Road traffic accidents are thought to kill up to a third of hedgehogs in local populations.
Despite their prickly exterior, European hedgehogs are extremely vulnerable.
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Populations have plummeted by 30 per cent over the last decade, leading to them being declared “near threatened” on the International Union for Conservation of Nature’s (IUCN) red list in 2024.
Habitat fragmentation, caused by urban development, roads and farming, continues to put them in harm’s way, forcing them into the path of vehicles and pushing them toward extinction.
But a new discovery could change their fate. Researchers at the University of Oxford in the UK have demonstrated, for the first time, that hedgehogs can hear high-frequency ultrasound – and it could be used to deter them from roads.
“It is especially exciting when research motivated by conservation leads to a fundamental new discovery about a species biology which, full circle, in turn offers a new avenue for conservation,” says study co-author Professor David Macdonald.
How could ultrasound save hedgehogs from road accidents?
Road traffic accidents are thought to kill up to a third of hedgehogs in local populations, one study found.
This number could be greatly reduced by fitting cars with ultrasound repellers to deter hedgehogs from roads, according to new research published on 11 March in the journal, Biology Letters.
Until now, it was unknown whether hedgehogs could hear these high-frequency sound waves, which are above the range of human hearing.
“The next stage will be to find collaborators within the car industry to fund and design sound repellents for cars,” says lead researcher Assistant Professor Sophie Lund Rasmussen.
If effective, it could have a “significant impact in reducing the threat of road traffic to the declining European hedgehog”, she adds.
How did researchers test hedgehogs’ hearing?
For the study, a small loudspeaker was used to play short bursts of sounds to 20 rehabilitated hedgehogs from Danish wildlife rescue centres.
Small electrodes were placed on the animals to record electrical signals travelling between the inner ear and the brain. These detected that the brainstem fired when sounds were played across a range of 4 to 85 kHz, with a peak sensitivity around 40 kHz.
The typical limit for human hearing is 20 kHz, with anything above this considered ultrasonic.
The hedgehogs were checked by a vet following the experiments, and were released back into the wild the next night.
Micro-CT scans of a dead hedgehog, which had been euthanised after being critically injured by a rat trap, provided further insight.
Using the scans to build an interactive 3D model of the hedgehog’s ear, researchers revealed a bone structure similar to that of echolocating bats, whose ears are able to pass very high-pitched sounds efficiently.
The scans also revealed that hedgehogs’ ear bones are structured to vibrate quickly, allowing them to transmit high-frequency sound waves.
Researchers conclude that it would be possible to design ultrasonic devices that can be heard by hedgehogs, but not humans or pets. Dogs can hear up to 45 Khz and cats 65 Khz.
As well as being fitted to vehicles, these ultrasonic repellants could be used on other threats such as robotic lawn mowers and garden strimmers.
“Our novel results revealed that European hedgehogs are designed to, and can, perceive a broad ultrasonic range,” says Dr Rasmussen.
“A fascinating question now is whether they use ultrasound to communicate with each other, or to detect prey – something we have already begun investigating.”