The ability of forest reserves to maintain original fauna – why has the Chiffchaff (Phylloscopus collybita abietinus) disappeared from eastern central Finland?

Abstract

We studied the occurrence of Chiffchaff Phylloscopus collybita at the Finnish and Rus-sian border at ca. 65° N. This species shows an interesting distribution in the region, being virtually absent from the Finnish side (Kainuu) but being a common breeder on the Rus-sian side (Viena). However, the species has been equally numerous on both sides of the border. In our study area, the landscape is structurally different on opposite sides of the border: in Russia, there is a continuous "green belt" of old-growth forests, whereas in Fin-land old-growth forests are embedded in a matrix of managed forests. However, fragmen-tation may not solely explain the difference in Chiffchaff abundance, because bird species even more strictly dependent on old-growth forests are either nearly equally or were even more abundant in Finland than in Russia. We suggest that the decline of the Finnish Chiffchaff population is due to multiple reasons, including the northern location. Frag-mentation has probably provided the final push resulting in a crash in the Kainuu Chiffchaff population. This study underlines the need for detailed species-specific autecological knowledge in predicting fragmentation effects. Furthermore, a change in subspecific composition of Finnish and Swedish Chiffchaffs is apparently taking place. The ecologically different yet morphologically similar Ph. c. collybita may replace the na-tive Ph. c. abietinus.