Humpback whale song or humpback whale sonar? A reply to Au et al.

Au and colleagues' arguments against the hypothesis that humpback whale son gs function as long-range sonar are based on questionable assumptions rathe r than on empirical data. Like other echolocating mammals (e.g., bats), sin ging humpback whales: 1) localize targets in the absence of visual informat ion; 2) possess a highly innervated peripheral auditory system; and 3) modu late the temporal and spectral features of their sounds based on environmen tal conditions. The sonar equation is inadequate for determining whether hu mpback whale songs generate detectable echoes from other whales because it does not account for temporal variables that can strongly affect the detect ability of echoes. In particular, the sonar equation ignores the fact that much of the noise encountered by singing humpback whales is spectrally and temporally predictable, and that audition in mammals is a dynamic and plast ic process. Experiments are needed to test the hypothesis that singing hump back whales listen for and respond to echoes generated by their songs.