I lost a Silkie this AM about 12 weeks old (was kind of expected) For the past 3 to 4 weeks, she had been rather lack luster. She would kind of sit in one spot and not move much, with notably heavy breathing. She would occasionally peck and eat from the ground and feeder. But has not developed much at all over the past month, in fact some spots are bare of feather under the wing, and she felt like skin and bones when I'd pick her up (she's only a little bigger than when I got her 5 or 6 weeks ago) while the Silkie from the same batch is about 3-4 times the size as when they both started. The rest of my flock is acting normal, running around. Full of energy, eating, drinking, ect. I don't see any signs or issues and they are all developing like I'd expect (like weeds). Any reason I should be concerned? Or does oy sound more isolated?