Bats have suffered a serious decline in the UK for three main reasons.
Firstly, because of the loss of roosts, since modern houses have fewer crevices in which they can hibernate; secondly since the wood preservatives often used there are toxic to bats, and thirdly since the bats resident in the UK feed on moths, beetles and other insects that are now less frequent. Of particular significance is the loss of our tall hedgerows supporting large numbers of insects and along which bats forage. It is therefore important to retain these ancient hedges to help safeguard our bats.
Bats use ultrasonics to locate their prey and to navigate at night, although they have excellent vision. It is possible to identify bats by the frequency of this call, which is normally beyond the range of human hearing. Modern techniques for reducing the frequency to bring it within the audible range include the heterodyne detector and the frequency division detector. Using the latter device it is possible to record the signal and play it back through a computer for the analysis of the frequency spectrum. From the shape and peak of this spectrum, the species of bat can be identified with reasonable certainty.
Of the 16 species of bat commonly found in the UK, two of these, the Lesser- and Greater-Horseshoe bats are particularly threatened, and South West England is the last stronghold of these species. The Horseshoe bats differ from others in the UK by emitting the call through their noses, which have a horseshoe-like shape, while all others emit the call from their mouths.
Probably the most frequent of the bats – the Common Pipistrelle – can still be seen flying around our houses. It is only in the last few years that work at Bristol University has shown that this was being confused with another species that is also quite frequent – the Soprano-Pipistrelle, which is almost identical in appearance, but distinguished on the basis of its ultrasonic call. The Soprano Pipistrelle, as its name implies, has a higher pitched call, and DNA sequencing has now confirmed the distinction of these bats.
As well as the Pipistrelles and Horseshoe bats, Noctule, Serotine and Daubenton’s (the water bat) occur quite often in North Somerset. There is a large colony of Lesser Horseshoe bats at Tyntesfield (National Trust) and special walks are arranged there to allow visitors to watch them emerge from their roost. Other colonies may be found at Brockley, at Chelvey, and at Barrow Hospital where they roost in the underground heating ducts.
To hear the call of the Pipistrelle bats, click here
This recording was made using the Batbox Duet Ultrasound Detector and a Sony MD Recorder. About a quarter of the way through, there is the much slower and lower pitched call of a Noctule bat. It is possible to hear the Pipistrelle feeding buzz on several occasions.
If you have a colony of bats, the North Somerset Wildlife Wardens will be interested to identify and monitor these. Please remember that all bats are now protected species and that it is against the law to disturb or handle them.