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If she is pulling out down I'd say she is close to going broody you can go in and mark the dirtiest eggs and once she begins to sit 24/7 take those out or just leave them all and see how many hatch, are you wanting a large amount of ducklings? if not them remove as many eggs as you want after she has begin to sit they won't start developing until she is sitting on the nest 24/7 and only getting up to eat drink swim and poop. She won't care how many eggs she has once she is in full broody mode as long as she has some. You have to think about what your plans are for the ducklings once their hatched if all of them do hatch. As long as the eggs haven't frozen and cracked they should be okay and are usually still good for incubation up until day 10 so the oldest may not hatch or have a lower percent of hatching. Keep us updated.