About Eptesicus nilssonii (Keyserling & Blasius, 1839)
Eptesicus nilssonii, commonly called the northern bat, has dark brown or black base fur, with gold-tipped hairs on its head and back. Its nose, ears, tail, and wings are black or blackish brown, while the fur on its underside is yellowish brown. This species has short, rounded ears. Body length ranges from 54 to 64 mm (2.1 to 2.5 in), wingspan from 240 to 280 mm (9.4 to 11.0 in), and body mass from 8 to 16 g (0.28 to 0.56 oz), with weight varying by season. The northern bat is widespread across Eurasia, and it is the most common bat species in the northern part of the continent. Its range extends from northern Scandinavia, beyond the Arctic Circle, south to northern Italy, and from eastern England east to northern Japan. It prefers forest upland habitats located between 200 and 2,000 m (660 and 6,560 ft) in elevation. Northern bat colonies can move distances of up to 450 km (280 mi) over multiple years. Breeding takes place in late autumn; after mating, female northern bats store male sperm through the winter. Hibernation runs from November or December to April. Females become pregnant in spring and give birth 50 to 60 days after conception. In summer, males live alone. In early summer, females form colonies of 10 to 80 adult individuals; these colonies disband in August, once young bats are capable of flight. During winter, the species forms colonies most often in houses, and in either natural or artificial underground habitats.
