Great Blue Herons are a magestic and common sight to see at a riverbank or coastline in North America; seemingly slow, but lighting fast when grabbing fish.
Great Blue Herons are the largest of the North American herons with long legs, a sinuous neck, and thick, daggerlike bill. The head, chest, and wing plumes give a shaggy appearance. In flight, the Great Blue Heron curls its neck into a tight “S” shape. Its wings are broad and rounded and its legs trail well beyond the tail. Great Blue Herons appear blue-gray from a distance, with a wide black stripe over the eye. In flight, the upper side of the wing is two-toned: pale on the forewing and darker on the flight feathers.
Great Blue Herons are taller and much heavier than a Great Egret but smaller and much less bulky than a Sandhill Crane. They have a length of 38.2-53.9 inches (97-137 centimeters), a weight of 74.1-88.2 ounces (2100-2500 grams), and a wingspan of 65.8-79.1 inches (167-201 centimeters).
An all-white subspecies, the Great White Heron, is found in coastal areas of southern Florida, along with individuals that are intermediate in plumage (showing a grayish body with a mostly white head and neck), known as “Würdemann’s Heron.”
Great Blue Herons occur from most of North America to the coasts of South America. They are partial migrants. Great Blue Herons generally move away from the northern edge of their breeding range in winter. They live in both freshwater and saltwater habitats, and also forage in grasslands and agricultural fields. Most breeding colonies are located within 2 to 4 miles of feeding areas.
DietGreat Blue Herons eat nearly anything within striking distance. They grab smaller prey in their strong mandibles or use their dagger-like bills to impale larger fish before gulping them down.
Great Blue Herons nest mainly in trees, but will also nest in other places. Males arrive at the colony and settle on nest sites; from there, they court passing females. Colonies can consist of 500 or more individual nests, with multiple nests per tree built 100 or more feet off the ground. Male Great Blue Herons collect much of the nest material, gathering sticks and presenting them to the female. She weaves a platform and a saucer-shaped nest cup, lining it with pine needles, moss, reeds, dry grass, mangrove leaves, or small twigs. Nest building can take from 3 days up to 2 weeks. The finished nest can range from a simple platform measuring 20 inches across to more elaborate structures used over multiple years, reaching 4 feet across and nearly 3.5 feet deep. Ground-nesting herons use vegetation such as salt grass to form the nest.
Great Blue Herons have one to two broods with two to six eggs in each per year. The eggs are pale blue, the color fading slightly with age. They have a length of 2.4-3 inches (6.1-7.6 centimeters) and a width of 1.8-2 inches (4.5-5 centimeters). Incubation period is 27-29 days and nesting period is 49-81 days. At hatching, the hatchlings' bluish eyes are open, covered in pale gray down, and able to vocalize.
Great Blue Herons forage, usually alone, across much of the U.S. It wades slowly or stands stock still, peering into the water for prey.
In flight the Great Blue Heron folds it neck into an “S” shape and trails its long legs behind, dangling them as it prepares to land or when courting. Breeding birds nest in colonies that can number several hundred pairs, where they build stick nests in trees, on bushes, or on the ground. Colonies perform elaborate courtship and pair-bonding displays that include a ritualized greeting, stick transfers, and nest relief ceremony in which the birds erect their plumes and “clapper” their bill tips. Pairs are mostly monogamous during a season, but they choose new partners each year. Away from the colony, Great Blue Herons defend feeding territories from other herons with dramatic displays in which the birds approach intruders with their head thrown back, wings outstretched, and bill pointing skyward. Gulls and even humans may also be a target of this defensive maneuver.
Great Blue Herons are most vocal on the breeding grounds, where they greet their partner with squawking roh-roh-rohs in a “landing call” when arriving at the nest. A disturbance can trigger a series of clucking go-go-gos, building to a rapid frawnk squawk that can last up to 20 seconds. If directly threatened, they react with a screaming awk lasting just over 2 seconds. The chicks give a tik-tik-tik call within minutes of hatching.
Other sounds they give are the snap their bill tips together males and females give as part of breeding and territorial displays, a behavior that may be analogous to a songbird’s territorial song. Paired birds often “clapper” at each other, chattering the tips of the bill together.
Great Blue Heron numbers are stable and increased in the U.S. between 1966 and 2014. However, notable population declines have occurred in some areas, particularly in the “great white heron” group in southern Florida, where elevated mercury levels in local waterways may be a factor. Because Great Blue Herons depend on wetlands for feeding and on relatively undisturbed sites for breeding, they are vulnerable to habitat loss and to impacts that can disrupt nesting colonies. Other threats include chemical pollutants or other causes of reduced water quality. Although contaminant levels have declined in many areas, pollutants such as PCBs and DDT and newer types of industrial chemicals continue to affect heron habitats and can contribute to factors such as reduced nest site attendance.
- Great Blue Herons in the northeastern U.S. and southern Canada have benefited from the recovery of beaver populations, which have created a patchwork of swamps and meadows well-suited to foraging and nesting.
- Along the Pacific coast, it’s not unusual to see a Great Blue Heron poised atop a floating bed of kelp waiting for a meal to swim by.
- Great Blue Herons have specialized feathers on their chest that continually grow and fray. The herons comb this “powder down” with a fringed claw on their middle toes, using the down like a washcloth to remove fish slime and other oils from their feathers as they preen. Applying the powder to their underparts protects their feathers against the slime and oils of swamps.
- Great Blue Herons can hunt both day and night thanks to a high percentage of rod-type photoreceptors in their eyes that improve their night vision.
- The oldest recorded Great Blue Heron was found in Texas when it was at least 24 years and 6 months old.
- Great Blue Herons have a specially shaped neck vertebrae, allowing them to quickly strike prey at a distance.
- Great Blue Herons are also called Garza Azulada (in Spanish) and Grand Héron (in French).