Sounding out underwater hearing

Hearing by Whales and Dolphinsedited by W.W.L. Au, A.N. Popper and R.R. Fay, Springer-Verlag, 2000. £89.50 (490 pages) ISBN 0387 949 062The song of the humpback whale and the whistles of the TV star ‘Flipper’ have excited popular imagination to some aspects of the bioacoustic behavior of whales and dolphins. However, these behaviors represent only a small portion of the richness in acoustic signals and the adaptations of cetaceans. For example, the sound frequencies emitted by whales and dolphins range from 10 Hz to more than 130 kHz, and sound intensities can reach 220 dB SPL. The duration of sounds range from clicks of a few milliseconds to songs that last minutes. This wide range of sounds serves a similarly broad array of behavioral situations and tasks, including navigation, echolocation, social group interactions and mate selection. To adapt to the underwater conditions of the acoustics, many cetaceans have evolved highly specialized and effective means to produce and receive sounds, strategies that can differ considerably from species that use airborne sounds.Specialized auditory behavior is a distinctive feature in vertebrate hearing. The echolocation behavior of bats, and the song learning and sound localization behavior of birds are two examples in which specialized behavioral repertoires have evolved, and these reveal general operation principles of the brain. Given the massive size and complex structure of the cetacean brain – much of it dedicated to the processing of sound – and the fact that they are curious and highly intelligent animals it would seem logical that their nervous system might have been extensively studied. However, their large size and aquatic mode of life has created many technical difficulties that have slowed such research. Nonetheless, progress has accelerated over the past two decades and much has been learned about hearing in whales and dolphins, of which the present volume is a prime example.Accordingly, the editors of the Springer Handbook of Auditory Research have added a twelfth volume that is dedicated to this topic. The editors invited a distinguished array of scientists to furnish an introduction and overview of the state of cetacean hearing research. In keeping with the successful design and execution of prior volumes in this series, such as those on the cochlea and hearing in bats, the goal was a comprehensive synthesis of the literature with emphasis on the fundamental concepts. This text provides an excellent service for several disciplines ranging from acousticians to neurobiologists, ethologists and psychologists at the postgraduate level. In spite of many technical details, the readability of most chapters is quite good. This is helped by a comprehensive introductory overview in the first chapter by W.W.L. Au. A wide range of issues is addressed, including: underwater communication and echolocation; electrophysiological recording techniques and acoustic models of sound production; anatomical aspects of the ear and the CNS; properties of acoustic communication and echolocation; and psychophysical and social considerations of auditory behavior. Their treatment is detailed enough for the specialist and yet accessible to generalists. The production values are superb, with lucid graphics and good layout. Overall, this volume is an excellent example of the strengths of the Handbook of Auditory Research Series, namely providing an overview without loss of focus or depth. One can only hope that forthcoming volumes will strike the same balance.