Preheat oven to 300 degrees F.
A day before roasting, remove the giblets and neck from the cavity of the bird and discard. Trim the neck flap and excess fat from around the cavity. Rinse and dry the bird well. Set the duck on a rack on a baking sheet, and refrigerate, uncovered, for 24 hours.
Pierce the duck skin all over (including the back), every 1/2-inch, with a skewer or small knife. Season the cavity with salt and pepper and stuff with strips or orange, lemon and lime zest and the onion. Set the duck on the rack in a roasting pan, and pour a cup of water in the pan. Roast the bird for 3 hours, removing the duck from the oven every hour to prick the skin again. Remove the duck from the oven and carefully, pour off the excess fat from the pan. (If desired reserve this fat for frying potatoes or wilting greens). Raise the oven temperature to 450 degrees F. Return the duck to the oven and roast until crisp and brown, about 30 minutes more. During the last 20 minutes of roasting, brush the duck with 1 cup of the orange glaze.
Let the duck rest for 20 minutes before carving. Brush the ducks skin with glaze 4 to 5 times during the resting period. Carve the duck and transfer pieces to warm serving platter. Serve the remaining glaze at the table to drizzle over the duck, if desired.
Brush the surface of the crepe with some sour orange glaze. Place a few slices of duck in the center of the crepe and top with a few sprigs of watercress. Fold over and roll up and serve.
Place the juice, garlic, fennel and peppercorns in a medium saucepan and cook over medium-high heat until reduced to 2 cups. Strain the sauce into a bowl and let cool to room temperature. Once cooled, remove 3/4 cup and place in bowl to serve with the crepes.
In blender, combine all of the ingredients and pulse for 10 seconds. Place the crepe batter in the refrigerator for 1 hour. Heat a small non-stick pan over high heat. Add butter to coat. Pour 1-ounce of batter into the center of the pan and swirl the spread evenly. Cook for 30 seconds and flip. Cook for another 10 seconds and remove to the cutting board. Lay them out flat so they can cool. Continue until all the batter is gone.