It shelters them from the weather and protects the pups from other animals that may want to hurt them. Packs sometimes use the same den year after year. At other times they make or find a new den each year. Pups grow inside their mother for about 63 days before being born. At birth they weigh only 1 pound and their eyes are closed.
Pups grow quickly.
About 12 to 15 days after they are born they open their eyes. By 2 weeks of age the pups can walk, and about a week after that they may come out of the den for the first time. At first they live only on milk from their mother. In a few weeks they start eating more and more meat. This is brought to them in the stomachs of the adult wolves.