Timing and synchronisation of breeding in a Marsh Tit Parus palustris population from a primaeval forest

Marsh Tits Parus palustris in Bialowieza National Park (E. Poland, 1985-97) were single brooded, laid their first eggs between 5 April and 11 May (mean 21 April). Nest building commenced on average 10-15 days before the first egg was laid, but overlapped partially with egg laying. Median dates of onset of laying in different years varied between 7 April and 26 April. Within a season laying was strongly synchronised as over 90% of birds commenced laying within ten days from the onset of the season. Early laying was correlated with high air temperatures. There were no differences in laying date between habitats. Females breeding for the first time on average laid two days later than in their following seasons. Otherwise, laying dates of individual females were repeatable between seasons. It is argued that the early and synchronised breeding of Marsh Tit is not so much an adaptation to the breeding season conditions but to a large extent a consequence of intra-specific competition among young birds for a chance to settle, with early fledged birds having strong competitive advantage

Wesolowski T., ARDEA 86 (1): 89-100