Well let’s start with what .gov has to say about it:
Survey methods
You can use any of the following methods to survey bats:
- visually inspect buildings or other structures
- inspect trees
- use bat detectors
(Bats: surveys and mitigation for development projects, 2021)
A Bat detector? Like a light you shine up to the sky with a bat symbol or something?
Almost, but with soundwaves instead of lightwaves. You can listen to bats echolocation with a basic Heterodyne detector like the Magenta 5, at an ideal beginners price of £96.
HETERODYNE BAT DETECTORS
Heterodyne bat detectors are tuneable, you select the frequency range to listen to, and bat calls near that frequency are converted to sounds which you can hear.
The bat calls are picked up by an ultrasonic microphone and compared against the frequency you set. A sound is then produced that is the difference between the set frequency, and the part of the bats call close to that frequency.
They produce sounds that are quite melodic and easy to listen to, and you will hear descriptions such as “wet slaps, dry clicks, whipcracks…”. With experience, it is possible to identify some species with heterodyne detectors.
You can use bat detectors if visual inspections suggest bats may be present.
You should:
- survey over several visits at dawn or dusk spread over several weeks between May and September
- only use hand-held detectors between dusk and dawn during the summer for buildings and trees, and during autumn for underground roosts
- survey buildings for up to 2 hours after sunset
- survey during the 90 minutes before sunrise and continue until 15 minutes after sunrise, after bats re-enter their roost
- in autumn, survey starting at sunset and continue for at least 1 1/2 hours to include the times of emerging for all bat species
You can use automated detectors linked to data loggers as well as thermal and infra-red imaging.
(Bats: surveys and mitigation for development projects, 2021)
Does this involve climbing trees?
nope, you should:
- inspect using high-quality binoculars
- use endoscopes to inspect cavities if possible
HOW DO I TELL IF SOMETHING IS THERE?
Bats can utilise many tree features including trunk hollows, knot holes, splits/cracks in branches and sheltered areas created by flaking bark. You may wish to have an initial look for these characteristics to establish a tree’s ‘bat potential’ as features can sometimes be identified from ground level during the day, with the aid of close-focusing binoculars.
OK, I'm ready to do this!
Brilliant! First, have a read of the bat report carried out by one of our volunteers, which you can find here. Then, reach out on the facebook group or email us telling us you are ready to go out and survey! We will link you with other members so you don’t have to go at it alone.