I was scratching my head over where they could get an idea like Berschlange (Bärschlange), bear-snake, and I suppose there are quite a few animals that are bear-like in shape that have long tails. There are bush dogs that look like bears, relatives of the raccoon family that are brown and somewhat bearlike, and quite a few other bear-like animals (except they are smaller).
As an alternate source, it occurred to me that the big bear/little bear constellation is frequently drawn within the snake and could possibly be the inspiration for a bear-snake myth:
Morgan M.389 1469