HEADLINE:
Hedgehogs hear ultrasound up to 85 kHz, outdoing dogs and cats
ARTICLE:
The Hedgehog Can Hear What Your Car Cannot Hide From
Twenty Hedgehogs, One Very Loud Secret
A European hedgehog (Erinaceus europaeus) can hear sound up to at least 85 kHz, a range that beats a dog’s upper limit of roughly 45 kHz and a cat’s roughly 65 kHz without even trying. That is the finding of a study published March 11, 2026 in Biology Letters, led by Sophie Lund Rasmussen of the University of Oxford’s Wildlife Conservation Research Unit with Danish collaborators. The team ran auditory brainstem response tests, a method that reads electrical activity in the nerve between ear and brain while bursts of sound play, on 20 rehabilitated hedgehogs from Danish wildlife rescue centers. The animals responded to tones between 4 and 85 kHz, with the sharpest reaction around 40 kHz. It is the first confirmed evidence that hedgehogs can hear ultrasound at all, a frequency range that starts above 20 kHz, the ceiling of human hearing.
A Skull Built Like a Tiny Bat’s
The physics behind that number came from a separate specimen: a hedgehog euthanized after a critical rat-trap injury, its ear preserved and scanned with high-resolution micro-CT to build a detailed 3D model. The scans showed middle-ear bones that are unusually small and dense, and a joint between the eardrum and the stapes (the tiny bone that hands sound vibration on to the fluid-filled cochlea of the inner ear) that is partly fused, stiffening the whole chain so it moves faster and loses less energy. The stapes itself is small enough to vibrate at speed, and the cochlea is short and tightly wound rather than long and loose. Put together, it is the same basic recipe seen in echolocating bats, animals that also need to shuttle very high frequencies through their ears without delay. Nothing here is about behavior yet. It is a stiffer lever, a shorter tube, a faster signal, and that is the whole story of how the hearing works.
A Frequency Band Nothing Else Is Listening To
Here is why the mechanism matters past the anatomy lab. Human hearing tops out near 20 kHz, dogs run up to about 45 kHz, cats reach about 65 kHz, and hedgehogs go to at least 85 kHz. That gap at the top is a frequency band almost nothing that shares a street with a hedgehog can register. Rasmussen and her co-authors point out that a device could, in theory, be built to emit warning tones tuned to that band, audible to hedgehogs and to essentially nobody and nothing else nearby, no barking dog, no startled cat, no annoyed neighbor. The reason this idea has weight rather than novelty: road traffic is estimated to kill up to one in three hedgehogs in some parts of their range, a pressure that helped push the European hedgehog onto the IUCN Red List as near threatened in its October 2024 reassessment. National counts show declines of 16 to 33 percent over ten years, with local populations down by as much as 50 percent in Bavaria, Germany, and Flanders, Belgium. An ultrasonic alarm tuned above a dog’s hearing is still a hypothesis. The decline it might address is not.
Nobody’s Built the Alarm, and Nobody Knows If It Would Work
No car manufacturer and no funding body has committed to building or testing an ultrasonic hedgehog deterrent. The researchers describe the next step as finding partners willing to design and pay for one, which has not happened yet. Even if such a device existed, it is not known whether a hedgehog hearing an ultrasonic warning would move away from it, since a hedgehog’s default defense against a threat is to freeze and curl into a ball, not to flee. It is also an open question why the animal can hear this high in the first place. Rasmussen has said the team wants to find out whether the range is used for communication between hedgehogs, for tracking insect prey, or is simply what you get as a side effect of an ear built this way. That work has only just started.
Then They Went Back to the Garden
After the hearing tests, all 20 hedgehogs were checked over by a veterinarian and released back into the wild the following night. They went back to whatever a hedgehog does with an evening: under a hedge, across a road, past a lawnmower left running too close to the flower bed. Every one of them can now register a pitch three animals down the food chain of household pets cannot, and not one of them has any idea. Neither, for the moment, does the lawnmower.