I do not know how roosters identify the 'state' of a hen but good mature roosters know which hens are laying and which are not. My rooster will not mate any pullets until they are about to lay, and he will not breed any hens that are not laying. He will also not feed those hens, he will only give food to hens that are laying.
I haven't got a clue how he knows this but he does without fail.

