I have 8 week old silkies. They have been doing great. They were acting normal all day, but this evening I went to check on everyone as they went down to bed. They were eating and drinking, but one started to shake its head and back up quickly and ruffle feathers. I thought this was strange, so I watch some more and the longer I watched, the more I noticed others doing the same thing. This literally just started within the last hour. They would shake their head, then stand still with their beak open for a few seconds, then go back to acting normal. What the heck? I inspected them for external parasites to see if they were getting bit by something, I didn't see anything. What do I do? Besides seperate from the other birds, I already have.