Red foxes force shrinkage of arctic fox territory

In the Arctic there has been a change in the distribution of both red and arctic foxes. Red foxes have expanded their territory to the North as the climate has warmed, at the expense of arctic foxes.

Due to a lack of observations of interactions between the two fox species, biologists have been unsure whether the loss of arctic fox territory was due to direct competition, or if they were indirectly competing for the same food. Rodnikova et al have now reported observing a red fox intruding upon a arctic fox den in 2007.

Researchers were working along the Yamal Peninsula in Russia in an area with twelve known arctic fox breeding dens. A red fox, in poor condition, made its way to one den's entrance and went inside. About thirty minutes later an arctic fox also approached the den, keeping against the wind and moving hesitantly, until lying down to watch the den, approximately 50m away.

When the red fox emerged later it lay on top of the den while the arctic fox barked at it for ten minutes. When the observer got closer the red fox went back into the den, but soon returned and starting the arctic fox barking once more. This continued until the observer left; when they returned, three hours later, the red fox was seen leaving but there was no sign of the arctic fox. Subsequent visits to the area showed no more foxes and no sign of the eight pups that been seen three days earlier.

This observation is the first sign of direct competition between the two fox species, although the researchers believe that the pups managed to hide in the den (which had eight known entrances and spanned 110 square-metres) and subsequently abandoned it.

Although red foxes and arctic foxes have been known to co-exist peacefully, it is also known that red foxes will sometimes kill arctic foxes even in farm conditions. This causes problems for arctic foxes who are almost never dominant against red foxes which are 25% bigger. Even here, when the arctic fox has a den and cubs, she was not prepared to fight the red fox.

Read more: A summary of the paper with quotes from the researchers is available from the BBC.