I have a small flock of laying hens (rir, nh reds, andalusians) and they have been shaking their heads and I cant figure out why. I thought lice or mites or worms, but cant make it stop. They shake their heads very often, as if they are shaking something off. I have tried permethrin, sevin, ivomec, and nothing seems to make them stop shaking. For the most part they look healthy, a few of them have feathers that dont look so well, with some of them losing a few feathers around the vent and the skin is red. But most of them look healthy. Please help, what is wrong and how can I help them to stop shaking?!?!