Bioacoustics of Eptesicus (Cnephaeus) nilssonii

Movements, Home range and Social organization. In winter, the Northern Serotine tends to move toward its hibernation sites. During hibernation, only single individuals have been found. Although it shifts roosts quite often between seasons, these movements are rather short, and maximum migratory distance is ¢. 450 km in Europe. A few banded and recaptured individuals suggest that it might be a short-distance migratory species, only occasionally flying long distances. During the breeding season, females form maternity colonies. Maternity colonies can contain tens to hundreds of individuals (very large colonies have been reported in Japan ). Single individuals, males, or non-reproductive females can be found roosting in a wide variety of different roosts. Males commonly roost alone year-round, rarely in small groups. Northern Serotines can fly up to 70 km each night to reach foraging areas, but they typically commute only 1-10 km, using up to eight different sites. Foraging areas range from 0-2 km? in summer to 66 km ? during swarming and are strongly affected by length of the night (0-91-17-2 km?). Females often establish small feeding territories (c. 100 m ?) with abundant insects, where they return every night, sometimes for subsequent years. Feeding territories of males and females are vigorously defended against intruders, involving aerial chases and audible vocalizations with maximum amplitudes of 14 kHz. These same territorial behaviors have been observed outside of hibernacula in autumn, suggesting that roosts are also defended. Foraging localities and activity peaks might be partially affected by competition with other bat species that forage in open spaces but do not forage at the same time, e.g. Eurasian Particolored Bats ( Vespertilio murinus ), Common Noctules ( Nyctalus noctula ), and Eurasian Serotines. Species that used narrow spaces foraged simultaneously with Northern Serotines (e.g. Daubenton’s Myotis , Myotis daubentonii ). Population density decreases at higherlatitudes, with densities at 57° N being five times higher than in similar landscapes at 65° N .

Activity patterns. Nightly activity of the Northern Serotine is generally bimodal, with two activity peaks after sunset and around dawn. Pregnant females usually have unimodal or bimodal activity pattern, with peaks always after dusk and sometimes before dusk; non-pregnant females forage intermittently throughout the night. Reproducing females at 57° N left the roost 47 minutes after sunset and spent an average of three hours outside the maternity roost each night. During pregnancy, however, ¢.20% of their time outside the maternity colony was spent roosting in trees, foraging for an average of 150 minutes each night. Lactating females foraged an average of 120-130 minutes/night just after giving birth, 220-260 minutes/night in mid-lactation, and 320 minutes/night at peak lactation, reflecting energetic costs of lactation. Female Northern Serotines tend to emerge increasingly later as pregnancy advances. Due to the cold climate in its distribution, swarming period occurs from mid-July into late autumn. Hibernation tends to occur from November or December until March or April. Northern Serotines typically choose hibernacula that have ambient temperatures of 0-2°C but will occasionally use roosts that get as cold as =5°C, roosting in houses, cellars, and sometimes caves and mines. Maternity colonies in summer are commonly located in buildings but sometimes in hollow trees. In most ofits distribution, nursery colonies are found in roofs of houses, walls, or empty large cavities below metal sheets. Search calls of the Northern Serotine are not well differentiated from the Eurasian Serotine and have broad overlap with some species of Nyctalus . Pulses are up to 20 milliseconds long and typically shaped as an FM/QCF sweep. Peak frequencies are usually 26-32 kHz. On Hokkaido , Japan , start frequencies were 51-8-64-7 kHz, end frequencies were 24-3-27.7 kHz, peak frequencies were 28-3-31-6 kHz, durations were 4-4-8 milliseconds, and interpulse intervals were 95-185 milliseconds. Swedish recordings had an average peak frequency of 32-4 kHz, end frequency of 30-4 kHz, duration of 7 milliseconds, and interpulse interval of 100 milliseconds. Social calls seem to be quite distinct, consisting of long QCF sweep, with duration of up to 60 milliseconds and powerful second and third harmonics.

Food and Feeding. The Northern Serotine forages along vegetation edges, forest edges or hedgerows in natural landscapes and around streetlamps in urbanized areas. It is adapted to hunt insects at just above freezing temperatures. It has been reported feeding primarily on small Diptera (specifically Nematocera), but it also captures Coleoptera , Lepidoptera , and Heteroptera in smaller quantities. It generally hunts by aerial-hawking, capturing prey in flight at heights of 2-20 m rather than capturing them on vegetation or the ground. Nevertheless, because it is not clutter specialist,it is capable of visually detecting and recognizing large (greater than 50 mm ) and brightly colored insects on the ground and capturing them using visual and acoustic senses. In someareas, it tends to select areas with streetlamps. In localities close to the ocean, Northern Serotines and Eurasian Serotines ( E. serotinus ) have been observed foraging over the ocean where insects are abundant.