I think it depends on a lot of factors, the first being do you mean fertility or hatchability?
with us we have had grea fertility rates, usualy 100% once they have beed together for a couple weeks.
But hatchability can be affected by a lot of things.
storage of eggs, cleanliness, disease, incubator conditions/failures, powe outages, failure of a hen to sit long enough, shipping conditions..the list can go on and no.
but overall, my experiance with ameraucanas is they are quite fertile.