Start of egg-laying in relation to latitude and elevation among Swedish Starlings Sturnus vulgaris in 1988—2003

Abstract

The Starlings Sturnus vulgaris breeding in sixteen nestbox groups, three in northern and thirteen in southern Sweden, were monitored in 1988—2003. Date of the first egg was found to correlate with both latitude and elevation when all sites were included (13 degrees of latitude; 5–430 m elevation). Restricting the analysis to only the south Swedish sites (4 degrees of latitude; 5–230 m elevation), only elevation had any effect. The absence of an effect of latitude in southern Sweden is interpreted as an effect of the large-scale Atlantic low-pressure systems that rapidly pass Sweden and bring mild spring weather to that whole area almost simultaneously, making local climate as determined by elevation more important than effects of latitude. Onset of laying at the sites in northern Sweden did not differ with more than two days in spite of one site being at the coast and the other two in mountain valleys at 380 and 430 m, possibly because the western birds winter at the Norwegian coast only c. 70 km away.