Acoustic communication
Ethologists have spent many years collecting and analysing wolf vocalizations, both in the field and in captivity (e.g. Theberge and Falls 1967, Harrington and Mech 1978, Schassburger 1993, Feddersen-Petersen 2000), but there is little available data on dog vocalizations. Nevertheless there is a general consensus that the two species share most vocalizations (Bleicher 1963, Cohen and Fox 1976, Tembrock 1976), with the exception that dogs howl less frequently and are 'noisier' than wolves because of their enhanced propensity to bark in various contexts. For wolves some descriptive data has been collected about the use of most vocalizations in the intraspecific context, and probably most sounds have retained their ancestral function in dogs. Interestingly, however, no detailed investigations have been carried out on dog barking.
Based on Schneirla's theory (1959), Cohen and Fox (1976) classified the vocalizations of the Canis species according to whether they elicit withdrawal or approach from the receiver. The acoustic patterns of these signals fall into two categories. One type of signal consists of harsh, noisy sounds emitted at low frequencies (e.g. growl, snarl, woof, bark); the other type can be characterized as clear, tonal, and consisting of harmonic sounds at higher frequencies (e.g. whine, yelp, whimper) (Schassburger 1993). Vocalizations belonging to the first category elicit withdrawal in the receiver but, more importantly from the sender's point of view, these are associated with agonistic inner states. Sounds in the other category usually signal friendly or submissive (appeasing) tendencies. Comparing several bird and mammalian species, Morton (1977) concluded that this categorization of vocalizations could provide a general rule for the relationship between inner state and the acoustic features of the sound (motivation-structural rules). As we shall see, this idea is not only valid for all Canis species but also seems to apply to the only vocalization that has changed during domestication: barking.
The role of barking in communication Researchers have often noted that in contrast to wolves, in which barking has been described as a signal for warning or protesting (Schassburger 1993), dogs invariably seem to bark in a wide range of contexts. Accordingly the barking of dogs is considered as a hypertrophied by-product of the domestication process (Cohen and Fox 1976) having no particular function in either species-specific or cross-species communication.
When Feddersen-Petersen (2000) recorded barks from different breeds in different contexts, she noted that barks vary both in frequency and in the relative amount of harmonics. In comparison to wolf barks, dogs emitted barks at much wider range of frequencies, and barks could be dominated by either harmonic or noisy sounds. Thus it seemed that as well as using barks more frequently, dogs also utilize different acoustic forms (Figure 8.5).
Yin (2002) argued that if Morton's rule is valid then the differences in the acoustic structure of barks should also reflect differences in the inner state. In support of this idea she found that the acoustic parameters of the dog barks depended on the recording context; for example, dogs barking in isolation produced higher-pitched sounds than when the dog was disturbed by a sudden noise (a ringing doorbell).
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