Great Blue Heron Ardea herodias
Version: 1.0 — Published March 4, 2020
Text last updated April 28, 2011
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Walks erect with long strides and wades in water, often up to its belly or nearly so; spreads its toes as the foot is placed on the ground.
Folds its neck in an S-shape and extends its legs along the body axis on long flights. Neck is extended and legs are dangled when preparing to land, when chasing other herons, when startled (e.g., when pursued by Bald Eagles, Haliaeetus leucocephalus), and at colony-sites during courtship flights. Flies with deep, slow wingbeats at 2.3 to 3.2 beats/s; flight speed 30 to 46 km/h (Palmer 1962a). Can soar to great heights and occasionally glides, and is capable of evasive maneuvers when pursued.
Preening, Head-Scratching, Stretching, Etc
Powder down on the flanks and a pectinated middle toe nail that is used for scratching are common to herons, including the Great Blue. It stands on one foot to scratch its head by lifting one leg over a closed wing, erecting its crest feathers, and lowering and twisting its head into a position where it can be reached by the pectinate toe. Preens by sliding its bill along the feathers. When preening its neck, it droops its wing slightly, and when preening its under-wing feathers, it partly opens its wing. When preening is complete, it shakes its head, body, and finally the tail in one motion. Bill is cleaned by wiping it on branches or by shaking it.
Sunbathing, Thermoregulation, Temperature Metabolism
Droops and exposes the inside of its wings on sunny days, perhaps to radiate body heat on warm days and absorb solar radiation on cool days (Kahl 1971c, Larkins 1989). Avoids strong winds by seeking shelter behind bushes, fences, etc., and leaves the nest to drink on hot days (Pratt 1977).
Sleeping And Roosting
Roosts alone or in loose flocks of (sometimes) up to 100 individuals on the ground, in trees, and on man-made objects near feeding grounds during the day. Some roosts are used repeatedly. Sleeps at night in trees with dense foliage. While asleep, it tucks it bill under its wing coverts.
Daily Time Budget
On the Pacific Coast (and likely in other coastal environments), Great Blue Heron activity is controlled mostly by the tides. Peak feeding activity occurs near low tide (Brandman 1976, Bayer and McMahon 1981).
Pair formation, courtship, and nest building generally occur just before or after foraging (Brandman 1976). Males spend 100% of their non-foraging time at the nest during pair formation (perhaps to guard against robbing of nest sticks or extra pair copulations), 50 to 60% of their non-foraging time at the nest during courtship, 100% of their non-foraging time at the nest during incubation, and 51% of their non-foraging time at the nest when chicks are > 4 to 5 wk old (Brandman 1976). Females spend 50 to 60% of their non-foraging time at the nest during courtship, 100% of their non-foraging time at the nest when brooding chicks that are < 4 to 5 wk old, and 31% of their non-foraging time at the nest when chicks are > 4 to 5 wk old (Brandman 1976).
Adult nest attentiveness declines from about 83-99% in the first week after hatching to near zero at 6 to 7 wk after hatching (Dowd and Flake 1985a). Feeding activity peaks when chicks are about 4 wk old. Males spend less time foraging and more time on the nest than females during the day (Brandman 1976), with an opposite pattern at night.
Individual Great Blue Herons erect their crests and fly toward conspecifics that approach within about 2 m of nests and nest sites. They also jab such intruders with their bills during courtship (see Figure 2c), and thrust their bills at herons that approach nests after eggs are laid.
The rich repertory of courtship displays from the Great Blue Heron at the nest is described below (see Behavior: Sexual Behavior). The non-breeding displays in this section were described by Bayer (Bayer 1984a).
The most spectacular display given by herons on the foraging grounds is the Upright and Spread Wing display that is given when two herons approach one another. The neck is nearly fully extended and tilted slightly over the back, the head and bill are held above the horizontal, and the wrists are drooped or held away from the body exposing the black shoulder patch of the adult. Sometimes the wing nearest the opponent is drooped lower than the opposite wing and the body plumes are erected. As opponents approach one another, the head and bill are raised closer to the vertical and the neck extended farther over the back. These displays usually cause the two herons to move apart but occasionally bring a chase. This display is sometimes directed towards gulls (Larus sp.), Great Egrets (Casmerodius albus), and even people.
A less spectacular display on the foraging grounds is the Vertical display (Bayer 1984a). A heron performing this display sleeks its plumage, extends the neck forward at about 45°, and tilts its head along its axis so its eyes alternately direct upwards. This behavior is used when predators and herons fly at high altitudes over the foraging grounds.
The Forward and Full Forward displays entail partly folding the neck with the bill facing the opponent and partly erecting the body plumes (a Forward display). From this position, an aggressor can thrust the bill at an opponent (a Full Forward display), although such attacks are not frequent. The Full Forward display occasionally results in serious injury and even the death of an opponent (Forbes and McMackin 1984). Bill duels, in which opponents alternately attempt to grab each other's head (Figure 2c), occur during some Full Forward displays.
Circle Flights involve a heron taking flight with the neck extended and parallel to or below the axis of the body. This display is used by territorial herons along boundaries and by nonterritorial herons pursuing one another. In the Arched Neck display, the neck is fully extended above or parallel to the body axis with a down-curve in the distal portion. This display is used by territorial herons after preening, stretching, or long periods of inactivity, during short flights within a territory, while walking and wading, and while flying to a roost or colony site. It also is used by herons in a pursuit flight, when flying from an approaching heron or predator, or when supplanted by another individual.
Displays on the foraging grounds may be analogous to displays at the nest (R. Bayer pers. comm.). Communicative interactions between chicks and their parents are not well documented and need study.
Individual distance of Great Blue Herons on the foraging grounds and at nests is maintained by displays and aggressive interactions (Bayer 1984a, Mock 1976). In Florida, Green and Leberg (2006) found that Great Blue Herons showed no tendency to either avoid or gather with other herons (of any species) while foraging. Green and Leberg (2006) also reported a mean distance to nearest conspecific of about 85 m while foraging, but in areas of rich foraging herons can be found in large groups close together (in prime foraging areas near Vancouver, British Columbia, hundreds of herons can be found foraging within several meters of each other; RGV). Non-territorial Great Blue Herons may overlap foraging grounds with herons from neighboring colonies (R. Bayer pers. comm.).
Adult Great Blue Herons defend territories along rivers, creeks, mudflats, and lografts during the day and at night (Bayer 1978, Butler 1991). Territories are maintained by displays, threats, and chases (Bayer 1984a). Territorial herons rest in exposed sites from where they display and launch chases of approaching herons (RWB). (Bayer 1978) measured the size of 32 territories in the Yaquina estuary, OR, and reported the following dimensions: mean length of shoreline was 355 m (SD = 168), and mean territory area was 8.4 ha (SD = 5.4). In freshwater marshes (n = 7 territories), mean length of shoreline was 129 m (SD = 28), and mean territory area was 0.6 ha (SD = 0.1; Bayer 1978).
The number of territories appears to decline through the winter. In the Yaquina estuary, 14% to 20% of territories were defended by juveniles in October, but none were defended in winter (Bayer 1978). On the Fraser River Delta in British Columbia, adult females and juveniles feed nonterritorially on beaches, estuarine marshes, and in fields in winter, while adult males defend year-round feeding territories (Butler 1991).
Mating System And Sex Ratio
Great Blue Herons are mostly monogamous. One study concluded that most birds choose new mates each year (Simpson 1984c). No information is available on sex ratios.
Little information available. Of 5 marked pairs in 1978, all had new mates the following year (Simpson 1984c). Herodias and Occidentalis group herons sometimes form pairs and produce viable offspring with white and blue plumages (Bent 1926, Powell et al. 1989; see Systematics).
Great Blue Herons have elaborate courtship displays that have been described in detail by Meyerriecks (Meyerriecks 1960a) and Mock (Mock 1976, Mock 1979, Mock 1980c). There is much variation among individuals and in the sequence of displays. Mock (Mock 1976) describes pair formation displays as follows:
The Stretch display (Figure 2b) is when an unpaired male extends his neck, raises his bill toward the vertical, and erects his neck plumes while exhibiting his bright soft parts. His neck is then retracted, accompanied by a moaning Gooo call (see Sounds: vocalizations).
In the Snap display, a heron erects its head, neck, and breast plumes as its head is lowered, while its mandibles are clapped together and legs flexed when the neck is nearly straight.
The Wing Preen display is when a heron leans forward, opens a wing slightly, and runs its bill along the edge of the primaries.
Circle Flights are where a heron flies laboriously in wide circles above a colony with its neck outstretched.
Landing call: a heron returns to its nest, erects its neck and head plumes, and utters a series of croaks (see Sounds: vocalizations).
The Twig Shake is when a heron grasps a twig on the nest tree and shakes it from side-to-side.
Crest Raising is when a heron erects its black occipital plumes.
The Fluffed Neck display is when a heron raises its head, erects its neck feathers, and holds its bill at or slightly above the horizontal.
The Upright display is when a herons' neck and bill are extended in a straight line about 45° above the horizontal.
The Arched Neck display entails the rapid erection of a herons' plumes while curving the neck so the bill points downward.
The Forward display (Figure 2a) is when a heron extends its wrists from its sides, retracts its neck on to its back, erects all its plumes, and then stabs forward with the bill while squawking and clapping its bill.
Bill Duels (Figure 2c) are where a paired male erects its plumage, stands tall, and lunges at the face of its mate with its wings held away from its body and its bill closed.
Bill Clappering is the rapid clicking of a herons' bill tips in mid air, directed toward a mate (see also Sounds: vocalizations).
These displays are not rigidly organized into predictable sequences (Mock 1976). The three display sequences seen most often by Mock (Mock 1976) were the Greeting Ceremony, Stick Transfer, and Nest Relief Ceremony. The Greeting Ceremony occurs when a heron joining its mate on the nest gives the Landing call. The bird on the nest usually responds with a Stretch or, less often, an Arched Neck or Fluffed Neck display. The Stick Transfer sequence occurs when a male brings sticks to its mate. She performs the Stretch display and takes the sticks. The male then Bill Clappers towards the female as she places the stick in the nest. During the Nest Relief sequence, an arriving heron utters the Landing call and its mate stands followed by a Stretch display. Often the pair Bill Clapper, preen, and even sleep before departure takes place.
For Great Blue Herons, copulation occurs mostly in the morning and evening because females generally are away from nests at midday. Few or no displays occur with copulation (Mock 1976), which occurs mostly on the nest. During copulation, the male places one foot gently in the centre of the female's back. The female leans forward, bends her ankles slightly, and holds her wings slightly away from her sides. The male then grasps the female's humeri with his toes and lowers himself onto his tarsi, often while flapping his wings. The female then moves her rectrices to one side while the male wags his lowered tail over her cloaca. The male grasps her head or neck while copulating, then steps off the female. Extra-pair copulations are considered to occur only rarely (Cottrille and Cottrille 1958, Brandman 1976, Mock 1976, I. Moul pers. comm.).
Social and Interspecific Behavior
Degree Of Sociality
Great Blue Herons forage alone (Kushlan et al. 1985) or in loose flocks throughout the year (see Spacing). They roost alone or in loose flocks, on the ground during the day and above ground at night. The hypothesis that colonies serve as information centres for location of food patches is not well supported (Mock et al. 1988).
Nestling and fledgling Great Blue Herons stab at inanimate objects (Davis 2001). Adult play has not been documented.
Interactions Other Than Predation With Members Of Other Species
Great Blue Herons utter mobbing calls toward mammalian and avian predators. Herons are mobbed while flying by nesting gulls and chased by nesting Ospreys (Pandion haliaetus). Bald Eagles Bayer 1979a), American White Pelicans (Pelecanus erythrorhynch; Johnson et al. 1996), Turkey Vultures (Cathartes aura; Kushlan 1978b), and (rarely) gulls (Bayer 1985b, Quinney et al. 1981) steal large food items from herons. In turn, herons steal food from gulls (Bayer 1985b) and (rarely) fish from Osprey nests (A. Poole pers. comm.). Herons catch fish driven near shore by Double-crested Cormorants (RWB). Occasionally Great Blue Herons feed with other ciconiiformes (Kushlan 1978b, Green and Leberg 2006) and larids (Bayer 1985b). Its nests are sometimes used by Canada Geese (Branta canadensis), House Sparrows (Passer domesticus), and Great-horned Owls (Bubo virginianus; Vermeer 1969d, RWB). The recovery of beaver (Castor canadensis) populations in the northeastern U.S. and in southern Canada has benefited this species by providing additional nesting and foraging areas (e.g., Andrle and Carroll 1988 for NY State).
Bald Eagles (Vennesland and Butler 2004), Common Ravens (Corvus. corax) (Simpson and Kelsall 1978, Butler 1989, Butler 1995), and American Crows (Corvus brachyrhynchos; Quinney 1983) eat unattended Great Blue Heron eggs. Predators of heron nestlings include Bald Eagles (Kelsall and Simpson 1980, Koonz 1980, Forbes 1987b, Norman et al. 1989, Vennesland and Butler 2004), Common Ravens (Simpson and Kelsall 1978), raccoons (Lopinot 1952, Hjertaas 1982), bears (Foss 1980, Parker 1980a), Turkey Vultures (Mehner 1951), Red-tailed Hawks (Buteo jamaicensis; Simpson 1984c) and non-native Fire Ants (Solenopsis invicta; Drees 1994). Egg and nestling predation (by eagles, crows and ravens) has been reported from disturbances caused by humans and eagles (Kelsall and Simpson 1978, Quinney 1983, Drapeau et al. 1984, Simpson 1984, Moul 1990).
Predation on adults and juveniles is not well documented, but there are several reports of Bald Eagles killing both adults and juveniles (Forbes 1987, reviewed by Butler 1997) and there is one report of a juvenile being killed by a Harris's Hawk (Woodward and Trussel 2003). Colony-sites have been abandoned after predators kill adults (Butler 1991) and nestlings (Kelsall and Simpson 1980, Simpson et al. 1987, Vennesland and Butler 2004).
In British Columbia, egg and nestling predation by eagles, and to a lesser degree human disturbance, was largely responsible for the abandonment of 59% of 1247 nesting attempts and 42% of 31 colonies in one nesting season (Vennesland and Butler 2004). See also Conservation and Management: Disturbance by Bald Eagles.