Great Blue Heron (Ardea herodias): Facts, Diet and Habitat

Appearance: how to recognize a great blue heron

From a distance a great blue heron looks gray, but its upperparts and wings have a soft slate-blue tint. The face is nearly white, and a broad black stripe runs from above the eye to the back of the head, ending in thin black plumes. The long neck is rusty gray with a streak of black and white down the front.

Look closely and you will see reddish-brown “thighs” and a dark stripe along each flank. The thick, pointed bill is dull yellow, and the long legs are gray. At the start of the breeding season the bill and legs briefly turn orange, and adults grow long, wispy plumes on the lower neck and back.

Young herons are duller, with a dark gray cap instead of a white face, no plumes and a grayer bill. Males and females look alike, although males average slightly larger.

In flight, the great blue heron is unmistakable. It tucks its neck into a tight S shape, trails its long legs behind and flaps with slow, deep beats of its broad wings. Cranes, which are often confused with it, fly with their necks held straight out (see heron vs crane).

How big is a great blue heron?

This is a big bird by any standard. Among living herons, only the goliath heron of Africa and the white-bellied heron of southern Asia are larger.

The weight surprises many people. A heron that stands almost as tall as a ten-year-old child weighs about as much as a small house cat, because its body is slim and its bones are hollow. Studies in British Columbia found adult males averaging about 2.5 kg (5.5 lb) and females about 2.1 kg (4.7 lb). The white Florida form is the heaviest, with males averaging around 3 kg (6.7 lb).

The great white heron of Florida

In South Florida, the Florida Keys and parts of the Caribbean lives a pure white heron with yellow legs and a heavy yellow bill. This “great white heron” is usually treated as a white form of the great blue heron within the subspecies A. h. occidentalis. It averages larger than other great blue herons, has a slightly different bill shape and is found mainly around salt water and mangroves.

Birds with a gray-blue body and an all-white head and neck also occur in South Florida. They are called Würdemann’s herons and are thought to be intermediates between the white and the normal form.

Whether the great white heron is a color morph, a subspecies or a separate species is still debated, and some ornithologists support splitting it. It is easy to confuse with the great egret, but the egret is smaller and slimmer and has black legs. The Great White Heron National Wildlife Refuge in the Florida Keys protects part of its range.

Habitat and range

Great blue herons live almost anywhere with shallow water and fish. You can find them in freshwater and saltwater marshes, swamps, mangroves, flooded meadows, lake shores, slow rivers, farm ponds, estuaries and rocky coasts. They adapt well to people and often hunt in city parks, golf course ponds and harbors.

The breeding range covers most of North America, from southeastern Alaska and southern Canada across the contiguous United States into Mexico, and also the Caribbean and the Galápagos Islands. In winter the range extends south through Central America to Colombia and Venezuela.

The bird is very rare in Europe. It has turned up as a vagrant in England, the Azores and Greenland. Its place in the Old World is taken by the closely related gray heron (Ardea cinerea), which is somewhat smaller and has a plain gray neck without the brown tones.

Diet and hunting

Fish make up most of the great blue heron’s diet, usually fish 10–20 cm (4–8 in) long, although it can swallow fish around 60 cm (24 in) long. The menu changes with what is common locally: one study in Nova Scotia found that flounder made up almost the entire diet, while herons in British Columbia ate mainly sticklebacks, gunnels, sculpins and perch.

Great blue herons are true opportunists. They also take frogs, toads, salamanders, small turtles, snakes, crayfish, crabs, shrimp, dragonflies and grasshoppers. In fields they stalk voles, mice, gophers and shrews; in one Idaho study voles made up about a quarter to two fifths of the diet. They sometimes catch ducklings, rails and other small birds. For more detail, see What do herons eat?

The classic hunting method is stand-and-wait. The heron stands motionless in shallow water, usually less than 50 cm (20 in) deep, or wades very slowly, watching for movement. When prey comes close it straightens its neck in a lightning-fast strike, grabbing or spearing the animal with its bill. Special neck vertebrae let it coil the neck into an S and release it like a spring.

Herons swallow prey whole, usually headfirst, and cough up pellets of bones and fur. They hunt by sight and are most active around dawn and dusk, although they also feed at night. Herons have been known to choke on prey that is too large.

Behavior and daily life

Away from the colony, the great blue heron is a solitary hunter. Individuals often defend a favorite stretch of shoreline and will chase away other herons with raised plumes, a stretched neck and harsh calls. Where fish are concentrated, loose groups sometimes feed together.

Herons are generally quiet birds. The most common call is a deep, hoarse croak, often given when a heron is flushed. At colonies they make a wider range of squawks, bill-clapping and greeting calls.

Like other herons, the great blue heron has patches of “powder down”, special feathers that crumble into a fine powder. The bird uses this powder, working it in with a comb-like edge on its middle claw, to clean fish slime and oil from its plumage.

Many great blue herons migrate. Birds from Canada and the northern United States east of the Rocky Mountains move south in fall, while those in the southern United States and along the Pacific coast stay all year. Some hardy individuals spend the winter far north as long as streams and rivers stay ice-free. Read more in Do great blue herons migrate?

Reproduction and nesting colonies

Great blue herons nest in colonies called heronries, usually in tall trees near water or on islands where raccoons and other climbing predators have a harder time reaching the nests. A colony can hold from a few nests to several hundred, and nests are often 9–21 m (30–70 ft) above the ground. Where trees are scarce, they may nest on shrubs, cacti, channel markers, artificial platforms or even on the ground.

Males arrive first and claim a nest, then court females with displays such as stretching the neck upward, fluffing the neck plumes and clattering bills together. Pairs usually stay together for only one season, and most birds take a new mate each year.

The nest is a bulky platform of sticks. It may start about 50 cm (20 in) wide, but nests reused for many years can grow to more than 1.2 m (4 ft) across. The female lays usually 3–6 pale blue eggs, and both parents incubate for about 27 days. The chicks hatch a few days apart, so the oldest is bigger and often wins most of the food.

Both parents feed the young by regurgitating fish. The chicks make their first flights at roughly 55–80 days old, earlier in the north and later in the south, and return to the nest to be fed for a few more weeks. Herons usually breed for the first time at about two years old. Find out more in Where do herons nest?

Lifespan

Life is hardest in the first year. Young herons catch only about half as many fish as experienced adults in their first months, and more than half of all young birds die before their first birthday.

Birds that survive this stage can live a long time. A commonly cited average for adults is around 15 years, and the oldest known wild great blue heron, recorded through bird banding, was about 24.5 years old.

Predators, threats and conservation

A full-grown great blue heron has few natural enemies, because its size and sharp bill make it a dangerous animal to attack. Bald eagles are the main predator and take herons of every age, from eggs to adults. Golden eagles and great horned owls occasionally kill adults.

Eggs and chicks are more vulnerable. Crows, ravens and turkey vultures take eggs, while raccoons, black bears and red-tailed hawks can take larger nestlings. When eagles keep raiding a colony, the herons may abandon it altogether. In many areas, recovering bald eagle numbers have changed where and how herons nest.

The main human threats are disturbance at colonies, loss of nesting trees and wetlands, and pollution. Because herons sit at the top of wetland food chains, they build up contaminants from the fish they eat, which makes them useful indicators of the health of a wetland.

Conservation status

The IUCN Red List classifies the great blue heron as Least Concern. It has a huge range and a large population, and it has benefited from reservoirs, farm ponds and its ability to live close to people.

In the United States it is protected under the Migratory Bird Treaty Act, and similar laws protect it in Canada and Mexico. Local colonies still need care, because a heronry that is disturbed early in the nesting season can fail completely.

Myths and facts

Myth: the great blue heron is a crane. Many people in North America call it a “crane”, but herons belong to the family Ardeidae and cranes to the family Gruidae. Cranes fly with outstretched necks, nest on the ground and eat a lot of plant food.

Myth: herons only eat fish. Fish are the main food, but great blue herons are flexible predators that also eat frogs, snakes, insects, small mammals and birds.

Fact: the “great white heron” really is a great blue heron. At least, most experts currently treat it as a white form of the same species, even though it looks nothing like its blue relatives.

Relationship with people

The great blue heron is one of North America’s most watched birds. Its patient hunting, prehistoric look and slow flight make it a favorite of photographers, and live webcams at several heronries attract large audiences each spring. John James Audubon painted it for The Birds of America.

Herons sometimes visit garden ponds stocked with fish, which can frustrate pond owners, but the birds are legally protected. For most people, the great blue heron is simply a welcome sign that a local wetland is healthy enough to support a top predator.