Sitting as in clamped down not leaving the nest or just laying? It's not unusual for the first few eggs to be duds. Is there a chance that either of them is a mule? A scovy is different from all other breeds of ducks. It is the one breed that is not mallard derived. It's like horses and donkeys - you get mules and mules are sterile. So if a scovy crosses with any thing other than another scovy - The resulting offspring are mules, and infertile.