In April I bought home [3500kms] four nearly grown Pekin Ducks.
I lost one to a snake some time ago so now they are three.
For the first few months I had them they ate prodigious amounts of food & commercial grain/pellets and were also free ranged. I was actually concerned at the amount they were consuming as they were becoming expensive 'pet's In the past 2 months their food intake has backed off to the point that their provided food is now negligible and often not finished. Nutrition wise they are doing well because the female is consistently laying 2 -4 eggs a week, which is pretty good all considered.
These birds are obtaining the bulk of their food requirements in around 2 - 2.5 hours of free ranging per day. They have access to a waterbath outside their pen and there is always something for them to graze. They are going for the broadleaf weeds thus have nailed all the amaranth but they are also getting rid of any ngari burr seedlings. This area is outside my civilised garden and is mostly couch. The ducks also have access to my little banana patch which is a damp sort of an area. About 10 bananas, cassava, arrowroot, pigeon pea, sweetpotato and a really happy HAPPY plant grow in 2 lines there.
I bought them, show bird quality [and expensive] because my wife likes ducks. I am really pleased that they have turned into a real permaculture duck for us. They are a big duck maybe 6kg so not really a backyard duck. If you keep their pen dry their manure is easily collected as a solid. It comes up like 40mm tiles. I put about 4 'tiles' a square shovel's worth around a smallish banana and I suspect I set it back. The only big plants I have seen the ducks eat is grapevine and banana as a last resort.
Now I supposedly uploaded a photo but no idea if and where it will appear.