The face of an important grey owl. Credit: James Duncan
Hovering over a goal helps giant-faced Great Gray owls pinpoint prey hidden beneath as a lot as two toes of snow.
Several of the owls’ bodily options, particularly components of their wings and face, assist them right for sonic distortions brought on by the snow, enabling them to search out their transferring meals with astonishing accuracy, in keeping with a brand new UC Riverside examine.
While most owls fly straight at their prey, this species hovers simply above a goal space earlier than dropping straight down and punching by means of the snow with its talons.
“These aren’t the one birds to hunt this manner, however in some methods, they’re probably the most excessive as a result of they’ll find prey to this point beneath the snow cowl,” mentioned UC Riverside biologist Christopher Clark, who led the examine. “This species is THE snow searching specialist.”
Clark and his workforce performed a sequence of experiments within the forests of Manitoba, Canada, this 12 months to raised perceive the owls’ precision regardless of snow-limited visibility and sounds. Their observations are documented in a brand new Proceedings of the Royal Society B paper.
A key discovering pertains to the owls’ broad disc-like face, which they use like radar to search out meals. The fleshy a part of our ears works the way in which their facial options do. An opening underneath their feathers funnels sound towards their ears, that are positioned close to the middle of their faces.
“It’s just like the way in which a canine can flip its ears to tune sound. Owls can do the identical factor,” Clark mentioned.
Bigger facial discs are extra delicate to low-frequency sounds. With the most important facial disc of any hen, nice grey owls are constructed for searching voles, their most popular meals. Often mistaken for mice, voles have high-pitched voices that get misplaced underneath snow cowl. However, their digging and chewing sounds beam straight onto the owls’ facial radar.
To show how snow impacts the voles’ sound, the researchers dug holes subsequent to those they watched the owls create whereas searching. Inside these holes, they positioned audio system taking part in quite a lot of sounds; white-noise, which is high-frequency, in addition to recordings of burrowing voles, that are low frequency.
Sounds rising from the snowpack from six completely different depths had been captured by an acoustic digital camera composed of a number of microphones. Analysis revealed that low-frequency noises transmitted greatest. Only sounds of three kilohertz or decrease transmitted by means of 20-inch-thick layers of snow; all excessive frequency sounds disappeared.
“The incontrovertible fact that low frequency sound passes by means of snow explains the facial disc of this species, as a result of they’ve higher low frequency listening to with such an enormous disc.”
The group’s sonic experiments additionally demonstrated that snow bends the voles’ sounds, creating an “acoustic mirage,” which could lead on owls astray. By spending a second immediately above their prey, the birds right for the snow’s distortions.
“The distance the sound has to journey from simply overhead is shorter, and there is much less snow for the sound to journey by means of from that spot,” Clark mentioned. “This undoubtedly helps the owls land the place they should.”
Great grey owls even have wings that seem to dampen the sound of flying, which can permit them to focus on the noises coming from the voles. Among all owls, this species is among the many quietest in flight, owing to lengthy, fringed wings coated in thick “velvet.” The sound-dampening qualities of those wings could also be significantly helpful through the hovering part of the hunt.
This final side of the work is of curiosity not solely to these fascinated by owls, but in addition to these creating quieter machines.
“Between the Nineteen Forties and 60s, airplane sounds dropped dramatically, however since then planes have not gotten a lot quieter. Studying how these owls’ wings operate might assist encourage new planes and drones that create much less noise,” Clark mentioned.
More data:
Christopher J. Clark et al, Great Gray Owls searching voles underneath snow hover to defeat an acoustic mirage, Proceedings of the Royal Society B: Biological Sciences (2022). DOI: 10.1098/rspb.2022.1164
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University of California – Riverside
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How giant-faced owls snag voles hidden in snow (2022, December 3)
retrieved 3 December 2022
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