Dave, you answered your own point before I had chance! "But to take "doe" or "fallow doe" literally as a deer, picking him up and carrying him on her back, seems ludicrous to me." Yes, it's as ludicrous as talking birds, horses in conversation or any domestic pet being impressed by a cage of gold. "Yeah, great! Thanks! A golden cage!" This post has been fascinating, despite - or perhaps because of - the lack of a definitive answer. I suppose I ought to have known better to expect a definitive answer where traditional song is concerned. Any more, anyone?