I have 9 chickens and 1 rooster. I'm getting 6-8 eggs a day. They are all fighting for the same box and 1 of my chicks is brooding in that same box. This doesn't seem to bother all the other chicks because they just push her aside and lay their eggs. My brooder rounds up all the eggs and sits on them. I have been collecting the eggs daily but I would like to have babies. My question is...How do I know if the eggs are fertile?