What age should my runner start laying? (she was born mid april) I have been finding a really light green egg in the morning that I thought was an easter egger egg and the lightbulb came on today that they might be duck eggs. How do I tell if it is a duck or hen egg? Its about the size of a large hen egg. I really feel stupid that I can't tell, but I have about 20 new hens that are or are close to starting to lay and I'm still learning who is leaving me what.