One of my girls (a 7 month old black Australorp) has been laying fart/fairy eggs for the past 1-2 months. She's been laying for about 3-4 months though. I'll get 2 normal eggs, and then 3 fart eggs! They're the size of a quarter, shelled, have membrane, no yolk. My flock of 4 eat the same things: layer pellets, eggs as treats, scratch grains (enough for a couple beak fulls each a day), and occasionally scraps from fruit or veggies. They also free range our 3.5 acres during the day. When this started she went a week with no eggs and then laid 2 small eggs, took a couple days off, then two regular eggs. Rinse and repeat. I got another small one today. Here is a picture for comparison of her other normal sized egg. She seems otherwise healthy. She's out and about all day with everyone grazing, drinking plenty of water and eating the pellets. I'm begining to wonder if she has something up with her egg-making equipment?