I have a buff orphington who is 2 years, 3 months old who has suddenly started acting like she's sitting on a nest. She had been a good egg layer, gave it up for a few months and just started again a couple of weeks ago. Now she won't leave the laying box except to eat and drink. She even sleeps there. Is this behavior odd, especially for an older chicken? Anything to be concerned about? Neither she nor any of the other hens has ever acted like this in the past.