Mallard ducks will migrate, following their food supplies and breeding locations. Fall migration takes them south where they will eat plants, and crop residues. As spring comes they will return to breeding locations.  So they will linger at one pond so long as there is food to support them.   Due to the influences of people feeding ducks, some Mallards will become resident, and will not migrate. This can at times prove fatal as their food source may dry up with colder weather, and people not visiting parks to feed. So folks should not feed wild birds, and make them migrate as it was intended.   Some extension info on this breed of duck:

https://wildlife.tamu.edu/wildlifemanagement/waterfowl/

https://lancaster.unl.edu/4h/embryology/games/whomallard.htm

And, a great migration map from ducks unlimited with movement reports:
http://www.ducks.org/migrationmap/

Thanks, G.