Haunt Fox (Vintage Paperback) by Jim Kjelgaard

This is the story of a red fox, of a boy and a dog who hunted him, and of the wilderness where it happened.

Because of the odd-shaped white patch on his chest that gave him his name, and the freak six toes on his front feet, Star was a marked fox from his youngest days. And because of his growing wisdom and cunning in escaping traps and dogs, he also became known as a "haunt" fox—an elusive prize eagerly sought by every hunter in the valley. Evading pursuit was a game Star enjoyed as much as did the hounds that trailed him.

Young Jack Crowley and his foxhound, Thunder, were the youngest hunters on the "haunt" fox's trail. The climax makes a surprising ending to one of the best wild animal stories Jim Kjelgaard has ever written.