EFFECT OF SPARROWHAWK-ACCIPITER NISUS PREDATION ON FOREST BIRDS IN SOUTHERN FINLAND

Predation patterns of the Sparrowhawk Accipiter nisus and the vulnerab ility of the prey species were studied at territorial and local popula tion levels, on the basis of four data sets of breeding bird censuses and prey remnant samples collected near nests. The magnitude of predat ion pressure on breeding populations of prey species was estimated. Du ring the breeding season, of the various avian prey individuals (n = 1 674; 62 species), 17.2% were derived from habitats other than forest. The most important prey species by number included Fringilla coelebs (17.1%), Parus major (10.7%), Phylloscopus trochilus (7.8%), Passer do mesticus (7.2%), Erithacus rubecula (6.9%), Anthus trivialis (5.4%), a nd Turdus philomelos (5.4%). The prey samples mainly included species and individuals weighing 15-30 g. The mean weight of prey was 26.6 g ( n = 1 666). The most important prey species by weight were F. coelebs (13.4%), T. philomelos (13.4%), P. domesticus (8.2%), P. major (7.3%), and T. pilaris (6.6%). Fifteen species were significantly less vulner able to Sparrowhawk predation than expected on the basis of their numb ers in the environment, in one or more of the data sets studied, while seven species were, in general, more vulnerable than expected. Low vu lnerability values were showed especially by Ph. trochilus, Regulus re gulus, Sylvia borin, T. merula, Ph. sibilatrix, and S. communis. Espec ially vulnerable species seemed to be P. caeruleus, P. major, F. hypol euca, Carduelis chloris and T. philomelos. Predation on adult birds du ring the three months of the breeding season was about 5-6%.