Wolf pups are born blind and deaf, and are covered in short soft grayish-brown fur. They weigh 300–500 grams at birth, and begin to see after 9–12 days. The milk canines erupt after one month. Pups first leave the den after 3 weeks. At 1.5 months of age, they are agile enough to flee from danger. Mother wolves do not leave the den for the first few weeks, relying on the fathers to provide food for them and their young. Unlike wolf mothers, the fathers do not regurgitate the pup's food, but carry them pieces from a kill. If the mother dies prior to the pups weaning period, they are suckled by the pack's other females. Pups begin to eat solid food at the age of 3–4 weeks. Pups have a fast growth rate during their first four months of life: during this period, the pup's weight can increase nearly 30 times.