I just went out to try and get the chickens back into the coop for the night and I was watching them while they were in the run. One of my hens walked up to me, then shook her head and sneezed. I looked at the others and they are all doing the same thing. Is this something I need to be worried about? They've never done this before. I forgot to add that they are 6 wks. old. Thanks!