Herons stand on their toes—indeed, all birds stand on their toes. The joint halfway up the leg that looks as if it were a backwards knee, actually corresponds to the ankle of a mammal. I have never seen a heron, or any other bird, rest on its heels—never, that is, until yesterday.
This is how a heron, or any bird, normally stands. Its toes touch the ground, but its ankle (the tibiotarsal articulation) is high off the surface. Its knee joint is close to the body and hidden by the wing. This heron is hunting.
This younger heron is also hunting. But, (what would be) its heels are resting on the rock—a stance unknown to me. This position is sufficiently odd that when I saw its distant silhouette, I thought I was looking at a dog.
This picture of the earlier heel-standing heron is included merely because I like it among the fireweed.
When I took the picture, I searched on heron, and found many images but none like mine. Later I searched on heron kneeling and found two that were similar. Clearly, this is not a typical stance.