Taken from East Shore Park, Ithaca, NY. Most of the birds are Black Scoters but the one on the far left and the one in front on the left are White-winged Scoters. Choose size "original" to see detail.

I combined 2x and 1.4x extenders on a 500mm lens. Mounting one extender behind another isn't recommended by Canon, but when birds are this far away there isn't much choice.