Bats are a much maligned group of mammals, thanks to a legacy of tales of their sinister associations. They do not entangle themselves in one's hair, and their representatives in our islands do not suck human blood. True, they do haunt dark caves, mine adits and ruined edifices and descend from holes in trees at the coming of darkness. They do sometimes cause consternation among churchwardens who do not realise the great horticultural virtues of bat guano, but they do not choose belfries in preference to quieter roof spaces. In Britain they do not harbour rabies or histoplasmosis, but they do help to reduce the numbers of noxious insects.
World-wide there are reckoned to be 977 species of bat, but in Britain we see only 15. Those commonly encountered in our daily wanderings are the small pipistrelles, which emerge after dark from roosts in buildings and flitter about in random fashion near the ground, and the larger noctules, which emerge before darkness falls and make long swoops high in the air, both seeking insects. Their social behaviour is not well understood, because of their crepuscular habit. In their roosts large numbers may cluster in hierarchical order. In winter repose a bat's body temperature may fall from 40C to 9C and its heart rate from 800 to four per minute. Its heart may stop for 30 minutes and its breathing for two hours without ill-effect.
The best known feature of the bat is its echolocation system, which operates at a frequency of 30,000-70,000Hz. Some people can hear the squeak, particularly of the noctule, but the quality of the sounds emitted can only be appreciated with the help of a frequency transformer which reduces the pitch to the range of the human ear and allows us to follow different hunting calls, a fascinating recreation for the wildlife enthusiast.
Unfortunately, the population of bats has decreased greatly over recent years, and the Bat Conservation Trust is monitoring eight threatened species. The reduction in numbers is attributed to loss of roosting spaces in trees, ivy-covered walls, caves, mine adits and ruined buildings, to a food supply reduced by farming methods involving pesticide sprays, and to aggressive chemical treatment of wood in modern buildings. Antipathy towards what are classified as endangered species also plays a part, since many people have a horror of bats which is quite unjustified and perpetuated by tradition. I must admit that I eagerly await the evenings when I encounter the dignified swoop of the noctules high in the sky, and the twittering flight of the pipistrelles under the trees and over the stretches of water where most of their food becomes concentrated.