How owls with huge faces catch voles hidden in the snow

The face of a great gray owl. Credit: James Duncan

Hovering over a target helps giant-faced great gray owls locate prey hidden under up to two feet of snow.

Some of owls’ physical features, particularly parts of their wings and face, help them correct for sound distortions caused by snow, allowing them to locate their moving food with amazing accuracy, according to a new study from UC Riverside.

While most owls fly straight for their prey, this species hovers just above a target area before falling straight down, clawing through the snow.

“These aren’t the only birds that hunt this way, but in some ways they’re the most extreme because they can find prey so far beneath the snowpack,” said Christopher Clark, UC Riverside biologist who led the study. “This species is THE specialist for snow hunting.”

Clark and his team conducted a series of experiments in the forests of Manitoba, Canada, this year to better understand owls’ precision despite reduced visibility and noise caused by snow. Your observations will be documented in a new one Proceedings of the Royal Society B Paper.

One key finding relates to the owls’ broad, disc-shaped face, which they use like a radar to find food. The fleshy part of our ears works like their facial features. An opening under their feathers funnels sounds to their ears, which are near the center of their faces.

“It’s similar to how a dog can rotate its ears to tune in to sounds. Owls can do the same thing,” Clark said.

Larger facial discs are more sensitive to low-frequency sounds. With the largest facial disc of any bird, great gray owls are built for hunting voles, their preferred food. Often mistaken for mice, voles have high-pitched voices that get lost under the snow cover. However, their digging and chewing sounds beam directly onto the owls’ facial radar.

To demonstrate how snow affects the sounds made by voles, the researchers dug holes next to those where they observed the owls hunting. In these holes they placed speakers that played a variety of sounds; white noise, which is high frequency, as well as recordings of burrowing voles, which are low frequency.

Sounds rising from the snowpack from six different depths were captured by an acoustic camera consisting of multiple microphones. The analysis showed that low-frequency sounds are best transmitted. Only sounds of 3 kilohertz or less will transmit through 20 inch layers of snow; all high frequency tones disappeared.

“The fact that low-frequency sound penetrates snow explains the facial disk of this species, because it has better low-frequency hearing with such a large disk.”

The group’s sound experiments also showed that snow warps the sounds made by voles, creating an “acoustic mirage” that could mislead owls. By spending a moment directly above their prey, the birds correct the snow’s distortions.

“The distance the sound has to travel from above is shorter, and there’s less snow for the sound to travel through from that spot,” Clark said. “This definitely helps the owls land where they need to.”

Great gray owls also have wings that appear to deaden the sound of flight, allowing them to focus on the sounds coming from the voles. Among all owls, this species is one of the quietest in flight, which is due to long, fringed wings covered with thick “velvet”. The sound deadening properties of these wings can be particularly useful during the hover phase of the hunt.

This last aspect of the work is of interest not only to those fascinated by owls, but also to those developing quieter machines.

“Between the 1940s and ’60s, aircraft noise dropped dramatically, but aircraft have not gotten much quieter since then. Studying how these owl wings work could help inspire new planes and drones that make less noise,” Clark said.

More information:
Christopher J. Clark et al., Great gray owl chasing voles under snow levitates to defeat acoustic mirage, Proceedings of the Royal Society B: Biological Sciences (2022). DOI: 10.1098/rspb.2022.1164

Provided by the University of California – Riverside

Citation: How Giant-faced Owls Snag Voles Hidden In Snow (2022, December 3) Retrieved December 3, 2022 from hidden.html

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