I get at least a couple like this each month, sometimes as many as one a week. I have 5 hens, but I have no earthy clue who is doing it. I think it's just something that happens. Everyone has an off day now and then. We call them a misfire.
It happen's sometime's.I had a couple of my bantam hen's lay a couple no bigger than a robin's egg before.I did incubate them out of curiosity but they weren't. Fertile.Dh said Lord I don't think I want to see something that little if it hatches what ya gonna do with it.He said be like raising a baby hummingbird.Anyway nothing but I had high hope's.Sometime's they have these egg's
.I kept one a long time and had it in a fake nest on shelf in kitchen for dec. but sadly it got broken last year.