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 female duck. Its male counterpart is the Mallard Drake.
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.