A Great Blue Heron was roosting along the lake shore and occasionally went hunting for frogs and fish. At one point it looked up, puffed out its feathers and did a funky dance. While looking through the camera, I could hear the classic croak of another Heron flying overhead. I don't know for sure but it seemed likely to me that the photographed Heron's odd movements were a response to seeing and hearing the Heron flying overhead.
(Photographed July 8, 2015 along shore of lower Chemong Lake, Emily Township, City of Kawartha Lakes, Ontario, Canada)