I was sitting in the grass watching my flock in the run and all the sussen my EE Big Girl made the chicken alarm call. Then the whole flock froze in their tracks, not moving a muscle. All the sudden one made this high pitched purring like sound. Then another one did it. Then another. Pretty soon all my chickens were standing around making a chorus of long purring sounds! Then, the EE who made the alarm call whirled around and raced into the coop. The rest then followed. I looked into the coop to see them all huddled in one corner, not moving. Something scared them, but I have no idea what it is. Maybe a hawk?