Bats use an ultrasound system to locate the source of echoes. Navigating and hunting prey requires very special hearing that is far superior to human sound perception – which is particularly exciting news for audiological researchers.

A bat is about two inches long, but its ears measure an inch-and-a-half; scaled up, that would be like a person having ears more than four-and-a-half feet in length. Bats have the largest ears relative to their body size in the animal kingdom, and though they are almost blind, there are only a few creatures that can hear as well.  

As bats are active during the hours of darkness, we rarely get to see the sophisticated skills with which evolution has endowed them. Their daring aerobatics against the evening sky allow bats to elegantly skirt any obstacle at 30 mph even as they are snapping prey out of the air, never colliding with trees or walls. How on earth do they manage it?

Up to 300 years ago, many people believed that bats were possessed by the devil, and this was the only reason why they could fly at breakneck speed through a pitch-black night without bumping into anything. This theory was refuted by the Italian naturalist Lazzaro Spallanzani, who began to research bats at the end of the 18th century, subjecting them to brutal experimental procedures. He discovered that those he blinded were still able to find their way in the dark, but others, whose ears he had stopped up, lost their orientation and fell to the floor. This proved that the secret to their flying skills had to lie in the bat’s ears. Spallanzani made a note: “Is it possible to see with your ears?” It took almost 200 years to arrive at an answer to this question, however, with researchers discovering the ultrasound cries of almost blind bats only in 1930. “It is a unique, highly complex, and extremely effective system of echolocation,” explains Stefan Launer, Sonova’s resident expert in audiological research and Senior Vice President Audiology & Health Innovation.

The animals can indeed hear high-frequency sounds of up to 200,000 Hz, whereas humans can perceive frequencies only up to 20,000 Hz. Bats make use of this skill when out hunting for prey, emitting sounds in the ultrasound spectrum; their large ears rotate towards the source of the echo and collect the reflected sound like a funnel. The echo allows them to calculate an image of their surroundings and they can catch insects even in the pitch dark: they “see” with their ears. Here it is likely that the animals are helped by the presence of the protein molecule prestin in the hair cells of their inner ears; the molecule works like an active muscle, targeting and amplifying certain sound frequencies. “This tracking is unique and infinitely more sophisticated than anything we humans have,” says audiology expert Launer.  

The animals use this sonar system to navigate and to hunt, although this has resulted in real “arms races” between hunter and prey, as Launer explains: “The bats will develop a sonar system to hunt butterflies, for example, who then realize that certain signals spell danger for them.  The bat then learns to be quiet at intervals, or to change its hunting frequency. This is noticed in turn by the butterfly, which then mimics the sounds of animals that are of no interest to the bat as prey.”  

But not only bats stand to benefit from their own exceptional hearing: “In our research, we try to imitate how the bat moves in a space and locates obstacles.” Looking to possible future developments, Stefan Launer believes that canes for the visually impaired might be developed with ultrasound sensors that use acoustic signals to make it easier for blind people to find their way about. It is also conceivable that such sensors could be fitted to the hearing aids of the future. “Or they could also be used as communication aids, worn on the ear by people with normal hearing,” says Launer.