Great Blue Herons live in both freshwater and saltwater habitats, and also forage in grasslands and agricultural fields, where they stalk frogs and mammals. Most breeding colonies are located within 2 to 4 miles of feeding areas, often in isolated swamps or on islands, and near lakes and ponds bordered by forests. Back to top
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.Back to top
Great Blue Herons nest mainly in trees, but will also nest on the ground, on bushes, in mangroves, and on structures such as duck blinds, channel markers, or artificial nest platforms. 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 from the ground and nearby shrubs and trees, and from unguarded and abandoned nests, 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.
|Clutch Size:||2-6 eggs|
|Number of Broods:||1-2 broods|
|Egg Length:||2.4-3.0 in (6.1-7.6 cm)|
|Egg Width:||1.8-2.0 in (4.5-5 cm)|
|Incubation Period:||27-29 days|
|Nestling Period:||49-81 days|
|Egg Description:||Pale blue, fading slightly with age.|
|Condition at Hatching:||Bluish eyes open, chick covered in pale gray down, able to vocalize.|
Great Blue Herons forage, usually alone, across much of the U.S. This largest of the North American herons 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. If you visit a colony, look for 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. Back to top
Great Blue Heron numbers are stable and increased in the U.S. between 1966 and 2019, according to the North American Breeding Bird Survey. Partners in Flight estimates a global breeding population of 700,000 and rates the species 8 out of 20 on the Continental Concern Score, indicating a species of low conservation concern. 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. Great Blue Herons can be found throughout the year all over North America. Because Great Blue Herons depend on wetlands for feeding and on relatively undisturbed sites for breeding, they are vulnerable to habitat loss and human impacts such as traffic, logging, motorboats, and other intrusions 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.Back to top
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