I think that with a smaller flock you are able to notice more things. Chickens are hard, i had pet parakeets and i figured their "expressions" pretty easy. Chickens expressions are all in the eyes, the body language. If you watch their face feathers, sometimes you can see it..............Kinda like how some dogs seem to smile?I had a chicken that looked a bit like these but had to get rid of him cause he was a he. Did have those puffy cheek patches though. Could you agree to better health as a reason for the changes you mentioned? Chicken expressions just seem far out to me. I'll take Novas advice and look more.
Ha ha aside. What's the thread that you have where Robin hangs out ?
Hard to explain, but it's there.
Hard to see, especially if you have a bunch of them, and especially if they aren't human friendly! My birds are always following me around and wanting in my lap just like any cat, so i can spend more time studying them.