Great Blue Heron. The largest and most widespread heron in North America, the Great Blue Heron can be found along the ocean shore, bays, lakes, streams or the edge of ponds. Although the Great Blue Heron eats primarily fish, it is adaptable and willing to eat other animals as well. Several studies have found that voles (mice) were a very important part of the diet, making up nearly half of what was fed to nestlings in Idaho. Occasionally a heron will choke to death trying to eat a fish that is too large to swallow. Great Blue Herons congregate at fish hatcheries, creating potential problems for the fish farmers. A study found that herons ate mostly diseased fish that would have died shortly anyway.