Its been 3 days i went by to have a look and i am sad to say that i could not see the egg in the nest and the the herons were nowhere to be seen. What would cause this. Could a predator have got at the nest and ate the egg so the parents just left. I stood in the same position as i did before with my 400mm zoom lens and i could not see the egg so i am pretty sure it is gone. You can see the egg in the first photo in the nest. I will check back again to see if i'm hopefully wrong.
