human care, the use of behavioral audiometry to test their hearing has been impractical. Knowledge of baleen whale hearing has historically been inferred from the frequency range of their vocalizations, although this is known to be a poor predictor of the full range of hearing in mammals and provides no information on hearing thresholds. Additional information on sound sensitivity in baleen whales has been obtained through behavioral response studies, anatomical modelling, and most recently, the use of electrophysiological methods. Collectively, these approaches demonstrated or predicted that baleen whale hearing ranges exceed the range of vocalization frequencies, which is a common feature of mammalian hearing. Within the last 2 years, a modified behavioral observation audiometry study with free-ranging humpback whales and an electrophysiological study with temporarily held common minke whales suggest higher-frequency sensitivity than previously predicted. These approaches provide information on sound sensitivity, and the approaches may potentially be combined to permit a baleen whale audiogram to be obtained.