Last year my best broody hen was easy to spot - she was the only feather-leg that I have, a buff cochin. Most of my chickens are buff orpingtons, with a few silver-laced wyandotte hens for good measure, and two "easter eggers" named Flower and Nemo that we keep for sentimental reasons.
This spring the hen went broody again, and sat on a dozen or so eggs in a nest box for a really long time. One egg finally hatched, but either the chick fell out of the nest box or she pushed it out; anyway, she had no interest in it and it died. She continued to sit on the eggs, and finally ended up sharing the nest with a broody game hen.
Since it's been a month since that lone chick hatched, I finally found the nest empty of both hens and decided to throw out what must be really stinky eggs by this time. Chicken eggs take 21 days to hatch, and these eggs were probably six weeks old or more. A couple have disappeared, so the chickens have been eating them. I carefully picked up the possible-stink-bombs, and headed outside the coop, and tossed them at a rock. The last one bounced. I picked it up and discovered a live chick inside. I peeled the shell off and it wiggled in my hand.
I really felt awful about that chick. I thought of the six-day-old guinea keets in the brooder, so I put the chick in a bucket and then into the brooder so they couldn't bother it, but so it'd have the warmth it needed to dry off and survive. It's doing fine and has become part of the "flock". I guess these keets will have a chicken brother or sister. I've read that it's good to raise a few chicks with keets so they learn to go in the coop at dusk. I've also read that it's good to raise a few keets with chicks so that the chickens learn to run from a hawk's shadow or other predators. Guineas are pretty wild birds.
The chick is evidently from one of the wyandotte hens. as it's silver instead of gold. It's a pretty special chick, born by Caesarian section, so to speak.