I really don't know what happens over here during incubation but I always have lopsided hatches. I hatched 5 ducklings originally, 4 were boys. I hatched 6 olandsk dwarfs - 5 were boys. My neighbor hatched a dozen of my eggs - all 10 that hatched were boys. Seems like the earlier I hatch in the year the more girls I get and the later in the season the more boys I get but that's not always the case as this group was later in the year (but still abnormally cold). I am really thinking it has to do with temperature. I was hoping one of the "big boys" that chicka sent me eggs to would be a boy so I could hatch some deliciously large birds but looks like they'll just have to be the female contribution. After my rooster purge a few weeks ago we only have legbars, a leghorn, some smallish unidentifiable birds and a really gigantic but slow to meat out jubilee sussex.