Geographic variation in breeding parameters of the Pied Flycatcher Ficedula hypoleuca

Variation in laying date, clutch-size and number of fledglings of the Pied Flycatcher Ficedula hypoleuca was studied in relation to altitude, habitat and latitude, using data from 99 breeding areas from 35 degrees N to 70 degrees N. Laying date significantly increased with altitude and showed a significant quadratic relationship with latitude, with the earliest values at about 50 degrees N. This quadratic relationship shows the same pattern as the relationship between arrival time of adults on the breeding areas and latitude. Clutch-size variation was significantly related to altitude and habitat, small clutches being laid at high altitude and in coniferous forests. Number of fledglings was significantly affected by habitat type, with lower values in the coniferous than in the deciduous forest. Mean clutch-size and mean number of fledglings showed the same quadratic relationship with latitude. In contrast to some earlier studies, an increased clutch-size with latitude was found, mainly because of new data from areas in the southern part of the species' distribution.