I apologize if this is a bit long... I have been hatching eggs in incubators for 7 or 8 years, on and off. My first attempts were in a Styrofoam still air incubator, eggs hand turned. I had consistent 70% success rates with geese, ducks, and chickens. I graduated to a forced air Styrofoam incubator (Hovabator) with an auto turner and had similar results most of the time. I used the factory settings and instructions for humidity (45-55% until settling, then 55-65%). The temps fluctuated, but stayed within the 99-101 degree range. Then 2018 arrived. I am hatching from a free range flock of mostly Marans Hens and the same Marans roo I used last year with good results. Some of the hens are his daughters. They range on the same untreated pastures and eat the same whole grains (organic peas, corn, triticale, wheat, sunflower) and organic supplements as last year (I make my feed based on Harvey Ussery's recipes). Everything is non-GMO and organic. I used the same Hovabator, same humidity levels. The first hatch in Feb was 66% with several dead chicks in the unhatched eggs. Some eggs were undeveloped (not fertile?). The following hatches got worse and worse, down to 25% with many undeveloped eggs and several with chicks in late development. Some pipped, even zipped, but never made it out without help. Some were shrink wrapped. Some pipped and then quit. I help them out and they were shrink wrapped. I did a lot of research, including on this forum. I got a lot of conflicting information: incubation humidity is too low or too high, hatching humidity is too low or too high. I experimented with humidity levels from 40-60% for incubation (air cells seemed normal size at 7 and 14 days at any level) and going as high as 70% (using sponges) for hatching, and still getting shrink wraps. I checked humidity levels and temps with secondary devices, even bought two new incubators (both Little Giant) with forced air and auto turners. The temp seems to be in normal parameters in both. Same results, possibly getting worse. The hatch just finishing now was a little better (10 out of 30) but I had one chick hatch rigid and one hatch with no yolk absorption and died. One problem I was having early on was that early hatchers were rolling pipped eggs and preventing them from hatching. I solved that by settling the eggs into plastic 30 count egg trays, which worked great. I am getting a wide range of hatch times, 19-23 days, where they hit almost exactly 21 days (for chicks) in previous years. I crack the non-hatching eggs later and find chicks that are in the air cell but dead. Some are well developed but dead. Some died halfway. Still about 50% are undeveloped at all. (I find that candling Marans eggs for early blood vessel development is unreliable because of the dark shells) Yesterday I had a batch of eggs hatch under a hen, using Ameraucana and olive eggs from the same flock. 7 of 9 eggs hatched. The eggs I am hatching in the incubators are the Marans, so there is more than one variable there. I have a batch of Marans eggs under a hen now, due in two weeks, just to see what happens. So what am I missing? The parameters that worked before no longer work. Changes aren't working. Is there something wrong with my breeding birds? They all appear healthy. The chicks that hatch successfully grow up well.