Ultrasound repellers could keep hedgehogs off roads, scientists hope | Wildlife

Hedgehogs were found to hear high-frequency ultrasound, raising hopes that they could be deterred from dangerous roads with ultrasonic repellents.

Vehicles are estimated to kill up to one in three hedgehogs, a major factor in the drastic decline of this much-loved mammal in Europe over recent decades.

Researchers from the University of Oxford collaborated with Danish colleagues to test the auditory brainstem response of 20 hedgehogs rehabilitated at Danish wildlife rescue centers. Small electrodes placed on the animals recorded electrical signals traveling between the inner ear and the brain, while short bursts of sound were played through a loudspeaker.

According to the study published in Biology Letters, electrodes detected that the hedgehog’s brainstem fired when signals were emitted over a range of 4 to 85 kHz, demonstrating that hedgehogs can hear very high frequencies in the ultrasound range (above 20 kHz). Humans only hear up to 20 kHz, dogs hear up to 45 kHz.

The researchers also took high-resolution micro-CT scans of a dead hedgehog to construct an interactive 3D model of the animal’s ear, revealing previously unknown features. The model revealed that hedgehogs have very small, dense middle ear bones and a partially fused joint between the eardrum and the first of these bones, which makes the chain of bones stiffer and helps it transmit high-pitched sounds effectively. Such features are a hallmark of mammals such as echolocating bats that use ultrasound to detect prey.

The researchers said the findings could help design trimmers and lawn mowers as well as vehicles equipped with ultrasonic repellents to keep hedgehogs at a safe distance. Although pets such as dogs hear in the ultrasound range, the high frequencies detected by hedgehogs make it possible to design repellents that do not affect pets.

Lead researcher Dr Sophie Lund Rasmussen, Assistant Professor at the Wildlife Conservation Research Unit at the University of Oxford and the University of Copenhagen, said: “Having discovered that hedgehogs can hear through ultrasound, the next step will be to find collaborators within the automotive industry to fund and design sonic repellents for cars. If our future research shows it proves possible to design an effective device to deter hedgehogs from cars, this could have a significant impact on reducing the threat of road traffic on European hedgehog decline.