Recent advances in the understanding of baleen whale hearing

Determining the frequency range of hearing and hearing sensitivity of baleen whales has long been a goal of marine mammal bioacousticians. Two recent investigations into baleen whale hearing, one on the common minke whale (Balaenoptera acutorostrata) and one on the humpback whale (Megaptera novaeangliae), have significantly advanced our understanding of baleen whale hearing. Thestudies used evoked potential audiometry, a direct measure of hearing, and modified behavioral observation audiometry, an indirect measure, to determine the frequency range of hearing and hearing sensitivity. Results from both studies suggest that these baleen whale species hear at higher frequencies than previously predicted based on vocalization frequencies and anatomical modeling. In the case of the minke whale, the frequency of best hearing sensitivity might reflect adaptations for predator detection or sound localization. In humpbacks, the received signal-to-noise ratios at which behavioral responses were observed were similar to critical ratios experimentally measured in multiple odontocete species. Additional research utilizing these techniques, and matched to species and populations where animals are available and show the behavioral and physiological traits suitable for their implementation (e.g., small size, predictable patterns of occurrence and behavior), will likely provide further information on baleen whale hearing.