Yay! Found this today on the clean end of the poop board. They've been "singing" loudly, or making a racket, depending on your musical sensibilities for a couple of mornings. I'm assuming this was from Buffy, the BO as she was the most restless and the noisiest, but it's possible that it could be the BR's. Not sure how to tell the difference without catching them in the act
https://www.backyardchickens.com/forum/uploads/54340_img_0452.jpg

https://www.backyardchickens.com/forum/uploads/54340_img_0452.jpg