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Pipistrellus pipistrellus emerge from their nursery roosts in north-east Scotland about 35 minutes after sunset, at light intensities of between 15 and 35 lux. Cloud cover, windspeed, ambient temperature, rain, light mist and moonlight have no apparent effect on the time or pattern of emergence. Throughout pregnancy and lactation, emergence lasts for about an hour. After weaning, when the adult females have left the roost, their young take about 40 minutes to emerge. The average rate of initial emergence is proportional to colony size, and the maximum rate of emergence occurs half way through the exodus.

During pregnancy in May and June most bats leave the roost once each night soon after dusk and return between midnight and dawn. After parturition in late June the activity pattern becomes bimodal and the numbers of bats outside the roost show peaks after dusk and immediately before dawn. There is intermittent activity in the vicinity of the roost all night and bats make two or three flights each night. After weaning in August the activity pattern gradually ceases to be bimodal, and the number of flights per bat falls to between one and two. The average time spent outside the roost varies between 2–5 and 5 hours during the summer. The recorded activity patterns of night-flying insects are all bimodal, with peaks after dusk and before dawn, corresponding with the maximum number of bats outside the roost during lactation.