By communing with the incredible powers of her spirit, the shaman forges a cherished bond with one specific servant of that spirit—known as a spirit animal. A spirit animal is a creature chosen by a shaman to serve as a conduit, allowing her to more fully access the magic of her spirit on a daily basis. The shaman's spirit animal also grants her special powers. This ability uses the same rules as the wizard's arcane bond class feature and is treated as a familiar, except as noted below.
From this we can see the Spirit Animal follows the rules for a Wizard's Familiar, except where the Shaman class description says otherwise (such as the Spirit ability, which enhances the Spirit Animal in a way unique to the chosen Spirit - Mammoth Spirits grant the Familiar more Strength, while Life Spirits grant it fast healing instead, for examples.)