How can you tell if a duck egg is fertilized?

Answer 1

if within 28 days to 31 days and the duckings haven't hatched,there is a good chance the ducks are dead of late death or because the eggs weren't handled carefully enough,although the ducks may hatch late but fragile.

Answer 2

you egg had to be about 1.5 weeks to tell..............

you take a really bright LED light into a dark room with the egg and you shoudl have some one with you . then you take one hand and make it into a c and join it with your other hand and make a "cup" have ANOTHER PERSON put the egg on your hands and hold it up to the light (wich has to be pointing up) and if you see a "spider" or a fat squiggle that is moving around then its fertile but if it is clear then its not

but remember IT HAS TO BE 1.5 TO 3 WEEKS OLD TO SEE IT!!!!