Somewhere inside a hedgehog's tiny, spiny head is a pair of ears that would put your dog's to shame.

Researchers at the University of Oxford have discovered for the first time that European hedgehogs can hear ultrasound — detecting frequencies up to 85 kHz, with peak sensitivity around 40 kHz. To put that in perspective, human hearing tops out at about 20 kHz. Dogs manage around 45 kHz. Even cats, those famously sharp-eared hunters, only reach about 65 kHz. The humble hedgehog outperforms them all.

It's a remarkable finding on its own. But what makes it matter — urgently — is what it could mean for a species in serious trouble.

A crisis on British roads

The European hedgehog was once a common sight in British gardens. Not anymore. Populations have declined dramatically since 2000, according to The State of Britain's Hedgehogs reports. From an estimated 1.55 million in 1995, numbers may have fallen to a few hundred thousand. In 2024, the International Union for Conservation of Nature reclassified the species as "near threatened."

Road traffic is one of the biggest killers. Studies suggest up to one in three hedgehogs in local populations die on the roads, with an estimated 167,000 to 335,000 killed by vehicles each year in Britain alone.

That's where the superhearing comes in.

An invisible shield of sound

Lead researcher Dr Sophie Lund Rasmussen, of Oxford's Wildlife Conservation Research Unit, believes ultrasonic car-mounted repellers could deter hedgehogs from wandering into traffic — using a frequency humans would never notice.

"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," she said. "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 sweet spot — around 40 kHz — is essentially a ghost frequency for us. Inaudible to humans, barely noticeable to dogs and cats, but crystal clear to a hedgehog.

Inside the hedgehog ear

The team didn't stop at testing hearing. Using high-resolution micro-CT scans, they built a stunning interactive 3D model of a hedgehog's ear — revealing anatomical features never before documented.

Deep inside the ear, a chain of impossibly small, dense middle-ear bones sits connected by a partly fused joint to the eardrum. That stiffness isn't a flaw — it's a feature. It allows the bones to transmit very high-pitched sounds with remarkable efficiency, much like the apparatus found in echolocating bats. The stapes, the tiniest bone in the chain (and the smallest bone in the hedgehog's body), is light enough to vibrate at extraordinary speed. And the cochlea — the snail-shell-shaped structure of the inner ear — is unusually short and compact, fine-tuned for processing ultrasonic vibrations.

It's an ear built for a world of sound we can't even imagine.

"Our novel results revealed that European hedgehogs are designed to, and can, perceive a broad ultrasonic range," Dr Rasmussen said. "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 long road ahead — but a hopeful one

There's work still to do. Researchers need to determine which ultrasonic frequencies hedgehogs find aversive, whether they'd habituate to warning sounds over time, and whether a signal could reach them early enough to let them escape an approaching car. Then comes the engineering challenge — and convincing the car industry to act.

But the foundation is laid. Co-author Professor David Macdonald put it best: "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."

The European hedgehog has been shuffling across this continent since the age of mammoths. It would be something if the secret to its survival had been hiding in its ears all along.