The Kine saga, book 2: Witchwood
Alan Lloyd1991

When their tranquil valley is invaded by the Rat King and his super-rats, the animals seek the help of the weasel Kine - champion and killer of the she-mink.

With Watchman, the aged rook, and the sparrows Flit and Farthing to guide him, Kine goes in search of Lord Rattun and his stronghold in the wild and swampy Witchwood - knowing he must prepare to dance the dance of death.