One of my hens has become unwell. She is keeping her eyes closed for much of the day and sits hunched up without moving much (except when I try to pick her up, when she scuttles out of my reach) with her head tucked into her back. I cannot hear any irregularity in her breathing, and she is eating and drinking, but this is now her third day of being under the weather. All the rest of my flock seem okay. Does anybody have any advice/experience that they could share with me please?