Soos-Quacken
Chirping
Disclaimer: this is all hypothetical, so it is illigal to possess either wild malards or their eggs. But what happens if a wild female mallard addops your flock and goes broody after mating with one of your ducks? Do you remove the eggs because there half domestic and violate the law surrounding wild ducks or let the eggs hatch and allow half domestic ducks to potentially enter the wild violating a separate law?