Comparative Reproductive Biology of Four Blue Tit Populations in the Netherlands

After a long period in which research on the population biology of holenesting birds was mainly conducted on the Great Tit (Parus major), recently more attention is being given to its counterpart, the Blue Tit (Parus caeruleus). This is partly due to the increasing number of studies from the mediterranean region (Blondel et al. 1987), where the Blue Tit is often the most numerous tit species. As this species seems to be a promising subject for a comparative demographical study over a large area of Europe, an analysis of data collected in several populations from the Netherlands is of interest. Correlative studies in contrasting habitats can give us clues about the factors that influence parameters such as date of egglaying, clutch size and breeding success, but they need experimental verification.