We don't have a rooster and one of our hens became broody. We really needed to replenish our flock, so we slipped in some of my friends fertilized eggs in place of some of the unfertilized clutch eggs she was sitting on. We marked them to know which ones to keep an eye on. After only four of the seven fertilized eggs hatched, we noticed our local feed store had just brought in new chicks (pullets), so we decided to get two chicks from the store to put under momma hen. The age of the original chicks and the ones we bought and put under her were only a few days difference, so we hoped they would be a natural fit. We introduced the new chicks by putting them under her with the new hatchlings, and after acknowledging by lightly pecking the chicks, she never pecked them again and accepted them as her own. She treated them with care and she turned out to be a great mom, very protective of her brood and always showing them the way to food etc. She never denied or discriminated against the two store bought chicks and treated them like the rest of the brood. Fast forward almost two months, and we just noticed that the momma hen is suddenly chasing off the two young pullets that we purchased. Why all of a sudden would she start doing this? Is this a natural pecking order thing, should we separate the two pullets from the rest of the flock? The only thing we can think of is the two pullets are a darker color (Barred Rocks) than the other red colored Wyandotte chicks. Sort of sad and concerning to watch them being rejected and treated like this all of a sudden.