"Being an expert on ducks, I get this question a lot. The answer is really quite simple. The duck has their internal organs stored either entirely in their heads or entirely in their feet depending on their gender. (females in the head and males in the feet. The bigger the feet the more mates) Therefore they are complety hollow in the rest of the body. That is how they float. When they wish to return home the store extra air into their bodies and go down into underwater caves where they can stay for up to 2-3 days. And as for migrating they do go north. North right up into space. On little duck space stations."
PhD in ducks