Foxes’ skulls are specially adapted for diving into snow

Some foxes can dive headfirst into snow without harm, and now we know how their skull shape is adapted for this technique.

In cold climates, where small rodents live deep under the snow, red foxes (Vulpes vulpes) and Arctic foxes (Vulpes lagopus) have a specialised hunting technique known as mousing. They use their strong sense of hearing to pinpoint the location of prey, jump into the air and then dive face-first into large piles of snow at speeds of up to 4 metres per second to catch them by surprise.

“It’s a very interesting and unique behaviour,” says Sunghwan Jung at Cornell University in New York. “Not all foxes do it either.”

To learn more about why red and Arctic foxes are so adept at snow-diving, Jung and his colleagues scanned the skulls of 13 fox species as well as those of other mammals, such as lynx and pumas, from museum collections.

Their analysis found that felines tended to have wider and shorter snouts compared with foxes. This gives them a stronger bite, says Jung, which is more useful for cats as they are usually solitary hunters.

Meanwhile, foxes, which hunt in packs, had much longer, pointier skulls. This leads to a weaker bite. Red and Arctic foxes share a similarly narrow muzzle that is slightly more elongated than those of other foxes.

The team dropped 3D-printed models of a regular Arctic fox skull and a flattened version of the skull into snow from a height of 50 centimetres.

“What we found was that the sharper snout reduces the impact, by compressing the snow less,” says Jung. This reduces the risk of injury. The lengthier, pointier snout gently pushes the snow to the side, almost like a fluid, he says. “This kind of elongated shape helps foxes dive into snow safely, so they can focus on hunting.”