Bats are our mystery mammals. Their black silhouettes flickering across a sunset are familiar enough to anyone living in the countryside, but naming the species is a trick beyond most of us. Not only are they difficult to identify but we still know remarkably little about their lives: where they breed, where they roost, even where they hibernate.
There are 951 species of bats in the world, making up a quarter of all mammal species. Just 32 occur in Europe and half of that number in Britain.
An indication of how much we still have to learn about bats was the discovery just a few years ago of a new species of pipistrelle in Britain. The pipistrelle is our smallest and most widespread bat and it was studies of the frequency of its echolocation calls that revealed the existence of a second species. The common pipistrelle echolocates on a frequency of 45khz but the newly discovered species, the soprano pipestrelle, does so at 55khz.
Echolocation is the technique bats use to locate their prey. The high-frequency calls bounce off the quarry, enabling the bat to home in and capture it either with its mouth or in its wing membranes which it uses as a scoop. A single pipistrelle eats around 3,000 insects a night.
Sadly, bat numbers have fallen sharply in Britain in the last 30 years. There are many reasons but the most important is agricultural changes which mean far fewer insects for the bats to feed on. Loss of roosting and breeding sites has also played a part, which is where we can help by providing bat boxes.