APPEARANCE
First described in 1758 by Linnaeus, the father of taxonomy, the great blue heron Ardea herodias is
among Amazonia's largest water birds, between four and five feet high, and a five or six feet wingspan.
It's typical of the heron family (Ardeidae): slender and long-necked.
The wings and body are grayish blue, streaked white and black, while the head is white with a black strip
over the eye. The bill is dull yellow, whereas the legs are greenish yellow. The great blue heron is known to
as a white variant, but this is not known from the Amazon region.
During flight, the heron holds its head close to the body with an S-bend in its long neck. The legs trail
behind as the bird flies with slow but strong wing beats.
HABITAT AND DISTRIBUTION
The great blue heron is migratory in Amazonia and ranges throughout the Americas in temperate and tropical
zones, occurring as far north as southern Canada during the North American summer. It ranges up to about 8,500
feet.
Although commonly seen in Central and South America, breeding is restricted to areas of milder weather. The
species is rarely seen far from water, preferring marshy areas, swamps, the edges of rivers and lakes. In
coastal zones, it is found in tidal flats, estuaries and mangrove forest.
FEEDING AND DIET
As an ambush predator, the great blue heron is usually solitary, and waits or walks slowly in shallow water
grabbing prey that passes by. As with other herons, prey is primarily small fish with lesser quantities of
other aquatic animals such as aquatic invertebrates, amphibians or even birds, usually spearing the prey with
its pointed bill. It hunts on land for small mammals and reptiles.
An adult heron may form a temporary territory in which it feeds, up to several hundred square yards, which it
defends.
BREEDING
This species breeds primarily in the northern part of its range in small colonies or singly, preferring
isolated areas.
Males display while standing or sitting on nest sites, with the neck arched over the back and the bill
pointing skyward.
The large untidy nest forms a robust platform, lined with twigs and vegetation. Nests are located
in trees or shrubs, usually close to water and 30 to 70 feet above ground.
Following courtship, from 3 to 6 pale bluish green eggs are laid, incubated for about 4 weeks. Both parents
participate in care, feeding young in the nest by regurgitating food.
Hatchlings are altricial, covered in pale gray down. At hatching,
the eyes are open, and chicks take about two months to fledge. Great blue herons live to about 15 years.
CONSERVATION
The great blue heron is among the commonest large aquatic birds, and populations seem to be trending upwards.
Formally, the species is considered to be of
"least concern."
Plume hunters in the late 19th and early 20th centuries impacted populations of this species less than of
other herons.
The main threat today is from loss of habitat, primarily drainage of wetlands due to urban development or
conversion to agriculture.
Some fish farmers consider this species to be a pest because it hangs around fish ponds. However, a study at
a Mississippi catfish farm found that the birds take fish near the surface of the water, and these tended to
be sick and would have soon died anyway (Glahn et al 2002). The authors conclude that "losses from great blue
herons are either insignificant or readily preventable."
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