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How great gray owls find prey under deep blankets of snow

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a) the acoustic position (heat map) of the sound changes with snow depth due to refraction. V: Vertical position above the loudspeaker. Star: The actual position of the loudspeaker. Beamforming settings: 1/3 octave bandwidth centered at 2.0 kHz, 1 second integration time (beamforming is shown in Figure 2a ). Images are cropped from the entire camera image to show the ROIs defined in the BeamformX software. (b) Experimental device. Snow depth = 38 cm (top 14 cm of snow already removed). (c) model geometry: L.: Length of horizontal distance from the sound source. D.: Depth of the sound source under the snow. H.: Height above snow. The V and asterisk indicate two possible attack strategies. The blue line shows the sound path refracted at the air/snow interface. The green dashed line indicates the apparent position. (d,e) L.,D. error angle as a function of γ and λ i>,H.. (a), the data shown inH.:D. = 2.6,L.:D. = 5.2.The snowy owl’s actual hunting strategy is to H.:D. approach with a ratio > 10:1. credit: Proceedings of the Royal Society B: Biological Sciences (2022). DOI: 10.1098/rspb.2022.1164″ width=”800″ height=”427″/>

Snow refracts sound, so at certain angles owls perceive an “acoustic mirage”. Acoustic positions are offset from the actual sound source positions. (a) the acoustic position (heat map) of the sound changes with snow depth due to refraction. V: Vertical position above the loudspeaker. Star: The actual position of the loudspeaker. Beamforming settings: 1/3 octave bandwidth centered at 2.0 kHz, 1 second integration time (beamforming corresponds to black squares in Figure 2)a). Images are cropped from the entire camera image to show the ROIs defined in the BeamformX software. (b) Experimental setup; snow depth = 38 cm (top 14 cm of snow already removed). (c) Model geometry: L.: Length of horizontal distance from the sound source. D.: Depth of the sound source under the snow. H.: Height above snow. The V and asterisk indicate two possible attack strategies. The blue line shows the sound path refracted at the air/snow interface. The green dashed line indicates the apparent position. (day, day) error angle γ When λ as a function of L., D.When H.. ( data ina) handle H.:D. = 2.6, L.:D. = 5.2. The Great Gray Owl’s actual hunting strategy is to get close to its prey. H.:D. > 10:1 ratio. credit: Proceedings of the Royal Society B: Biological Sciences (2022). DOI: 10.1098/rspb.2022.1164

Three researchers from the University of California, Discover Owls, and the University of Washington discovered how the Great Gray Owl finds and traps voles under two feet of snow.In their paper published in Proceedings of the Royal Society BChristopher Clark, James Duncan, and Robert Dougherty describe spatially localizing sound sources under snow using acoustic cameras.

Previous research has shown that the screech owl can detect its presence. preyUnder a blanket of deep snow, such as rabbits and voles. Once spotted, the owl can swoop down and push its paws through the snow to catch its prey. In this new effort, researchers sought to understand how it does that.

This work involved venturing into the forests of Manitoba, Canada, which is covered in a thick blanket of snow each winter. They searched and found dive holes, evidence of owls diving into the snow to catch prey. In this case, mainly voles.Then I dug a similar hole next to the one I found and buried speaker under the snow.

They set up an acoustic camera that could record a wide range of sounds near the embedded speakers. The researchers then played the sound through a speaker and used the acoustic camera’s microphone to measure the sound heard through the snow. We slowly removed the layer of snow covering the speaker to see what sounds were able to penetrate through how much snow.






A video of a great gray owl hunting a vole on the snow and defeating a mirage. Credit: Proceedings of the Royal Society B: Biological Sciences (2022). DOI: 10.1098/rspb.2022.1164

they found it white noise could penetrate thin snow layers, but only very low frequency noise could penetrate deep snow. Researchers note that the screech owl’s large, round face has sound-reflecting feathers that allow it to hear low-frequency sounds, such as the sound of voles digging through snow.

The researchers also noted that the birds typically circled over their intended target for a few seconds before diving. snow.

For more information:
Christopher J. Clark et al., Great Gray Owl hunting voles on the snow Proceedings of the Royal Society B: Biological Sciences (2022). DOI: 10.1098/rspb.2022.1164

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