Читать книгу Extreme Nature - Mark Carwardine - Страница 41

NAME	greater horseshoe bat Rhinolophus ferrumequinum
LOCATION	Europe and Morocco east to Afghanistan and Japan
ABILITY	tracking and catching insects at speed in total darkness

© David Hosking/FLPA

To hunt and orient oneself in the dark requires an extreme sense. Bats do it by ‘seeing’ with echolocation. They emit high-frequency (ultrasound) pulses from their mouths or noses and analyse the returning echoes to determine the size, shape, texture, location and movements of the smallest of objects. A bat’s nose structure helps focus the sound, and its complex ear folds catch the returning echoes. Echoes from above hit the folds at different points to those from below. And by moving its ears, a bat can hear sound bouncing back from different angles.

The noise is so intense that, to avoid going deaf, most bats ‘shut off’ the sound in their ears as they signal. A bat may ‘shout’ – at 110 decibels, in the case of the little brown bat, which hunts in open spaces; or it may ‘whisper’ at 60 decibels, in the case of the northern long-eared bat, which catches insects around vegetation. Bats using lower frequencies (longer wavelengths), such as the greater horseshoe, tend to glean insects off vegetation or hunt large ones; those using higher frequencies (shorter wavelengths) generally catch flying insects at closer range.

While it is difficult to be certain that the greater horseshoe bat has better hearing than other bats, its echolocation system is one of the few studied in detail and it is undoubtedly impressive. But many other bats have incredibly keen hearing, too, and it is possible that the real record-holder has yet to be discovered.