Northern birch mouse

The northern birch mouse is a small mouse with a relatively long tail. The adult head and body length is 2 to 3 in (51 to 76 mm) with a tail of 3 to 4.25 in (76 to 108 mm). Adults vary in weight between 5 and 13 g (0.2 and 0.5 oz). The upper parts are yellowish-grey with a brown sheen and the underparts are a pale greyish-yellow. A black stripe runs along the spine from the head to the base of the tail. Its voice is a high-pitched whistle.[3]

The northern birch mouse occurs in Scandinavia, Central and Eastern Europe, and Northern Asia. Its main range extends from the Baltic region, Poland and the Czech Republic eastwards as far as Lake Baikal in Siberia, and from the Arctic Circle southwards to the Carpathians. There are isolated populations in Norway and Sweden, Denmark, Germany and Austria.[1] Its natural habitat is coniferous forests, mixed deciduous woodland, marshy woodland and damp bushy grassland and it is sometimes found in cereal crops.[3]

The northern birch mouse is largely herbivorous and feeds on buds, shoots, grass seeds and berries, but it also takes earthworms, insects and snails, often finding these under loose bark. It is a skilful climber and often clambers around in trees and shrubs, gripping the twigs and branches with its five-toed feet and using its prehensile tail for additional support.[3][4]

In the summer, the northern birch mouse makes a nest of dry vegetation in a bush, clump of moss or tussock of grass. Breeding takes place between May and August and a single litter of up to six young is produced after a gestation period of four to five weeks.[3] This mouse hibernates in winter, seeking out a natural crack or the burrow of another animal, in a dry location such as on an embankment or in a bushy place. Other sites chosen can be in a hollow tree, in a tree stump or fallen log, or in a gap under a rock.[4] During the hibernation period, which may last from October to May, the tail is wrapped spirally around the animal's body.[3]

The northern birch mouse has a very large range. In Western Europe it is generally uncommon with isolated sub-populations, but further east it is very common. The population trend is unknown but the IUCN lists the species as being of "Least Concern" as it considers that it is unlikely to be declining at such a rate as to justify including it in a more vulnerable category. No specific threats to this mouse have been identified but agriculture may affect its numbers in Germany, and deforestation may affect it in Romania.[1]

• Forest dormouse
• Balkan mole-rat