Great blue herons can be found in the Nearctic and Neotropical regions. During the spring and summer, they breed throughout North and Central America, the Caribbean, southern Canada and the Galapagos. Some populations migrate to Central and South America during the winter months, but do not breed there. (Hancock, 1990; Terres, 1995)
Great blue herons always live near sources of water, including rivers, lake edges, marshes, saltwater seacoasts, and swamps. They require tall trees near water to nest in, and often nest in groups or "rookeries" which require a stand of suitable trees. They have been found breeding at elevations of up to 1,500 m. Most tend to avoid marine habitats along the east coast and instead live inland. (Hancock, 1990; Terres, 1995)
Great blue herons are the largest herons in North America. They stand approximately 60 cm tall and are 97 to 137 cm long. They weigh 2.1 to 2.5 kg. They feature blue-gray upperparts with long, thin white-gray plumes adorning their backs and wing scapulars. In flight they have bi-colored wings with dark bluish-gray primaries and secondaries. Individuals often have patches of reddish or black feathers on their sides, flanks, and thighs. The long legs are yellowish-green to dark gray in color. Their long necks vary in color from white to buffy, rusty-red, or gray, usually lightest nearer the head. A ring of white or gray plumes surrounds the base of the neck. Throat, crown and auriculars are white, and eyes are pale yellow in color. They feature a thick, blackish face stripe that begins at the lores, extends through the supercilium, partially down the back of the nape and into several, long plumes. Their straight, pointed bills are mostly yellow, but the upper mandible may be gray near the base.
Males are slightly larger than females, but no further sexual dimorphism exists in this species.
Juvenile great blue herons have darker plumage overall. They have a dark crown and feature significantly darker coloration on their face and neck.. Young herons lack the long, thin plume feathers of adults. Their necks are heavily streaked with dark gray which may extend through the chest and belly as well.
A white morph of great blue herons exists in some marine habitats along the coast of Florida, the Florida Keys, and the southeast Atlantic states. They are overall white in coloration with much shorter plumes than the dark morph. Their legs are buffy-gray and they average 10% larger than the dark morph.
Where the dark and white morph populations overlap, there is the chance of an intermediate morph or "Wurdemann's heron." These birds most often occur in southern Florida. They usually have the gray-blue bodies of dark morphs, but feature an all white head and neck like those of the white morphs. (Hancock, 1990; Terres, 1995)
Great blue herons generally have one mate per breeding season. Males will perform courtship displays while perched at his nest. Males often stretch their necks and fluff their plume of neck feathers. They may also fly in a circle around a nest or shake twigs to impress a female. Once he gets the attention of a potential mate, she perches next to the male and together they will raise their crest feathers and clatter their beaks together. Pairs may repeat these behaviors throughout the breeding season to reinforce the pair-bond. (Ehrlich, et al., 1988)
Great blue herons typically breed from March to May in the northern part of their range and November through April in the southern hemisphere. Male great blue herons often arrive at the breeding grounds first and most will select an existing nest to use for the season. However some, mostly younger, males will build a new nest. Nests are large and consist mainly of bare sticks and branches. These herons prefer to nest at greater heights than most herons, and nests are built 9 to 21 m off the ground. Great blue herons often nest in large groups, or rookeries, with other great blue herons or conspecifics.
After mating, females lay between 2 and 7 pale blue eggs. Birds living further north tend to have more eggs. Both parents incubate the eggs. The eggs hatch after 26 to 30 days of incubation. After living in the nest for about 2 months, the young are ready to fledge. Herons become sexually mature when they are about 22 months of age. (Ehrlich, et al., 1988; Hancock, 1990; Terres, 1995)
Males and females of this species participate in all aspects of reproduction including nest building, incubation, and chick brooding and feeding. The young are born semialtricial and require a significant parental investment to survive. Upon hatching, chicks are downy and their eyes are open but they are immobile and unable to feed themselves. The young are fed mostly fish, and the largest chicks often receive the most food. (Ehrlich, et al., 1988; Hancock, 1990; Terres, 1995)
The oldest wild great blue heron was said to be 23 years old, but most do not live so long. The average lifespan for a great blue heron is around 15 years. The young suffer the highest mortality rate as more than half (69%) of the great blue herons born in one year will die before they are a year old. (Hancock, 1990; Terres, 1995)
Great blue herons are mainly active in the mornings and at dusk when fishing is best. They are stalk-and-strike hunters that visually locate prey and thus hunt during daylight. They are solitary predators however, they do often breed in rookeries and during the night they will sleep with flocks of over 100 other herons. Great blue herons are also extremely territorial and will aggressively defend their nests.
This species is mostly migratory, but populations of the southern United States may remain in one region year-round. Northern populations must move south to the Southern United States, Central or South America to avoid frozen water as they are piscivores and would starve. (Hancock, 1990; Terres, 1995)
Territory size and home range for great blue herons are unknown.
Great blue herons are relatively quiet compared to other related species. They release a soft "kraak" when they are disturbed in flight. Other heron calls include a "fraunk" when they are disturbed near their nests which usually lasts about 20 seconds, and an "ar" when they are greeting other members of their species. These herons are known to have up to 7 different calls. They also snap their bills together and use complicated body movements in courtship displays. Like all birds, great blue herons perceive their environments through visual, tactile, auditory and chemical stimuli. (Hancock, 1990; Terres, 1995)
Great blue herons fish primarily during the day or occasionally at night, but most of their activity occurs around dawn and dusk. Herons use their long legs to wade in shallow water and their sharp spear-like bills to catch their food. Great blue herons' diet consists of mainly fish, but also includes frogs, salamanders, lizards, snakes, young birds, small mammals, shrimp, crabs, crayfish, dragonflies, grasshoppers and many aquatic invertebrates. Herons locate their food by sight and usually swallow it whole. Herons have been known to choke on prey that is too large. (Hancock, 1990; Terres, 1995)
Northwest crows and common ravens have been reported eating heron eggs. Eagles, raccoons, bears, turkey vultures, and red-tailed hawks prey on the young birds and sometimes even the adults. Birds often abandon a rookery where they have been living after a predator has killed an adult or chick in the area.
Nesting in rookeries is a way for great blue herons to avoid predation. If a heron nests within a large group, there are many more eyes and ears to keep watch for predators. Also, the chances that one particular nest will be predated decreases significantly when there is a high density of nests. (Hancock, 1990; Terres, 1995)
There are no known positive effects of great blue herons on humans.
People who create and stock fish ponds may find that their expensive fish are being eaten by great blue herons. This can be prevented by installing bird netting or using decoy herons to scare the birds away. (Ferguson, 1998)
Great blue herons are listed as Least Concern by the IUCN Red List. Their populations are widespread and on the increase, thus they do not merit special protection. As a migratory species, great blue herons are protected under the United States Migratory Bird Treaty Act. Habitat destruction by humans is the greatest potential threat to this species. Many herons are also killed each year due to collisions with utility wires.
George Hammond (editor), Animal Diversity Web Staff, Tanya Dewey (editor), University of Michigan-Ann Arbor, Rachelle Sterling (editor), Special Projects.
Robert Naumann (author), University of Michigan-Ann Arbor.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
living in the southern part of the New World. In other words, Central and South America.
uses sound to communicate
young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
uses smells or other chemicals to communicate
the nearshore aquatic habitats near a coast, or shoreline.
used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.
active at dawn and dusk
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
mainly lives in water that is not salty.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
marshes are wetland areas often dominated by grasses and reeds.
makes seasonal movements between breeding and wintering grounds
Having one mate at a time.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
an animal that mainly eats fish
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
Ehrlich, P., D. Dobkin, D. Wheye. 1988. The Birder's Handbook: A Field Guide to the Natural History of North American Birds. New York, NY: Simon & Schuster Inc.
Ferguson, P. 1998. "The Dreaded Predator" (On-line). Accessed 16 May 2000 at http://www.ponddoc.com/WhatsUpDoc/Predators/DreadPred.html.
Hancock, J. 1990. The Herons Handbook. London, England: Christopher Helm Publishers Ltd.
Terres, J. 1995. The Audubon Society Encyclopedia of North American Birds. New York: Wings Books.