Your animals definitely have moods based on hot/cold, hay/grass and whether or not they have been petted or fed. If your coop ran out of hay and a chicken didn't get fed, you'll get the grumpy bubble.
Polaris covered it well, but just to expand a bit, when your chickens are grumpy they won't produce eggs (or at least not as high quality ones) so it's work keeping them happy. During the winter you'll want to make sure that there's always hay on the feeding bench and a heater is placed somewhere inside the coop. During the other seasons, you can just leave the coop door open and let them find grass to eat on your farm. Although if it's a rainy day they'll want to stay inside and eat hay.