Certain fox species plunge-dive into snow to catch prey, a hunting mechanism called mousing. Red foxes (Vulpes vulpes) and arctic foxes (Vulpes lagopus) can dive into snow at speeds ranging between 2 and 4 m/s. In new research, scientists at Cornell University found that the elongated snout with higher curvature generates less impact force when it penetrates the snow, reducing the possibility of injury during impact. This skull shape also allows foxes to reach deeper into the snow, providing an advantage for catching small rodents located at greater depths. As a result, the authors predict that red and arctic foxes living in snow-covered areas will have a higher hunting success rate when mousing in snow.
Yuk et al. examined the hunting technique employed by red and arctic foxes, known as mousing, wherein they dive head-first into snow to capture prey. Image credit: Yellowstone National Park.
Red and arctic foxes dive into snow to catch prey, a behavior known as mousing.
These foxes can identify the location of animals under several feet of snow through their exceptional sensitivity to rustling noises, which have the peak in 2 to 10 kHz frequencies.
When foxes detect prey location and swiftly leap into snow at speeds of 2 to 4 m/s, they catch their prey completely by surprise.
Previous studies explored this mousing behavior in terms of the diving mechanism and success rate.
Red foxes tend to jump in a north-easterly direction, and the success rate of hunts was much higher when the foxes jumped in this direction, in comparison to all other directions, suggesting that foxes use the Earth’s magnetic field to hunt.
However, the mechanical aspects of snow diving, which are also critical to hunting success, are not well understood.
“The fox’s sharp snout doesn’t significantly compress the snow, it penetrates it without much resistance,” said Professor Sunghwan Jung, a researcher in the Department of Biological and Environmental Engineering at Cornell University.
In the study, Professor Jung and colleagues scanned skulls of red and arctic foxes as well as of lynx and puma skulls.
They 3D-printed the skulls and attached each to a sensor that measured impact force.
The skulls were then dropped into both snow and water, and the researchers entered data into computer models to compare impacts of both.
They found that the foxes’ sharp snouts penetrated the snow with little resistance, minimizing potential tissue damage during a headfirst dive.
“Without much compression, in spite of the high-speed impact, the snow behaves like water,” Professor Jung said.
“But the flat felid snouts compressed the snow upon impact, creating a large and potentially damaging resistance.”
When mousing in snow, the fox’s long snout also allows it to reach its prey earlier, as mice are very sensitive to movements in their environment and can quickly escape.
Other behavioral studies have shown that prior to pouncing, foxes shake their heads to listen to the rustling sounds of mice or other animals beneath the snow’s surface, thereby gauging the depth of the sound source.
“This is a very dangerous process, but we haven’t had reports of foxes getting injured,” Professor Jung said.
The research is described in a paper in the Proceedings of the National Academy of Sciences.
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Jisoo Yuk et al. 2024. Effect of skull morphology on fox snow diving. PNAS 121 (19): e2321179121; doi: 10.1073/pnas.2321179121
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