Activity of Leisler's bat Nyctalus leisleri (Kuhl) in the field in south-east County Wexford, as revealed by a bat detector

Foraging calls of Leisler's bat Nyctalus leisler were monitored, for sample periods of 15 min, on eighteen nights from May to September at eighteen si tes. Bats were recorded at all habitats, including canal, estuary/open wate r, roadside, street lights, orchard, mature trees, pasture, farmyard, railw ay embankment and stream. There was little indication of habitat preference , but street lights were used relatively often. Activity was most intense i n the first third of the night, when airborne insects are most abundant, an d was then independent of temperature. Thereafter activity was correlated w ith air temperature, particularly in the last third of the night, when elev ated temperatures intensify a secondary peak in abundance of flying insects before dawn. A peak in activity was recorded on one night during lactation and on another night shortly after the young flew. There was a fall in act ivity in September. No Leisler's bats were detected over winter in early ni ght monitoring at sites that had been most used in summer, possibly because the winters are mild in the study area and the bats migrate inland.