Great Blue Heron

The Great Blue Heron is the biggest heron in North America: a tall, long-legged, long-necked wader, blue-gray above, with a white face and a broad black stripe over the eye that ends in long black plumes. Look for the yellowish, dagger-like bill, the black patch at the shoulder and the rusty-chestnut thighs and bend of the wing. The front of the neck is streaked black, white and rust, and in spring adults grow long, shaggy plumes on the back and breast.

In flight it pulls its neck back into an S, trails its legs well beyond the tail and beats its broad, rounded wings slowly and deeply; from above the wing is two-toned, pale gray in front and dark on the flight feathers. It flies with its neck stretched out and legs hanging mainly when coming in to land, chasing another heron, fleeing danger or displaying at the colony.

It is 38-54 in (97-137 cm) long, with a wingspan of 66-79 in (167-201 cm), and weighs only 4.6-5.5 lb (2.1-2.5 kg) for its size. Standing upright it is a little over 5 feet (1.6 m) tall. It stands taller and weighs far more than a Great Egret, while a Sandhill Crane is bulkier still. Size varies across the continent: the biggest birds live in the Southeast and the smallest in the Great Basin.

Males and females look alike. The female is a little smaller, by about 5% on average.¹ In the breeding season the male's longest plumes tend to be a bit longer. In a British Columbia sample, adult males averaged 5.5 lb (2.48 kg) and females 4.7 lb (2.11 kg), and males had longer bills; bill length alone sexes about 70% of adults there.¹ See Female Great Blue Herons.

Young birds lack the white crown: a juvenile has a solid dark gray cap, a duskier bill, a browner, looser look and rusty edges to its back and wing feathers, with no long plumes. White creeps into the crown over the first winter, the cap is mixed gray and white by the second fall, and most look like adults by their third fall. See Baby Great Blue Herons.

In south Florida and the Caribbean lives an all-white form, the Great White Heron. It is the same size and shape as a Great Blue but white all over, with a long yellow bill and pale yellowish legs, and it lives almost only in shallow salt water, especially the turtle-grass flats of Florida Bay and the Keys, nesting on mangrove islands. It is usually treated as a subspecies or color form of the Great Blue Heron (A. h. occidentalis), though some authorities have called it a separate species.

Where blue and white birds meet in south Florida, intermediates called Wurdemann's Herons have a blue-gray body and a mostly white head and neck. Mixed broods have long been reported: a white chick and a Wurdemann's chick shared a nest in 1872 and again in 1875, and in 1908 a nest on Clive Key in the Keys held one white chick and two that looked like blue birds.² A 2019 study in Florida Bay found white and blue birds of similar size: white birds nest mainly on islands and blue birds on the mainland, with their nesting peaks at different times, and each pairs with its own color more often than chance; together with outer Keys birds they form a genetic group distinct from blue birds of the Florida peninsula, though some genes pass between them. The authors argued for treating the white heron as a species.³ BirdLife International, which assesses birds for the IUCN Red List, already does, as Ardea occidentalis, listed as Endangered in 2020;⁴ AviList and the Clements checklist keep it as a subspecies of the Great Blue Heron.⁵

A Great Egret is all white too, but it is smaller and slimmer, with black legs; a Great White Heron is bigger, with pale legs.

People often call it a crane, but a Sandhill Crane is all gray with a red patch on the head, a shorter bill and a bustle of shaggy feathers at the rear, and a different build. A Little Blue Heron is much smaller and dark slate-blue all over. The Gray Heron of Europe, Asia and Africa, a rare stray to the Americas, is slightly smaller, with a paler neck and no chestnut on the thighs; see how to tell the two apart.

Great Blue Herons have no song and are mostly silent away from their colonies. The call you are most likely to hear is a harsh squawk, given when a heron is startled, flushed or squabbling with another heron. It may explain a local New England coastal name for the bird, "Crank".

At colonies the birds are noisier: a study of breeding colonies listed seven calls, which vary a lot and run into one another, from clucking series when a disturbance builds slowly to screams when a predator attacks and croaking series as a bird lands at its nest.¹ Males snap their bills loudly in display, paired birds clatter their bill tips together, and chicks start a ticking call within minutes of hatching.

Great Blue Herons live across most of North America wherever there is shallow water: the edges of lakes, ponds, rivers and marshes, sea coasts, estuaries, tidal flats and mangroves, and city parks and backyard ponds. They also hunt in fields, pastures and prairie. They breed from southeast Alaska and southern Canada through the United States to Mexico and Central America, and on the Caribbean islands and the Galapagos, and they can be seen all year in much of the US.

Colonies, called heronries or rookeries, are usually in tall trees on islands, in swamps or beside lakes and rivers, but some are in parks and towns. On the Pacific coast herons stand on floating kelp beds and wharves, and many colonies are shared with egrets and other wading birds.

Partly. Most Great Blue Herons from Canada and the northern US fly south for winter, some as far as the Caribbean, Central America and northern South America, while birds of the Pacific Northwest, south Florida and the Galapagos stay put. Some stay as far north as they can find open water, and the species winters farther north than most herons. Northern birds leave from mid-September to late October and come back from February in the Midwest to April or early May on the Canadian Prairies and in the Maritimes. They migrate alone or in small groups, by day and night.

Young birds wander widely before they head south: banding records show juveniles travel an average of 471 miles (758 km) in their first winter.¹ Strays have reached Greenland, Hawaii, the Azores and Spain. One even landed on a ship in the North Atlantic in October 1968 and stayed aboard for days.¹ See Do Great Blue Herons Migrate?.

Fish are the main food, but a Great Blue Heron will eat almost any animal it can catch and swallow: frogs and salamanders, snakes and turtles, crustaceans, insects, rodents such as voles and gophers, and birds. Most fish it takes are 2-12 in (5-30 cm) long; very large prey is a small part of the diet, and herons have occasionally choked to death on large prey.¹

What it eats depends on what is plentiful. In Nova Scotia, flounders made up 98% of 124 food items; in one Idaho study, voles were 24-40% of what the chicks were fed; in British Columbia, young herons rely on voles in winter fields.¹ See also What Do Herons Eat?.

Most of the time it stands stock-still or wades very slowly in shallow water, sometimes belly-deep, then strikes with a lightning thrust of the neck. It grabs small prey in its bill, spears bigger fish, and swallows most prey whole; spiny fish are carried ashore and shaken first. In a New Jersey study of five heron species, it waded more slowly and paused longer than the others.¹ It also hunts on foot in fields for rodents, especially in winter, and it can feed at night as well as by day.

Now and then one hunts from floating objects or kelp, plunges in feet first, or even swims. One Great Blue Heron was seen using bread as bait, catching the fish that gathered around it.¹ On tidal shores its day follows the tide, with most feeding on the falling and low tide.

Great Blue Herons nest in colonies, usually of fewer than 500 nests, though at least one has held more than 1,000 pairs, and a few pairs nest on their own.¹ Most nests are high in trees, usually 20-60 feet (6-18 m) up and sometimes more than 100 feet (30 m); where there are no trees they nest in shrubs, mangroves, on the ground on predator-free islands, or on duck blinds, channel markers and nest platforms. Colonies form near good feeding areas, on average 1.4-4 miles (2.3-6.5 km) away, and some are used for decades: one in Stanley Park, Vancouver, had been in use for 71 years.¹

Males arrive first and court females from a nest site with displays such as the Stretch, pointing the bill skyward with plumes raised, then giving a low moan; pairs clatter their bills, and the male hands sticks to the female. The male brings most of the sticks and the female builds a platform with a shallow, lined hollow, in anything from a few days to two weeks. Old nests can grow to 3-4 feet (0.9-1.2 m) across. Pairs form for the season and seldom reuse their old nest: in a British Columbia study, 13 of 14 marked herons used a different nest the next year, and all five marked pairs had new mates.¹ See Great Blue Heron Nesting.

First eggs are laid from late February in Oregon and northern California to late April in Alberta; the white herons of Florida can nest in any month. The clutch is 2-6 pale blue eggs, laid about two days apart; average clutches range from about 3 in California to 5 in Alberta, and are larger farther north.¹ Both parents incubate for about 27 days.

In a California study incubation began with the first egg, so the chicks hatched over several days and the oldest were bigger. Both parents feed them by regurgitating fish into the nest. In Texas, Great Blue Heron chicks seldom attacked or killed their nestmates, unlike the Great Egret chicks next door, but heron chicks raised by egrets on small fish became aggressive.⁶ Elsewhere, fights between nestmates have been found to be a leading cause of chick deaths.¹ In a 13-year study of a California colony, pairs raised 1.45 young per nest on average, and more young starved than were taken by predators, with deaths peaking in the chicks' second week.⁷ Young make their first flights at about 7-8 weeks, come back to the nest to be fed for a few more weeks, and leave for good at about 2-3 months.

Great Blue Herons nest together but usually feed alone. Some defend a feeding territory along a shore or river by day and night, a few all year: on an Oregon estuary, 32 territories averaged 1,165 feet (355 m) of shoreline.¹ A heron warns off a rival with an upright pose, neck stretched back, bill pointed up and wings drooped to show its black shoulders; gulls, egrets and even people sometimes get the same display.

They rest and scratch standing on one leg, using a comb-like claw on the middle toe to groom, and on sunny days they droop their wings to sunbathe. They roost alone or in loose groups and sleep at night in leafy trees. Bald Eagles, pelicans and Turkey Vultures sometimes steal their catch, and herons in turn take fish driven inshore by cormorants.

Its flight is slow and steady, with deep beats of broad wings, about 2-3 beats a second, at about 19-29 mph (30-46 km/h).¹ It can soar high and twist away when chased by an eagle.

Great Blue Herons can live more than 20 years. The North American banding records hold one bird of at least 24 years 6 months, banded as a nestling in Texas in 1977 and found dead in the same state in December 2001, and another of at least 23 years 3 months, banded in Ontario in 1947.⁸

Most die much younger. An analysis of band recoveries published in 1972 suggested that about 69% died in their first year, 36% in their second and about 22% a year from then on.¹

Predation on adult Great Blue Herons is little documented, though Bald Eagles have killed adults and young. Eggs and chicks are taken by eagles, ravens, crows, raccoons, bears, Turkey Vultures and Red-tailed Hawks, and a disturbed colony loses more. In a 1998-1999 study of 35 colonies in south-coastal British Columbia, 59% of 1,247 nests failed; Bald Eagles, which took eggs, nestlings and fledglings, were probably responsible for most failures, and colonies raised fewer young where people on foot were often nearby.⁹ Eagle attacks on heronries there rose from one every 10.3 hours in 1988 to one every 4.3 hours in 1999, in two separate studies.¹⁰ Some herons there appear to have responded by nesting in smaller colonies, or within about 650 feet (200 m) of an active eagle nest, where the resident pair may keep other eagles away, though the herons still lose some eggs and young to them.¹⁰

Hard winters that freeze feeding places can kill northern birds, and wetland loss and disturbance at colonies are the main threats from people.

The Great Blue Heron is common and widespread. It is listed as Least Concern on the IUCN Red List.¹¹ Partners in Flight estimates about 700,000 birds, 620,000 of them breeding in the US and Canada, and rates it of low conservation concern.¹²

Over the long run, numbers have gone up: the North American Breeding Bird Survey shows a rise of 0.27% a year from 1966 to 2025 (95% credible interval 0.02 to 0.48), and 0.64% a year in the US, while Canada shows a decline of 0.87% a year. But the survey index peaked in the mid-1990s and has fallen since: by 1.24% a year from 2015 to 2025 (95% credible interval -1.86 to -0.64), leaving numbers more than a quarter below the peak but still above 1966. The biggest long-term rises are in the interior Southeast and Midwest, and the steepest falls in Alaska, Nova Scotia, Florida, Minnesota, British Columbia and Ontario.¹³

The Pacific Great Blue Heron of the British Columbia coast is listed as Special Concern under Canada's Species at Risk Act.¹⁰ About 4,000-5,000 live in Canada (a 2008 estimate), roughly half of the world's Pacific herons, and the number of young fledged per nest may have fallen by as much as half since the 1970s.¹⁰

Great Blue Herons were probably hunted for plumes and food in the late 1800s, though records are sparse. The white herons of Florida were hit hard and had recovered by the 1930s;¹ the Great White Heron National Wildlife Refuge in the Florida Keys was set up in 1938 as a haven for them.¹⁴ Accounts of the time differ: A. C. Bent, who visited Florida Bay in 1903 and 1908, judged the Great White Heron in no danger of extermination.²

DDT, PCBs and similar chemicals were linked to poorer breeding in the past, but by 2011 they seemed less of a problem. Loss of wetlands may have done the most harm over time, yet the Great Blue Heron has recovered better than many herons, helped in places by returning beavers and restored marshes.

Colonies are easily upset, especially early in the season, when birds desert nests readily. Herons have abandoned colonies after building, logging, road work and repeated visits. A Florida study recommended keeping people about 330 feet (100 m) from wading-bird colonies,¹⁵ and many studies suggest 800-1,000 feet (250-300 m) for Great Blue Heron colonies in the nesting season.¹

In the US the Great Blue Heron is protected under the Migratory Bird Treaty Act, which makes it unlawful to take, kill or possess the bird, its parts, nest or eggs except as regulations allow; it is on the federal list of protected species, and the Great White Heron is covered as part of it.^{16, 17} No federal depredation order covers herons, so killing one needs an individual federal permit, while no permit is needed simply to scare birds away;¹⁸ the Fish and Wildlife Service has named the Great Blue Heron among birds that fish farms report as causing damage and issues permits case by case.¹⁹ In Canada it is protected under the Migratory Birds Convention Act, 1994.²⁰