Scientists at the University of Oxford say ultrasonic acoustic devices could one day help reduce the number of hedgehogs killed by cars. Their idea comes from a new study published on March 11th. biology letters For the first time, hedgehogs have been shown to be able to hear high-frequency ultrasound waves.
The European hedgehog is one of Europe’s best-known wild mammals, but its numbers are rapidly declining. In 2024, the International Union for Conservation of Nature reclassified the species as “near threatened.” Road traffic is a major cause of these losses, with estimates that as many as one in three hedgehogs die in vehicle collisions in some areas.
New findings suggest that ultrasonic repellents could be used to deter hedgehogs from entering roads and other dangerous areas. Until now, researchers didn’t know whether hedgehogs could hear sounds in this frequency range.
Lead researcher Associate Professor Sophie Rand Rasmussen (Wildlife Conservation Research Unit/Department of Biology, University of Oxford and University of Copenhagen) said: “Now that we have discovered that hedgehogs can hear ultrasound, the next step is to help the automotive industry.” “This could have a significant impact if future research proves it is possible to design effective devices to keep hedgehogs away from cars.” It helped reduce the threat from road traffic to the declining European hedgehog. ”
Test your hedgehog’s hearing
To investigate hedgehog hearing, researchers at the University of Oxford teamed up with Danish collaborators to measure the auditory brainstem responses of 20 hedgehogs rehabilitated from a wildlife conservation center in Denmark. This technique uses small electrodes placed on the animal to record electrical activity between the inner ear and the brain, and plays short bursts of sound through a small speaker.
The measurements showed that the hedgehog’s brainstem responds to sounds in the 4-85 kHz range, with the highest sensitivity around 40 kHz. This confirms that hedgehogs can detect ultrasound waves (starting at frequencies above 20 kHz) and can hear frequencies up to at least 85 kHz. After the experiment, the animals were examined by veterinarians and released back into the wild the next night.
The structure of the ear considering high-frequency sounds
The researchers also used high-resolution micro-CT scans to examine the ears of dead hedgehogs, which were euthanized after being severely injured in a mousetrap. Using these scans, the team created a detailed interactive 3D model of the hedgehog’s ear, revealing previously unknown features.
This model showed that hedgehogs have very small and dense middle ear bones, with a partially fused joint between the eardrum and the first bone. This arrangement strengthens the bony chain, allowing it to transmit very high-pitched sounds more efficiently. This is a common characteristic of animals such as echolocating bats, which can detect ultrasound waves.
The scans also showed that hedgehogs have a small stapes bone, the smallest middle ear bone that connects the chain of ear bones to the fluid-filled cochlea in the inner ear. The smaller and lighter the stapes, the faster it can vibrate and therefore transmit high-frequency sound waves more effectively. The researchers also discovered that the cochlea itself is relatively short and compact, which helps it process ultrasonic vibrations.
Ultrasonic repellent could reduce hedgehog deaths
Taken together, these findings show that ultrasonic repellents could be designed to be audible to hedgehogs, but not to humans or pets*. If future research proves that such a device is effective, it could be used to keep hedgehogs away from roads and other hazards such as robotic lawn mowers and garden mowers.
Dr Rasmussen added: “Our new findings reveal that European hedgehogs are designed to, and can, detect a wide range of ultrasound waves. The interesting question now is whether they use ultrasound to communicate with each other or to detect prey, and we have already started investigating this.”
Co-author Professor David McDonald, from the University of Oxford’s Wildlife Conservation Research Unit/School of Biology, said: “It’s especially exciting when conservation-motivated research leads to fundamental new discoveries about the biology of a species, which come full circle and provide new avenues for conservation. The key question now is whether hedgehogs respond to ultrasound in a way that reduces the risk of collisions with robotic mowers or even cars.”
The study involved scientists from the University of Oxford, the Danish Museum of Natural History at the University of Copenhagen, City Dyreklinik (Copenhagen), Aarhus University, Aarhus University Hospital and the University of Southern Denmark.
*Human hearing range is 20-20,000 Hz, dog hearing range is 67-45,000 Hz, and cat hearing range is 45-65,000 Hz.
