Evolution has resulted in the great grey owl developing advanced, scientific skills to detect voles 50 cm below the snow just by the sound that they make. And it is doubly astonishing they can do this because snow this deep is a great sound dampener and distorter.
Christopher Clark, from the University of California, Riverside, who conducted the study on the predatory skills of the great grey owl said:
“It’s kind of amazing they can do this, locating their prey under a thick layer of snow. The snow deadens the sound so much, yet they rely on sound absolutely for their hunting”.
Clarke added that snow is “basically about the same as acoustic foam. It’s what you put on the walls when you want to soundproof a room.”
And it refracts a vole’s sounds as they pass through the snow upwards. The Times Science Editor Tom Whipple says, in his article on November 23, 2022 that “Each layer of the snow has different densities, affecting the speed of sound travelling through it. This means the route taken by the sound will bend”. In other words, it is refracted as it passes through the snow.
This would present a problem to a predator trying to detect a prey animal through sound emission. But the great gray owl gets over this through its fabulous skills. It employs a very intricate operation to get at those voles 50 cm below the snow.
As the great gray owl completely silently swoops over the snow they detect a vole scrabbling under it. A quick reminder: owls are very silent in flight. This is because they have feathers on their wings which magically create silent flight. I’ve discussed this in another article which you can access by clicking on this link.
And secondly, the great grey owl has a head “like a little radar dish” according to Clark. Owls have flat faces to enable them to capture sound waves which they direct towards their ears. The sound waves are stopped by their face and the feathers and are funnelled towards the ear canal allowing them to pinpoint the source of sound.
So they detect the source of the sound under the snow and then they hover directly above it. They need this last step to be sure of precise pinpointing of the prey animal. This takes energy but it is necessary. They don’t know how deep or how hard the snow it is. But they know a vole is down there.
The owl dives down and smashes through the snow capturing the vole in their talons. Up until that catastrophic moment the vole was completely unaware what was happening above. They are silent killers.
There are two hypotheses as to why owls have sound-dampening feathers which are particularly oversized in this species of owl. One hypothesis for the sound dampening feathers is that it allows the owl to sneak up on the vole as described. And the second hypothesis is that the owl has to fly silently so as not to interfere with the owl’s sensitive listening for the prey’s sounds coming from the snow.
The main reason is probably the latter because they are, after all, trying to detect very faint sounds which have been refracted in deep snow. The owl needs all the advantages that they can get to carry out this very delicate and difficult manoeuvre.
The study is published in the journal Proceedings of the Royal Society B.