Ducklings need their mom for quite a while. Even though they can swim right away, their feathers are not waterproof & the mother takes her oils and puts it on them. Without it they will die shortly, suddenly, & of apparently nothing. Without these protecting oils they will get sick & die from being in water. Our ducks were born last May & eventually decided to live on the river but still come up to the house daily to be fed a little. They made it through the cold winter just fine & being domestic, they never migrated. If you see ducks that stay all winter, it's because they are either partially(descendants of) or totally from domestic stock & don't know to migrate. They are however hardy & totally waterproof.