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Recent changes in forest bird populations in northern Finland

Olli Järvinen and Risto A. Väisänen
Annales Zoologici Fennici
Vol. 15, No. 4 (1978), pp. 279-289
Stable URL: http://www.jstor.org/stable/23733659
Page Count: 11
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Recent changes in forest bird populations in northern Finland
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Abstract

Recent decades have witnessed great changes in the densities of land birds in Finland. This study, based on habitat censuses made in northern Finland (Kainuu and Kuusamo) in 1943—1945 and 1970—1973, examines the relative importance of two components of population change: have the populations increased (decreased) within their previous habitats, or has the area of suitable habitats increased (decreased)? The results of the habitat censuses are compared with line transect data collected from northern Finland in 1942—77. Changes in habitat area were probably responsible for population changes in certain species, such as Perisoreus infaustus and Phoenicurus phoenicurus, which have decreased with the clear-cutting of old pine forests. Within-habitat changes were more important in the majority of common species; thus Parus cristatus and P. montanus have decreased and Turdus iliacus, Phylloscopus trochilus and Muscicapa striata have increased. The within-habitat changes are suggested to be linked with changes in forest structure affecting winter resources (Parus spp.) or with habitat expansion resulting from increases in population due to increases in the amount of forest edge, in the bush layer of the forests, and in the extent of trees of young age classes. As shown by a comparison between observations made during an excursion to Kuusamo in 1917 and the density estimates obtained in the line transect censuses in the 1970s, the bird fauna has changed considerably in Kuusamo during this century; population increases are more characteristic than decreases.

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