Long snouts protect foxes when diving headfirst in snow

The fundamental research sheds light on the biomechanics of the unique hunting behavior (known as mousing), advances our understanding of animal adaptations and offers insights into snow injuries people experience during snowboarding or skiing.

The study published April 29 in the Proceedings of the National Academy of Sciences.

While there have been many studies of water birds and animals such as porpoises and dolphins diving from air into water, interactions between animals and the air-snow interface have not been well-researched. Snow has fluid-like properties when light and fluffy, and solid-like properties when compacted, such as when people make snowballs.

"The fox's sharp snout doesn't significantly compress the snow, it penetrates it without much resistance," said Sunghwan Jung, the paper's corresponding author and professor of biological and environmental engineering. Jisoo Yuk, a doctoral student in Jung's lab, is the paper's first author.

In the study, the authors scanned skulls of red and arctic foxes (from the Canidae family) and lynx and puma skulls (from the Felidae family) at the American Museum of Natural History in Manhattan. 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.

Jung and colleagues 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," Jung said. But the flat Felidae 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," Jung said.

The study was funded by the National Science Foundation.