A comparative study of song in European thrushes
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
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
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
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.