The effect of pasture on starling (Sturnus vulgaris) breeding success and population density in a heterogenous agricultrual landscape in Southern Sweden

Abstract:
Populations of European starlings have declined over large parts of northern and western Europe during the last 20 years. It has been suggested that reduced availability of pasture in the agricultural landscape was one reason for this decline. To investigate this, breeding colonies for starlings were established in southern Sweden, in agricultural landscapes with different availabilities of pasture. Agricultural land-use was classified in a circular area of 500 m around each colony. Production of young per nest was positively related to the availability of pasture close to the breeding colony, not because the availability of pasture affected clutch size or hatchability of eggs, but because nestling survival was higher in colonies surrounded by pasture. The growth rate of an offspring feather character, but not offspring final mass or tarsus length, tended to be related to the availability of pasture. When availability of pasture was low, the variability of breeding success between years was high. Breeding density was also positively related to the availability of pasture near colonies. The combined trends in reproductive success and breeding density in this study support the contention that the reduction of pasture in modern agricultural landscape may be one reason why starling population size has declined.