I'm scratching my head over this one. I have been hatching for several months now and had no problems (some 100% hatches). Until I started hatching my Cuckoo Marans' eggs. This past hatch I set 15 RIR, 9 Ameraucanas, 9 Cuckoo Marans, and 1 Serama mix. Temp was 100 with no variations, humidity 55%-61% with spikes during hatch. I culled out 2 Marans and 1 RIR for lack of development partway through the hatch. We got 14 RIR's, 9 Ameraucanas, the Serama and only 1 Marans. Of the 7 that made it to day 18, 1 chick, 2 no-shows, and 4 pipped then died. This was my 4th setting of Marans, and every time I get 1-5 chicks out of 9 -15 eggs. They are the only breed showing problems. Could it be breeder age (they're about 34 weeks old)? Genetic? Or are they more sensitive to temp/humidity than the other breeds? The chicks I do get are large and healthy--they pass the other breeds up in size by a couple of weeks. I have an older, unidentified cabinet-style incubator with auto-turning that works wonderfully. Any help would be GREATLY appreciated.