Scientists at Oxford have found that Europe’s most beloved garden mammal has a hidden sensory ability that no one knew about, and it could be the key to keeping hedgehogs off roads
Every year, across roads and garden paths throughout Europe, hedgehogs die in enormous numbers. Road traffic is thought to kill up to one in three hedgehogs in local populations. Their primary defence against predators, freezing and curling into a ball of spines, evolved long before cars existed and offers no protection at all against a moving vehicle. For decades, conservationists have lacked any practical tool to steer hedgehogs away from roads before the collision happens.
A new study published March 11 in the journal Biology Letters suggests that such a tool may now be within reach. Researchers at the University of Oxford have demonstrated for the first time that European hedgehogs can hear high-frequency ultrasound, opening the door to ultrasonic repellents that could warn the animals away from approaching vehicles, without making a sound that humans or their pets can detect.
Testing Hedgehog Hearing
The research team, led by Assistant Professor Sophie Lund Rasmussen of Oxford’s Wildlife Conservation Research Unit, worked with colleagues in Denmark to measure the auditory brainstem response of 20 rehabilitated hedgehogs from Danish wildlife rescue centres. The technique involves placing small electrodes on the animals’ heads to record electrical signals travelling between the inner ear and the brain while short bursts of sound at different frequencies are played through a small loudspeaker.
The results were clear. The hedgehogs’ brainstems responded to sounds across a range of 4 to 85 kHz, with peak sensitivity around 40 kHz. Human hearing tops out at approximately 20 kHz. Anything above that threshold is ultrasound. The hedgehogs were not merely hearing at the edge of that range but well into it, detecting frequencies more than four times beyond what humans can perceive. After the experiments, each animal was checked by a veterinarian and released back into the wild the following night.
An Ear Built for High Frequencies
The team went further than behavioural testing. Using high-resolution micro-CT scans of a hedgehog that had been euthanised after a critical injury from a rat trap, the researchers constructed a detailed interactive 3D model of the hedgehog ear, revealing anatomical features that had never been documented before.
The scans showed that hedgehogs have very small, dense middle-ear bones and a partially fused joint between the eardrum and the malleus, the first bone in the chain.
This arrangement stiffens the entire bone chain and allows it to transmit very high-pitched sounds more efficiently, a structural hallmark of animals that can hear ultrasound, most notably echolocating bats. The hedgehog’s stapes, the smallest of the three middle-ear bones, was also found to be notably small and light. A lighter stapes vibrates more rapidly and transfers high-frequency sound waves more effectively.
“Our novel results revealed that European hedgehogs are designed to, and can, perceive a broad ultrasonic range,” Rasmussen said in a statement released by the University of Oxford. “A fascinating question now is whether they use ultrasound to communicate with each other, or to detect prey, something we have already begun investigating.”
A Near-Threatened Species With Few Good Options
The timing of the discovery matters. The European hedgehog was reclassified as near threatened on the International Union for Conservation of Nature red list in 2024, reflecting a documented and accelerating population decline across the continent. Fewer than one million hedgehogs are estimated to remain in Britain. Urban expansion, intensified agriculture, and habitat fragmentation have all contributed, but road mortality stands out as a large and, in principle, preventable cause of death.
The problem has always been that hedgehogs do not behave in ways that help them avoid cars. Their freeze-and-curl response is triggered by direct threat, not by the approach of a large object at speed. By the time a hedgehog perceives a car as a threat, it is typically already too late. Standard roadside deterrents have failed to account for how hedgehogs actually sense their environment.
The new findings suggest that their auditory system may offer a way in. Because hedgehog hearing extends well above the range of dogs (up to 45 kHz) and cats (up to 65 kHz), there is a frequency window where a device could emit a warning signal audible to hedgehogs but silent to most domestic animals and humans. The next challenge is determining whether hedgehogs respond to ultrasound in ways that cause them to move away from a sound source, and whether that response can be triggered reliably enough to be useful.
The Road Ahead
“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,” Rasmussen said in a statement. “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.”
Co-author Professor David Macdonald of Oxford’s Wildlife Conservation Research Unit noted the satisfying circularity of the result. “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,” he said in a statement. “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.”
That last point is not incidental. Robotic lawnmowers have emerged as a significant and underreported threat to hedgehogs in garden settings, often operating at night when hedgehogs are active. An ultrasonic deterrent that could be fitted to such machines, as well as to vehicles, could address two of the animal’s major modern hazards simultaneously.
Sources
The paper, “Hearing and anatomy of the ear of the European hedgehog Erinaceus europaeus,” was published March 11, 2026 in Biology Letters by Sophie Lund Rasmussen and colleagues at the University of Oxford, the Natural History Museum Denmark at the University of Copenhagen, City Dyreklinik, Aarhus University, Aarhus University Hospital, and the University of Southern Denmark. DOI: 10.1098/rsbl.2025.0535.
Quotes in this article are drawn from a press release issued by the University of Oxford on March 11, 2026.
Jane holds a BSc in Biology from the University of Regina and a Master of Science in Bioscience, Technology and Public Policy from the Univesity of Winnipeg. Her reporting interests include Life Sciences, Physical Sciences and the Cosmos.