about 5 years should be good, but most ducks drop eggs anywhere so available to crows magpies, rats weasels and all sorts..... also you might find a hidden nest somewhere, not easy to find as they cover the eggs with grass...... ive been short sometimes and found a nest with 30 eggs... all no good as you dont know how old they are...... if you find a nest laying area dont remove all the eggs as they clear off and find somewhere else to lay... leave 2 china eggs in the nest , it can be hard to get them to lay in a man made nest box like a chicken, people leave them locked up till about 9 am as they lay early morning.