Reproduction[edit]
Arctic foxes do not hibernate and are active all year round. They build up their fat reserves in the autumn, sometimes increasing their body-weight by more than 50%. This provides greater insulation during the winter and a source of energy when food is scarce. They live in large dens in frost-free, slightly raised ground. These are complex systems of tunnels covering as much as 1,000 m2 (1,200 sq yd) and are often in eskers, long ridges of sedimentary material deposited in formerly glaciated regions. They have multiple entrances and may have been in existence for many decades and used by many generations of foxes.[7]