i have chicks hatched 1 week ago and i noticed that 4 of them already have full wing feathers that overlaps their vent area and already has half centimeter tail feathers and the remaining 3 of them still looks like day old with slow wing development and no tail. although some chicks came first in hatching, the overall duration of their hatching from first to last is about 6 hours. im really confused. can this give me a clue of what gender they are? by the way, they are leghorn cross. (leghorn roo and australorp hen) here is their pic when they are all DAY-OLD.