From Ring of Brodgar
|Creature-Products||Dead Mallard: Mallard Feather, Entrails, Mallard Meat, Bone Material or Wishbone|
This data is specified at the individual Terrain pages.
It's a male duck. Its female counterpart is the Mallard Hen.
Mallards can easily be caught on horseback. Come at them from behind so that they won't flee in the direction of the water on which they spawned and then simply run after them.