The Arctic Fox

Arctic fox territory
http://animals.nationalgeographic.com/animals/mammals/arctic-fox/

About

The arctic fox is a species well adapted to the freezing climates.  They are generally found in the northern regions indicated on the map.  Arctic foxes have shorter legs, ears, and muzzles than other foxes, which accompanied by their thick fur allows them to maintain an adequate body temperature despite sub-zero surrounding temperatures.  Arctic foxes can thrive in temperatures as low as -50 degrees Celsius.  During the winter, the foxes display a white coat to camouflage themselves with the snow and trade it for a brown coat in the summer when the snow starts to melt.

An arctic fox sneakily trailing a polar bear
http://www.gossiprocks.com/forum/pets-animals/95484
-pictures-polar-bears-youve-never-seen-them-before.html

Diet

Arctic foxes are both hunters and scavengers.  Their primary diet includes lemmings and voles, but they will eat anything they can get their hands on.  When food is scarce, they have even been known to trail around polar bears, waiting for bear to hunt so they can pick up the leftovers.  Their white coats allow them to stay camouflaged around the polar bears, keeping them from becoming a snack themselves.

During the winter season food is scarce.  The foxes overcome this in a couple of ways.  Whenever the foxes have a surplus of food, it is always stored for later.  Foxes have been known to create caches of food large enough to last them a whole month.  They also lower their metabolism, which allows them to go longer without food.  During the winter, it is not uncommon for a fox to go 10-14 days without food.  In a study done, researchers gave an excess of food to arctic foxes during both winter and summer, and found that they ate 275% more food during the summer.  This change in metabolism allows them to survive when food is scarce.

Arctic fox pups in their den
http://www.turtletrack.org/Issues01/Co08112001/
CO_08112001_Fox_Saves_People.htm

Reproduction

The mating season for arctic foxes is usually February-May with litters being born April-July.  Usually 6-12 pups are born in a litter and are kept inside dens to protect them from the cold until they mature.  The amount of pups born in a litter is highly variable with the amount of food available.  When food is plentiful, litters of up to 15 pups have been recorded.  However in the absence of foods, a litter can contain as few as 2 pups.  When food has continued to be scarce, there are documented cases of the stronger pups eating their weaker siblings to survive.  The amount of surviving offspring is very closely linked the amount of food available to the foxes.