My ameraucana is the top hen and has been trying to sit on eggs multiple times in her short life. She's about 18 months or less. She was all hunkered down on the pile of eggs a few weeks ago (this had become typical) and I lifted her off after getting pecked and put her on the ground while I collected the eggs. I got halfway back to the house and she came screaming out of the coop following me through the yard putting up a ruckus, flapping and yelling. She was really mad that I took those unfertile eggs she was working into the house and kept doing it everyday! So I put two fertile eggs under her. They never developed so I put wood eggs under her which I let her keep til the night before a hatch from the incubator. I wrapped two welsummer eggs in a warm towel and took them out to replace the wooden eggs. And here is the result. She is happy as a little clam and so are her two chicks.