On a calm evening stroll, a small figure quietly flutters overhead, weaving erratically through the sky. In the dim light, one can recognise the unmistakable outline of a small bat, but not many details. Although the bat seems quiet, the bat is actually yelling to sense the surrounding habitat and to track flying insects for food; a biological phenomenon called echolocation. Most bats echolocate at frequencies above the range of human hearing. However, we can listen in on the lives of the bats living around us using sonic amplifiers called bat detectors.
People’s hearing reaches about 20 kilohertz (kHz) depending on age and hearing sensitivity. There are many sounds that are higher in pitch than human hearing including some parts of bird songs, crickets, rustling, and the echolocation of bats. Bat detectors “translate” the high frequencies of bat’s echolocation to tones people can hear. The bat detectors tone down everything that it detects (bats, birds, crickets, and background noises), so learning bat calls is needed to decipher which noises are bat noises, the species of bat, and different types of bat calls.
Different bat species make different calls at different frequencies, making some bats easy to differentiate. The Common Pipistrelle bat makes rapid “wet slaps” that are the loudest at 45kHz, whereas the Noctule bat makes long “chip-chop” noises around 20kHz. Bat detectors can help us learn about who our bat neighbours are.
Bat detectors can also reveal what bats are doing as they make different calls for different reasons. More regular evenly spaced calls are typically commuting calls, as they are scanning their environment. More rapid evenly spaced calls, can indicate that the same bat is exploring a more cluttered environment. Commuting calls that become faster and blur into a buzz, typically indicate that the bats are closing in on their flying insect prey; called a feeding buzz.
There are also calls so different from those usual commuting and foraging calls, that you could mistake them for different species, but they are actually social calls, like mating calls in the autumn. A simple bat detector can reveal a new dimension of the natural world!
There are many different kinds of bat detectors that you could buy, but there is no need if you come to an EWG bat walk. Led by one of our trained volunteers, you will be guided into the world of bats, and bat detectors are provided for the event.
Bat walks are seasonal, during their active season until they start hibernating around October. We have two bat walks scheduled in Northala Fields on 19 June at 21:00 and around Hanwell Viaduct and Brent Lodge Park on 11 July at 21:00 when we will also seek out the Edible Dormouse (Glis glis).
Nadya Mirochnitchenko
EWG Ecology Officer
Header photo © Uploads from the Somerset Bat Groups events and members
