The common and soprano are almost identical in appearance, but the soprano is slightly smaller. The most reliable way to distinguish the species is by the frequency of their echolocation calls. Echolocation (a biological sonar) is the way these bats locate their prey and avoid flying into obstacles.

If you have a tuneable (Heterodyne) bat detector the best tuning for common pipistrelle is around 45 kHz while soprano pipistrelle is higher at around 55 kHz. Both sound like rhythmic wet slaps. Click on the audio play button to hear a sample.

We can also make a sonogram of what the call looks like over time; the figure shows the typical common pipistrelle pattern of signals. The red spots fall close to the 45 kHz and the spacing matches the regularity of the ‘wet slaps’ in the audio clip.

These bats are small: the common pipistrelle’s wingspan is normally around 20cm and it weighs no more than a pound coin.

Common pipistrelles can fly fast as they chase their insect prey, up to seven metres per second! They hunt a wide range of small insects: mainly flies but lacewings, mayflies, midges and mosquitoes are also taken.

Like all bats in the UK pipistrelles are nocturnal and hibernate over the coldest winter months. Around October, common pipistrelles become less active and by December will have entered full hibernation. The bats normally hibernate in buildings, taking advantage of the warmth and shelter provided. As the weather begins to warm up in March, the bats start emerging, usually becoming fully active by May.

Common pipistrelles normally mate in late summer/early autumn, but the females will not give birth until the following summer. After mating, the sperm doesn’t fertilise the female’s egg until the following spring. This is called ‘delayed implantation’. Pregnancy lasts about eight weeks. When ready to give birth, females gather in large maternity roosts. Typically, they have one young, known as a pup, which is able to fly at around three weeks old and become fully independent two to three weeks later. Male bats usually roost singly or in small groups through the summer months.

Trees and woodland are important habitat features for common pipistrelles. Trees close to roosts provide cover as bats emerge. When foraging, they tend to follow woodland edges to aid navigation.

The fact that common pipistrelle normally roost and hibernate in buildings means this is one of the bat species you are most likely to spot. Take a walk at dusk on a summer evening and there is a good chance you will actually see these bats flying about, especially if you are close to water as this is where the bat’s insect prey is most abundant. They fly from tree top height often down to just above our head height or lower with lots of twists and turns.

For more information on pipistrelle species and other bats check out the Bat Conservation Trust website .