Green Heron

Common name: Green Heron
Class: Aves
Order: Ciconiiformes
Family: Ardeidae
Genus: Butorides
Species: Butorides virescens


photo Ivan Andrijevic

 

Taxonomy/ Description


Green herons are small and stocky, with legs that are relatively short, compared to other herons. Their body length ranges from 41 to 46 centimeters.  Adults have a glossy greenish-black cap and back, wings that are black grading into green and/or blue on the edges, and a grey underbelly.  The bill of a green heron is dark with a long, sharp point and the legs are orange. Female adults tend to be smaller, with duller and lighter plumage than that seen in males, particularly in the breeding season.
  The coloration of immature herons is different. The neck and chest are striped with white and shades of brown. Their backs are also brown with white and beige spots.  The coloration of both immature and adult birds is quite cryptic in dense vegetation.


photo Ivan Andrijevic

Habitat/ Diet
 

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 sedentary populations occur on the west coast.  During the breeding season they are found primarily 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.  Small vagrant populations winter in Hawaii and the United Kingdom.  Some populations migrate and others are sedentary populations.  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. Spring migration occurs from March to April, an earlier arrival than most other herons. 
 


photo Ivan Andrijevic

 

Green herons are carnivorous, mainly eating fish and invertebrates.  In addition, they are foragers with a broad prey base, depending on the availability of species present.  They exploit superabundant food resources, such as breeding frogs.  The green heron 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 used by green herons is to stand in a crouched position, horizontal to the water surface, with neck and head retracted.  They then stand still for long periods of time before changing sites.  Standing is often interspersed with slow walking in a crouched posture in the water or bordering vegetation.  

 

Herons use their feet to cause potential prey to move and then capture them.  They may also dive from perches head first into deep water, becoming submerged, although this isn't a very efficient method.  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.  Green herons stand motionless near the bait until a small fish or other animal approaches and then grab the prey.

 

Behavior/ Reproduction
 

Green herons are seasonally monogamous.  Courtship displays are stereotyped. They begin with flying around displays resembling natural flight, but oriented to breeding sites with skow calls.   Next pursuit flight, circle flight and forward displays are used.  Crooked-neck flight displays are more aggressive, where the neck is partially flexed, legs are dangled, and wingbeats are audible.  Much like the Crooked-Neck Display, the Flap Flight Display shows the greatest intensity of flight displays.  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 scapular feathers erect and often giving a roo-roo call before landing.  Nonaerial displays are interspersed with display flights.  In the snap display, the male perches, then points body, head and neck down until bill tip is at or below the level of his feet and then snaps his mandibles together, producing a click 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 interscapular 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 engages in mutual bill-snapping and feather nibbling, though those behaviors are reduced soon thereafter.  Mating occurs on the nest platform during the nest-building stage.  After the last egg is laid, mating ceases, and incubation lasts for 19-21 days.  Fledging occurs when chicks are 16 to 17 days old, and independence is gained between 30 and 35 days.  Nesting takes place in forest and swamp patches, over water or in plants near water.  Nesting pairs normally nest alone, but loose aggregations of mated pairs can form.  Green herons are shy birds so are rarely observed, although they may be quite common.  They are active during the day, and have a characteristic slow, deliberate walk and in flight they have slow and steady wingbeats.  Green herons may also swim on occasion in pursuit of prey, are territorial, and will aggressively defend both foraging and nesting territories from conspecifics.

 

Where to see them in WNY
 

One good place to find the green heron is on the Swallow Hollow Trail at the Iroquois National Wildlife Refuge.  From the parking lot, take the trail heading to the left.  Be sure to begin looking once you reach the earthen dike; emergent marshes like this one are great habitats for these birds. 

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