My line generally does... this pic is old but this Angel's first 18 eggs. All dated left to right, back to front. She started out all wonky, 4th egg a double yolk. By the second week she was getting consistent.
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A few more visuals...
Lil Jessies first 4 eggs last year
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One of her first this year after break. Pic is shadowed a bit. True color is a little lighter. A decent 6.
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A Rebel pullet I kept to follow. Mom doesn't lay a dark egg, a pretty consistent 4, so expectation wasn't high on this one. But I've never hatched from her so here we are. She is surprising me with all these speckles tho, in her first 14 eggs and she's turning out to be a beautiful girl. Makes me want to hatch more from her Mom.
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I also agree with second year in some are darker than the first year. Lil Jessie is one that I took notice of this year when she started back up.
As a general rule, with Marans we want to follow the first 20 eggs to achieve they're true color average they will lay. I tend to keep following to 30 eggs just for funsies, and continue to follow/stalk all my hens.
@Chooks man taught me years ago...we must know our hens and what shape, size, and color average each lays. This has rung true as having close to 20 girls now when I grab an egg, I can typically know exactly who layed it without having to stalk nest boxes now.....
as much.