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 are tall waterbirds with long, S-shaped necks that have shaggy feathers. They have long, rounded wings, long pointed bills, and short tails. The bills are a yellowish color and the legs are yellowish-green to gray. Great blue herons have gray upper bodies, and their necks are streaked with white, black and rust-brown. They have gray feathers on the back of their necks with chestnut colored feathers on their thighs. They feature a plume of black feathers that starts behind their eyes and extends out behind their heads. Males tend to be slightly larger than females.
Young great blue herons are overall darker in color. They have dark gray crowns and many dark gray streaks on their necks. Young great blue herons do not have plumes on their heads or shaggy neck feathers like adults have. (Hancock, 1990; Terres, 1995)
Great blue herons can be found in Canada, the United States, Central and South America. These birds migrate and may spend different seasons in different regions. During the spring and summer, they breed throughout North and Central America, the Caribbean, southern Canada and the Galapagos Islands. 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 generally have one mate per breeding season. Males will perform courtship displays to attract a female. A male will perch at his nest, stretch his neck and fluff his plume of neck feathers. He may also fly in a circle around his nest or shake twigs to impress a female. Once he gets the attention of a potential mate, she perches next to the male and they will both raise their crest feathers and clatter their beaks together. Pairs may repeat these behaviors throughout the breeding season. (Ehrlich, et al., 1988)
Great blue herons use large nests mainly of bare sticks and branches. These herons prefer to nest in tall trees and most nests are built 9 to 21 m off the ground. Great blue herons often nest in large groups, or rookeries, with other herons.
Great blue herons typically breed from March to May in the northern part of their range and November through April in the southern hemisphere. Females lay between 2 and 7 pale-blue eggs. Both parents take turns incubating the eggs, which hatch after 26 to 30 days. After living in the nest for about 2 months, the chicks are ready to fledge, which means they are old enough to leave the nest and survive on their own. Herons are usually old enough to reproduce when they are about 22 months old. (Ehrlich, et al., 1988; Hancock, 1990; Terres, 1995)
Both great blue heron parents care for the young. Males and females build a stick nest, high in a tree. Parents take turns incubating the eggs, and after the eggs have hatched they will take turns caring for the chicks. The young herons are born helpless and rely on their parents for warmth, protection, and food. Chicks are fed mostly fish. (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. As with most animals, they are most vulnerable when they are young. More than half 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 solitary predators, preferring to hunt alone. However, they do often breed in groups called "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.
Many great blue herons migrate south for the winter. These birds depend on fish for food, and would starve if they stayed in a cold habitat with frozen water. Some heron populations in the southern United States may live in the same place year-round if the climate is warm enough. (Hancock, 1990; Terres, 1995)
Great blue herons are relatively quiet compared to other related species. Their main call is 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, raise their feathers, and shake twigs in courtship displays. (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. Great blue herons obtain water by scooping up water with their bills and tipping their heads back to drink. Great blue herons live in aquatic habitats and are surrounded by water for nearly their entire lives. (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)
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 a delight to watch and are important members of healthy, freshwater ecosystems.
This is the most well-known and most widespread heron in North America. Human interference with the heron primarily involves destruction of habitat. Many herons are also killed each year due to collisions with utility wires. As a migratory species, great blue herons are protected by the United States Migratory Bird Treaty Act. Great blue herons have no special protection in the state of Michigan since their populations are large and healthy.
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.
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.