Acoustics and Social Behavior of Wild Dolphins: Implications for a Sound Society

Abstract

Understanding and documenting the characteristics and features of the social sounds and associated behavior of free-ranging delphinids has historically been limited by lack of access to animals and poor underwater viewing conditions. Communication studies of delphinids have been undertaken in both captivity (see Herman and Tavolga 1980 for review) and in the wild (Connor et al. 1992; Norris et al. 1994). Even with a wealth of information about dolphin sound production and hearing capabilities from captivity, there are significant gaps in understanding how dolphins detect, decode, and decipher both their environmental and social signals in the wild. Although the abilities of dolphins to actively produce both echolocations signals and social sounds have been documented, little is understood about the sensory exposure and information available to, and utilized by, free-ranging delphinids. One way to address this issue is to review the use of conspecific social signals and behavior. Dolphins, like other animals, have been under evolutionary pressures for increased efficiency in their communication system. By observing critical environmental and social aspects of delphinid society we might gain insight into how these animals learn and selectively filter information in their environment. This chapter will outline the characteristics of social sounds and associated behavior of delphinids, specifically Stenella frontalis, the Atlantic spotted dolphin, and Tursiops truncatus, the bottlenose dolphin. These two species have been the focus of a long-term, underwater natural history study in the Bahamas. The major emphasis of this chapter will be on the available information in the dolphin's environment, the contextual use of conspecific vocalizations, developmental behavior, and low-frequency (but sometimes significant event) behavior. Potentially valuable future lines of inquiry into delphinid communication and hearing will be discussed in the last section.