Polar bears--Ursus maritimus, are at the top of the food web in the Arctic habitat. They consume seals--ringed or bearded. This is their preferred food source. The seal's blubber helps the bears to build up the insulation they will need to survive in the harsh Arctic climate. However, they can also consume walruses, beluga whales, reindeer, bird eggs, rodents, fish and even berries and other vegetation. Bears hunt on the ice however, due to global warming, the ice is melting and sometimes they can become stranded. They are not good at swimming after prey. During late fall through the early spring when seals make breathing holes in the ice, bears wait for them to come up to breathe and grab them. This technique is called still hunting. Polar bears are active year round, with the exception of pregnant females. They are capable of fasting for several months during late summer and early fall because the sea is unfrozen and they cannot hunt for seals then. This is when they eat other foods or live off their own fat reserves.