https://www.allaboutbirds.org/news/to-c ... ic-mirage/#
To Catch Voles Under The Snow, Great Gray Owls Must Overcome An Acoustic Mirage
New research into the weird ways snow distorts sound offers new hints about the extraordinary hunting strategies of a winter phantom—the Great Gray Owl.
From the Winter 2024 issue of Living Bird magazine. Subscribe now.
Perhaps no species of owl is as superbly adapted for hunting in snow as the Great Gray.
Found throughout the boreal forests of the Northern Hemisphere, Great Gray Owls dine primarily on small mouselike rodents called voles. In winter, voles retreat to tunnels deep under the snow—but that doesn’t stop Great Grays. Hunting from an exposed perch, an owl listens intently for its target, then swoops down from above, punching through the crust of snow with its long, powerful legs. Able to reach prey almost 18 inches below the surface of the snow, Great Gray Owls have been known to penetrate snow crusts thick enough to support a 175-pound person.
What hasn’t been clear, despite decades of research about Great Gray Owls, is how they do it—how do Great Grays hunt prey animals no longer than a ballpoint pen, which they can’t see, using only faint burrowing sounds more than a foot under the snow to guide them in plunging strikes with surgical precision?
Some intriguing new hints arrived recently via quirky research conducted by an unlikely pair of scientists. One, a California biologist who had spent most of his career studying the sounds made by hummingbird feathers, had long dreamed of working with owls; the other, a Canadian expert on owl field biology, had always wanted to study sound.
Close up of an owls face with round shape.
The Great Gray Owl’s facial disc collects and directs even the softest sounds toward its ears, helping the owl to pinpoint a sound’s precise location. Photo by Frank Sorger / Macaulay Library.
A little furry animal in the snow.
In winter, meadow voles move around in tunnels under the snow. Photo by Jim Duncan.
In their study, the researchers explored how Great Gray Owls use a set of finely tuned adaptations for gathering sound and localizing its source in deep snow. The Great Gray Owl’s facial disc, a bowl-shaped circle of feathers that frames its face, is the largest of any owl species, collecting and directing even the softest sounds from the environment toward its ears. And like other owls that hunt by sound, its ears, hidden under feathers, are asymmetrical. A higher ear opening on one side than the other enhances its ability to pinpoint a sound’s precise location.
To test the hunting-by-hearing capabilities of Great Grays, the researchers used an array of microphones buried under the snow to carry out a complex and unique set of experiments in the cold of Manitoba. Their research, published in the journal Proceedings of the Royal Society B in November 2022, uncovered new hints about the weird ways snow muffles and distorts sound—and the Great Gray Owl’s incredible ability to hear a vole hidden in the snow, which it turns out depends largely on the owl’s unique feathers.
Illustration of the details of an owl's feathers.
Feathers for Silent Flight. The combs and fringes on the edges of a Great Gray Owl’s wing feathers break up the air currents during flight, reducing the noisy turbulence that would otherwise be created by the flapping of wings. Graphic by Jillian Ditner.
[Lots more article and pics at the link!]
