Aquarium of the Pacific - Online Learning Center - Species Print Sheet
The Great Blue Heron is the best known and most widely distributed of all North American herons. These large gray-blue birds with their long legs, necks, and bills are familiar sights throughout many parts of the United States as they stand silently and majestically in shallow water poised to launch at unsuspecting prey, or fly overhead with neck curled over their shoulders, long legs extended, and widespread wings slowly and gracefully beating.
At the Aquarium
The Great Blue Heron is illustrated on The Wave’s mosaic tile mural, Rios de la Vida (Rivers of Life). The fountain, mural, and accompanying graphics illustrate the story of our Los Angeles and San Gabriel Rivers. Although not on exhibit in the Aquarium, this bird is included in our website animal database to expand on the information touched on in The Wave fountain exhibit.
Breeding: coastal Alaska and southern Canada into south Mexico, West Indies, Galapagos Islands. Winter: southeast Alaska, south to Mexico, Central and South America, Caribbean. Year-round: California resident
Great Blue Herons occupy a variety of habitats in fresh water and marine coastal ecosystems: lakes, ponds, rivers, flooded farmlands and meadows, irrigation ditches, and wetlands. Nesting sites require tall trees, such as are found in wooded swamps. Nests are often on islands safe from predators. They also adopt tall human built structures for nests such as channel markers.
The Great Blue Heron is the largest North American heron. These tall thin birds have long necks, bills, and legs and a very wide wingspan. Both sexes have similar coloration. The back is blue-gray, breast white with black streaks, and top of head white. A black stripe on each side of the body extends from the eyes to slender black plumes at the back of the head. Neck feathers are often cinnamon colored. Legs are black and eyes yellow. In breeding season, their colors are brighter and they have long plumes called nuptial plumes on their back, flanks, and breasts.
Adult herons are 1.1-1.3 m (3.5-4.3 ft) long and have a wingspan up to 2.1 m (7 ft). Hollow boned, they weigh 2.3-3.6 kg (5-8 lb). Males are slightly larger than females.
Diet and Feeding
These herons forage most actively just before dawn and at dusk, but may also feed during the day and even at night. Seventy-five percent of their diet is non-game fishes. In addition, they forage for amphibians (mostly frogs), snakes, crabs, shrimps, shrews, young rats, mice, ground squirrels, pocket gophers, insects (grasshoppers and dragonflies), and sometimes small birds.
They use two fishing techniques. In the first, the heron stands motionless in shallow water with head extended at a 45o angle to the water’s surface, moving only its head and eyes. After waiting patiently for a few minutes, if no dinner has come by, it moves a short distance and again strikes a pose. This time spotting a fish, the heron slowly moves its head back and forth, then cautiously moves one leg in the prey’s direction. Suddenly, the bird plunges its head into the water to catch the fish in its bill crosswise. Then, if the fish is less than one half the length of its bill, it swallows it whole after manipulating it to go down its throat headfirst. If the fish is too large to be swallowed immediately or has dangerous spines, the crafty heron uses its beak to violently and repeatedly toss the fish into the water until it is dazed and easy to eat or the spines snap. Sometimes the fish is tossed on the ground until it breaks up into smaller portions.
In the second less effective strategy the heron wades around in shallow water until a fish is driven out of its hiding place at which time the bird stops and extends its neck. When the prey is within striking distance, the bird uncoils its body and thrusts its head into the water in an attempt to catch the fish.
Great Blue Herons first mate at two years of age. They select a new mate each year. They usually nest with other Great Blues in colonies called heronries. Courtship includes many displays—vocalizing, bowing, bill tapping, and stretching to show off nuptial plumes Mating occurs when the pair bond is established. The male selects the nest site which may be new, or reconstruction of one used previously. It is usually located high on rock ledges, sea cliffs, or at the top of tall trees (pine, cypress, eucalyptus) or man-made structures. The ground is occasionally used. The male gathers the building materials and the female weaves them into a nest. It takes less than a week to build a nest strong enough to support the parents, eggs, and eventually, several large chicks. The nest is sometimes lined with moss, lichen, twigs, pine needles, reeds, and/or marsh grasses. Twigs will be added from time to time while the eggs are incubating and after the chicks emerge.
Both sexes participate in the incubation, brooding, and feeding of their offspring. Three to seven (average four) pale blue to olive-green eggs are laid from March to May. The male incubates the eggs during the day and the female at night. The bird doing the incubating uses its bill to roll the eggs over about once every two hours. The gestation period is about 28 days.
Hatchlings are almost naked, their eyes are closed, and they are helpless, but they develop rapidly. The parents place regurgitated food (usually fish) in their mouths at first, and then on the floor of the nest for the chicks to pick up. At two weeks of age the chicks start cleaning their feathers, stand upright with wings half opened, and vibrate their throat membrane to cool off. At this time the parents start spending more time away from the nest and less time brooding the chicks. At six weeks of age, the chicks start preparing for flight by walking around the nest and adjacent tree branches, and at eight weeks fly clumsily from tree to tree returning to the nest to be fed. They become independent when 10 weeks old.
These herons communicate with a wide range of sounds with the result that heronries are noisy raucous places, especially after the eggs hatch. The birds sound “frawnk” in breeding colonies when alarmed; “gooo” at the end of one of the courtship display; “ee” when flying; and a series of clucks when foraging. The bird returning to the nest lets its mate know it is arriving by uttering a “roh-roh-roh” sound, to which the nest- bound mate responds with a series of displays. In addition to announcing his arrival, the male often brings the female a twig. She takes the stick and weaves it into the nest as the male taps her bill side-to-side. A heron bringing food back to feed the chicks, perches a short distance away from the nest for as long as five minutes. In the meantime, the hungry chicks shriek noisily in a chorus demanding to be fed.
They exhibit as many displays as they make sounds. While preening its feathers with its serrated bill, the heron extends its neck and tilts its head so that its eyes can alternately look upward to check for other herons or predatory birds flying over the foraging grounds. When two birds approach in a foraging area, each extends its neck fully, tilts its head over its back, partially opens its wings, and erects its body plumes. During courtship; males make loud bill snaps, and females snap their bills at approaching unwanted males. Paired birds often do a rapid side-to-side tapping of each other’s bill tip.
Herons that are not year-round residents depart for warmer climates in early fall. The usual migrating group is three to 12 herons but may sometimes be as many as 100. They travel day and night.
The ability of Great Blue Herons to strike at prey with incredible speed is due to the structure of their neck bones. A modification of the sixth cervical vertebrae allows the bird to draw its neck into an S shape and then shoot its head and bill forward with lightening speed. This adaptation combined with long legs and a long neck allows these herons to forage successfully in a variety of aquatic environments and on an extensive menu of prey. Their bill is adapted for probing, grasping, and on occasion spearing prey. Serrated talons are useful in preening.
It is believed that Great Blue Herons may live 17 years.
These herons have few predators. Birds of prey, crows, ravens, and raccoons try to steal their eggs and chicks. Bald eagles attack juveniles and adults occasionally.
They were widely hunted in the past, almost to extinction. Howver, since they are migratory, they are now protected under the Migratory Bird Treaty Act. In selected habitats in some states, they are listed as a species of special concern. Florida’s Great White Heron, now believed by many taxonomists to be a color morph of the Great Blue and not a separate species, is federally listed as endangered.
Draining of wetlands, alteration of waterflow in watersheds, and development in many of their habitats are serious threats to their survival.
Great Blue Herons usually nest in areas relatively free of human disturbances. Such is not the case at the Seal Beach National Wildlife Refuge in Seal Beach, California, which is surrounded on three sides by human activities including housing tracts. Here in a busy narrow channel leading in and out of a marina, the year-round residential herons nest on navigation buoys on a 23 m (75 ft) open tower within sight and hearing of a major east-west highway, and in eucalyptus grooves next to office buildings and maintenance yards. While this is amazing, even more so is the fact that the herons return to the same nests year after year.