I was watching the ducks in my backyard today, and found it interesting that the Mallards seemed to stand guard for the smaller Wigeons while they looked for grub in the soggy yard. When the mallards decided it was time to go, it seemed as though they started "herding" the Wigeons back to the pond. Curious behavior. This clip is the mallards "herding" the wigeons to the other part of the pond.
Backyard pond ~ Kent, WA