I'm raising my first batch of chicks. I have 5 total but 2 RIRs. They were bought the same day, were the same size, and out of a "pullet" bin, but now (only two weeks later)- one has 4 rows of wing feathers, back feathers, and tiny tale feathers. The other is barely starting it's second row of wing feathers and barely has it's tail feathers. Are they just maturing at different rates? Is this normal? Or is it more likely that I have a pullet and a cockerel?