Stuff the chicken cavities with the reserved fennel ribs, chopped, and truss the chickens. In a large heavy skillet heat the butter and the oil over moderately high heat until the foam subsides and in the fat brown the chickens, patted dry and seasoned with salt and pepper, in batches, transferring them as they are browned to a flameproof roasting pan. Pour off all but 1 tablespoon of the fat and in the fat remaining in the skillet cook the sliced fennel over moderate heat, stirring, until it is golden and softened. Spoon the fennel around the chickens and add the wine and 1/2 cup of the water. Roast the chickens in the middle of a preheated 400°F. oven, basting them every 15 minutes and adding enough of the remaining 1/4 cup water as necessary to maintain about 1 cup pan juices, for 40 to 50 minutes, or until a meat thermometer inserted in the fleshy part of a thigh registers 180°F. and the juices run clear when the thigh is pierced with a skewer.
Transfer the pan to the stove top. In a small saucepan heat the Pernod over moderately low heat until it is warm, ignite it, and pour it carefully over the chickens, letting the flames go out. Transfer the chickens to plates, and garnish each serving with a parsley sprig. Boil the pan juices until they are reduced to about 2/3 cup, season the gravy with salt and pepper, and transfer it to a gravy boat.