Principles of Marine Bioacoustics (2008)


(…) Sound emissions by odontocetes (toothed whales and dolphins) can be classified into two broad categories of frequency-varying continuous tonal sounds referred to as whistles and broadband clicks (Evans, 1967), including burst pulse sounds. Whistles and burst sounds can be categorized as social sounds. Whistles appear to be used for intraspecific communications (Herman and Tavolga, 1980). Most of the research on social sounds has been performed on whistles and very little work has been done on burst pulse sounds. Perhaps, the main reason for this state of affairs is that the fundamental frequency of whistles is mainly in the sonic or audible range and are therefore easily recorded by off-the-shelf audio tape and DAT recorders. Later in this chapter, we will show that burst pulse sounds tend to be broadband and have significant ultrasonic frequency components and therefore require equipment that has frequency bandwidth larger than standard audio equipment. In our discussion of sound emissions, we will limit ourselves to the sounds that are produced internally by the animals and not consider the sounds produced by an animal striking an object or the water surface with any part of its body. Social sounds are those that are used by odontocetes in a social context and could be, but not necessarily, used for communications. In this chapter, we will focus more on the characteristics of the emitted sounds and not so much on the purpose or behavioral context under which certain sounds are produced. (…)