Some — but not all — species of ducks mate for life. Geese are known to mate for life, and although ducks are social animals who prefer to live in large groups, they typically have multiple mates.
Mallard ducks pair up in October or November each year to mate. Once the female lays her eggs, the male leaves her to care for the young. Male mallards will forcibly mate with females who are unattached, regardless of their species and regardless if they already have a brood of babies.
Geese are the largest members of the duck family. Geese always mate for life and both parents are involved in raising their young.