Dynamics of Finnish Starling Sturnus vulgaris populations in recent decades

Abstract

The development of the Finnish Starling Sturnus vulgaris population was studied, using data from 20 local populations and from the national ringing scheme extending from the beginning of the 1960s to the end of the 1980s (data for 7-26 years from each population). According to local studies, the population size started to decrease in the late 1960s, and fell to about 20%by the early 1980s. In the timing ofthe decrease, there were clear regional and local differences. Clutch size varied significantly among local populations (range of the means of annual means in three populations: 4.7-5 .3 eggs ; data from 12-21 years), but there were much greater differences in the number of fledglings (range in the same populations: 2.33-3.99 fledglings, with 3 .52-4.87 for four other populations; data from 5-21 years) . These differences were caused by differences in foraging habitat. According to national ringing data, brood size at the age of ringing increased significantly (by 0.04 nestlings/year) during the period of 1968- 89 . The mean brood size decreased towards the north. This decline seems be due to large-scale abandoning of dairy farming in southern Finland. This has resulted in losses of good foraging habitats (pastures and leys) forthe Starlings, and, as consequence, to reduced reproductive success in the whole south Finnish population . The continuous increase of brood size at the age of ringing reflects the disappearance of Starlings from poor breeding habitats and the strong decrease in northern Finland.