When the atmospheric conditions are right, water turns into snow, blanketing the environment, and this can be a challenge for creatures when their livelihood disappears beneath the snow cover. Snow foxes (Vulpes lagopus) and red foxes (Vulpes vulpes) are often found in snowy parts of the world and have a unique way of hunting. They leap and then plunge into the snow to catch their prey, in a distinctive behaviour known as mousing. However, little was known about how the snow's granular properties and the animals’ unique head shape enables the foxes to penetrate the snow swiftly to capture their next meal without detection, and how they manage to protect themselves from damage. Jisoo Yuk, Anupam Pandey, Leena Park, William Bemis and Sunghwan Jung from Cornell University, USA, decided to find out more about the secrets behind mousing success.
First, Yuk and her collaborators analysed video recordings of the foxes when they hunted in their natural environment to determine the top speed of their dives to use later in laboratory experiments, revealing that foxes can jump as high as 60 cm and reach a top speed of 4 m s−1. Then they recreated the skulls of a snow fox and a red fox in plastic with a 3D printer, based on skulls kept in museums, before attaching a load cell to each model to measure the forces of impact as they dropped the models into a bucket of water and a bucket of snow.
The researchers discovered that the foxes’ uniquely pointed snouts allow them to slice through snow like water, with very little resistance, as the grainy snow, with pockets of air trapped between, does not compress as the skull begins to penetrate, minimizing the risk of injury to the fox as it faceplants in the snow. Also, the unique shape of the fox's head makes it almost impossible for the prey to detect the danger and escape, as the fox’s head moves faster through the snow than the give-away pressure wave, triggered by the impact, that would warn unsuspecting rodents of an impending attack, to give the foxes an advantage when mousing. The foxes’ long noses also allow them to reach deeper into the snow than shorter snouted animals, allowing them to snap up rodents that might be able to evade other predators. And when the team compared how the blunter skulls of distantly related carnivores, such as lynxes and pumas, would penetrate snow if they tried mousing, it was clear that the cat-like skulls generated much higher forces as they landed nose first in the snow, to compress the snow rather than slicing through it.
So, snow foxes’ faces are perfectly evolved for hunting in the snow without causing any damage to their elegant snouts, and without warning rodents hidden beneath the blanket of an impending attack.
