E-Fauna BC: Electronic Atlas of the Wildlife of British Columbia

Butorides virescens (Linnaeus)
Green Heron
Family: Ardeidae

Species account author: Jamie Fenneman

© David Blevins  Email the photographer   (Photo ID #9362)


Distribution of Butorides virescens in British Columbia.
(Click on the map to view a larger version.)
Source: Distribution map provided by Jamie Fenneman for E-Fauna BC

Species Information

Adult
The back, scapulars, rump, and upper surface of the wings are dark blue-grey with a greenish tinge, with longer scapular feathers that often drape across the upperwing coverts. The wing feathers (including the upperwing coverts, tertials, and inner seconderies) are also very narrowly fringed with whitish-buff, giving the upperwing a scaled appearance; the leading edge of the wing is buffy-white. The very short, squared tail is dark greenish-grey with a bluish cast. The belly, undertail coverts, and underwing are dark slate-grey and the thighs are often tinged with rufous. The head, neck, and breast are dark rufous or chestnut-brown, with bold black and buffy-white streaking extending from the chin down along the centre of the throat to the centre of the breast; there is also a short buffy-white malar stripe at the base of the bill below the eye, and the forehead, crown (down to the eye), and nape are greenish-black and form a distinct cap. The feathers at the back of the crown are slightly longer and can be erected to form a short, bushy crest. The long, slender, straight, pointed bill is usually dark blackish-grey on the upper mandible and paler greenish-yellow on the lower mandible (brightest at the base), but becomes glossy black during the breeding season. The bare skin between the eye and the base of the bill is dark grey, usually with a contrasting pale greenish-yellow spot along the upper edge and extending around the rear of the eye (lores entirely bluish-black at the height of breeding). The iris is yellow to orange and the legs and feet are dusky-yellow to yellow-orange (the iris, legs, and feet become brighter and more orange at the height of the breeding season). The plumage of males averages slightly brighter than that of females.

Immature
Immature plumage is usually acquired during the first fall and retained throughout the following summer. First-winter immatures are similar to juveniles, but have a darker and more sharply contrasting crown, whiter streaking on the chin, throat, and underparts, and broader whitish-buff streaking on the upper breast and sides of the neck. By the following summer (and following a partial molt in late winter or early spring), the plumage pattern more closely resembles that of the adult but is duller and browner, usually with some buffy-white spots on the upperwing coverts and some white streaking on the neck and breast.

Juvenile
This plumage is generally held throughout the first fall, although some birds retain juvenal plumage through their first winter. It is overall similar to the adult, but the plumage is overall notably duller and browner, particularly on the upperparts which are strongly washed with brown. The neck and breast are paler rufous-brown than in the adult and are extensively streaked with buffy-white, and the dark cap is finely streaked with rufous-brown (thus contrasts less sharply than in the adult). The upperwing coverts are finely spotted with buffy-white. The underparts are buffy-white with brownish streaking. The bare part colouration is generally similar to the non-breeding adult, but the colour of the bill, legs, and feet is duskier.

Measurements
Total Length: 45-50 cm
Mass: 210-250 g

Source: Davis and Kushlan (1994); Sibley (2000)

Biology

Identification

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.
Vocalizations

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)

Breeding Ecology

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)
Foraging Ecology

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)

Habitat


This species typically breeds in rather secluded and heavily-wooded wetlands, such as wooded sloughs, swamps, beaver ponds, wooded creeks, oxbow wetlands, and marshes, usually where there is an abundance of overhanging brushy vegetation around the perimeter of the wetland or watercourse. Breeding birds occasionally nest in wooded areas away from water (sometimes >1 km from nearest water source), including heavily wooded suburban parks and gardens, although all foraging occurs in wetlands. Foraging birds sometimes occur in more exposed habitats, including sheltered brackish and marine environments as well as freshwater locations. These individuals can be found in coastal lagoons, sloughs, estuaries, tidal channels, irrigation ditches, canals, golf course ponds, reservoirs, lake shores, and sewage lagoons, although they rarely stray far from some form of protective cover. It regularly occurs year-round at coastal salmon hatcheries, where there is both suitable cover and an abundance of prey.

Source: Campbell et al. (1990a)

Distribution

Global Range

Breeds throughout the eastern and southwestern United States, ranging northward in the east to southern Ontario and southern Quebec, as well as along the Pacific coast to southwestern B.C. It winters primarily in California and the southeastern U.S., and is resident farther south throughout Mexico, Central America, and the Caribbean.
BC Distribution

Breeding
Uncommon and very local on the south coast, where it is restricted to the Lower Mainland (east to Hope) and along the southeast coast of Vancouver Island from Sooke to Campbell River (including the Alberni Valley). An isolated population of 1-2 pairs occurs in the southern Coast Mountains near Whistler.

Winter
Rare in winter throughout the Lower Mainland (east to Chilliwack) and along the east coast of Vancouver Island north to Campbell River.

Migration and Vagrancy
This species is primarily a summer resident in B.C., although a few individuals spend the winter months in the province each year. An increase in observations typically occurs in late April or May as returning birds begin to resettle traditional territories in preparation for breeding. The most notable increase in observations coincides with the dispersal of juveniles in late summer/early fall (August-September), and this is the time of year when the species is most commonly observed. Following juvenile dispersal, populations begin to decline through the fall, with few birds remaining in the province by late October.

This species is a vagrant across southern B.C. outside of its rather limited range. On the coast, it is casual to very rare along the west coast of Vancouver Island and very rare along the Sunshine Coast (Strait of Georgia) from spring through fall, with the highest frequency of observations coinciding with spring (May) and fall (August-September) migration/dispersal. It is also casual to very rare throughout the southern interior north to Williams Lake and east to the southern Rocky Mountain Trench, with observations again occurring primarily in May and August/September (occasional reports during the summer, late birds lingering exceptionally into October).

Source: Campbell et al. (1990a); Fraser and Ramsay (1996)

Conservation

Population and Conservation Status

The Green Heron is a relatively recent addition to the B.C. avifauna, having been first recorded in the province in 1953 following a well-documented northward extension of its breeding range along the Pacific coast of the United States (i.e., first reported in Washington in 1939). By the 1970s, this species was established as a local breeding species on the south coast, including both the Lower Mainland and southern Vancouver Island, although breeding may have potentially occurred in the province as early as 1961. Despite continued population increases, the Green Heron remains a relatively uncommon and localized breeding species in British Columbia, and its total population may number fewer than 100 pairs in the province (and is certainly less than 500 pairs).

As a result of this scarcity, as well as the severe development pressures throughout its range in the province, the species is currently placed on the provincial ‘blue list’ (species of special concern) by the B.C. Conservation Data Centre (CDC). It is not recognized as a species of conservation concern by COSEWIC (Committee on the Status of Endangered Wildlife in Canada), however, likely due to its abundance in eastern Canada.

Source: Campbell et al. (1990a); Fraser and Ramsay (1994)

Taxonomy


This species, which is restricted to North and Central America, was formerly considered conspecific with the similar, but much more widely-distributed, Striated Heron (Butorides striatus), which is found throughout South America as well as through much of the Old World. North and Central American populations are now considered distinct from the Striated Heron, however, as are isolated populations that are resident on the Galapagos Islands (Lava Heron, Butorides sundevallii).

Four subspecies of Green Heron are currently recognized, with two occurring in North America and one (B.v.anthonyi) occurring in British Columbia. This western subspecies differs from the nominate B.v.virescens, which is widespread in eastern and central North America, in its marginally larger size and paler plumage.

Source: Davis and Kushlan (1994)

Status Information

Origin StatusProvincial StatusBC List
(Red Blue List)
COSEWIC
NativeS3S4BBlueNot Listed
BC Ministry of Environment: BC Species and Ecosystems Explorer--the authoritative source for conservation information in British Columbia.

Additional Range and Status Information Links

Additional Photo Sources

General References


Recommended citation: Author, Date. Page title. In Klinkenberg, Brian. (Editor) 2019. E-Fauna BC: Electronic Atlas of the Fauna of British Columbia [efauna.bc.ca]. Lab for Advanced Spatial Analysis, Department of Geography, University of British Columbia, Vancouver. [Accessed: 2020-07-11 11:41:10 AM]
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