I saw these two Herons land in the tree on the other side of the pond from me. They were considerable distance away so I applied the 1.4 T.C. to the 200-500 mm lens and used the additional crop factor of the D500 camera; thus, getting a 35 mm equivalent of 500 x 1.4 x 2 = 1,400 mm focal length. I used a monopod, and the light was good from behind. I was pleasantly surprised that nearly all the shots taken came out clear and sharp with this setup and distance.

Note: this image combines two shots of the pair, with the first having the young, upper,
heron in good focus and with the second the lower adult in good focus.