The main thing I am looking for is how it acts. Does it stay inactive, hunched up, fluffed up, and just setting there instead of interacting with the others. This may be sitting in a corner or staying on the roost. Don't get this confused with pecking order stuff if you have immature birds or are integrating new ones. They are going to stay separate and away from the bullies, but watch how they look and act.
Look for physical deformity, especially with the neck and legs. Is something just not right? Is it walking funny or holding its head wrong?
Is it making different sounds? With chicks that plaintive distress peeping is a clear sign something is just not right, but sometimes they can make croaks and other sounds that just don't fit in, especially if it sounds like it affects breathing. Chickens make a lot of different sounds so don't freak at everything unusual, but kind of watch that chicken for a while if it makes different sounds, especially if it is consistently making those sounds.
Way down on my list for worry but just to be alert for something possibly being wrong is anything different, like that poop color you noticed. Feather loss, different feathering out, differences in size and weight gain, all these are perfectly normal and occur in any flock, just look for something really out of synch and then observe.
I'm sure I've missed some things. Maybe others will help you out.
Look for physical deformity, especially with the neck and legs. Is something just not right? Is it walking funny or holding its head wrong?
Is it making different sounds? With chicks that plaintive distress peeping is a clear sign something is just not right, but sometimes they can make croaks and other sounds that just don't fit in, especially if it sounds like it affects breathing. Chickens make a lot of different sounds so don't freak at everything unusual, but kind of watch that chicken for a while if it makes different sounds, especially if it is consistently making those sounds.
Way down on my list for worry but just to be alert for something possibly being wrong is anything different, like that poop color you noticed. Feather loss, different feathering out, differences in size and weight gain, all these are perfectly normal and occur in any flock, just look for something really out of synch and then observe.
I'm sure I've missed some things. Maybe others will help you out.