I have six hens, three are 4 years old and three are a little over one year old. They free range. One of my 4 year old hens has not been acting quite right for several days. Instead of hopping up on the roost at night she lays in a corner of the small hen house. Sometimes they do this and will have laid an egg the next morning, but no egg in that nest for some time. A couple of nights ago she didn't return to the hen house at all; she was nowhere to be found. Two mornings later she emerged from under a nearby shed. I checked and no eggs under there. During the day she forages with the other hens (I let them out of their pen about 11:00). I tried picking her up today but she ran away (this would be normal for them and I took it as a good sign). The only outward sign of anything on her is a very small bare patch on the back of her head. The thought crossed my mind she might be egg-bound, but I thought this only happened in young birds. Maybe it's just old age. Any thoughts or suggestions would be welcome. Thanks.