in the novel white fang,

The She-Wolf's body is becoming slower and she lacks stamina. At last she and One-Eye find what she has been looking for, a cave near a small river where the two wolves settle down. One-Eye goes out to look for food and upon returning hears "faint, strange sounds from within." Having experienced this many times in his life, One-Eye knows that the she-wolf has given birth to cubs. Nature takes over at this point and the mother becomes protective of the little ones, growling, snarling, and snapping at One-Eye, who instinctively goes on a hunt for food for his new family. "The urge of his awakened instinct of fatherhood was stirring upon him. He must find meat." All of this is done by instinct. You can find more at the GradeSaver link below: