Malards on my mind

My office here at the institute has a beautiful view of the unter-Warnow, the tidal harbor area just before the Warnow River flows into the Baltic. The city of Rostock and many of its suburbs are arrayed along both banks of the unter-Warnow, and the Institute is right above the banks, allowing marvelous views. There are some drawbacks to this for a person easily distracted by birds, as I am. I frequently find myself watching the gulls chasing each other, the swans terrorizing the mallards, or the rooks, hooded-crows and jackdaws playing in the wind.
The last several days I have noticed that the same two groups of mallards are always in the same two spots. In the river, near the institute there is a consistent group of six males and five females, always floating in about the same spot. In a drowned foundation on the abandoned port-facility just west of here, there are always four male and three female mallards, with one of the males showing the white splotching indicating it has some ancestry among the domestic mallards. These several birds always seem to be in the same two groups, in very similar spots, and I can only assume they have found something good to eat there, as they don't seem to move elsewhere to feed. I wonder if they will stay all winter. I wonder what I should have done in the time I spent censusing mallards.