Hey there, how old are your call ducks? If they are older than 3 years that may decrease the fertility and hatching rate...are your female call ducks just starting to lay and if so have they become broody yet? My call ducks make great brooders and raise all the ducklings themselves..maybe try natural incubation and let them sit?! I have also found that it difficult to hatch call duck eggs in incubators and my incubator also has an automatic turner..did you check the humidity levels and where abouts is your incubator placed..? Also how do you know the eggs are fertile? Have you candled them at different stages during incubation to see their development and at what stage did the embryo's usually die at? I can give you more advise once you've answered the above questions