It depends on how old the hens are, also what breed, as some breeds never go broody. It takes the younger ones awhile to understand the eggs need to be sat on. Even then they don't know how long. But established hens will watch till they figure they have enough eggs they can comfortably cover and some steal even too many eggs before they go broody. The sign of going broody is a reluctance to leave the nest and getting irritated when you take her egg. Regardless of if it is the only one.
Still even then its hard to say when a chicken will go broody. Or even if they will continue. If you want to try sure leave a clutch of say 6 eggs and see who tries to set on it. Then keep an eye on that one. Mark the eggs as you go so you know what ones are old and remove them after two weeks cause the embryo could be dead.
OR you can use a set of eight golf balls. They don't know the difference. And then get them to go broody and then replacing the golf balls with eggs once she has become extra broody. A broody hen will lay almost flat on the nest spreading herself all over the eggs. Not up right as if she were laying.
I know this sounds complicated but then so is a broody hen lol...
Arklady
