I see the wing feather growth - how old is it?
I don't know the answer to your question, but it's very cute. I find it very interesting.
Few more questions:
Was it much smaller than the others when it hatched?
It is it growing?
Is it eating and drinking well?
Is it as active as the others?
Sorry for all the questions, I'm trying to rule out underlying health problems. I hope it's completely healthy and just itty bitty adorable!
If you have a postal scale, you should consider weighing it every few days or weekly to track its growth rate percentage compared to the others.