I am starting to let my older pullets free range when I am outside with them. Today the blue jays started to go crazy in a tree in the next yard over. My chickens got low to the ground under a fern and started to coo or purr almost to the other chicken that was out in the open. That chicken then started to coo back and almost low crawl to get to the others. Is this a type of warning system they use to warn of danger? They all set flat on the ground until I picked them up and put them in the coop.