Rinse the pieces of guinea-fowl under running water, then put them in a bowl with cold water.
Put in a cast iron or heavy bottomed pot a few tablespoons of extra virgin olive oil, the finely sliced red onion and the diced pancetta. Cook over low heat for about 15 minutes, until the onion is soft and transparent.
Add the pieces of guinea fowl, the rosemary, the sage, the salt and the freshly ground black pepper. Stir with a wooden spoon and cook for about 45 minutes with the lid, over medium heat. Turn frequently the pieces of guinea fowl to ensure that every piece is well browned on all sides.
When the guinea-fowl is almost cooked, squeeze an orange and pour the juice over the meat, add half an orange cut into thin slices, stir and cook for the last 5 minutes.
When all the orange juice is reduced, the meat is ready.