Could be they are too hot. Heat isn't necessary, and can make them uncomfortable.They get to run the backyard almost every day, and when they don't they have 5x10 with roosts which are not much higher than what's in the coop. They aren't cold at night because they have a heated coop with fresh food, water, and bedding. 4 batches of six hens have been using the same coop/setup over the past 14 years and NEVER has there been an issue.