We have four Rhode Island Red hens, or at least we thought we did. They all look like hens, but I've noticed several eggs that appear to be fertile. Since I don't 'candle' our eggs for obvious reasons, I find the usual 'blood' in the yolk common to a fertile egg when I actually use the egg. We generally get three to four eggs per day. So, today, I witnessed one of the "hens" exhibit mating behavior with another of the hens. Since they look so much alike, I'm not sure I could fix the guilty party unless I had a paintball gun and caught him/her in the act. One of these hens is very friendly and attentive when we're in the pen, the others, not so much.I believe we've got a ringer. I guess I'd better start candling the eggs to see what's going on and if the eggs are viable. One of the hens seems to spend a lot of time in the nest box. We raised these hens from chicks purchased at the feed store. Any suggestions on determining, which, and how to determine if the eggs are fertile and viable?