I found the cannonical source for the rats distinguishing japanese from dutch but not backwards.
Interestingly (for some values of interesting) rats trained on Dutch (fwd) could differntiate it from Japanese (fwd) but rats trained on Jap could not spot Dutch. Backwards confused them all. As far as a quick scan of the paper showed they did not train rats on Dutch or Japanese backwards. Perhaps I can get funding for that one.
But still no ducks or German found, where did that meme come from, wishful thinking at the reg ?