Bats are the only true flying mammals. In Britain they are insectivorous (eat insects), and contrary to popular misconception they are not blind; many can actually see very well (6). All British bats use 'echolocation' to orient themselves at night. Bats emit bursts of sound that are of such high frequencies they are beyond the human range of hearing, and are therefore called 'ultrasound' (7). They then listen to and interpret the echoes bounced back from objects, including prey, around them, allowing them to build up a 'sound-picture' of their surroundings (7). The serotine bat emits echolocation calls in the range of 15 to 65 kHz, but most calls are at 25 to 30 kHz (5). It emerges at early dusk (2), often when it still fairly light (5), and hunts mainly for beetles such as chafers and dung beetles as well as flies and moths (5).
The mating season starts in August, but its duration is unknown (2); very little is known of the mating behaviour of the serotine bat (5). Fertilisation is delayed; the females store sperm internally throughout the winter hibernation until spring (6). Maternity colonies, usually consisting of 10 to 50 females (6) begin to form in May (5). A single young is produced, usually in early July, and if the colony is disturbed during its first few days of life, the mother may carry it to a new site (5). By the third week of life the young bat is able to fly, and at around five weeks it is able to forage independently (2). During the summer, males are solitary or occur in small groups (5), but they occur with females in spring and autumn (6). This species hibernates between October and late March or April (2). Serotine bats can live up to 19 years of age (2).