Size and parental effort in the Great Tit Parus major.

We experimentally reduced clutch size of Great Tits Parus major to investigate the effects on parental care (including Daily Energy Expenditure, DEE, measured with doubly labelled water). and the relationship between DEE and the residual reproductive value. The length of a working day was not affected. but the nestling phase was 0.7 days (4%) shorter in experimental clutches. Males fed reduced broods at a lower rate, but DEE and mass (loss) were not significantly affected by the experiment. However, male DEE was positively correlated with feeding frequency, and this relationship did not differ between control and experimental males. This suggests that the experiment resulted in a slight reduction in male DEE, and lack of statistical significance can be attributed to the power of the test applied. Females fed reduced broods at a lower rate, but female DEE and mass (loss) were not affected by the clutch size manipulation. Female DEE was not correlated with feeding frequency, the original number of eggs in the nest or the actual number of young.

Verhulst S. & Tinbergen J.M., ARDEA 85 (1): 111-126.