Hello ! I was wondering if anyone can help me . We have 3 hens who live in a walk in aviary 3.5 metres long and then they have a run 6 metres long attached, where they can dust bath, scratch etc . They happily lay every day. But they have started to make a new noise - they seem to whistle . Does anybody know what this means ? It doesn't sound like a stressed noise , I would be mortified if it was and am hoping someone will tell me that it's a sign they are contented !