Northern Serotine

The northern serotine is a compact dark vesper bat, formerly named Eptesicus nilssonii. Adults measure about 54–64mm, with a 37–44mm forearm and 240–280mm wingspan. The upper fur is very dark brown to nearly black, often frosted with yellow-gold on the back and neck; the face, ears, and wings are dark, while the underside is beige to warm yellowish brown, creating a subtle contrast. (BatMonitoring species account)

This is the most northerly breeding bat, with a broad Palearctic range from Europe across northern and central Asia to Hokkaido; the Mammal Diversity Database explicitly includes Mongolia. It forages in forested and human-modified landscapes and frequently uses buildings as roosts in parts of its range. Its ability to breed north of the Arctic Circle separates its climatic range from most bats, though no Mongolian viewing site was supported. (BatMonitoring; Mammal Diversity Database)