We’ve all seen the silky, bright orange coat of a red fox against the snow. But did you know that their survival depends on tiny, little rodents that are very difficult to see?
Red foxes have all the tools they need to be excellent hunters in winter. Their hearing is extremely acute. So much so, that they can hear small prey moving under 3 feet of snow. They detect the slightest movement or squeak while hunting.
Once the prey is spotted, they use their powerful hind legs to propel themselves into the air and dive head first into the snow. As it sinks into the snow, it grabs the prey with its mouth, pops its head out and shakes off any snow that may have gotten lodged in its ears or nose. This unique hunting technique is called “mousing” (BBC 2014; PBS 2021).
Why is their hearing so acute and how do they dive to the right spot?
First, each ear can be moved separately to track different sounds and rotate 150 degrees. More than 12 muscles are used to precisely position the ear canal to allow it to locate a sound more clearly (BBC 2014).
Secondly, the earth has a magnetic field that can be compared to a magnet whose poles (North and South) are the points of attraction. It is said that foxes have the ability to see the magnetic North, which is invisible to the human eye. This could be due to a protein in the eyes of foxes (which we lack) called cryptochrome, which is sensitive to the magnetic field of the earth. This strange ability is not insignificant, since by aligning their prey with the northern direction of the magnetic field, coupled with the sound of the prey, they can calculate the exact distance they must dive to catch the prey, which runs through their tunnels. This calculation is very accurate since with the prey sound aligned with the magnetic north direction, the hunting success rate increases from 18% to 73% (BBC 2014; PBS 2021).
Foxes are inevitably great hunters, but what prey do they hunt that requires them to develop such unique techniques? Lemmings and voles are small rodents that move through highways of tunnels dug directly under the snow. It is in the area known as the subniveal that they are able to build habitats. Snow does not fall evenly everywhere; in many places, trees or plants trap the snow and prevent it from settling on the ground. This creates empty air pockets, which can be used as a chamber for feeding or resting, for example. In addition, the heat from the ground will cause the snow to sublimate, i.e. change from a solid to a gas. The hot gas will rise to the snow layer above and solidify it into a rigid roof. All of the chambers will then be connected to each other by tunnels dug by the rodents (Mackay 2014).
But why do they need to live in the snow?
First of all, to feed. As rodents are herbivores, their food on the ground is buried at the beginning of winter. The chambers under the snow give them access to moss, grass, seeds and berries from buried plants. Then, the solid snow layer keeps them warm and protects them from the weather outside.
Obviously, living under the snow protects them from predators. Red foxes, but also owls and other large birds are fond of these rodents. Even ermine, which manage to get into their tunnels to hunt, are a threat. So it’s not perfect protection, but it’s still much safer than being out in the open (Mackay 2014; Free high quality documentary 2022; PBS 2021, 2022).
However, when the snow melts, lemmings are exposed to predators and must move to new shelters. These moves are risky: they must be made through the water of the melting snow. There is a myth that in the spring lemmings commit mass suicide by jumping into the water. This is not true, as they are only trying to make their migration and are forced to cross bodies of water. They are good swimmers, but the water is still dangerous, hence the high mortality rate (Free high quality documentary 2022).
Voles and lemmings are food for our red fox, but they are also very important for plants. Their small droppings left under the snow all winter will serve as fertilizer for plants, starting in early spring. So many species will have access to food very quickly because of them (Mackay 2014).
Both prey and predators must develop techniques to survive. Such is the beauty of nature’s complex ecosystems!
PBS Nature, Nature on PBS. « Fox Hunts Prey Deep Under Snow. » YouTube, 3:23. 10 novembre, 2021. URL : https://www.youtube.com/watch?v=RwumvtCxcpg
Free High-Quality Documentaries. « Lemming – The Little Giant Of The North. » YouTube, 49:38. 4 mars, 2022. URL : https://www.youtube.com/watch?v=rMJpytDpn0w
PBS Nature, Nature on PBS. « Dramatic Vole Escape Caught on Camera. » YouTube, 3:11. 21 octobre, 2022. URL : https://www.youtube.com/watch?v=hgK0o1uISds
BBC, BBC Four. « How foxes use magnetic fields to catch prey – The Wonder of Animals: Episode 5 Preview – BBC Four. » YouTube, 3:12. 04 septembre, 2014. URL : https://www.youtube.com/watch?v=1MWoPKlAXx4
Mackay, B. 2014. The Subnivean Zone: Shelter in the Snow. The Outside story, Northern Woodlands.