Bioacoustics of Pipistrellus kuhlii

Activity patterns. Flight of Kuhl’s Pipistrelle is slow, erratic, unpredictable but rather agile, and relatively maneuverable in cluttered spaces. Commuting flightis significant ly faster than foraging flight (9-3 m/s vs. 4-7 m/s). In cities, Kuhl’s Pipistrelle emerges quite early (although later than the Common Pipistrelle), a little before sunset, and can be observed foraging around streetlamps or following linear structures, alone or in groups. It has bimodal activity, with an activity peak during the first hours after sunset and a second activity peak before dawn. Although not many data are available during hibernation, they have been found hibernating in rock crevices, expansion joints, cellars, bridges, and buildings in the Balkans. Hibernation in some Mediterranean countries is commonly interrupted because they tend to forage during mild winter days. In some cases, they use the same roosts all year. Echolocation calls have typical pipistrelle-like pulses, with peak frequencies of c.34—41 kHz, sometimes overlapping with Savi’s Pipistrelle in the lowest frequencies and the Common Pipistrelle in the highest. Shape and frequency of calls are highly variable depending on environment, behavior, and weather conditions. Pulses are relatively long and can reach durations of up to 14 milliseconds. During acoustic surveys, Kuhl’s Pipistrelle can only be separated from Nathusius’s Pipistrelle using its social calls, which consist of two distinct quick FM pulses of c.14-16 kHz, but even this is sometimes problematic.

Breeding. Maternity colonies of Kuhl’s Pipistrelles can have tens to several hundred individuals (rarely exceed 200 individuals), almost all of them adult females and their young. These colonies are usually found in crevices or large empty cavities in buildings, bat boxes or hollow trees, andcliffs. In urban areas, nursery colonies are commonly found in window blinds, roll-down shutter boxes or roofing tiles, often causing some disturbances to the buildings’ owners due to strong smell and noise. Adult females start to congregate in mid-March, and they remain together until late August. They give birth, mostly to twins, from mid-June to July. Young females become reproductively active the first autumn of their life. During the mating period, a kind of swarming behavior occurs, and males try to attract females by displaying with flight displays or social calls from August to early November. Maximum longevity is less than eight years.