Green herons are small and stocky, with legs that are relatively short, compared to other herons. Body length ranges from 41 to 46 cm. Adults have a glossy greenish-black cap and back, wings that are black grading into green and/or blue on the edges, and underparts that are gray. The bill is dark with a long, sharp point and the legs are orange. Females tend to be smaller, with duller and lighter plumage than that seen in males, particularly in the breeding season.
The colors of young herons are different. The neck and chest are striped with white and shades of brown. The back is also brown with white and beige spots. The color patterns of both young and adult birds makes them difficult to see in dense vegetation. (Hancock and Kushlan, 1984; Davis and Kushlan, 1994)
Green herons have a wide range in North America, but are generally found near wetlands. They occur as far north as southern Canada and as far south as northern South America. They are found throughout the eastern United States as far west as North Dakota and the Great Plains states, although some occur on the west coast. During the breeding season they are found mainly in the eastern United States, with some populations in the Pacific Northwest as well. Non-breeding individuals are found in Mexico and Central America, Texas, southern New Mexico and Arizona, and the Caribbean islands. Some populations migrate and others are sedentary (they stay in one place throughout the year). Sedentary populations occur along the east and west coasts of the United States and Central America. Most populations in North America, however, are migratory. After breeding they disperse southwards, in mid-September. The spring, northwards migration occurs from March to April, an earlier arrival than most other herons.
Green herons live along forested water margins, they are generally restricted to areas with wetlands. They are found in both salt and fresh water habitats. Favored habitats are mangrove-lined shores and estuaries, and dense, woody vegetation fringing ponds, rivers, and lakes
Green herons form mated pairs each breeding season. Courtship displays are elaborate and consist of a specific series of displays. They begin with Flying Around displays resembling natural flight, but oriented to breeding sites with skow calls. This is followed by Pursuit Flight, Circle Flight and Forward displays, where a rasping 'raah-raah' call exposes the red mouth-lining. Next come Crooked-Neck Flight displays, where the neck is partially flexed, legs are dangled, and wingbeats make a noticeable sound. Much like the Crooked-Neck Display, the Flap Flight Display is more intense. Here, the male lurches through the air with exaggerated flapping producing a whoom-whoom-whoom sound in a crooked-neck posture with crest, neck, and shoulder feathers erect and often giving a roo-roo call before landing.
Displays that don't involve flying occur also. In the Snap Display, the male perches, then points body, head, and neck down until his bill tip is at or below the level of his feet and then snaps his mouth together, producing a clicking sound while also erecting his feathers. The Stretch Display involves the male pointing his bill straight up, stretching his neck, and then bending it backwards until the head almost touches its back with the shoulder plumes erect and fanned. In this posture, he sways his neck and head from side to side with crest, breast, and flank feathers sleeked back, eyes bulging, and iris possibly turning from yellow to deep orange while emitting an aaroo-aaroo sound.
Males perform this Stretch Display before a female is allowed to enter the eventual nest area. The female then performs a less intense Stretch silently after the male, which confirms the pair-bond. At this time, the male stops Flight and Snap displays. The pair then nibbles each other's feathers and snap their bills.
Green herons lay 2 to 4 eggs in a nest at two-day intervals. The eggs are incubated for 19 to 21 days, the young fledge (leave the nest) at 16 to 17 days old and become independent at 30 to 35 days old.
Nests are built in vegetation near water, from ground level up to 20 meters high. The preferred nest spot is a branch in a tree. Nesting pairs normally nest alone, but sometimes nest in small colonies.
Both parents feed and brood their young, though less often as the nestlings grow.
The oldest know wild green heron was a banded bird that was captured when it was almost 8 years old. There is very little information on lifespan in these birds.
Green herons are shy birds so are rarely observed, although they may be quite common. They are active during the day. They have a characteristic slow, deliberate walk and in flight they have slow and steady wingbeats. They may also swim on occasion in pursuit of prey. Green herons are territorial and will aggressively defend both foraging and nesting territories from other herons.
Green herons use their keen vision, hearing, and sense of touch to perceive their environment. They have especially acute vision that helps them to capture prey. Green herons have an elaborate set of calls and body postures that they use for communicating with other green herons. Examples are their elaborate courtship displays, warning calls when a predator is detected, and territorial displays. (Davis and Kushlan, 1994; Hancock and Kushlan, 1984; Hancock, 1999)
Green herons are carnivorous, mainly eating fish and invertebrates. They eat almost anything that they can find and capture. Their invertebrate diet includes: leeches, earthworms, dragonflies, damselflies, waterbugs, grasshoppers, and crayfish. Some of the many fish eaten are: minnows, sunfish, catfish, perch, eels, and, in urban areas, goldfish. Other vertebrates eaten are rodents, lizards, frogs, tadpoles, and snakes.
The heavy bill of a green heron enables them to capture large prey. Feeding can take place at any time, day or night. Typically, prey is captured with a darting stroke of the head and neck, lunging the body towards the victim and either grabbing or impaling the prey. The most common feeding technique is to stand in a crouched position with neck and head retracted. Standing often alternates with slow walking in a crouched posture in the water or bordering vegetation. Herons use their feet to stir up animals in the water, making them move and then capturing them. They may also dive from perches head first into deep water, although this isn't a very efficient method. Green herons do best catching prey in shallow water (up to 10 cm deep).
Green herons are one of the few tool-using birds. They use a variety of baits and lures, such as crusts of bread, mayflies, and feathers. They then put the bait on the water surface and wait for prey to attack the bait. They stand motionless near the bait until a small fish or other animal approaches and then grab them.
Snakes, crows, and common grackles are known to eat green heron eggs. Raccoons eat nestlings. Adult birds may be preyed on by large birds of prey. Green herons remain vigilant to protect themselves from predators. They also utter warning calls when predators approach.
Green herons are important predators of fish and invertebrates in the aquatic ecosystems where they live.
Green herons eat fish that may be important economically, but their impact is very small.
Green herons are enjoyed by birdwatchers.
Green herons are not considered threatened or endangered. They are fairly common in appropriate habitats throughout their range. They are killed by fish hatcheries to prevent them eating young fish, suffer as a result of wetland loss to farming and development, and can accumulate poisons in their tissues from pesticide use and toxic releases into waterways.
Tanya Dewey (author), Animal Diversity Web.
Josh Butzbaugh (author), Natural Resources And Environment, Terry Root (editor), University of Michigan-Ann Arbor.
Davis, W., J. Kushlan. 1994. The Green Heron. The Birds of North America.
Hancock, J. 1999. Herons and Egrets of the World. London, UK: Academic Press.
Hancock, J., J. Kushlan. 1984. The Herons Handbook. New York City, NY: Harper and Row Publishers.