The Great Egret (Ardea alba)

Nov 23, 2008 Features / Columnists, Interesting Creatures in Guyana

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The Great Egret (Ardea alba), also known as the Great White Egret, or Common Egret, is a wading egret, found in most of the tropical and warmer temperate parts of the world, although it is very local in southern Europe and Asia.

This long-legged, S-necked white bird is commonly seen throughout the Americas. It is typically the largest white egret occurring anywhere in its range (only the white-coloured form of the great blue heron is larger).

The Great Egret is a large bird with all-white plumage that can reach 101 cm in height and weigh up to 950 g. It is only slightly smaller than the Great Blue or Grey Herons.

Apart from size, the Great Egret can be distinguished from other white egrets by its yellow bill and black legs and feet.

It also has a slow flight, with its neck retracted. This is characteristic of herons and bitterns, and distinguishes them from storks, cranes and spoonbills, which extend their necks.

Great Egrets are found near water, salt or fresh, and feed in wetlands, streams, ponds, tidal flats, and other areas.

They snare prey by walking slowly or standing still for long periods, waiting for an animal to come within range of their long necks and blade-like bills. The deathblow is delivered with a quick thrust of the sharp bill, and the prey is swallowed whole.

Researchers have found that, standing still, Great Egrets are able to ingest more prey of intermediate size than if they moved around. This suggests that their goal is not to catch the largest quantity of food, but to catch high quality food.

Fish are a dietary staple, but Great Egrets use similar techniques to eat amphibians, reptiles, mice, and other small animals. They are considered to be heterotrophs.

Typically, these birds nest in trees, near water and gather in groups called colonies, which may include other heron or egret species. Their nests are a flimsy platform constructed of sticks, twigs, and stems built as high as possible.

They are monogamous, and both parents incubate their three to four eggs for about 23 to 24 days. The eggs are a pale greenish blue.

With a clutch size of only 3-4 eggs, Great Egrets will lay replacement eggs if any of the first eggs are damaged. Great Egrets are capable of reproducing after two years and raise one brood per year. The breeding season begins mid-April.

Young egrets are aggressive towards one another in the nest, and stronger siblings often kill their weaker kin so that not all survive to fledge in two to three weeks.

Both male and female Great Egrets also participate in feeding the semi-altricial young. Nestlings are initially fed by regurgitation, followed by bill-grabbing, where the parent holds prey over the nestling to grab at as it eats.

Great Egrets have a lifespan of about 15 years in the wild (22 in captivity). The Great Egret is partially migratory, with northern hemisphere birds moving south from areas with cold winters. It builds a bulky stick nest. The call at breeding colonies is a loud croaking “cuk cuk cuk”.

These birds are very territorial when it comes to courtship, nesting and feeding. They are diurnal feeders and at dusk they gather from surrounding areas to form communal roosts. Post-breeding dispersal is very common among great egrets.

After the young hatch, they accompany the adults on long journeys. Many heron species rob other species in order to obtain more food. Great Egrets steal a very high percentage of their food from other smaller herons.

They also fight for food within their own brood. For many avian species food availability has an effect on aggression. However, it has been found that great egrets are highly aggressive in many situations even when food is not limited.

The Great Egret is the symbol of the National Audubon Society and represents a conservation success story. The snowy white bird’s beautiful plumage made it far too popular in 19th-century North America.

Great Egrets were decimated by plume hunters who supplied purveyors of the latest ladies’ fashions. Their populations plunged by some 95 percent.

Today, populations are doing well. However, there are still many human-induced threats to the survival of Great Egrets. Loss of habitat, water pollution, and various air pollutants all contribute to the dangers faced by Great Egrets.

Hydrocarbons are especially problematic because they cause Great Egrets to lay thinner eggs that are more susceptible to cracking or damage before the young hatch. Mercury has been found at high levels in the feathers of numerous avian species including Great Egrets.

The amount of mercury found depends on age, sex, geographic location, and mercury concentrations in the habitat around them including the air, soil and organisms they consume. These contaminations have also been found to negatively affect behaviour, physiology, and reproduction.

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