Chesapeake Bay Field Office
Northeast Region

Great Blue Heron (ardea herodias)

Great blue heron. Photo by Gary Kramer, USFWS
Great blue heron. Photo by Gary Kramer, USFWS

Almost everyone has glimpsed one somewhere: the dignified image is emblazoned upon magazines, clothing and even a special license plate, for it is rivaled only by the blue crab as the symbol of Chesapeake Bay wildlife. The stately great blue heron is the largest, most widely distributed of American herons. Whether flying majestically overhead or standing motionless at the water's edge on a still, misty morning awaiting an unsuspecting fish, the great blue heron embodies grace and elegance.

The great blue heron is easily distinguished from other members of the heron family. It is a four-foot tall wading bird with a dark gray body, brown neck, chestnut thighs, and white crown, cheeks, and throat. Two distinguishing long, black occipital crests arise from the crown stripe in adults. As is typical of herons, great blues have a short, blunt tail, extremely long legs and neck, and a sharp bill. In flight, the legs trail behind the body, and motion is maintained by slow, powerful strokes of wings that can span six feet.

Life History
Great blue herons breed across the United States and southern Canada, and more than half of the Atlantic coast's breeding population nest in Chesapeake Bay—predominantly in wetlands. Although many herons migrate through the Bay region, some great blues remain in the Bay area year-round. These waterbirds use a variety of different feeding methods to procure their primary diet of small fish, which they swallow head first. They also eat frogs, salamanders, lizards, snakes, crawfish, small birds, rodents and insects. Great blue herons are one of the top predators of the Bay food chain.

Nesting
Herons form pair-bonds, usually in March and April, after a series of courtship rituals performed by both sexes. The occipital crests are raised in display during courtship and both sexes change body coloration, although the male becomes more brightly adorned.

Although great blue herons occasionally nest singly, most breed in localized colonies of up to hundreds of nesting pairs. Heron colonies are often termed rookeries after a European member of the crow family, the colonial rook, that also nests in colonies. In Chesapeake Bay, nesting sites are primarily living, but occasionally dead, trees and bushes. The location of the colony depends upon an available food supply for raising the young in close proximity to nesting trees; however, the birds show a preference for stands of loblolly pine, beach, oak and large, old sycamore trees. Initially, the inner section of a stand of trees is utilized, but continual colony use may eventually kill that area. When the center of the tree stand dies, the colony moves circularly outward in succeeding years. This strategy creates a "donut" or "bullseye" effect when the tree stand is aerially viewed. Nests are constructed of sticks and, if not collapsed by winter weather, may be repaired and used year after year. The nest is lined with reeds, mosses and grasses to help cushion three to seven eggs that are laid during March and April. Eggs hatch after about 28 days, and both parents care for the chicks. The young are initially fed a diet of regurgitated food, but eventually eat whole fish dropped into the nest. Juveniles leave the nest after about 60 days and, if they survive their first winter, may live for another fifteen years.

Abundance
Recently, the Maryland Department of Natural Resources and the Virginia Commission of Game and Fisheries have sponsored surveys to monitor populations and annual nesting success of great blue herons. They also monitor colonies of other species of herons and egrets. In early spring before the trees have leaves, aerial surveys are conducted to locate colony sites and count nests. At larger colonies, ground counts are made of active nests.

Chesapeake Bay, the nation's largest estuary, and surrounding areas provide both the ideal food and habitat necessary for great blue heron survival. In 1990, surveys found 4600 great blue heron pairs in more than 38 colonies in Maryland. The Nanjemoy Creek colony in Maryland may be the largest along the entire Atlantic coast, with 1100-1200 nests counted in recent surveys. Fortunately, that land area is protected by the Nature Conservancy.

In the past, herons and egrets were shot for their feathers, which were used as cooking utensils and to adorn hats and garments, and they also provided large, accessible targets. The slaughter of these birds went relatively unchecked until 1900 when the federal government passed the Lacey Act, which prohibits the foreign and interstate commercial trade of feathers. Greater protection was afforded in 1918 with the Migratory Bird Treaty Act, which empowered the federal government to set seasons and bag limits on the hunting of waterfowl and waterbirds. With this protection, herons and other birds have made dramatic comebacks.

In recent years, great blue herons have had to face new challenges. Loss of nesting sites, and deterioration of water quality and wetland habitat are issues of concern for heron survival. Natural generation of new nesting islands, created when old islands and headlands erode, has decreased due to artificial hardening of shorelines with bulkheads. Poor water quality reduces the amount of large fish and invertebrate species available in wetland areas. If suitable feeding and nesting areas are not maintained, populations of great blue herons will eventually decline. Toxic chemicals that enter the Bay from runoff and industrial discharges pose yet another threat. Although great blue herons currently appear to tolerate low levels of pollutants, these chemicals can move through the food chain, accumulate in the tissues of prey and may eventually cause reproductive failure in the herons.

Care must be taken to preserve nesting sites, as well as feeding areas. Erosion of island nesting areas due to artificial structural development, as well as sea level rise, needs to be carefully monitored. Nesting sites should be observed from a distance of at least 200 meters to minimize disruption of the colony. If herons are disturbed frequently, they may abandon their nests or neglect their young. Deterioration of submerged aquatic vegetation limits foraging area potential. Wetland foraging sites within 15-20 kilometers of heron colonies need special protection to ensure prey availability.

Currently, Chesapeake Bay is home to relatively stable, substantial populations of great blue herons, but we cannot become complacent in our efforts to preserve them. Preservation of shallow water habitat, feeding areas and rookeries must remain a priority if we want to continue to enjoy this majestic symbol of Chesapeake Bay.

Some migratory birds in the Chesapeake Bay area:

Bald Eagle

Black Rail

Canada Goose

Canvasback

Cerulean Warbler

Field Sparrow

Great Blue Heron

Red Knot

Osprey

USFWS Office of Migratory Bird Management

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Last updated: January 28, 2011