| Summary: | In this thesis several aspects of the singing behaviour of six European members of the genus Turdus have been studied. It has been-demonstrated that these six species show three distinct types of singing behaviour. They are; 1. Species with small repertoire size and stereotyped song characteristics (ring ousel and redwing). It is suggested that song in these species functions primarily as a territorial 2. Species advertisement. with medium to large repertoire size and stereotyped song characteristics (blackbird and mistle thrush). It is suggested and observations support the contention that one important function for song in these species is territorial. The large repertoire characteristic of individuals of these species indicates that there may also be an important mate attraction component. 3. Species with large to extremely large repertoire size and variable song characteristics (song thrush and, possibly, fieldfare but results are based on measurements from only one recording of one individual). Observations indicate that the song of the song thrush probably functions primarily in mate attraction and it is suggested that song may play a similar role in the fieldfare. It is suggested that in other avian species in which individuals possess large repertoire sizes and sing in a complex or unpredictable manner that song is likely to function primarily in mate attraction. A series of experiments was conducted on individuals of the mistle thrush, blackbird and song thrush. These revealed that individuals of these species use a second kind of singing behaviour in situations simulating territorial intrusion. (Jommon to all species is an increase in sound frequency of song during or following playback of conspecific song. The singing behaviour of three individual song thrushes was studied in an attempt to find rules governing sequencing of song types. The most important point to emerge is that individuals of this species seem to organise their singing behaviour in a hierarchial manner. It is possible to identify groups of song types within which transitions occur more frequently than at random. This is like the singing behaviour of the blackbird and it may be that hierarchical organisation of singing behaviour is a common phenomenon in species in which individuals possess large song repertoires. The functional significance of such behaviour is unclear. Finally, with a view to confirming or refuting Hartshorne's anti-monotony threshold principle, the singing behaviour of the six European species and that of eight others from various faunal regions was studied to see to what extent it conforms with predictions of the principle. Several measures of song continuity and versatility were i applied and it was found that for macro measures (see Chapter 4) there is a very significant relationship between the two parameters. 'Other predictions of Hartshorne were not confirmed. It is suggested that although the principle seems to apply to some aspects of Turdus song its major failing is that it does not provide an explanation for interspecific differences in repertoire size.
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