Tricolored Heron Egretta tricolor (PL Statius-Muller)

Ardea tricolor PL Statius-Muller, 1776. Natursyst. Suppl. p.111-ex Daubenton Pl. Enl. pl. 350: Cayenne.

Subspecies: Egretta tricolor ruficollis Gosse, 1847: Burnt Savanna River and Bluefields Creek, Jamaica.

DESCRIPTION

The Tricolored Heron is a medium, thin heron, distinguished by its white underside and dark head, neck, and back, found along the coast in tropical and subtropical Americas.

ADULT:
Its head and neck are slate grey to black grey. The relatively long and thin bill is brown yellow to orange. The iris is brown. The lores are yellow. The head, bill, and neck are all very long and thin, and at times snake like. The back and upper wings are blue grey to black grey. Lanceolate plumes on back are purple maroon. The chin and down the front of the throat is white or with a thin red brown stripe continuing onto the chest. Belly and under wing are white. Legs are grey yellow.


During the breeding season, the bill is bright blue with a black tip. The lores are cobalt blue. The iris is scarlet red. Head plumes are white. Long feathers on the neck and mantle are violet mauve. Filamentous mantle plumes are buff; there is a rufous tinge to upper scapulars and back of neck. The legs are deep pink maroon.

VARIATION: Males are larger than females (average 415 vs. 324 g). The sexes are alike in plumage but in breeding, female plumage color is less intense. Geographic variation occurs. The race ruficollis is larger, with slaty upper parts, white chin and front of neck. Tricolor is smaller, with lighter back and back of neck, red to chestnut line on fore neck. Baja California birds are larger than those from east North America. Trinidad birds have chin and middle of throat chestnut and front of neck more rufous. Additional study of geographic variation is needed.

JUVENILE:
Juvenile birds have an olive brown back and wings and brown neck. The chin, fore neck and belly are white. The breast is streaked chestnut grey. The bill is yellow with dull black tip. Legs are green yellow.

CHICK: The chicks have dark grey down covering backs and wings and the white belly. It has a crest of long brown hair like down. Bill is light green. Iris is yellow white.

VOICE:
The “Aah” call is the aggression call, used also in Upright and Forward displays. Short guttural “Aahrr” call is the alarm call. A “Uunh” call is given as part of the Snap display. “'Culh,” call, rendered “culh, cuhl” or “houn, houn,” is flight call and used mutually in Greeting Ceremony. The “Scaah” call is used to approach nest. Bill Snap is used in Stretch. Wings make “Whomp” sound in Circle Flight.

WEIGHTS AND MEASUREMENTS: Length: 60-70 cm. Weight 200 – 415 g.

FIELD CHARACTERS

The Tricolored Heron is identified by it white belly and slaty dark head, neck and back. In profile its long bill, head and neck and slender body are readily identified. It flies with steady wing strokes with head and neck drawn back.

It is distinguished from other medium herons in its range by its combination of dark back and white under sides.

SYSTEMATICS

It is likely most closely related to the other New World medium
Egretta. The taxonomic implications of geographic variation within the species need to be better understood. Two subspecies are recognized on the basis of size and some color difference. Birds of Baja California (occidentalis) and Trinidad (rufimentum) also have been recognized as subspecies, but later synonymized.

RANGE AND STATUS

The Tricolored Heron occurs in eastern and southern North America, Central America, the West Indies and South America.

BREEDING RANGE: Its North American nesting range is along the Atlantic and Gulf of Mexico coast from south Maine through Texas. Inland nesting occurs rarely and with varying success in such inland sites as South Carolina (Belser and Post 1987), west Texas, Kansas, South Dakota (Frederick 1997). It nests along both coasts of Mexico, Central America, the Greater Antilles and the Virgin Islands, and coastal South America to the mouth of the Amazon River in Brazil on the Atlantic coast and to central Peru (Lima) on the Pacific coast.

The race tricolor occurs in northeast Brazil, to eastern Venezuela, and Trinidad (if only two subspecies are recognized). Ruficollis occurs from North America south through Central America, West Indies, northwest Venezuela, Colombia, to south Peru.

NONBREEDING RANGE: Birds winter through most of the breeding range, including locally in mild winters as far north as New Jersey, New York and Delaware. Its more common winter range is from South Carolina southward. Birds also winter in south California. The core wintering range is probably south of the Untied States.

MIGRATION: Birds from east and south east United States migrate southward following the coast to Florida and then to wintering areas, some through Bahamas, to the West Indies and also to Central America and north South America to Colombia and Ecuador. Birds from Texas migrate south to Mexico and Central America. Return is in February and March. Some birds make a cross-gulf migration. South American birds are sedentary. Wintering and resident birds overlap in unclear ways from south United States through north South America.

Post breeding dispersal is characteristic of this species. As the population has expanded, vagrants are often seen throughout much of the continental North America from New Brunswick, Ontario (James 1984), Ohio, Kansas, Colorado, Oregon (Gillson 1994), inland Texas, and Arizona and in South America to Chile. Vagrants occur in the Lesser Antilles, Fernando de Noronha (Oren 1984), and the Azores (Parrott
et al. 1987).

STATUS: The Tricolored Heron is common along its coastal range and rare inland. Overall it historically is one of the most abundant herons in North America. Having not been the target of the plume trade, its numbers were not reduced in the early 1900’s to the extent of other species. After the 1940’s populations increased range wide, and it substantially expanded its breeding range east North America, Virginia through Massachusetts. It also expanded it winter range in east North America and winter populations increased markedly in Louisiana (Fluery and Sherry 1994). In the 1970’s the United States population exceeded 200,000 birds. Range wide surveys, such as occurred in the 1970’s have not been repeated. However, information from Florida and Louisiana suggest decreases in nesting birds in areas where they previously were more abundant. Outside the United States information is scarcer. It is common and widespread in Mexico and fairly common in parts of Central America. It is common in Suriname (10,000 pairs) and Guyana (5000 birds) (Spanns and De Jong 1982, Haverschmidt and Mees 1994, Dejohnge et al. 1992).

Tricolored Heron

HABITAT

The Tricolored Heron is a coastal heron. It is a bird of shallow marshes, shorelines and coastal lagoons. Among its specific habitats are mud flats, salt marshes, tidal creeks, mangrove swamps, open shallow bays, fresh water marshes, swamps and crayfish aquacultural ponds. Although found in salt to fresh water, it nests more frequently in salt or brackish water areas. It has been seen as high as 600 m in Honduras. In Brazil is has been found in dry Ceara habitats (Teixeira et al. 1993). It favors natural habitats, unlike other species, and flies long distances to feed there (Smith 1995b).

FORAGING

The feeding behavior and ecology of the Tricolored Heron is fairly well understood through studies over much of its range (Kent 1986 a, b, Acosta et al.1990, Ramo and Busto 1993, Chavez Ramirez and Slack 1995, Strong et al. 1997, Miranda and Collazo 1997, Smith 1997). The Tricolored Heron feeds during the day in shallow to relatively deep water, perhaps deeper than most medium herons. It tends to feed solitarily, scattered over the marsh or along streams and defends its feeding sites with Alert Posture, Upright, Forward, and Aerial Fighting. It does associate with feeding aggregations however when prey is abundant, assuming feeding positions more to the edge of the group. It Stabs prey, often making a nearly horizontal rather than vertical stroke. It will Hops or take a short flight, Lunging at prey on alighting.

It feeds by Walking Slowly and Walking Quickly. It also feeds by Standing and by Running after prey it sees. It has a characteristic low Crouch in which the bird squats very deeply, with its neck and belly nearly touching the water. It uses Hopping, Wing Flicking, Open Wing Feeding, and Underwing Feeding. In active pursuit of prey, it may Hop, with flapping wings and lunging strikes or it may spin its body in the direction of its open wing. It also uses other active behaviors on occasion, including Foot Stirring, Foot Raking, Hovering, Hovering Stirring, Dipping, and Foot Dragging. It mixes up its repertoire of behaviors. It may Walk with slow steps stalking prey then run with wings flapping, turning before stopping to wait spotting another fish. This tactical sequence is called “Walk Quickly-Run-Open Wing” (Rodgers 1983).


Small fish are the primary food of the Tricolored Heron, making up 90% of the diet. They particularly eat various species of killifish (Fundulus), the common small tidal marsh and tidal swamps fish in the region (Hammatt 1981, Kent 1986a,b, Post 1990). They also eat frogs, prawns (Palaemonetes), snails, and insects when available.

BREEDING

The nesting biology of the Tricolored Heron is fairly well understood owing to studies in several parts of its range (Rodgers 1977, 1978, Alfaro and Russi 1989, Frederick 1997) The nesting season is in the spring and summer (March-June) in east North America, although as early as February in Florida. Further south, nesting depend more on the rainy season, and is variable from February to August in the Guyanas and Trinidad.

It nests on islands and vegetation islands within coastal
marshes, swamps, lagoons, rivers, and inland in swamps and marshes. Very occasionally they are recorded on dry ground or other odd places. The nest is typically in trees, bushes or herbaceous plants usually in thick vegetation and low, less than 3 m above ground in mangroves or willows and even lower when lodged in low reeds, such as Phragmites. Tricolored Herons are colonial, in small single species colonies or in large mixed species colonies, but generally toward the periphery rather than in the center of the colony, reflecting their being less social than some of the other herons. The nest is a flat platform of sticks, 25-30 cm wide. It is made of twigs with leaves for lining, gathered nearby.

The male stakes out its nesting territory by Alert Posture, Twig Shaking, Preening, Fluffed Neck and Crest Raising displays and begins building a nest platform (Rodgers 1977, 1978). It performs its courtship displays from the platform or nearby, especially using the Stretch display with all plumes erect, wings out and down, with and snap or twig grasp at the down part and the “Unh” call at the peak. The Tricolored Heron display combines features of usual Snap and Stretch displays into a single sequence. This behavior displays the colored iris, lores, bill, and bill tip. Other behaviors are Twig Shaking, Circle Flight featuring exaggerated wing beats and extended neck, Preening with very rapid strokes, Bill Clappering near head and body making a rattling sound. It defends the nest with Upright and Forward displays, the Forward involving extreme erection of the neck feathers, back plumes, and Crest Raising. Once the pair is established, the Greeting Ceremony includes Crest Raising, the “Culh” call, and Bill Clappering. After pairing, the male gathers sticks and the female continues to make the nest.

The eggs are pale green blue. They measure 44 X 32 mm in North America, and may be smaller in South America, 40 X 30 mm. The clutch is usually 3-4 eggs (2 – 7), perhaps smaller, 2-3, in South America. The incubation period is about 21 - 24 days. Both members of the pair incubate.

Chicks hatch asynchronously. They are brooded for 12 days and fed by regurgitation, grasping the parental bill crossways. They are brooded to day 12. After 2 weeks adults visit chicks only to feed them and by 4 weeks the chicks seek out adults for food.
Young are altricial, growing quickly, especially feet and legs (McVaugh 1972). They can move around nest in five days and can climb from nest in 11 days. By 17 days, they are perching above the nest. They can fly away from the nest locations by 24 days and by 30 days form groups of young in the branches. They moult into juvenal plumage by 30 days. Windstorms heavy rains, predation, and food limitation cause nestling mortality. Storms can disrupt nesting (Dindo and Marion 1992). Crows (Corvis), grackles (Quiscalus), and gallinules (Porphyrula) take eggs. Hawks (Buteogallus), mongoose (Herpestes) and Black Vultures (Coragyps atratus) take nestlings. Most mortality is due to failure of the food supply. Brood reduction to 1 to 2 chicks is usual.

POPULATION DYNAMICS

They probably first breed as second year birds (21 months). Mortality is 79% in first year and 32% after that. Longevity is up to 17 y (Clapp et al. 1982). Little is known about factors affecting adult mortality.


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