That is completely ludicrous, LOL. I have no idea what book or author you are talking about. Is it more a book about wild species? Anyway, as far as domestic breeds, obviously there are considerably more than 5 breeds and there has been for centuries. There are probably at least 15 or more breeds (just breeds, not varieties) that have existed for more than 80-100 years even, some far more ancient even the ones you mentioned for example Aylesburies and Hookbills (Hookbills even mentioned by Darwin back in the 1800's). Anyway, I am headed out the door right now, but I imagine I could come up with a list of probably 20 or more breeds and 75 or so varieties of domestic ducks easily.