Powerful, swift and silent, a great grey owl on the hunt is a wonder to watch. From exposed perches up to 50 metres away, these owls use acute hearing to launch attacks on rodents under a thick blanket of snow with nearly pinpoint accuracy. But exactly how does the world’s largest owl species do it? That question was the subject of a study which saw researchers observe and record great grey owls as they hunted voles about 120 kilometres northeast of Winnipeg.

The researchers first studied how snow dramatically muffles sound, allowing only very low-frequency noises to penetrate the surface. Here, the great grey owl’s wide, disc-shaped face — the largest disc of any owl species — comes to the fore. That bowl-shaped circle of feathers directs the softest of sounds towards the owl’s ears, making it possible for it to hear the low-frequency scratching of a vole tunnelling beneath the snow.

But while a great grey owl is able to perceive this frequency at a distance, it is still tricky to pinpoint the location of its prey with accuracy. That’s because — as researchers discovered when they inserted a speaker under the snowpack to replicate the sounds of a burrowing vole — snow distorts the sound waves, producing what is known as an “acoustic mirage.” Basically, sound is bent as it travels through snow, shifting the apparent position of the vole by as much as five degrees relative to its actual position.

Luckily, the great grey owl has a second adaptation to overcome this acoustic double-whammy. As it flies closer to its prey, researchers suggest the owl continues to listen and correct course. Specialized feathers on its wings allow it to fly silently, meaning it can focus on just the sound of the vole without any distraction.

The bird’s penultimate step in battling bad acoustics is a brief hover, like a calming exhale, above the expected location of the vole. Its face is now directly over the low-frequency scratching sound, a position that reduces the acoustic mirage and allows the hungry predator to lock in on the vole’s exact location. One final listen, and the owl strikes.