Distribution of the Siberian flying squirrel (<i>Pteromys volans</i> L.) in taiga isthmuses between Baltic and White Sea regions

We focused our attention on three narrow isthmuses between the White and the Baltic Seas, which form important connections for the elements of northern taiga ecosystems, such as the Siberian flying squirrel. The method that we employed is based on the search of flying squirrel’s excrements on randomly selected 9 ha plots (more than 11700 plots studied in Russia and in Finland). Relative abundances of the flying squirrel in Russian Karelia and the Karelian Isthmus seem to be slightly higher than in Finland. The border of the flying squirrel’s range in the North-West could be delineated from the national park Kalevalski, across the Segezha region to the southern part of the White Sea, and further to the east. We suppose that the connection between flying squirrel populations of Scandinavia and Russia is mainly implemented through a narrow ‘middle-taiga corridor’, i.e. the isthmus between Ladoga and Onega Lakes, and only partly by the isthmus between Lake Onega and the White Sea.