According to researchers, European hedgehogs are extremely vulnerable, with populations having plummeted by 30% over the last decade. In 2024, they were declared 'near threatened' on the IUCN red list. The study notes that habitat fragmentation, caused by urban development, roads, and farming, puts hedgehogs in harm's way, and road traffic accidents are thought to kill up to a third of hedgehogs in local populations.
Until now, it was unknown whether hedgehogs could hear high-frequency sound waves above the range of human hearing. Researchers at the University of Oxford have demonstrated for the first time that hedgehogs can hear high-frequency ultrasound. They tested 20 rehabilitated hedgehogs from Danish wildlife rescue centers using a small loudspeaker and electrodes.
The study found that the hedgehog brainstem fired when sounds were played across a range of 4 to 85 kHz, with peak sensitivity around 40 kHz. The typical limit for human hearing is 20 kHz, with anything above considered ultrasonic. Micro-CT scans of a dead hedgehog revealed a bone structure similar to echolocating bats, allowing efficient transmission of high-pitched sounds.
Researchers say hedgehogs' ear bones are structured to vibrate quickly, enabling transmission of high-frequency sound waves. After experiments, hedgehogs were checked by a vet and released back into the wild the next night. Researchers conclude it would be possible to design ultrasonic devices that can be heard by hedgehogs.
They suggest ultrasound could be used to deter hedgehogs from roads, and fitting cars with ultrasound repellers could greatly reduce hedgehog road deaths. However, it remains unknown how effective ultrasound repellers are at deterring hedgehogs from roads in real-world conditions, and what the cost and feasibility of fitting cars with them on a large scale would be. ' The research offers a potential new tool to address one of the major threats to hedgehogs, though other conservation measures beyond road safety are also being pursued to protect their populations.