An Owl’s Ability to Hunt By Sound
Barn Owl dives towards the sub-surface sounds of a wild vole under deep snow. (Canon 7D1, EF 300mm f/4L + 1.4X II at 1/1600 sec, f/9, ISO 200 handheld). Undisclosed location, not baited, not called, not setup.
Out on a remote snow covered road my truck slowly crawled along in four-wheel drive as I scanned the winter landscape for owls. This was a somewhat unique situation. Owls normally hunt during the night. On this particular cold winter day I had been seeing some Barn Owls (Tyto alba) and some Short-eared Owls (Asio flammeus) hunting in the daylight. Although nobody knows for sure, the theory is that these owls were challenged for calories during a long-period of sequential snow-storms and prolonged cold, and therefore hunting all night and day just to survive.
The snow depth varied between 30 cm – 50 cm. Over the course of a few hours I watched many owls successfully dive through the snow and catch wild voles and mice. No visible trace of the voles could be seen on the surface of the snow. These small rodents forage between the snow-ground interface. The owls were not seeing any trace of prey beneath the deep snow. They were locating the invisible voles through their sophisticated listening ability.
Hungry Barn Owl hunts a cold winter day. In periods of prolonged cold and snow some populations of Barn Owls hunt during the day, in addition to their normal night schedule. Ice, or frost, can be seen on the tops of this owl’s wings. Yes, it was cold!
Surprisingly the owls were able to fly at heights of 50 meters above the ground, at speeds of 25-40 mph, pick up on the sound of a vole underneath the snow, and dive through the snow with their long skinny legs and sharp talons and catch the prey. They were very good at doing this! Based on my observations that day I estimate they were doing better than 75% at successfully catching prey (i.e. they would only come up dry about 25% of the time).
When you think about this extraordinary acoustic ability it baffles the mind. The sounds of vole moving around is approximately that of leaves rustling in the wind (~ 20 decibels). Snow is a great insulator of sound ( ~ 0.05 – 3.5 dB / cm). The sounds of a vole moving around below the snow would also need to be isolated from the engine noise of my truck (~ 60 dB). The owls flying at 30 mph, 100 feet above the snow were able to instantly hear the voles under the snow, dive down without seeing them, and grab them with their talons. Simply amazing!
Success! Barn Owl with a wild vole caught underneath the snow. (Canon 7D1, EF 300mm f/4L + 1.4X II at 1/1600 sec, f/9, ISO 200 handheld). Undisclosed location, not baited, not called, not setup.
The Barn Owl and Short-eared Owl are not the only owls that hunt by sound. The facial disk of an owl, made up of stiff feathers, collects sound and directs the sound waves to the owls offset ears. Owls ears are offset relative to each other. The offset helps the owl determine direction and distance using stereographic acoustic location. An excellent video of a Great Gray Owl hunting for voles beneath the snow can be seen in this BBC video.
Yes, owls eyes are indeed mesmerizing. Many of us associate an owl with incredible eyesight. Although owls do have keen eyesight, it is sound that helps them locate prey that is out of sight, underneath deep snow, or layers of vegetation. Laboratory tests with Barn Owls proved they could locate a mouse in total darkness, blindfolded, by the sound of the mouse’s heartbeat. In addition Barn Owls can audibly distinguish prey species by the different movement sounds they make.
“Most of the successful people I’ve known are the ones who do more listening than talking.”
― Bernard M. Baruch