Great blue herons (Ardea herodias) are easily recognized by their elegant silhouettes, beautiful blue-gray plumage, and impressive wingspans that can reach up to 7 feet. These birds are spread throughout the Americas, especially North America, and can also be found in the Galapagos Islands. These birds have staged a staggering comeback in the past few decades due to hunting pressure and pollution. Now, these statuesque wading birds can be seen at ponds, lakes, and rivers of all sizes, often in surprisingly urban areas.
Habitat and Distribution
The Great Blue Heron has a wide range across North America. They are found throughout California, inhabiting a variety of wetland environments. They favor shallow estuaries and wetlands, and are found less frequently in riverine and rocky marine shores, croplands, and pastures. At lower elevations these birds can be found in areas with abundant water sources such as marshes, mudflats, and agricultural fields. Northern populations east of the Rockies are migratory, some going to the Caribbean, Central America, or northern South America. Migrates by day or night, alone or in flocks. Some wander well to the north in late summer. Populations along the Pacific Coast may be permanent residents, even as far north as southeastern Alaska.
Nesting and Social Behavior
Blue herons nest in large colonies called heronries of up to 400 nests. They may also nest in small heronries of breeding pairs or entirely alone. While they do link up to mate, breed, and sometimes nest and hunt, these are pretty solitary birds. Herons are tree-nesters that make their home in a variety of different trees, depending on what’s available. A study of heronries along the Pacific coast of British Columbia found that a colony of blue heron nests serves as an information center that helps the birds to find food. Herons left the heronry in groups to forage different sites each day. This study found that herons feeding in groups caught fish more quickly and efficiently than solitary herons. While this may be the case in some habitats, herons typically have success as solo hunters. They are more solitary during the fall and winter months and live in colonies during the spring and summer.
Great Blue Herons typically breed in colonies known as heronries, which are often located in tall trees near water bodies. Nesting begins in February, with males selecting nesting sites and attracting females through displays. The nests are constructed high in trees and are made from sticks lined with softer materials. Females lay 2-6 pale blue eggs, which are incubated by both parents for 25-30 days. The chicks hatch asynchronously, and the parents continue to feed them for about two months until they can fly and for several weeks thereafter.
Physical Characteristics
The Great Blue Heron is the largest heron in North America, standing at a little under one and a half meters tall, with a wingspan of up to two meters. Adult great blue herons stand almost 1.4 meters (4.6 feet) tall and weigh between 2.1 and 3.3 kg (4.6 and 7.3 pounds), with males being slightly larger and heavier than females. They are distinguished by their long necks which they can coil into an “S-shape” for quick striking of fish in the water. This is made possible by specialized modifications of their neck vertebrae. Great Blue Herons also have specialized “powder down” feathers on their chest. These birds have gray-blue wings with white plumes of feathers, long necks that range in color from white to gray with patches of rust-red, black crowns, long legs, and yellowish pointed beaks.
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Hunting and Foraging Behavior
They forage for food along lakeshores, marshes, ponds, creeks, slow-moving rivers, grassy fields, and wetlands. Impeccable night vision allows blue herons to hunt both day and night. They will stalk their prey by walking slowly, wading in shallow water. Occasionally they’ll flick their wings out and back repeatedly, making shadows that cause fish to panic and flee, becoming more visible. Blue herons are patient predators often standing very still waiting for prey to swim or scurry by close enough for capture. They may stand on one leg for long periods of time, making them appear more like a stick than a feared predator. When hunting in aquatic areas, they are very adaptable and skilled with a range of methods. They will sometimes take advantage of floating objects and perch on them while they search below. They’ll dive for prey underwater both head-first and feet-first. Blue herons locate their prey by sight and catch them with a quick thrust of their neck.
The most common place to find Great Blue Herons is at the edge of a wetland, where they will stand stock-still, tracking the movements of fish and frogs and waiting for the perfect moment to strike. Although they will happily feed in backyard ponds and rivers in urban areas, the approach of humans tends to startle them, causing them to fly away while uttering a gravelly croak.
Great Blue Heron Diet
Blue herons primarily eat fish, small mammals, amphibians, reptiles, and insects. They are carnivorous wading water birds that consume other animals. As aquatic wading birds, it comes as no surprise that the mainstay of blue herons’ meals is fish. In a population of great blue heron whose feeding habits were studied, fish were found to make up 44% of their prey but comprised 88% of the mass of their diet. So, while they’ll take advantage of any meal that comes their way, they do get the bulk of their food from finned swimmers. They even have specialized chest feathers that are helpful for removing fish slime and other oils as they preen.
The diet of the Great Blue Heron is diverse, though primarily focused on fish, which constitutes about 75% of their intake. They also consume small mammals, amphibians, reptiles, insects, and occasionally other birds.
Great Blue Herons eat nearly anything within striking distance, including fish, amphibians, reptiles, small mammals, insects, and other birds. They grab smaller prey in their strong mandibles or use their dagger-like bills to impale larger fish, often shaking them to break or relax the sharp spines before gulping them down. The Great Blue Heron is very adaptable, foraging in any calm, fresh waters or slow-moving rivers, and also in shallow coastal bays.
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Fish
Given most people most often see Great Blue Herons foraging in shallow water along shorelines, it’s easy to imagine the birds dine on nothing but small fish. Although small fish are a staple of the Great Blue Heron diet, they won’t hesitate to take a larger fish if the opportunity presents itself. They are primarily fish eaters that often feed near dawn and dusk. They also prey on rodents, insects, amphibians (such as frogs and salamanders), crustaceans, and even turtles or other birds. As surreal as it may seem, Great Blue Herons have occasionally choked to death when they captured and tried, unsuccessfully, to swallow a fish that wouldn’t fit all the way down through their gullets.
Other Animals
In addition to their primary prey, blue herons on the coast will eat crustaceans and hatchling sea turtles. When upland and especially in the winter, they will eat small mammals like squirrels, chipmunks, cottontail rabbits, and voles. At times, they will eat small birds like blackbirds, starlings, and swallows along with their eggs. Great Blue Herons will even catch and eat other birds. They also prey on rodents, insects, amphibians (such as frogs and salamanders), crustaceans, and even turtles or other birds. Has been seen stalking voles and gophers in fields, capturing rails at the edge of marsh, and eating many species of small waterbirds.
Threats and Conservation
European settlers over-exploited Great Blue Herons between 1840 and World War I. The birds were killed by the millions to satisfy the demand for feathers in women’s fashion, particularly for hat decorations. The demand for heron feathers was enormous: in 1903, plumes were worth $32 per ounce, about twice the price of gold at the time. In 1886 alone, an estimated 5 million birds were killed for their feathers. The founding of the Audubon Society in 1905 was partly in response to the devastating effects of the plume trade on waterbirds, including herons. With the killing of herons for their feathers no longer taking place, the Great Blue Heron population in California now appears to be stable. However, because herons function as top predators in aquatic ecosystems, they will always be prone to bioaccumulating toxins that have been transferred up the food chain. In addition, Great Blue Herons are sensitive to human disturbance, especially during nesting season. Expanding human populations can also lead to direct habitat loss when wetlands are drained for residential development. Even if a nesting area is protected, loud noises can cause herons to abandon their nests. Layered on top of these immediate threats is the uncertain impact of climate change.
Blue heron chicks leave the nest 8-10 weeks after they hatch. After developing their flight feathers, chicks will join adults on the journey to and from feeding grounds. After their first long flight, they will typically return to the nest and be fed by the adults for about 2-3 weeks. Heron parents feed their young about 4 times during daylight hours and may bring food to them once or twice during the night. Chicks eat the same diet as the adults only in another form. The primary predator of the blue heron is the bald eagle. Black bears have also been found to capture and eat blue herons. Some colonies will change nest sites often and this is likely due to attacks by predators in the area. Young chicks and eggs in the nest are especially vulnerable to attack and can become food for ravens, golden eagles, great-horned owls, red-tailed hawks and racoons.
Conservation Status
Owing to the great blue heron’s large population size, adaptability, and vast geographic range, it is listed as a species of least concern by the International Union for Conservation of Nature and Natural Resources (IUCN). Formerly, it was often shot simply because it made a conspicuous and easy target, but this rarely occurs today. Colonies of Great Blue Herons may be disrupted by human disturbance, especially early in the season. Still common and widespread, numbers probably stable.
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