Siberian Flying Squirrel

Description: A small to medium-sized glider, its winter fur is darker than drab grey, a shade more intense than light mouse-grey. Its tail is brownish-grey on the middle and pale straw-coloured on the edges. Its tail underneath is an intense black-grey with lightly coloured greyish patterns.

The fur on its back in summer is of a tint between drab and mouse-grey.

Distribution: Includes Finland, Estonia, Latvia, Belarus, Russia, Siberia, southward nearly to Germany, eastward into Scandinavia, and to northern China including Xinjiang (Altai) in the north-west and Heilongjiang and Jilin in the northeast, and Korea and Hokkaido Island, Japan.

In Finland it is found in mixed forest, especially spruce forest dominated by mature birches and conifers; in China it is found in subalpine coniferous forest; while in Korea it occurs in the extreme northeast boreal forests as well as southward along the Tae-bak Mountain range.

Reproduction: The mating season ranges from late February to June. The male follows the female calling with a low ‘juk, juk, juk’ that sounds like an insect. Males may also fight over females in oestrous.

After mating, the female nests, giving birth alone in a tree cavity or nest box to between two and six young (average three). The young become independent by mid-June to early July and a second litter is born in late July to mid August.

Diet: Eats buds, shoots, leaves, seeds, nuts, berries and occasionally bird nestlings and eggs. During winter it feeds mainly on catkins of Alder and Birch, caching the catkins in nest holes (sometimes of up to 5 litres capacity) and on branches of old spruces. Its summer diet includes mainly leaves of deciduous trees, especially Alnus.

In Finland it feeds on the seeds of Birch, Aspen, Alder, Norway Spruce (Picea abies) and Scots Pine. In summer, it eats the leaves of deciduous trees. In Japan, during spring and early summer, it feeds on the young shoots of willows, birches, black alders and Japanese elms, and in late summer and autumn on birch, black alder, maple, and mizunara oak seeds.

It does not store food or hibernate, but feeds instead on the seeds in autumn to store fat and increase its weight by 15–20 per cent.

Ecology: Nests in cavities, in abandoned woodpeckers’ holes or in nest boxes, lining its nest with wild ivy and vine bark (which is torn into strips), moss from old birds’ nests and animal hairs. From May to October it starts its daily activities approximately 15 minutes after sunset and ends them 20 minutes before sunrise, during which approximately 75 per cent of the time is spent feeding.

During winter its hours of peak activity become extremely short, often less than an hour. The average home range of animals studied in Finland was 60 hectares for males and 8 hectares for females.

Predators include Blakiston’s fish owl (Ketupa blackistoni), the Ural Owl (Strix uralensis), the European Sparrow Hawk (Accipiter nisus), the Black Hawk (Buteogallus anthracinus), Sable (Mustela sibirica) and Domestic Cat (Felis catus). The longevity of the Siberian Flying Squirrel has been recorded to be 4–5 years in captivity, but rarely over three in the wild.

Status: Least Concern. It is listed as Rare in Estonia, Vulnerable in Finland and Endangered in Korea.