The late eggs will not hatch. Hens may desret their nest if another dumps in it. Dumping also results in excessive size clutch, to many to incubate. Still, there is some advantage. At least some hatch.
Hen expends less energy.
Major portion of population migrates down Mississippi flyway to winter on Gulf coast. Others winter in Mexico and Chesapeake Bay. Tend to feed in shallow water on vegetation. May tip like dabblers rather than dive. A Maine Nester.