I had a Muscovy duck decide to sit on eggs this fall. I let her.
now, in hindsight, since it was so cold when she was sitting (20s to 40s), I should have taken out a few of the eggs so that I knew for sure she could cover them all well (I let her sit on 17). Also, in hindsight, as soon as most hatched, I should have taken those that weren't yet hatched, into the house, and kept them warm until they hatched, and then reintroduced them.
Other than those two points, she did fine.
She actually managed to properly cover all of those eggs, but three were just a bit slower than the rest. Once all the other eggs were hatched, she was no longer tightly sitting on the last three, and two of the three chilled too much mid-hatch and died. I managed to save one.
I did have her in a completely draft free area. Once the ducklings hatched I did put in a heat lamp, but it had also gotten colder. We went down to 5F.
My power went out once, and she just crammed all of the ducklings (11 made it) under her. I think they might actually have been fine if I had never put in the heat lamp.
I put the heat lamp next to the food and water so the ducklings wouldn't get chilled while eating and drinking.
