Congrats on your incoming eggs. My boys comb up pretty early, by 2-3 weeks and the copper starts appearing earlier. This is probably due to my Sire having a good size comb and over coloring in his chest.
Some breeders that focus on smaller combs may make this a little more difficult with slower maturing lines. I've had my BCMs for 4 yrs now, so I've gotten pretty good at spotting the boys early.
Hatch day Easter Sunday March 31, 2024
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April 16, 2024
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If I can offer a bit of advice ...I would follow your breeders recommendations on incubation humidity as Marans eggs typically like a lower humidity known as 'Dry hatching' as the harder shells and darker pigment retains more moisture.
I've had good results doing this with 20-30% the first 18 days and not over 50% at lockdown with a calibrated external hygrometer is highly recommended also.
Best of luck with your hatch.