I think deep in your heart you already know that this yet another reincarnated duck seeking revenge. You might do a quick calculation of how many ducks you've wronged just to see how many more are gonna start coming for you.
I woke up this morning with an epiphany ... Your stalker must be a duck that you've wronged that has come back to life reincarnated as a vampire chickadee. Moral of this story; Be Nice To Ducks!