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Introduction
Whatever the range over which mammals communicate, their repertoire almost invariably includes the use of sound. In human society this truth is self-evident, but it applies throughout the mammals, and beyond to other classes. Collectively, mammals use a wide spectrum of sound. The smallest rodents and bats produce ultrasonic messages beyond human hearing. Elephants, the largest living terrestrial mammals, communicate over long distances using infrasonic rumbles (Payne et al., 1998). In the underwater ocean environment, sound persists far beyond the limits for light (Urick, 1986), as the most effective medium for the wide range of signals used by marine mammals in acoustic communication.
Attempts by human researchers to interpret the signals of another species often follow a similar course. Answers are sought to a series of questions of increasing complexity, but the first step is to catalogue the repertoire of sounds produced by the species (Bain, 1986; Richardson et al., 1995; Barklow, 1997). This is the task of this chapter. Thereafter, specific sounds produced may be linked with concurrent activities, and inferences drawn as to the functions of the sounds (Clark, 1982; Clark, 1983; Tyack, 1998; Riede & Zuberbuhler, 2003). These are sometimes tested by playing back recorded sounds to observe the reactions elicited (Clark & Clark, 1980; Tyack, 1983; Seyfarth & Cheney, 1992; Hopp & Morton, 1998; Fichtel & Hammerschmidt, 2003; Parks, 2003a; Parks, 2003b).
The vocal characteristics that separate one species member from another also facilitate the recognition of kin, neighbours and strangers. Identifying these characteristics leads to a more intimate knowledge of the mechanisms at work in acoustic communication (Reby et al., 1998; Tyack, 2000; Illman et al., 2002; Phillips, 2003).
The sounds produced by right whales Eubalaena sp. have attracted interest since at least the late nineteenth century (Scammon, 1874). In the southern hemisphere, research has proceeded since the early 1970s, when the repertoire was first described (Cummings et al., 1971; Payne & Payne, 1971; Cummings et al., 1972; Saayman & Tayler, 1973; Cummings et al., 1974). In the following decade, calls were associated with behavioural states (Clark & Clark, 1980; Clark, 1982; Clark, 1983; Clark, 1984).
In the northern hemisphere the vocalisations of Eubalaena glacialis received attention earlier (Schevill, 1962; Schevill et al., 1962; Schevill & Watkins, 1962; Schevill, 1964) with a blossoming of marine acoustic research. Recent concern about the conservation status of northern right whales (Fujiwara & Caswell, 2001) due inter alia to threats from entanglement in fishing gear and vessel Chapter one: Acoustic repertoire of southern right whales in South African waters 2 strikes (Knowlton & Kraus, 2001), has led to a renewed focus on right whale acoustics in the northern hemisphere, as an advertisement of presence. More recently, the behaviour surrounding surface active groups (SAGs), including vocal activity(Kraus & Hatch, 2001; Parks, 2003b; Parks & Tyack, 2005a; Parks et al., 2005b) and call rates of northern right whales(Matthews et al., 2001) have attracted attention.
There is apparent consensus on the three broad signal types used by right whales; calls, blows and slaps. There have been many attempts to break down these large groups of right whale calls according to various criteria. Some are descriptive (Schevill, 1962; Schevill et al., 1962; Schevill & Watkins, 1962; Schevill, 1964; Cummings et al., 1971; Payne & Payne, 1971; Cummings et al., 1972; Saayman & Tayler, 1973; Cummings et al., 1974; Kraus & Hatch, 2001; Matthews et al., 2001). Others are more quantitative in nature (Clark & Clark, 1980; Clark, 1982; Clark, 1983; Clark, 1984; Wright, 2001; Parks, 2003a). These have generated call descriptions with many names, encompassing overlapping sets of calls. In general, calls have most of their energy between 50 Hz and 500 Hz, though energy sometimes persists into the 2000 Hz region and beyond. Calls tend to be either more tonal (closer to pure sine-wave, harmonic, and with a clear pitch) or more pulsed (and broadband, with more non-harmonic elements caused by vibration of obstructions in the vocal tract), but these categories are not absolute, and many sounds are apparently points along a continuum, with adjacent calls having very different sound qualities (Payne & Payne, 1971; Clark, 1982). Some existing classification systems encompass extremely diverse calls within a singly named call type, which of necessity glosses over the many differences between calls falling within that group, so that call classification is ambiguous.
In this chapter, southern right whale vocalisations are classified using a simplified system derived from and compared with existing methods, but employing a categorical matrix to allocate thirteen call types based on onset frequency and acoustic contour (12 call types within the matrix, one call type, the gunshot, excluded by it). The system is offered with the intention of providing an objective tool for locating and assessing the many and varied calls produced by southern right whales, some of which could conceivably fall into several previously described, overlapping call groups. The system is ntended to be effective independent of visual observations of the whales which may be producing the sounds, as remote sensing of acoustic signals (a growing area of interest in whale acoustics) normally precludes the presence of observers.
Summary
Acknowledgements
Acronyms
CHAPTER ONE Acoustic repertoire of southern right whales in South African waters
CHAPTER TWO Acoustic behaviour of southern right whales in South African waters in relation to numbers of whales present
CHAPTER THREE Localising calling southern right whales in a noisy environment, using a dual-axis suspended hydrophone array
CHAPTER FOUR Individual variation in the calls of southern right whales
