I usually embark with 10 female ducks and two male ducks. I always create a pasture where all of my ducks (both male and female) live. Almost all of my female ducks lay fertile eggs when they first arrive, but they only seem to lay non fertile eggs after that. What do I need to do to get them to lay fertile eggs?
Update and further details: I just created a large open (but indoor) pasture room with many nest-boxes installed in the pasture area and all of my male and female ducks pastured in it. I have more than a dozen each of both sexes. I have forbidden the door to the pasture room so my dwarves are not disturbing the eggs after they are laid in the boxes. I am running the 2014 version of DF. I then let the game run a few seasons; The females are laying many non-fertile eggs in the nest-boxes; apparently the males are still having problems fertilizing the eggs.