In my order of 7 chicks, I got 2 RIR. One of them is not developing her wing feathers as quickly as all the others, including the other RIR. They are all a week old and have nice long wing feathers coming in; the one RIR has just shortish wing feathers so far. She is about the same size as the other RIR, and is acting fine and healthy otherwise. Do some chicks develop more slowly?