What Happens When a Hen Goes Broody? and Other Chickeny Mysteries, Part 1 :
There are some things your parents don’t tell you and schools simply don't teach and even books don't fully explain. Some “Beginners’ Guides to Whatever” seemingly packed with interesting stuff but, annoyingly often, not the actual answer you need. So, after three years of keeping chickens, and in no particular order of priority, here are some of our observations on chooks, chicks and cocks and what they sometimes get up to.
Broody hens : It seems to us that it’s hormonal. Adult hens lay eggs and then there comes a time when they go broody and sit. And broody hens will sit on nothing and not budge, as firmly as they’ll sit on a clutch of eggs.
Just before they become broody, they may change their behaviour and stop laying in the nest box—where you conveniently collect their eggs each day—and find a hiding place, where they’ll lay an egg a day until they have a clutch, whereupon they stop laying, start sitting and go missing. Or, they continue to lay in the nest box, so you see no change to the routine until one day she sits down and doesn’t leave.
They also persuade other hens to lay in their nest, evidenced by clutches of mixed chicks hatching out under one hen. The largest clutch we found was of 22 eggs, which we reduced to a more manageable dozen, eleven of which went on to hatch out.
Perhaps you do notice a change, that you’re not collecting the same amount of eggs as usual each day from their nest box. Then one evening, when it’s time to round up your free-range flock into their fox-proof henhouse for the night, you notice a hen missing. You check out the usual places, call to her, rattle the food bucket and all to no avail. Your heart sinks as you think you’ve lost her to a fox or a dog.
However, the following day, you catch a glimpse of her at feeding time. But then she disappears again. Putting two and two together (lower egg count and missing-appearing-missing hen), you realise she’s gone broody and native at the same time. 
You continue your sleuthing, as Sherlock Holmes would have done, had he kept chickens, and set up an “obo”, patiently tracking her when she slopes off again, back to her nest. With the help of an assistant, you then grab her and carefully pick up all the warm eggs, transferring the nascent ensemble into another nest box with enclosed run—we use our chicken tractor—where she can sit in safety for the rest of her “pregnancy”.
Part 2 soon … along with the reason why we now date the eggs under our broody hens (see photo at top).
