It's a wild and dangerous world out there. The ducks might be able to hide their nests and eggs from view to minimize the predators, but there are also a lot of creatures in the undergrowth that would appreciate a meal of duck eggs. :-)
Do you have to take the poultry in in winter or do they find a way to survive in the cold.
The ducks have a shelter but prefer to wander around the yard, if they hear a predator they swim into one of the two ponds. Once the pond freezes over they are more of a target.