Hedgehogs have been found to hear high-frequency ultrasound, raising hopes that they can be deterred from dangerous roads with ultrasound repellents.
Vehicles are estimated to kill up to one in three hedgehogs, a major factor in the drastic decline of the beloved mammal across Europe in 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 traveling between the inner ear and the brain, while short bursts of sounds were played through a speaker.
According to the study published in Biology Letters, the electrodes detected that the hedgehog’s brainstem was activated when signals were played in the range of 4 to 85 kHz, demonstrating that hedgehogs can hear very high frequencies in the ultrasound range (above 20 kHz). Humans can only hear up to 20 kHz, dogs hear up to 45 kHz.
The 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 previously unknown features. The model found 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 more rigid and helps it transmit high-pitched sounds efficiently. These features are a hallmark of mammals like echolocating bats that use ultrasound to detect prey.
The researchers said the findings could make it possible to design garden trimmers and lawnmowers, as well as vehicles with ultrasonic repellents to keep hedgehogs at a safe distance. Although pets, such as dogs, listen in the ultrasound range, the high frequencies detected by hedgehogs allow repellents to be designed 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 using 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 is possible to design an effective device to keep hedgehogs away from cars, this could have a significant impact on reducing the threat from road traffic to the declining European hedgehog.”
