Common pipistrelle

The bat you are most likely to meet, and the best reason to buy a bat detector. Common pipistrelles weigh about 5 grams, roughly a 20p coin, and usually leave their roosts around 20 minutes after sunset to hunt along hedgerows, woodland edges, farmland and suburban yards. Watch a streetlight or the gap between two trees and the darting, jinking flight soon shows. Tune a heterodyne detector to about 45 kHz and the silent hunt becomes a rapid run of clicks that speeds into a buzz as a bat closes on an insect. Their calls can sit anywhere between about 45 and 70 kHz, so sweep the dial if the first setting goes quiet.