Oxford Finds Hedgehogs Hear Ultrasound to Dodge Traffic

A sound you'll never hear might one day save thousands of hedgehogs from becoming roadkill.

Oxford researchers just discovered that European hedgehogs can detect ultrasonic frequencies up to 85 kilohertz, far beyond what humans or even most pets can hear. The breakthrough matters because road traffic kills up to one in three hedgehogs in local populations, adding pressure to a species newly classified as near threatened in 2024.

The study tested 20 rehabilitated hedgehogs from Danish wildlife rescue centers using auditory brainstem response testing. Researchers played sounds ranging from 4 to 85 kilohertz while tiny electrodes measured the electrical signals traveling between the animals' inner ears and brains.

All 20 hedgehogs responded across that entire range, with peak sensitivity around 40 kilohertz. After the experiments, every hedgehog recovered fully and was released back into the wild.

But the team didn't stop at hearing tests. They also scanned a deceased hedgehog's ear anatomy using high-resolution micro-CT imaging to understand how this ultrasonic ability works.

What they found was remarkable. The hedgehog's middle ear bones were small, dense, and partly fused, creating the stiffness needed to handle very high-pitched sounds. The stapes bone was especially tiny and light, perfectly designed to transmit rapid vibrations.

The Ripple Effect

This discovery could protect more than just hedgehogs. Lead researcher Assistant Professor Sophie Lund Rasmussen from Oxford's Wildlife Conservation Research Unit says the next step is partnering with car manufacturers to design ultrasonic warning devices for vehicles.

An effective repeller could operate above 65 kilohertz, meaning it would alert hedgehogs without bothering humans, dogs, or cats. The same technology might also keep the spiny creatures away from robotic lawnmowers and garden strimmers, two other major threats.

The conservation potential extends beyond immediate safety. Dr. Rasmussen's team is now investigating whether hedgehogs use ultrasound to communicate with each other or detect prey, which could unlock entirely new understanding of how these animals survive.

Of course, important questions remain unanswered. The study proved hedgehogs can hear ultrasound, but not whether they'd actually move away from those sounds when a car approaches. Researchers still need to determine which frequencies hedgehogs find unpleasant, whether they'd adapt over time, and if warning sounds could reach far enough ahead of speeding vehicles.

Those gaps don't diminish the promise. For the first time, conservationists have scientific evidence that an ultrasonic solution is even possible. Before this study, nobody knew if hedgehogs could detect frequencies above human hearing range.

The road from laboratory discovery to roadside protection will take time, funding, and collaboration with the automotive industry, but the foundation is now solid.