I have only four chickens at the moment, three females and one male. The male I've had to keep inside for parts of the day since he started crowing due to neighbour complaints and I've noticed he shakes his head every time I speak. Its like a quick rough jerk/shake. If I speak a lot he does this repeatedly. And it is only when I or someone else speaks near him. Not with any other loud sound. Today i went out to check on the hens when they were settling down for the night and noticed one of them doing the same head shake while she was sitting down listening to me. The other two were so busy finding a comfy spot to roost that I don't think they were listening, or maybe they are not doing it. Anyway I cant see anything wrong with them all and am baffled as to the reason for this. Cant find any other cases of this kind of head shaking ONLY when listening to humans speaking. Is this normal? I'm worried it could be an issue with their ears.