Findings from a long-term study of the breeding biology of a Scandinavian population of the Great Tit Parus major

Abstract

In the surroundings of the small community of Råda, Sweden (60°00'N, 13°36'E) approximately 350 nest boxes were checked annually during 20 years (1985–2004) with more or less daily visits during the breeding season. Data for 950 original clutches, 125 replacement clutches and 77 second clutches of Great Tit producing at least one fledgling were recorded. The mean date of laying the first egg was 10 May without any trend in spite of increasing trend of spring temperature. However, annual date of laying was correlated with April spring temperature (at least one degree warmer than average advanced laying with at least two days). The mean size of all first clutches was 8.74 eggs, which is less than shown by other long-term studies from the Nordic area. The number of eggs laid by young females was the same as for other females, a result that differs from other studies. In the studied area the ratio of second clutches in relation to the number of original clutches was 0–16.7% (average 8%), which is far less than normally reported.