Wolf pups at birth weigh about one pound and are darkly furred. They are deaf, blind, have little or no sense of smell and cannot regulate their own body heat. For their safety, wolf pups are born in a den. Wolf dens can be in rock caves abandoned by other animals, in the hollowed bases of large trees, or in shallow surface beds. More commonly, pregnant female wolves dig dens themselves, often as early as three weeks before the pups are born.
Wolves prefer their den sites to be located on elevated areas near water.
Dens are typically tunnels that extend six to fourteen feet into the earth. At the end of the tunnel is an enlarged chamber where the newborn pups are kept. Between the time the pups leave the den and the next winter, the young wolves remain at rendezvous sites while the adults hunt the surrounding countryside. When adults return from the hunt, the pups lick the muzzles of the adult animals, and the wolves regurgitate predigested food for the young pups. As the pups grow, some of them will be very assertive in their play, while others in the same litter will be weaker and more submissive.