I'm going to say that looks like decay, especially since the ducklings hatched last Tuesday.
Dark spots in duck eggs often mean bacterial growth (They can mean a misplaced pip, but that is not a localised little pip).
I'd probably have already thrown it out at this point, but if you're still worried that it may be alive, candle. Go into a dark room, take a bright flashlight, hold it against the fat end of the egg, and see what it illuminates. Healthy eggs look like these onesshould we try cracking it open or wait a bit longer?