So .... a hormonal imbalance, perhaps? That has now been corrected through the process of brooding?
I dono... just guessing. What a mystery!

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Just to make a proper job of finishing the thread (I hope) here is Bracket. She's finished mothering full time although one of the three hens that hatched the chicks still spend the night with them in the next box. Bracket has perched for three nights in a row. She hasn't fallen off, I've checked both nights.
I'll never really know what the problem wasView attachment 1968612
.