Effects of Sparrowhawk Accipiter nisus predation on forest birds in southern Finland

Abstract

Predation patterns of the Sparrowhawk Accipiter nisus and the vulnerability of the prey species were studied at territorial and local population levels, on the basis of four data sets of breeding bird censuses and prey remnant samples collected near nests. The magnitude of predation pressure on breeding populations of prey species was esti- mated. During the breeding season, of the various avian prey individuals (n = 1674 ; 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%), Phyllo- scopus trochilus (7 .8%), Passer domesticus (7 .2%), Erithacus rubecula (6 .9%), Anthus trivialis (5 .4%), and 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 vulnerable to Sparrowhawk predation than expected on the basis of their numbers in the environment, in one or more of the data sets studied, while seven species were, in general, more vulnerable than expected . Low vulnerabil- ity values were showed especially by Ph . trochilus, Regulus regulus, Sylvia borin, T. merula, Ph . sibilatrix, and S. communis . Especially vulnerable species seemed to be P. caeruleus, P. major, F. hypoleuca, Carduelis chloris and T. philomelos . Predation on adult birds during the three months of the breeding season was about 5-6% .