Consequences of domestication on the song structures in the canary
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This study on the organization and detailed acoustic morphology of birdsong deals with the implication of domestication upon behaviour. The songs of wild canaries (Serinus canaria) and different domesticated strains of canary were studied. These included border canaries, bred for appearance in Britain and song canaries, selected for song quality in Germany. The basic rules for developing song architecture, involving rules for assembling individually learned utterances into songs emerge by self-differentiation without any auditory or feedback stimuli. By contrast, the fine structure of notes is shaped by individual learning. A comparison of songs of wild canaries and of different domesticated breeds reveals how selective breeding can alter the behavioural programmes and the general acoustic morphology of learned notes. The results of this comparison can be summarized as follows: 1. All canaries sing phrases according to an identical programme. The temporal patterning of single utterances is very similar. 2. Quantitative differences are found in the proportion of single notes and trilled sequences or tours: Single note complexes are dominant in wild canary song, whereas in the domesticated breeds tours form the bulk of the songs. This quantitative difference is responsible for a highly contrasting impression to our ears of songs that are highly variable in the wild form, and very stereotyped in domesticated song canaries. Canary breeders select strongly for longer repetitions of identical utterances (duration of tours). Border canaries, which are not selected for this trait sing short tours, far more similar to the wild conspecifics than to the song canaries. 3. Low-pitched songs are highly esteemed by bird fanciers. The maximum frequency used by song canaries is much lower than that used by wild birds. 4. One can distinguish by ear approximately ten main syllable-categories, which recur in nearly every individual repertoire. This categorization is based on differences in their acoustic properties. To assess the subjective impression that individual learning is highly channeled in a few predictable overall categories, a reproducible method to define these universal categories has been developed: Individual repertoires depicted on sonagrams were analysed by using a dichotomous key of specific song characteristics and divided into 31 classes: The frequency of use of the syllable categories by individuals with totally different song repertoires was surprisingly similar: Some classes are highly overrepresented, whereas others are underrepresented. Thus wild and domesticated canaries form their individual repertoires according a similar array of characteristics. Thus species-specificity in the general acoustic morphology is based on rules for linking variable components of notes. Individuality is an attribute of single components, such as the pattern of frequency modulation and sequential patterning. One can demonstrate that the general acoustic morphology has remained astonishingly stable during the long process of domestication. The learning process seems to be restricted to a limited set of combinations of note components. Only a few characteristics of syllables appear to have been changed by domestication: e.g. rough syllables have nearly been eliminated, whereas very short syllables (below 50 ms) have become far more frequent.