I recently purchased three young bantam pullets from a breeder. They are all healthy looking and acting birds, but one of the pullets sneezes frequently. Anytime I visit their pen I hear the same pullet sneezing. Sometimes she has a clear, thin nasal discharge. I have heard the other two sneeze occasionally. I am worried that this could be a contagious respiratory disease. I put a chicken from my established flock in with them two weeks ago and she shows no signs of illness. Does this sound like symptoms of a respiratory disease or could it be just an allergy from something in the environment?