Ultrasound repellers could keep hedgehogs off roads, scientists hope

Hedgehogs have been discovered to hear high-frequency ultrasound, raising hopes that they could be deterred from dangerous roads with ultrasound repellers.Vehicles are estimated to kill up to one in three hedgehogs, a big factor in the much-loved mammal’s drastic decline across Europe over recent decades.Researchers at the University of Oxford collaborated with colleagues in Denmark to test the auditory brainstem response of 20 hedgehogs rehabilitated in Danish wildlife rescue centres. Small electrodes placed on the animals recorded electrical signals travelling between the inner ear and the brain, while short bursts of sounds were played through a loudspeaker.Dr Sophie Lund Rasmussen, the lead researcher, said the study could have a significant impact on reducing hedgehog road deaths. Photograph: Joan OstenfeldtAccording to the study published in Biology Letters, electrodes detected that the hedgehog’s brainstem fired when signals were played across a range of 4 to 85kHz, demonstrating that hedgehogs can hear very high frequencies in the ultrasound range (greater than 20kHz). Humans can only hear up to 20kHz, dogs hear up to 45kHz.Researchers also carried out high-resolution micro-CT scans of a dead hedgehog to build an interactive 3D model of the animal’s ear, revealing hitherto unknown features. The model found that hedgehogs have very small, dense middle-ear bones and a partly fused joint between the eardrum and the first of these bones, making the chain of bones stiffer and helping it pass high-pitched sounds efficiently. Such features are a hallmark of mammals such as echolocating bats that use ultrasound to detect prey.Researchers said the findings could make it possible to design garden strimmers and lawn mowers as well as vehicles with ultrasound repellers to keep hedgehogs at a safe distance. Although pets such as dogs hear into the ultrasound range, the high frequencies detected by hedgehogs make it possible to design repellers that do not affect pets.The lead researcher, Dr Sophie Lund Rasmussen, an assistant professor at the Wildlife Conservation Research Unit at the University of Oxford and University of Copenhagen, said: “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. 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.”