Actually a rooster doesn't instinctively know. Fertility of a particular bird can be determined by the comb color and shape. Combs are visual clues to other birds on reproductive status. When hens go out of lay the combs shrink and lose their color. Same will happen to an unwell rooster. When birds are productive and fertile combs are big and bright red.That is a really good point! Haven't thought of that.
Nothing wrong with that! We definitely don't mind, and I am sure our girls appreciate the chance to regrow their feathers for the winter without having them plucked out daily by our vigorous rooster![]()