Vixen, Animal Man, Bwanan Beast, and essentially everyone else who has animal powers in the DCU get their abilities from the same place.

I think it has changed since it was revealed in Animal Man, but their are essentially totems like Vixen and BB rock that allow them to tap into some energy field that gives them animal abilities. These same aliens recontructed Buddy Baker's body from scratch so that his body could tap into the field without alternative measures. Essentially his whole body is the totem.