Clutch size, nestling growth and nestling mortality of the Starling Sturnus vulgaris in south Finnish agroenvironments

Abstrakti

The breeding success of Starlings Sturnus vulgaris was studied in six nest-box colonies in habitats varying from mixed farming to intensive cereal and root crop cultivation . In the colonies studied, only a few Starling eggs failed to hatch and a small number were lost through desertion or predation. In the areas of specialized cultivation, however, only 20-30% of the hatched eggs produced fledglings, whereas in mixed farming areas the proportion was 70-90% . The nestling weights were lower and within-brood weight differences larger in specialized than in mixed farming areas. In the areas of cereal and root crop monoculture, many nests were fouled and suffered from heavy mortality because of wet nestling faeces . Nestling mortality was high when the mean weights were low and between-sibling weight differences large. The starvation of chicks and fouling of nests suggest that the amount of food available is smaller and its quality poorer in monoculture than mixed farming areas. It is suggested that changes in farming at least partially explain the recent decrease of the Finnish Starling population. In southern Finland, farmers have largely specialized in cereal and root crop production, so that the number of cattle and extent of pastures have greatly decreased and mixed farming has become rare over large regions.