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These birds are 4 feet tall and have a wingspread of 6 feet. Despite their large frame, they weigh just 5 to 8 pounds. Great blue herons eat fish, frogs, and snakes in the summer. In the winter, the herons that winter in the upland grasslands depend on small mammals, such as meadow voles and shrews.

Herons choose nesting sites where food will be plentiful onsite or in very close proximity, where they can have a penthouse view so they can watch for predators, and where they won't be disturbed by people. The Black River Riparian Forest offers these birds plentiful food (though the water is highly contaminated); mature, tall, black cottonwood trees that give the herons a clear view from all directions, and an island location, which keeps disturbance of the human kind at bay.

Great blue herons nest colonially, meaning that they nest in groups. The correct term for a heron colony is a heronry (many people say "rookery" but that term refers to colonies of other animals, not herons). Some heronries are enormous, with well over 400 nests.

Unique Subspecies in the Puget Sound region

The great blue heron, the largest heron of North America, is widely distributed in the United States and Canada but the estimated 1,500 pairs of blue heron in the Puget Sound region and extending into coastal British Columbia are distinct from herons elsewhere.

The fannini subspecies (also called the Coastal or Pacific heron) are non-migratory and remain isolated year round from heron populations that migrate. This isolation has led to adaptations that include a darker plumage and subspecies classification, Ardea herodias fannini.

Biologists are concerned about the long-term health of the Fannini herons' population as their numbers are declining an estimated 9.4% per year (see link that follows).

For current, comprehensive information about this subspecies, see the Canadian Wildlife Service website: http://www.ecoinfo.ec.gc.ca/env_ind/region/herons/heron_e.cfm. The information applies on both sides of the U.S.-Canada border.

Parent standing guard over her four-week old nestling to protect it from bald eagles and other predators. This very young bird will fledge in about four weeks, at age two months. By that time, the chick will have reached its full adult size of 4 feet tall, with a 6 foot wingspan.  Photo: Michael C. Hamilton ©

The nesting cycle

The herons return to the Black River Riparian Forest every year late February to evaluate the site for nesting. They seem to consistently return and leave en masse several times before they decide to nest here in February. By mid-March, they are usually in full swing of nesting preparation. Herons reuse their nests year after year, repairing the previous season's nests. The largest nests are the oldest.  Herons arriving after the existing nests have been claimed build new nests.

When you start to see several herons sitting on nests, you can be fairly sure that they are sitting on eggs. This generally happens about mid-March. Great blue herons lay between 3 - 7 eggs per clutch, and the average number of eggs that hatch at this colony is between 3 and 4 per clutch.     

The incubation period for the eggs is 28 days, meaning that you should start hearing the chicks about mid-April. There are some important IF's though -- if no bald eagles, red-tailed hawks, or American crows predate (eat) the eggs, and if nothing else destroys the eggs, such as human or other disturbance that would force them to have to lay more than one clutch. Each time they lay an egg, it will take another 28 days to hatch.

Once the eggs hatch, it takes the chicks 60 days before they are ready to take their first flight. Imagine what it must be like to go from the size of a heron egg (4-6 inches long) to 48 inches tall with a 6-foot wingspread in just 60 days.

After the first month, the parents usually spend most of their time outside the colony, returning only to feed the young and stand watch for short periods. However, if their chicks are threatened by predation, a parent usually remains on the nest, which can severely compromise their ability to adequately feed all their nestlings.

An adult arriving at the heronry from the food hunt usually gives a dull guttural cry. The young vocalize frequently and grab at each others' bills. When returning to the nest with food, the adult rarely flies straight to them, perching instead a few yards from the nest. After a short time, the adult goes to the nest and regurgitates predigested food. The oldest and largest chicks take the lion's share by grasping the adult's bill and catching the food. As the nestlings mature, the parents bring in whole fish so the chicks learn how to eat the food they will depend on once they leave their nest.

Soon it's time to learn vital flying maneuvers. The nestlings have never tested their flying skills, nor have they had any experience with navigating in the wind, landing on a branch, or recognizing (and avoiding!) deep water. Their first flight has to be successful. If it is not, they will pay with their lives. Watching a young heron will give you a new appreciation of just how difficult it is to apply the laws of flight physics, learn how to feed, and master the rules of heron survival in such a short time. Not only do they have a lot to learn -- it's a crash course. They have only two weeks to learn to be fully self-sufficient, and then they must leave to compete for wintering grounds, where they will forage in meadows and farmland instead of Black River's fish-filled wetlands and pond.

Typically, two to three chicks in each nest survive to fledge (take their first flights), meaning that about 300 fledged during the 2006 season. Of those 300 chicks, only 10% to 15% will survive to their first birthday. If they survive their first year, they have an excellent chance of living a long life.

New fledgling practices fishing technique. After they leave their nest, young birds have about two weeks to learn how to hunt and hone their flying skills. During this short window of time, they return to their nests at night to be fed by their parents. They then disperse to the nearby wetlands where they will spend the winter. Photo: Michael C. Hamilton ©

Fishing techniques

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 water surface. Only its head and eyes move to locate the prey. If no fish 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.

Using the second technique, the heron slowly wades around in shallow 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.

Conservation

The population of the fannini subspecies that we see here in the Puget Sound region is declining an estimated 6% annually, which concerns biologists.

The size of the Black River colony might cause you to think that our resident heron population is flourishing and maybe even increasing. Unfortunately, research indicates that is simply not true.

The primary causes of mortality are predation by eagles, hawks, and crows; habitat loss due to development, starvation (often associated with habitat loss); human disturbance; and disease.

Heron etiquette : How to watch without disturbing the birds

Herons are particularly sensitive to disturbance while nesting.  To determine if a heron is disturbed, look at their body language. If its neck is outstretched and the bird is focused on you, then you need to back off from your location until the bird settles into its relaxed posture with its neck in the characteristic “U” shape.

The herons in the Black River colony have shown no indication that they are disturbed by our presence on the walking path along the south edge of the pond. This path existed before the herons chose Black River to raise their young (an important distinction when developers try to argue for smaller buffers for a new project).

To clearly view the herons, you will need binoculars. Do not attempt to get close to the birds or their nests. They are extremely shy and want to be far away from people and their domestic pets.

Nesting schedule

August - January: A small permanent population of herons remains at Black River. They can sometimes be seen in the trees in their winter loafing area, which is toward the center of the pond along the far shore. 

Mid-January: The number of herons starts increasing as they return from their nearby wintering areas. The winter loafing area transforms into a staging area, where they can easily observe their nests to evaluate the site for safety. They may also start the mate selection process.  

Late February through March: The herons return to their nests and then commence with their earliest nesting activities, bringing in sticks, repairing nests, claiming locations for new nests, and conducting courtship activities. The trees have not yet leafed out, making visibility excellent.

Mid-April: The trees leaf out, making it more difficult to see the nests. You will be able to see the herons flying into and out of the colony. This is typically a peaceful, quiet time as they incubate eggs and rest. Some eggs from the earliest nests may start to hatch. Listen for the soft sounds of young nestlings, a little like what you might expect tiny lawn mowers to sound like. It’s not like anything you’ve heard before.  

As the season progresses: More chicks will hatch and the sounds of the nestlings should get louder if all is proceeding normally.

Early June – late August: New fledglings take their first flights. They will be exactly the same size as the adults. Look for birds with all-dark heads (the young birds have no white markings). Their landing skills will be poor and they may look unsure of themselves when in flight.  

Once they fledge: It’s a crash course. They have only about two weeks to become fully self-sufficient. Then they leave to compete for wintering grounds where they will forage in meadows and farmlands for small mammals instead of wading in Black River’s fish-filled wetlands, pond, and nearby rivers and lake.

The chicks will continue to mature on the nests and fledge throughout the season. The size of this colony virtually guarantees that there will be a long nesting season. New herons may join the colony as late as May to start their nests, which means their chicks will not fledge until August.

June is typically peak season for seeing the largest number of fledglings.

Fast facts

• Herons typically select new mates at the beginning of each nesting season. They are seasonally monogomous. Some herons may chose to nest with the same mate year after year, particularly if they were successful as parents and worked together well. The dynamics on each nest vary considerably. Some pairs work together easily and well, while others are not nearly as compatible.
• Eggs hatch after being incubated 28 days.
• The chicks fledge at about eight weeks of age.
• A female can lay one egg every day and a half, and she will lay on average about four eggs. She begins incubating her eggs as soon as they are laid, meaning that once her chicks hatch out, the oldest may be one full week older (and stronger!) than the youngest. That gives the older chicks a tremendous advantage over the younger ones when they compete for food from their parents.
• Stages: Egg, nestling (or chick), fledgling, yearling, adult (at age 2).

Did you know ...

Scientists recommend that there should be no development within 1,000 feet of the near edge of a heron colony and no disturbance in or near colonies from January 15 to August 1. Each colony has its own specific needs based on its location and the unique dynamics of the heron community living there. 

Some colonies are located close to human activities such as Park and Rides or a shopping center.  These colonies are the exceptions. They are typically very small and much more prone to predation, indicating that the herons using these compromised locations may be subordinate and possibly unable to successfully compete for space in a colony that has more protection from disturbance.