ower animals actually are not a part of the Wiccan or Witchcraft tradition,
but were actually used by native Americans.  However, many covens do
in fact have a totem which is known only to those within the group. 

Witches have been known to have what we refer to as familiars.  Familiars
are animals that live in the home and assist with magickal workings. 
Cats are very high on the list (Thus the whole Black Cat Thing) and
dogs, snakes, ferrets and other small animals are also used quite often
physical form.  Familiars, however, or not just ANY animal.  They are a
specific psychic derivitive of ur spiritual self.

Not all witches work with physical familiars, obvoiusly, there are many
limitations, such as money, space, and the time needed to tend to the
animals.  A familiar, actually, represents the positive qualities of 
it's species.  A familiar offers and provides a link to the powers of
the Animal Kingdom, the essence of that power.  A power that is quite 
large indeed.  Thus the words, "Power Animal" (see...all makes sesne)