goosedragon's explanation of their history explains why I have them.
I am a gardener, and live in New England - land of the slugs. They are great foragers, and love slugs. Their waste is my plant fertilizer. They eat a number of weeds (dandelions, chickweed, and violets - I think violets are wildflowers, DH calls them weeds).
They have a secure area and during the day when I am in the garden, I bring them with me to different areas, using portable fence. While I weed and tend, they forage for insects, worms and grubs. Yes, worms are the gardener's friend, but the population can stand a little pressure, especially since the ducks are also eating many pests, and laying down nutrients as they go along.
BTW, they are a hoot! Sweet and funny, exuberant, cheerful, inquisitive, beautiful. (chocolate and black)
They only weigh a little over three pounds each. DH and I can carry all eleven in a dog crate wherever we need to move them, if necessary. Outside, they generally move themselves.
During foraging season, which roughly aligns with laying season, they provide much of their own food.
Did I mention eggs? For me, that is the icing on the cake. Runners lay (conservative guess on my part based on reading - this is our first year and ours are only eleven weeks old) from 160 to over 300 eggs per duck per year. Not bad.
