Unbeknownst to us, a mallard pair (Mallards (Anas platyrhynchos) built a nest in our yard and laid eggs in it. We discovered it by chance when Lizzie accidentally scared up the hen while playing in the yard. On the second occasion of that, when I investigated, I found a nest with six eggs in it.
I placed recently dropped tree branches around the nest to dissuade Lizzie from wandering over to the nest. Lizzie has no interest in birds so I was not concerned she would pester the nest but I wanted to keep her away from the nest so as to reduce stress on the hen.
Unfortunately, two week later, the eggs were destroyed. I suspect raccoons (Procyon lotor) found the nest and ate the eggs.