The identification of this species is straightforward in the context of British Columbia. Juvenile birds, with their streakier plumage, may be confused with juvenile Black-crowned Night-Heron, but are easily distinguished by their noticeably smaller size, longer and more slender bill, darker plumage, dark crown, and more uniformly dark upperparts with, at most, fine white speckling on the wing coverts (upperwings boldly spotted with white in juvenile Black-crowned Night-Heron). These two species should be easily separable under even marginal viewing conditions.
| The commonly-heard call is a sharp, loud, explosive SKEEW or SKEOW, usually given in flight or during take-off, especially when alarmed. Birds that are disturbed near the nest sometimes give low, knocking ku-ku-ku-ku or skuk-skuk calls, as well as a stronger, more hostile raaah, raaah. Source: Davis and Kushlan (1994); Sibley (2000) |
Courtship
Courtship and pair formation occur on the breeding grounds in spring or, in some cases, during spring migration (birds return to nesting territory already in pairs). A variety of courtship displays are performed by the male in the vicinity of the nest site when a female enters the territory. Most displays are accompanied by the loud skow call and are performed in flight, although during early stages of courtship the male may also call repeatedly from an elevated perch. During a typical courtship sequence, the male flies around the potential nest site to advertise his presence. The male will also fly in pursuit of the female, often with his neck only partially retracted. At the peak of the courtship display (Flap Flight display), the male lurches through the air with exaggerated flapping that produces a whoom-whoom-whoom sound, crooks the neck, dangles the legs, gives loud skow calls, erects the feathers of the crest, neck, and scapulars, and sometimes gives several roo-roo calls before landing. When not performing display flights, the male may adopt a posture in which the head and neck are extended forward and held low and the feathers of the head and neck are held erect, during which he will snap the mandibles together to produce a loud click sound; this display may also be accompanied by head bobbing and bowing. Prior to the female entering the nest site, the male performs a ‘Stretch’ display, in which he points the bill straight up, stretches the neck, erects the scapular feathers, and bends the neck backwards until the head almost touches the back; the head is then swayed back and forth while emitting a aaroo-aaroo call. The female also performs a ‘Stretch’ display, but this is less exaggerated than that of the male.
Nest
This species is not generally colonial in its nesting behaviour, unlike many other heron species, but in where common it may nest in loose aggregations; however, given the low density of nesting pairs in B.C., it is expected that most pairs in the province breed singly (although two pairs have been observed nesting together on Vancouver Island). Nesting sites are chosen by the male upon arrival on the breeding grounds, and old nests are often re-used during subsequent years (after some renovation); this species also sometimes uses the old nests of other bird species. For new nests, the male initiates the construction process but once the pair has formed the female does most of the construction (although the male brings sticks to the female). Nest building likely takes 3-14 days to complete. Nests are placed 1-10 m (rarely to 20-25 m) above the ground in a deciduous or (less commonly) coniferous tree, or sometimes in a dense shrub, and are usually placed near the end of a sturdy branch. Many nests are placed in vegetation above water, but others may be built as much as 1 km or more from the nearest wetland. The nest is variable and ranges from a small, flimsy platform to a thicker, bulkier, and sturdier platform (usually older nests). Nest dimensions range from 20-30 cm in width and 8-24 cm thick, with some nests being elongate rather than rounded. The nest is composed primarily of sticks, and may include reeds or other vegetation, but is usually unlined.
Eggs
A single clutch of (3)4-5(6) eggs is laid between mid-May and early June and is incubated by both parents for 19-21 days before hatching. The smooth, non-glossy eggs are pale greenish or bluish when first laid, but quickly fade to chalky white during incubation. Eggs are generally present in B.C. between mid-May and early July, but may occur as late as late July (probably replacement clutches).
Young
The young are semi-altricial and downy upon hatching, with pinkish skin and smoky-grey to greyish-brown down that is paler on the underparts and darker on the head; the down is generally thin, but is thicker on the back and is rather bushy on the head. The young are tended by both adults and remain in the nest for 16-17 days before fledging. After fledging, they spend the first 5-6 days clambering among the vegetation in the vicinity of the nest but are able to fly weakly at 21-23 days of age (and able to fly relatively well by 25 days of age). The fledglings remain with the adults for ~15-20 days before dispersing and becoming independent. Nestlings and dependent fledglings are present in B.C. between, mid-June and early September.
Source: Campbell et al. (1990a); Davis and Kushlan (1994); Fraser and Ramsay (1996); Baicich and Harrison (1997)
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The Green Heron is primarily a fish-eating species, although it does consume small amounts of other prey such as aquatic insects and their larvae, spiders, leeches, earthworms, aquatic snails, crayfish, crabs, frogs, tadpoles, salamanders, snakes, and even small rodents. Individuals forage both by wading into shallow water (<10 cm deep) along the edge of the wetland and by perching on overhanging branches, rocks, docks, and log booms in order to reach deeper water. Foraging occurs throughout both day and night. Much of its foraging involves perching (often in a crouched posture) for extended periods of time concealed within dense overhanging vegetation and opportunistically spearing prey from the surface of the water; as a result of this rather secretive behaviour, this species can often be difficult to locate. It also forages in more open habitats where it is more easily visible, particularly during the late summer and fall. When prey is spotted, the bird lunges forward with its head and bill (and sometimes the body) to grasp the prey in its bill; the prey is sometimes speared by the bill rather than grasped. On rare occasions, this species will dive from a perch to capture deeper prey, sometimes submerging the entire body. Many populations of Green Heron have been observed baiting fish with various lures such as crusts of bread, bits of plastic, insects, and feathers and then capturing the fish that come to investigate the lure; this baiting behaviour is fairly common in Green Heron populations but is rare among other species of herons.
Source: Davis and Kushlan (1994); Fraser and Ramsay (1996)
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