Thousands of hedgehogs could be saved from being run over by cars if designers took advantage of their super-hearing, the University of Oxford has suggested.
For the first time, researchers have demonstrated that hedgehogs can hear ultrasound at a much higher frequency than humans, dogs or cats.
One in three hedgehogs is killed by vehicle collisions, but the researchers believe that ultrasound repellers could be fitted to cars to stop the deaths.
Similar devices could also be fitted to strimmers or robotic lawnmowers, making them emit a piercing sound that would ward off hedgehogs.
Dr Sophie Lund Rasmussen, assistant professor at Oxford’s wildlife conservation research unit, said: “Having discovered that hedgehogs can hear in ultrasound, the next stage will be to find collaborators within the car industry to fund and design sound repellents for cars.
“If our future research shows that it proves possible to design an effective device to keep hedgehogs away from cars, this could have a significant impact in reducing the threat of road traffic to the declining European hedgehog.”
The population of the European hedgehog is in serious decline in Britain, with the species classed as “near threatened” by the International Union for Conservation of Nature in 2024.
There are estimated to be fewer than one million hedgehogs left in Britain, in comparison with an estimated 30 million in the 1950s.
The University of Oxford suggested that understanding more about their hearing might offer new ways to protect the animals.
Researchers collaborated with colleagues in Denmark to test the auditory brainstem response of 20 rehabilitated hedgehogs from Danish wildlife rescue centres.
Because hedgehogs cannot tell scientists what they can hear, the team placed small electrodes on the animals to record electrical signals travelling between the inner ear and the brain, when sounds were played through a small loudspeaker.
The electrodes detected that the brainstem fired when signals were played between 4kHz and 80kHz, with a peak sensitivity around 40kHz.
The study demonstrates that hedgehogs can hear in the ultrasound range – which starts at frequencies greater than 20kHz – up to at least 85kHz.
Do hedgehogs need ultrasound hearing?
Scientists are baffled as to why the hedgehogs need to hear at such high frequencies but have speculated that it may be used for communication or detecting prey in the dark.
Animals such as bats and dolphins use ultrasound for navigation and to detect small prey in murky waters or in the dark.
High-frequency waves have short wavelengths, which are better at reflecting off small objects, such as insects, and may help hedgehogs find food at night.
Dr Rasmussen added: “A fascinating question now is whether they use ultrasound to communicate with each other, or to detect prey – something we have already begun investigating.”
Humans have already used high-frequency sounds to ward off some animals.
Ultrasonic devices are available to keep away rodents and seagulls and, in the early 2000s, many councils experimented with anti-loitering systems to emit uncomfortable sounds only audible to people under the age of 25 to disperse young people.
The Oxford team also built an interactive 3D model of a hedgehog’s ear and found the creatures had stiffer ear bones, similar to those of bats, which helped high-pitched sounds pass through more efficiently.
They also have small bones within the ear that can vibrate more quickly and transmit high-frequency sound waves.
Prof David Macdonald, of Oxford’s wildlife conservation unit and co-author of the study, said: “It is especially exciting when research motivated by conservation leads to a fundamental new discovery about a species’s biology which, full circle, in turn offers a new avenue for conservation.
“The critical question now is whether the hedgehogs respond to ultrasound in ways that might reduce the risks of collisions with robotic lawnmowers or even cars.”