Shape at Rest and In Flight
When standing, the Great Blue Heron is about four feet high to the top of its raised head, a distinctive attitude of this bird. The legs are long, the neck thin and long, the tail is relatively short, and the beak, which is thick at the base, symmetrically tapers to a very sharp point. Occasionally the neck will be folded and the head couched on the shoulders. Often the bird will stand on one foot only, the other drawn up and all but hidden in the underside plumage. With encroachment of another Great Blue Heron on its territory, the bird will stretch its neck upward fully, point its beak toward the sky, and advance slowly and menacingly toward the intruder, and chase it away. In flight it is an uncommonly large bird, with long, broad, round-tipped wings. Except when first taking off and landing, the neck is folded back and the head is couched upon the folded neck. This, incidentally, quickly differentiates it from cranes and flamingos, which fly with heads and necks outstretched. The Great Blue Heron also trails its long legs far behind in flight.

The flight begins as the bird leans forward with neck outstretched. Then (sometimes with an assisting step or two) the great wings beat powerfully and it is launched. For a moment the neck remains outstretched and the legs dangle; but then the legs go back straight and stiff, trailing behind and acting as a rudder to assist the very short tail. At this point the head is couched on the folded neck. The early vigorous wing-beats settle down to slow, powerful strokes. Landing is slightly more graceful than the takeoff, as head and neck are again outstretched and long legs come forward, reaching for purchase as the broad wings brake the bird and which drops the bird lightly to the ground or onto its selected perch.

Length and Wingspan
This species averages about 47 inches and has an impressive wingspan of around 70 inches.

Beak
The sharp beak is about 5 inches long and yellowish, often turning considerably more orange during the breeding season.

Legs, Feet, and Claws
Legs and feet are blackish in coloration, except that the soles of the feet are yellowish. The outer toe is longer than the inner. The hind toe is not elevated, but is on the same level with the others; all toes are long and slender, with small webbing connecting the base of the outer and middle toes. The long claw on the middle toe has comb like serrations on the underside (pectinations) which are used as an aid in preening.

Crests, Plumage, Annual Molt
The body plumage, generally, is loose and long. In the breeding season, the bird's back is without any lengthened and loosened plumes. The lower fore neck has considerably lengthened feathers and in the breeding season the crest, which is more or less present all year, becomes much more pronounced and develops two very long, slender, filamentous occipital plumes. The lore’s are bare.

Voice
The voice is a hoarse gronnk or graack, or occasionally a low, heavy, and coarse grunting quack. It has been reported, though not verified, that when extremely angry, the Great Blue Heron will sometimes issue a very harsh shrieking sound not unlike the sound of a heavy desk being pulled across a wooden floor.

Sexual Differences: Size, Coloration, and Voice
In coloration and voice, the sexes are virtually identical. The male is slightly larger than the female.

Coloration and Markings: Adult
The sharply pointed beak is generally yellowish, especially on the lower mandible, with the upper mandible having a dusky greenish ridge. The lore’s are a faintly dusky bluish-green and the irides are a bright, clear chrome yellow. The brow and crown are pure white, but with the sides of the crown and the plume feathers black. The neck is light gray with streaks of white, black, and rust on the sides of the neck toward the front. Cheeks and chin are white. The back and scapulars are a general slate-blue-gray. The tail is deeper slate-gray, as are the primaries, which shade into black. The longish plumes of the lower neck and breast are a light gray with, on the abdomen, streaks of rust interspersed on the white background. Under tail coverts are pure white and the legs and feet are a dusky gray, with the soles of the feet yellowish.

Coloration and Markings: Juvenile
Much like the adults except for a generally browner coloration. Most of the crown is black, and there are no lengthened feathers, neither crest nor plume, on the head. There is a strong rufous edging to the feathers of back and scapulars, while the lesser wing coverts are a rufous brown. The underside is an ashy gray-white, with the legs dingy grayish-black.

Habitat and Roosting
A wide variation of habitat is enjoyed by the Great Blue Heron but almost always on a solitary basis. It might be seen in newly plowed farm fields, in meadows, in marshes, swamps, bogs, and along the margins of lakes, streams, and ponds. Roosting is sometimes done on the ground and frequently the bird will sleep (often standing on one leg) while in knee-deep water. Most roosting is done, however, in relatively dense cover: deep willow margins, low swamp oak, and similar growth near watery areas. The roosting bird normally perches in a hunched position on a sturdy branch close to the trunk for long-period roosting. However, for short-term resting or observation, the Great Blue Heron will frequently land in the very uppermost branches of a tree and stand silhouetted against the sky.

Enemies and Defenses
Once it has acquired its full growth, the Great Blue Heron has few natural enemies. Its powerful beak is a formidable weapon. Unfortunately, because of its great size and distinctiveness, the Great Blue Heron is often destroyed by thoughtless or uncaring people with guns who are just looking about for something to shoot.

Food and Feeding Habits
The Great Blue Heron is most often seen standing motionless waiting for prey in shallow waters. In the shallows it may move about in a very stealthy manner, walking slowly and carefully, so that no sound is heard and scarcely a ripple made. Very frequently in the marshes this is the principal means used by this species for capturing frogs and small turtles, which it devours greedily. In upland meadows and plowed fields it hunts field mice, shrews, moles, garter snakes, frogs, and the young of ground-nesting birds. The principal prey, however, is fish of almost any variety. It captures fish by thrusting the powerful beak spear like into the fish's side or back; then, partially opening the beak, it prevents the impaled fish from wriggling free until the fish can be carried to dry ground and stabbed again repeatedly until dead. The fish is then juggled until positioned headfirst and is swallowed with a series of convulsive gulping. Often the size of the fish swallowed is remarkable. Instinctive care seems to be taken, however, with species such as catfish which have spines that prevent regurgitation. Smaller prey - whether fish, amphibian, or reptile - caught while the bird is wading, is not usually taken to shore. If not killed with the first thrust, the prey will be repeatedly tossed into the air, caught, and mouthed until dead (sometimes beaten against the water surface or against floating debris) and then juggled in the mouth until it is headfirst down the throat and swallowed. Practically without exception, immediately after swallowing the prey, whether in the water or out of it, the Great Blue Heron will dip its beak into the water and shake it back and forth several times, apparently to clean off any slime or other foreign matter which may be clinging to it, before resuming the hunt. Digestion is rapid and the digestive juices are of such acidity that bone matter swallowed is almost completely dissolved. Occasionally a compact pellet of undigested or partially digested feathers and fur is regurgitated.

Courtship and Mating
Shortly after the spring migration north has been completed, the Great Blue Herons will sometimes assemble in large numbers to engage in mock flights. Soon the paired birds begin leaving for nesting areas. Great Blue Herons usually copulate with the female standing on the ground. Even if she is on a low limb, invariably she will come down to the ground herself before permitting the male to mount her for the brief copulatory activities.

Nest and Nesting Habits
The Great Blue Herons usually tend to nest in small colonies of perhaps ten to thirty pairs, although sometimes the groups are larger. The nests are usually at the very uppermost branches of a tree, although the tree might be as low as 10 ft or as high as 100 ft. Now and then numerous nests will be placed in a single tree. Where colony-nesting successfully occurs, the Great Blue Herons are inclined to come back year after year to re-nest in the same area. In such colonies, the old nests are almost always enlarged and reused. Twigs from old nests may be used in the construction of new nests. Choice of tree species does not seem to be a terribly important consideration, although a certain preference is shown for larger, high pointed conifers. Sometimes the herons will nest in the top or very low bushes. Some ground-nestings have been reliably reported. Where the habitat is conducive to it, nesting will occur in crevices or on ledges of cliffs. Of prime importance in nest selection is isolation - far more so than height of nesting tree. Great Blue Herons demand isolated remoteness in its choice of nesting sites. The nest is a large affair, usually from 30-40 inches across but sometimes as much as 4 ft and rarely smaller than 20 inches. The nest and the ground beneath it become, as the nesting season progresses, increasingly whitened by the excrement of the adult Great Blue Herons and their young.

Eggs and Incubation
The three or four pastel blue or green eggs are usually smooth-shelled, though sometimes there is a slight granulation. They are fairly large, averaging 2.5 inches x 1.7 inches. The incubation, shared equally by both parent birds, lasts for twenty eight days.

Young
Great Blue Herons in the nest, from the time of hatching until fully feathered, are among the ugliest birds in the world. In addition to being ugly, they are ungainly and awkward. They tend to keep crouched down and out of sight while the parent birds are away, but as soon as a parent returns, they stand and start a great hubbub of squawking and vying for position in the nest. Though they're fed in order, the largest and most aggressive youngster usually winds up getting the most food. At first the food is predigested (or partially digested) fish. The baby bird grips the parent's beak crosswise in its own and the parent there upon, with crest and plumes erect, pumps until regurgitation occurs, the result of which is avidly swallowed by the young. Later, as the young grow more able to fend for themselves, the parents cease regurgitation of predigested food, and instead regurgitate small whole fish into the bottom of the nest. These are then picked up by the youngsters and swallowed. The young birds remain in the nest, under ordinary circumstances, until fully fledged and as large as the adults. However, they are freighted easily and in such case will leave the nest and walk out on the slender surrounding branches and remain perched there. Full adult plumage is not assumed by the young bird until the first post-nuptial molt in its second year. After that there is little seasonal change except that the adult may be slightly more handsome in the spring breeding season than at other times of the year.

Migration and Range
Great Blue Herons are definitely migratory in the northernmost portion of its range. Sometimes the bird migrates by itself or in flocks of from five to thirty birds. Many of the Great Blue Herons have winter ranges which overlap with the Ward's Heron or other subspecies to the south or west. The southward migration in autumn usually begins early in October. Northward migration in spring occurs in March or early April. Following the breeding and nesting season, young birds wander in all directions. The range of the Great Blue Heron extends from southern Canada to Mexico, and in winters extends to northern South America.