“I wanted to investigate whether it would be possible to make targeted sound repellers for hedgehogs, because they are declining all over Europe. So we set out to measure the hearing of the European hedgehog for the first time, ” says Rasmussen.
Working with bio-acousticians who measure hearing in animals, she developed a soundtrack of pulses and beeps to play to anaesthetised hedgehogs from a rescue centre.
The researchers measured the animals’ brain responses to pinpoint the frequency of sounds they could hear.
“We discovered, to my great surprise and joy, that hedgehogs can hear up to 85kHz” Rasmussen said.
Humans can hear up to 20kHz, and all sounds above that are called ultrasound. Cats hear up to 45kHz, while dogs’ range extends to 65kHz.
After building a 3D model of a hedgehog’s ear, the scientists found it has a stiff chain of bones that allows high-pitched sounds to pass through efficiently, in a similar way to echolocating bats.
“It’s amazing because this allows us to actually build targeted sound repellents that wouldn’t bother us or our pets,” she says.