This is a recipe specifically for wild ducks that are not morbidly obese. It will not work well with hugely fat ducks or domestic ducks. For those ducks, use my slow roasted duck recipe. You will want to set the birds out for 30 minutes to an hour to warm up; roasting a cold duck doesn’t work well.
Preheat oven to 450°F or higher. I often cook ducks at 500°F, and small ducks are best cooked at these high temperatures. (You can get away with 425°F if that's as high as your oven will go.) Let the oven preheat a good 20 to 30 minutes. Let the ducks rest at room temperature while the oven heats up.
If the duck is reasonably fat, use a needle to pierce the skin where there is a lot of fat under it: The front of the breast, between the breast and legs, at the flanks, and all over the back of the bird. Be careful not to pierce the meat of the breast. Rub lemon over the bird and dust it with a good salt. Stuff the spent lemon or orange wedge inside the duck.
Place a few celery stalks onto an oven-proof pan (I use a cast-iron frying pan), arranging them so you can rest the ducks on top. This prevents the ducks from sitting in their own juices. Roast in the oven as follows: About 10 to 15 minutes for teal or other small ducks, 13 to 20 minutes for anything up to the size of a gadwall, 18 to 25 minutes for a mallard or canvasback. The key here is an internal temperature of about 140 to 145°F at the deepest part of the breast meat, which is in the front third of the breast. Don’t have an instant read thermometer? Get one. Ducks need to be cooked medium-rare to medium. An overcooked duck is a sad thing.
Take the duck out, move it to a cutting board and rest it. Let small ducks rest about 5 minutes. Large ducks need to rest closer to 10 minutes, and geese up to 15 minutes.
If you want a simple pan sauce, remove the celery and stir a tablespoon or two of flour into the drippings. Let this cook on the stove (you might be able to do this solely with the residual heat in the hot pan until this roux is the color of coffee-with-cream. Add a tablespoon of Worcestershire sauce, some wine or brandy and the juice of a lemon. If the sauce is too thick, add a little water or stock. Whisk everything to combine and add salt to taste. Turn off the heat, add a tablespoon of minced parsley and a knob of butter. Swirl to combine and serve.