My bantam Buff Cochin has been laying for several months and then suddenly quit. I have four red cross-links that are same age as the bantam and they are all still laying. What are the most common causes of this? We did introduce seven you poults to the flock about a week prior to her stopping and now it has been over a month since she has layed. There aren't any areas that she could be hiding them so she has obviously quit.