This morning I watched both my ducks watch an airplane pass overhead. (Small bi-plane, probably a crop duster on its way to work somewhere - not the usual, much higher commercial aircraft.) They stood stock still, with their heads tilted to follow the airplane with one eye, the only movement being a slight adjustment of the tilt and angle of their heads to keep the "up" eye trained on the airplane. The flock of chickens also stood very still for a moment or two, but THEY figured out there was no danger before the ducks came out of Alert Observation Mode.
