Ardea cocoi Linnaeus, 1766

Taxonomy and Common Name

The cocoi heron (Ardea cocoi) is the largest heron species native to South America.

Total Length and Regional Size Variation

It measures 95–130 cm (37.5–51 in) in total length, with regional size variation; southern individuals are likely the largest.

Adult Body Weight

Adult individuals of both sexes weigh between 1.14 and 3.2 kg (2.5 to 7 lb).

Specific Adult Morphometric Measurements

Recorded measurements for adult birds are: wing length 421–455 mm (16.5–18 in), tail length 161–173 mm (6.5–7 in), culmen from the base 128.5–148.7 mm (5–6 in), and tarsus 179–192 mm (7–7.5 in).

Size Comparison to Great Blue Heron

Its size is similar to the great blue heron, its North American counterpart, though the great blue heron averages slightly larger on average.

Sexual Morphological Similarity

The sexes are identical in both body size and coloration.

Adult Plumage and Body Coloration Base Pattern

Adult birds have grey backs and upper wings, with white S-shaped necks, thighs, under-tail wing coverts, and scapulars.

Neck and Breast Black Markings

Black streaks are present on the neck and upper breast.

Head and Crest Coloration

The forehead and crown are black, and this black coloration extends down to the eye area and up into a pointed crest that hangs down the nape.

Additional Torso Black Markings

Additional black streaks appear on the neck, and black patches are located on the sides of the lower breast and abdomen.

Leg and Iris Coloration

Legs have been recorded as black, brownish-grey, or dark green. The iris is usually yellow, and the bill is dull yellow.

Bare Facial Skin Coloration

The bare skin of the orbital region is pale greenish.

Breeding Adult Color Variation

Some breeding cocoi herons observed in Argentina have bright yellow bills with a red tinge at the base, and dusky pink legs.

Flight Characteristics

In flight, its large wings make it a slow but sturdy and graceful flyer.

Vocalization

Its call is a deep croak.

Comparison to Grey Heron Appearance

Overall, the cocoi heron is similar in appearance to the grey heron, but the cocoi heron has slightly darker coloration, a longer neck, and a longer crest.

Juvenile Underpart Coloration

Juvenile cocoi herons have ash grey underparts streaked with buff.

Juvenile Upper Body and Neck Coloration

Their necks and upper body surfaces are pale brownish, with a faint ash grey tinge on the neck.

Juvenile Crown and Under-tail Covert Features

Compared to adults, the juvenile crown is duller, and the under-tail coverts have dusky streaking.

Juvenile Plume and Crest Absence

Juveniles also lack the long plumes and occipital crest that are typical of adult birds.

Downy Chick Color Pattern

Even downy chicks, while paler in overall color, already show the species-typical contrast between a dark head and pale neck seen in adults.

Overall Geographic Range Context

The cocoi heron occurs across most of South America, excluding the Andes and some parts of Argentina.

Native Country List

It is native to Argentina, Panama, Suriname, Colombia, Venezuela, Bolivia, Brazil, Chile, Ecuador, French Guiana, Guyana, Paraguay, Peru, and Uruguay.

Range Extent and Southern Limit

Overall, the species has a notably wide range, extending from Central America to the mainland shores of the Strait of Magellan, though it is rarely found further south than Argentina’s Chubut province.

Estimated Extent of Occurrence

It has an estimated extent of occurrence of 20,600,000 km².

Chaco Habitat and Vagrant Locations

It inhabits the wetter regions of the Chaco, and occurs as a vagrant in the Falkland Islands, Saint Helena, Ascension Island, and Tristan da Cunha.

Non-breeding Visitor Range

It is a regular non-breeding visitor to Trinidad and Tobago.

Core Wetland Habitat Types

Its habitat includes almost any body of water or wetland located away from dense forest, including lake shores, swamps, rivers, and estuaries.

Secondary Feeding Habitat Types

Gallery forest, grassland, and beaches are also recorded as suitable feeding grounds.

Disfavored Habitat and Prey Rationale

Pastures appear to be disfavored, likely because these habitats support a large proportion of insects, which are less preferred as prey than fish and mammals.

Falkland Islands Vagrant Habitat

In the Falkland Islands, vagrant individuals are found around small streams.

Paraná River Habitat Preference Ranking

One study along the Paraná river found that water with aquatic vegetation was the most preferred habitat, followed by open water, with beaches having the lowest preference.

Elevation Range

This heron is found at elevations up to 2550 m above sea level.