You perhaps have never thought about it, but duck legs are too short to negotiate stairs. And their knees bend the wrong way. So, unless you are prepared to carry each bird in separately, (quite time-consuming if there are very many), you are not likely to have many ducks as house guests.
I hate to think that I may have limited my acquaintances with the feathered fowl due to this issue…but there it is.
Cheers,
Gus