When some people look at herons, they see either an unusual bird or a majestic bird. They move with beautiful rhythms and look stately and noble, especially the tall great blue heron. But, behind these interesting looking birds is a vicious killer that will eat just about anything and anyone. Large herons, like the great blue, also have "eyes bigger than their stomachs" and will kill prey much larger than they can eat.
Many people I've come across are surprised when I tell them what herons eat. People seem to assume that they only eat fish and maybe a frog or two. I used to think that until, one day, I came upon a black-crowned night heron hunting ground squirrels. Later, I found out through observation, that ground squirrels were a regular on many heron species' menus. Their job is made easier when people leave food out for the squirrels, setting the table for the predators.
Another common prey for herons is birds. Herons will eat any kind of bird they can catch, usually when the bird is unaware. I've seen them go after killdeer, for example. They will also eat ducklings, coots, baby grebes, and even nearly-grown clapper rails. Ducklings aren't safe from the herons until they are, at least, four weeks old. Even then, there might be an ambitious heron that might go after them at that size.
But, fish and amphibians do make up the bulk of most herons' diets. They also will eat rats and other rodents and sometimes snakes and lizards. Fish seems to be their favorite. It would seem they would seek fish, first, and if anything else is around, they will try to grab it. I've seen ducklings swimming around near herons being ignored because the fishing was good. Some of the prey herons eat also prey on young waterfowl, thus balancing things out.
Herons hunt with slow, methodical, stalking. Their slow movements put prey at ease and sometimes the target forgets they're there. Then, once the heron has inched within striking range, they grab their prey quickly. They seem to have the greatest patience of all hunters. They will stalk their prey for long periods and even when they miss, they begin again with more stalking.
Where I live in San Diego, we have several species of herons living in the same area ranging from small to big. Great blue herons are the most common, but we have yellow and black-crowned night herons, green herons, least bitterns and sometimes American bitterns. Herons are everywhere around here.