I recently added 3-15 week old chickens to my small backyard flock. I now have 5-13 week old mixed breed chickens and the 3-15 week olds. About 3-4 days ago I noticed two of the newest chickens started sneezing and shaking their heads as they sneeze. I currently have about 4 inches of pine shavings, and the occassional dusting of DE. After reading all the threads about Poultry respitory disease I'm worried it maybe something more serious. All my chickens are eating well and they free range for about an hour a day. On a side note I did notice 3 days ago the two sneezing chickens aren't sleeping on the roost, they are down in the pine shavings at night. Welcome any and all suggestions. This is my first young backyard flock. Thanks