Breeding success and laying date of NuthatchesSitta europaeain relation to habitat, weather and breeding density

Abstract

The paper describes an analysis of 409 breeding records of Nuthatches Sitta europaea from nestboxes in 13 study areas in West Germany over 16 years. We found one true second brood and eight replacement broods. Mean date of first egg was 19 April, mean clutch size 6.49 eggs and mean number of fledglings per clutch 5.14. Seventy-six per cent of all clutches produced fledglings. We found habitat effects on laying date and clutch size but not number of fledglings, and the patterns were not consistent with literature data on habitat-related breeding success and habitat selection. Clutch size decreased with laying date but only in early clutches. In heterogeneous habitats older birds bred earlier than young birds, which suggests a relationship with territory quality. All aspects of breeding success and laying date varied between years. Breeding success was higher if rainfall in March was high and population density low. The latter relationship may be indicative of density-related variation in territory quality.