Egg size in the Great Tit Parus major: individual, habitat and geographic differences

Abstract

Factors affecting egg dimensions were investigated in two neighbouring Great Tit populations breeding in a poor urban and a rich rural habitat in southeast Estonia. About 80% of variation in egg size was heritable; however, the effects of female condition were also remarkable. In both populations, females laying large eggs were heavier during the second half of the nestling period, indicating that egg size reflects the component of female condition which is persistent throughout the breeding period . In the urban population, egg size decreased seasonally, most likely because of a poor phenotypic quality of late breeders . In the rural population, large clutches tended to contain small eggs, which points to a trade-off between the size and number of eggs . The analysis of literature data from 30 Great Tit populations revealed no evidence of a trade-off between egg size and clutch size at the inter-populational level, but rather a positive correlation between these traits among populations. Egg size increased with latitude .