Cross Fox in warm sun on the snow.

“Cross Fox Stare”

A cross fox (a partially melanistic red fox) warms in the winter sun on a -27 deg F day, Wyoming.

Cold Sun

On a bright and sunny February day in the Grand Tetons, it was hard to believe the thermometer in my truck reading -27 degrees Fahrenheit. As long as the sun was shining on me, I did not feel cold. Later that night, the cold was insane as I camped out inside the camper shell on my truck.

The hardship was worth it. I love the Tetons in the winter. Whether it is backcountry skiing or nature photography, it is a joy to be there.  

While photographing landscapes, I noticed a beautiful fox. It was grey, instead of the expected red. However, I could tell by the shape of its head it was not a member of the gray fox species (Urocyon cinereoargenteus). It turned out to be a partially melanistic red fox (Vulpes vulpes). Instead of the typical fiery red, this red fox was mostly gray and brown, except around its eyes.

Like me, the fox enjoyed basking in the warm sunlight on this bright cold day. I watched it hunting ducks in a tiny creek buried deep in the soft snow. To catch a duck in the deep snowfall, the fox had to sneak up very close before it made its final charge. At times I watched it leap high into the air and dive nose-first into the snow after voles.  

As I observed this beautiful fox curl up and nap in the sunshine, I wondered how difficult it must be for it to consume enough calories to stay warm and active in such a cold environment.  

A Different Red Fox

The term “cross fox” confuses many people as they think it is a crossbreed. It is not. When looking at these foxes from above, there is a cross-shaped dark region as a result of melanism.

Melanism refers to increased levels of the dark-colored pigment melanin in the skin or hair.

Cross foxes are more abundant in northern latitudes. In Canda, the estimate is that about 30% of their red fox population is of the cross fox variety.

Watching the fox jump high into the air and dive nose first to catch a vole hidden under many feet of snow baffles the human mind. How can the fox locate a vole under so much snow, and then pounce through the thick snow and catch it?

Scientists have known that foxes do use their keen sense of hearing to listen for prey movement under the snow. They now think that foxes may also use the Earth’s magnetic field to help locate prey in the snow.

Observations of foxes diving for sub snow surface prey measured a clustering in the angle the fox dives relative to the magnetic north. Foxes dive in a northeast direction independent of the time of day, cloud cover, or other factors. Researchers studying the foxes considered that the foxes must be using the magnetic field of the Earth to help orient which direction and how far to jump.

This theory considers that a fox may see a ring of “shadow” on its retina, that is superimposed on its surroundings and always fixed towards magnetic north. The fox would line up the shadow with where it hears its prey and is thus always at a fixed distance away from the victim when it launches its attack.

When I watched the foxes jump high into the air above a featureless snow surface, I did wonder how the fox could reference its location and direction to where it heard any sounds from prey deep below the snow surface.

The same cross fox leaps high above the snow to pounce on a vole deep below the snow.

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(c) 2016, Ed MacKerrow/In Light of Nature, LLC.  All Rights Reserved.