That's the trouble with duck mothers! Totally clueless. They always take their brood on a little walk about through their 'neighbourhood' instead of staying home where it's safe!
We have a pond in front of our house and every year we've had a mother and family show up suddenly when the babies are tiny little balls of fluff. And they'll be there for a couple days, cavorting and frolicking in the quiet safety of our pond and suddenly they're gone and then they're back and then they're gone and too often there's one less in the family.... One year a mom started out with eleven babies and within a couple weeks she was down to three and one had a serious limp! They're like 'self-limiting' in their population.