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Want to Learn More?
About the Great Blue Heron
Facts About Great Blue Herons
Management Recommendations for Washington's Priority Species, Volume IV: Birds

HERONS (Ardea herodias)

Wading great blue heronThe great blue heron (Ardea herodias) is a large, grayish-blue wading bird with a long bill, neck, and legs. It is practically the only large "crane-like" bird in the Pacific Northwest (the sandhill crane (Grus candensis) is native but uncommon). In flight, the great blue heron can be recognized by its long neck folded back on the shoulders, its long trailing legs, and its slow, deep wing beats. Adults can be recognized by the presence of a blue plume. Males and females are virtually identical.

Great blue herons are found year-round throughout the Pacific Northwest, except for the arid grasslands and interior forests. They are at home in both salt and fresh water and are seen on lakes, ponds, rivers, marshes, mudflats, irrigation ditches, farm fields, and meadows. For information on belted kingfishers, see "Notes on the Belted Kingfisher."

Great blue herons reach 4 feet in height and have wingspans of nearly 6 feet. Because of hollow bones, adults weight an average of only five pounds. They have long necks and a long bill adapted for grasping prey.

Facts about Great Blue Herons

Food and Feeding Habits

  • Great blue herons are stand-and-wait-predators that remain motionless for long periods of time, waiting for prey to venture near.
  • Their large size enables them to feed on a variety of prey, including fish, frogs, turtles, young birds and bird eggs, snakes, and insects; also mice, moles, gophers, and other small mammals.
  • Herons feed during the day or night (in lighted areas), generally within 3 miles of their colony. They tend to be solitary feeders, but where the food supply is abundant, they can be found feeding together.
  • The adult heron rarely flies straight to the young, perching instead a few yards from the nest. After a few minutes, the adult goes to the nest and regurgitates predigested food. The oldest and largest chicks take most of the food share by grasping the adult's bill and catching the food.

Nest Sites and Nests

  • Great blue herons nest in colonies, often called rookeries or heronries. Heronries are usually in isolated spots away from potential disturbance and near suitable feeding areas.
  • Herons that have been frequently exposed to human disturbance may be more tolerant and may nest in large public parks and greenbelts.
  • Herons nest in deciduous or evergreen trees, usually near the top on vertical branches. Nests are usually constructed in the tallest trees available, on islands, or in trees with water around the base, presumably to reduce the risk of predation by mammals.
  • Where trees are absent, nests may be located on large shrubs, cliffs, and artificial structures.
  • Nests are constructed from branches and twigs gathered from the ground, trees, and old nests. Nests are 25-40 inches in diameter and 12 or more inches thick.
  • Heronries may be used for decades; however, herons will relocate their colonies in response to increased predation on eggs and young, declines in food availability, human disturbance, and death of trees supporting the nests.

Reproduction

  • Herons begin returning to a colony to breed in February and March. Nest building begins in March or April.
  • Three to five pale, greenish-blue eggs are incubated for 25-29 days by both sexes.
  • Young first fly at around 60 days of age and leave the nest at 65-90 days, at which time they are similar in size to adults.
  • Great blue herons have one brood (clutch) per year, however, they may renest if their first clutch fails.

Mortality and Longevity

  • Adult great blue herons don't have many predators, though bobcats, coyotes, red-tailed hawks, crows and bald eagles do occasionally kill an adult.
  • Mortality of the young is high: both the eggs and young are preyed upon by crows, ravens, gulls, eagles, and raccoons. Heavy rains and cold weather at the time of hatching also take a heavy toll.
  • Herons may live to be 15 years old, but six to eight years of age is the norm.
  • Great blue herons were nearly hunted to extinction in the late 1800s because of a fashion trend for using their plumes on women's hats. In the 1960s, they were vulnerable to egg-shell thinning as a result of exposure to the pesticide DDT, which lowered reproductive success.

Feeding Habits of the Great Blue Heron
The great blue heron has two principal fishing techniques. The first consists of standing motionless, its neck extended at an angle of about 45 degrees to the surface of the water. Only its head and eyes move to locate the prey. If no prey comes within range after a few minutes, the heron gradually moves a short distance away and takes up a similar position. When a potential meal comes close enough, the heron slowly folds its neck back and moves one leg in the direction of the prey. Suddenly, its entire body unbends, its head plunges into the water, it catches the prey in its bill, and it swallows it outside the water, using a deft movement of the head to drop the prey headfirst into its gullet.

A similar technique is used to hunt small rodents in pastures, meadows and similar habitats. Herons stab or clamp on their prey, using their bills like barbecue tongs.

Using the second technique, the heron slowly wades around in 6-12 inches of water until it drives a fish out from its hiding place. The heron then stops and slowly stretches its neck. When the prey is within range, the bird uncoils its body and thrusts its head into the water after it. After eating the catch, the heron resumes its walk. Should the bird fail to find sufficient fish in an area, it flies a short distance away and resumes fishing.

When its catch is too large to be gulped down immediately or has dangerous spines, the heron drops it back into the water and grabs hold of it repeatedly and violently with its beak until it is dazed or the spines snap. Then it can be swallowed more easily. Sometimes two fish are caught simultaneously.

Other techniques are observed more rarely: for example, great blue herons in flight sometimes dive underwater to catch fish; others hover over the water and submerge their heads to catch fish; and some swim in deep water and feed on fish found near the surface.

Tips for Viewing Great Blue Herons and Signs of Them
People most often observe great blue herons as the birds fly slowly and steadily, wings arching gracefully down with each beat, neck bent back, and feet trailing behind. They are also seen feeding-standing motionless and staring into shallow water, or walking with measured steps as they search for prey.

Herons are great birds to watch if you are a beginning birder. Their large size and interesting behaviors will provide you with many hours of enjoyable viewing. In urban areas, these birds have acclimated to people so you can get a close view of them hunting without disturbing them.

The nesting behavior of great blue herons is not often witnessed since they nest in colonies in fairly isolated areas. Heron rookeries should not be disturbed during the nesting season (Feb. 15 to July 31). Several studies have shown that human disturbance during the breeding season can cause adult herons to abandon the entire rookery. Herons are least tolerant of disturbance during the pre-nesting and courtship periods, becoming progressively less likely to abandon nests after laying eggs.

Even if you can't see great blue herons in their rookeries, they are fascinating to watch on their feeding grounds. Great blue herons often congregate at mudflats and ell grass beds during low tides from June to December where they feed on small fish. Here you may have the opportunity to view many herons at once.

To prevent problems from occurring, use high-powered binoculars or spotting scopes to observe herons. Nesting herons should be left alone and follow area regulations and closures to protect colonies. Many designated viewing areas have been set up by naturalists.

Things to listen and look for include:

  • Tracks and trails: Great blue heron tracks are easily found in the mud or sand next to a feeding site. Their tracks show four toes and the webbing may or may not appear, depending on the hardness of the surface.
     
    Great blue heron tracks and trail. The track from front to back is about 6 inches long and a claw imprint shows clearly at the end of each toe. The hind toe is well-developed for standing and walking. The walking stride is about 10 inches. The trail is fairly straight, and feet point forward.
     
  • Droppings and pellets: Great blue heron droppings are semi-liquid and mostly white. Solid droppings vary from 2-3 inches in length, and contain signs of fish, frogs, small rodents, and other prey. The ground beneath nests can become coated with droppings. Undigested material may also be coughed up as pellets.
     
  • Calls: The normal call of a great blue heron is a deep, hoarse fraaaahnk or braak. In aggressive situations or when frightened, the call is a short, harsh frank frank frank taaaaaw. Herons call in flight and on the ground, during the day and at night.
     
    An adult arriving at the rookery usually gives a dull guttural cry. The young cry constantly and grab at each others' bills.

Tips for Attracting Herons
If you put out a bird feeder, you have to expect the birds to come and eat. A pond full of fish makes a wonderful heron (and kingfisher) feeder. Keep the pond stocked with cheap feeder goldfish, give the heron a good place to stalk them, and enjoy the show. In order to give fish a place to hide, one or two areas can be kept as hunting spots for herons and the other areas can be heavily planted to block access into the pond. Because kingfishers tend to dive from a perch to catch fish, a simple perch can be built for them if a dead tree or large bare branch doesn't exist nearby.

To help preserve heron habitat:

  • Preserve shoreline trees.
  • Protect eelgrass beds because they provide great habitat for herring. Herring is a major food source for herons, kingfishers, salmon, seals, and other marine mammals.
  • Protect wetlands.
  • Keep pets under control and away from great blue herons.
  • While visiting the beach or boating, give herons and heron rookeries plenty of space.
  • Minimize development near heron colonies.

For detailed management recommendations for great blue herons and their colonies, http://wdfw.wa.gov/publications/pub.php?id=00026.

Why do Birds Nest in Colonies?
Why do some birds nest in colonies? The habit is widespread-Brewer's blackbirds, great blue herons, and gulls all nest in such a way.

In eastern Washington, Brewer's blackbirds forage for insects in short vegetation around ponds and streams, mostly close to the colony nest site, but sometimes a mile or more away. The birds appear to concentrate their feeding in areas where prey is most abundant. This habit apparently developed because it allows less adept birds to follow more successful foragers when they leave the colony to feed, and perhaps also because it provides some protection against predation.

Cliff swallows exhibit similar behavior. Cliff swallows that have been unsuccessful in finding food (flying insects) return to the colony and follow a successful forager to a food source. Most seabirds that nest together also forage for fish together, suggesting that they too can benefit from each other's good fortune on the hunt.

Some birds such as the great blue heron, however, nest colonially and generally forage alone. So is it less likely that the colony serves as an "information-center" for its members?

Among herons, young birds may benefit from the learning opportunities presented by colony living. Older, more experienced herons are better able to find food. However, if their younger colony mates follow them to the feeding grounds they are likely to have less success at foraging, because of the increased competition.

Why, then, do older herons live in colonies? One hypothesis is that the older birds benefit through protection from predation. Being more dominant birds, they are able to acquire the safest nesting sites, located in the center of the colony. Adapted from "The Birder's Handbook."



Heron Conservation and Stewardship Groups
Seattle Audubon Society - GBH Research
Herons Forever
The Heron Working Group
Heron Habitat Helpers
 
To explore places to find birds in Washington - Great Washington Birding Trail
Related Links
Bibliography & Links
Canadian Wildlife Service - Great Blue Herons
Hinterland Who's Who - GBH Fact Sheet
California Academy of Sciences Library - GHB Bibliography
USFWS - Great Blue Herons, a Monitoring Species?
Environment Canada