Often the only accurate method to identify bat species is through their complex echolocation calls. Bats use high frequency calls normally beyond the range of human hearing to build up a sound picture of their surroundings. This echolocation system enables them to navigate at night and locate and capture their often tiny insect prey. The use of a bat detector and appropriate sound recording equipment transforms these calls making them audible to humans.
For example the recording above is of several soprano pipistrelles foraging within an old barn in the Scottish Borders. The recording was made using a Batbox Duet which divides the incoming frequency by 10. Therefore, the soprano pipistrelles, which typically echolocate around 55 kHz, (well beyond the upper limit of 20 kHz for humans) is transformed to 5.5 kHz which is clearly audible. If you listen carefully you should also be able to hear a number of different call types including:
A video of Soprano Pipistrelles emerging from a large maternity roost is also available in the video gallery.