Song and territory in the Great tit Parus major

It is common knowledge that bird song has one or both of two functions: territorial advertisement and mate attraction (Thorpe, 1961; Armstrong, 1973). However, beyond the simple correlation between the seasonal peak of singing and territorial or reproductive activity, there is remarkably little direct evidence for either proposed function of song. Here I am concerned with the role of song in territorial behaviour in the Great tit (Parus major). The spring peak of singing coincides with the establishment of a territory, which occurs after pairing in the Great tit (Hinde, 1952; Krebs, 1971), perhaps indicating that mate attraction is less important than territorial advertisement in this particular species. The question I attempt to answer is 'Does song act as a signal to keep intruders out of a territory?'. I also discuss how the organisation of song might relate to territorial exclusion.