Fall 2003

Table of Contents

Living with Washington's Wildlife: Great Blue Heron

(Editor’s note: If you’ve got a pond in your Backyard Wildlife Sanctuary, or simply live near a body of water, chances are you’re occasionally visited by a great blue heron. Depending on your outlook, heron visits can be a joy or a frustration. We’ll take a look at this bird in an excerpt from the “Living With Washington’s Wildlife” series being compiled by WDFW’s Seattle-area urban wildlife biologist Russell Link. This series of factsheets should be available soon at WDFW regional offices and on the website, and will be part of a new book, “Living With Wildlife in the Pacific Northwest” due out next year.)

• Herons feed on a variety of prey, including fish, frogs, young birds and bird eggs, snakes, and insects, as well as mice, moles, gophers, and other small mammals.
• They are “stand-and-wait” predators that remain motionless for long periods of time, waiting for prey to venture within striking range of their long, stabbing bills.
• Herons feed during the day and at night in lighted areas, generally within three miles of their nesting colony. They tend to be solitary feeders, but where the food supply is abundant, many can be found feeding together.
• Where water freezes, heron populations concentrate along major open-water rivers where food is available, or they hunt rodents on land.

• Great blue herons nest in colonies, also called “rookeries,” which may contain a few or hundreds of nests.
• Rookeries are usually in isolated spots away from disturbance and near suitable feeding areas, although some are in large public parks and greenbelts.
• Herons nest in deciduous or evergreen trees and snags, usually near the top of the tallest ones on vertical branches, often 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 25 to 40 inches in diameter and 12 inches or more thick, constructed from branches and twigs.
• Rookeries 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 when nest trees fall.

• Adult herons can arrive on the nests as early as February. Nest building and repair usually begins in March.
• Three to five pale, greenish-blue eggs are incubated for 25 to 29 days by both sexes.
• Young birds first fly at around 60 days of age and leave the nest at 65 to 90 days, at which time they are similar in size to adults.
• Great blue herons have one brood per year, although they may re-nest if their first clutch fails.

• Adult great blue herons don’t have many predators. Bobcats and coyotes occasionally kill adults feeding at ground level.
• Mortality of the young is high: crows, ravens, gulls, eagles, and raccoons prey upon both the eggs and young. Heavy rains and cold weather at hatching also take a toll.
• Six to eight years of age is the normal life span.

Great blue herons are great birds for the beginning birder to observe, partly because of their size. In urban areas, herons have acclimated to people so you can get a close view of their hunting behavior. A pair of binoculars or a spotting scope will allow for exceptionally close views of their black plumes and yellow eyes.

The nesting behavior of great blue herons is not often witnessed because, with some urban exceptions, they nest in colonies in fairly isolated areas. Nesting herons should be left alone, and area regulations and closures to protect colonies should be followed. Several studies have shown that human disturbance during the breeding season can cause adult herons to abandon the entire colony.

Great blue herons often congregate at mudflats and eelgrass 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.

Tracks: Great blue heron tracks are easily found in the mud or sand in a feeding site. Their six-inch-long tracks show four toes and the webbing may or may not appear, depending on the hardness of the surface.

Droppings and pellets: Great blue heron droppings are semi-liquid and mostly white. The ground beneath nests can become coated with droppings. Undigested material is coughed up as 2 to 3 inches pellets, containing signs of fish, rodents, and other prey.

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 can cry loudly and constantly when hungry and about to be fed.

A pond full of small fish makes a wonderful heron feeder. Keep the pond stocked with cheap feeder goldfish, give the heron a place to stalk them, and enjoy the show. 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 and provide cover for the fish.

To help preserve heron habitat:

• Preserve shoreline trees and any tall groups of trees by the water.
• Protect eelgrass beds, which are great habitat for herring — a major food source.
• Protect wetlands.
• Keep pets, especially dogs, under control and away from great blue herons and rookeries.
• While boating or visiting the beach, give herons and heron rookeries plenty of space.
• Minimize development near heron rookeries.

Many people are willing to lose some inexpensive feeder fish to great blue herons in exchange for the opportunity see one of these magnificent birds. However, some homeowners have expensive fish in their pond or have bonded to the ones they placed there and watched grow. Others object to the mess herons sometimes leave behind.

Predation can occur at any time of the year, although the problem is greatest in spring and early summer, when the birds feed their young. Each day, an adult heron needs about 13 ounces of food, which is equivalent to three six-inch koi or 10 twoinch goldfish. Herons take twice this amount when feeding their young.

Herons usually visit ponds when everything is quiet, usually early in the morning or in the evening. Once they’ve found an easy source of food, such as colorful fish in a shallow pond, they will return on several consecutive days until most of the fish have been taken.

There are several ways of reducing heron attacks on your pond fish. All are most successful when in place before the birds discover the easy food source.

(Keep in mind that all heron species, nests, and eggs are protected year-round from persecution, hunting, and harassment under federal and state law. A federal permit may be obtained from the U.S. Fish and Wildlife Service to use lethal means to control herons when extreme damage is occurring on private property. Such a permit is only granted after all other non-lethal control techniques have proven to be unsuccessful.)

Create an overhead barrier: Suspend a taut net (with a mesh size of three inches or less) above the pond surface. Make sure the net is at least two feet above the pond and cannot fall into the pond when a heron lands on the net and tries to spear the fish through it. While this may not be the best looking solution, it is by far the most effective deterrent for most herons.

Exclude herons from large ponds by suspending parallel strands of steel wire (28-gauge) or monofilament line (50- pound test) over the pond. Wire or monofilament lines should be spaced no more than 12 inches apart. Wire or line barriers should be installed at least two feet above an area needing protection. Prevent herons from entering under the barrier by installing a two-foot high wire fence or a perimeter barrier as described below.

These barriers need to be checked daily for maintenance and entangled birds. Brightly colored top nets are more visible to birds and reduce entanglement problems.

Create a perimeter barrier: Herons will not normally land directly in the pond, as they will scare the fish. Instead, they land nearby and slowly walk toward the water. Install two strands of electrified wire, eight and 18 inches off the ground, and back from the water’s edge to prevent the heron from leaning over the barrier to catch the fish. (Strong fishing line may be tried at first, but herons are likely to go under or over it.)

The wires can be hooked up to a switch for discretionary use; when you want to work near the wires, turn the system off. Be sure to keep the wires away from shoreline plants that can short the power out.

For safety, tie a sign, cloth, or other material on the wire for visibility.

Alternatively, or in addition to a perimeter fence, secure a two-foot wide strip of chicken wire flat around the inside of the pond edge and just under the water in areas where a heron is entering the water. (Cut the wire as needed to match the curvature of the pond.) Herons will have difficulty reaching over the wire, and will tend to not stand on it because of its instability. To camouflage and extend the life of the wire, paint it with darkcolored automobile undercoat paint or other rustproof paint.

Provide hiding places for fish: Plant mat-forming aquatic plants, such as water lilies, for protection during the growing season. For year-round protection, construct hiding places on the bottom of the pond using cinder blocks, ceramic drain tile, wire baskets, or upside-down plastic crates held in place with heavy rocks. Deepen areas of the pond to at least three feet — too deep for the heron to reach.

Preventative pond and planting design: When designing a pond it is possible to make life difficult for herons. Dense growths of tall marginal plants or shrubs around the pond will limit their access to the water. Ensuring the pond side is steep and the water is eight to 12 inches below the edge of the pond willalso help because the heron will not be able to reach the fish.

Scare tactics: Although law protects these birds, you may harass them without obtaining a permit as long as the birds are not nesting or touched by a person or an “agent” of a person (e.g., a trained dog). There are a number of commercial devices available that work in different ways. Some work on a “tripwire” basis, producing a loud noise and, in some cases, a visual deterrent which scares the heron away. The “Scarecrow“” detects the presence of the heron using infrared detection, and scares it away by spraying a high-pressure jet of water. The effectiveness of scare devices is often short term as birds may quickly become accustomed to them.

Plastic herons: Artificial plastic herons are very popular. Their success is based on the principle that herons are territorial and will not feed close to another heron. Unfortunately, this is not completely effective at any time, especially in late winter and early spring when the herons are searching for a mate. In this case, it may actually attract herons to your pond.