Activity patterns of the soprano pipistrelle Pipistrellus pygmaeus throughout the year in southern Norway

Abstract

Background: Most temperate bats are regular hibernators in the winter. Knowledge about the length of their active season and how they adjust their nightly activity throughout the season, is critical to conservation. The characteristics of these are likely to vary with climate as well as latitude. This study investigated the flight activity of the soprano pipistrelle Pipistrellus pygmaeus in Frafjord, a small valley in the south-western corner of Norway (58° 50′N 6° 18′E) with an oceanic climate. Results: Activity was recorded with an ultrasound recorder throughout April 2018 to June 2019 at one site, with supplemental recordings in March to June 2020, i.e., covering all months of the year. Recordings at other nearby sites were made in the summers (June–August) of 2016, 2017, 2019 and 2020, as well as some of the last days in December 2019 to the first days of January 2020. Overall, soprano pipistrelles were recorded flying in all months of the year, but very few in December–March. Regular activity was recorded from late April or early May until late October, and some recordings were also made in November. The highest numbers of recordings were made in August and September. Social calls, i.e. male song flights, were recorded from April to November, with the vast majority in August and September. Nearly all recordings were made between sunset and sunrise. Conclusions: The soprano pipistrelle in this region showed regular activity through 6–7 months of the year. It adjusted its activity to the changing night length throughout the year, closely following sunset and sunrise. It was rarely recorded flying before sunset and almost never after sunrise. Most activity was recorded in the middle of the night, and social calls also followed this trend closely. Harems in late summer and autumn were confirmed in a bat box, which was also used for winter hibernation.