Green Heron
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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. |