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Great
Blue Heron
Ardea
herodias fannini
 The
great blue heron (Ardea herodias) is a large, grayish-blue
wading bird with a long bill, neck, and legs. It is practically
the only large "crane-like" bird in the Pacific
Northwest (the sandhill crane (Grus candensis) is native but
uncommon). In flight, the great blue heron can be recognized
by its long neck folded back on the shoulders, its long trailing
legs, and its slow, deep wing beats. Adults can be recognized
by the presence of a blue plume. Males and females are virtually
identical.
Great
blue herons are found year-round throughout the Pacific Northwest,
except for the arid grasslands and interior forests. They
are at home in both salt and fresh water and are seen on lakes,
ponds, rivers, marshes, mudflats, irrigation ditches, farm
fields, and meadows. For information on belted kingfishers,
see "Notes on the Belted Kingfisher."
Great
blue herons reach 4 feet in height and have wingspans of nearly
6 feet. Because of hollow bones, adults weight an average
of only five pounds. They have long necks and a long bill
adapted for grasping prey.
Facts about Great Blue Herons
Food
and Feeding Habits
- Great
blue herons are stand-and-wait-predators that remain motionless
for long periods of time, waiting for prey to venture near.
- Their
large size enables them to feed on a variety of prey, including
fish, frogs, turtles, young birds and bird eggs, snakes,
and insects; also mice, moles, gophers, and other small
mammals.
- Herons
feed during the day or night (in lighted areas), generally
within 3 miles of their colony. They tend to be solitary
feeders, but where the food supply is abundant, they can
be found feeding together.
- The
adult heron rarely flies straight to the young, perching
instead a few yards from the nest. After a few minutes,
the adult goes to the nest and regurgitates predigested
food. The oldest and largest chicks take most of the food
share by grasping the adult's bill and catching the food.
Nest
Sites and Nests
- Great
blue herons nest in colonies, often called rookeries or
heronries. Heronries are usually in isolated spots away
from potential disturbance and near suitable feeding areas.
- Herons
that have been frequently exposed to human disturbance may
be more tolerant and may nest in large public parks and
greenbelts.
- Herons
nest in deciduous or evergreen trees, usually near the top
on vertical branches. Nests are usually constructed in the
tallest trees available, on islands, or in trees with water
around the base, presumably to reduce the risk of predation
by mammals.
- Where
trees are absent, nests may be located on large shrubs,
cliffs, and artificial structures.
- Nests
are constructed from branches and twigs gathered from the
ground, trees, and old nests. Nests are 25-40 inches in
diameter and 12 or more inches thick.
- Heronries
may be used for decades; however, herons will relocate their
colonies in response to increased predation on eggs and
young, declines in food availability, human disturbance,
and death of trees supporting the nests.
Reproduction
- Herons
begin returning to a colony to breed in February and March.
Nest building begins in March or April.
- Three
to five pale, greenish-blue eggs are incubated for 25-29
days by both sexes.
- Young
first fly at around 60 days of age and leave the nest at
65-90 days, at which time they are similar in size to adults.
- Great
blue herons have one brood (clutch) per year, however, they
may renest if their first clutch fails.
Mortality
and Longevity
- Adult
great blue herons don't have many predators, though bobcats,
coyotes, red-tailed hawks, crows and bald eagles do occasionally
kill an adult.
- Mortality
of the young is high: both the eggs and young are preyed
upon by crows, ravens, gulls, eagles, and raccoons. Heavy
rains and cold weather at the time of hatching also take
a heavy toll.
- Herons
may live to be 15 years old, but six to eight years of age
is the norm.
- Great
blue herons were nearly hunted to extinction in the late
1800s because of a fashion trend for using their plumes
on women's hats. In the 1960s, they were vulnerable to egg-shell
thinning as a result of exposure to the pesticide DDT, which
lowered reproductive success.
Feeding
Habits of the Great Blue Heron
The great blue heron has two principal fishing techniques.
The first consists of standing motionless, its neck extended
at an angle of about 45 degrees to the surface of the water.
Only its head and eyes move to locate the prey. If no prey
comes within range after a few minutes, the heron gradually
moves a short distance away and takes up a similar position.
When a potential meal comes close enough, the heron slowly
folds its neck back and moves one leg in the direction of
the prey. Suddenly, its entire body unbends, its head plunges
into the water, it catches the prey in its bill, and it swallows
it outside the water, using a deft movement of the head to
drop the prey headfirst into its gullet.
A similar
technique is used to hunt small rodents in pastures, meadows
and similar habitats. Herons stab or clamp on their prey,
using their bills like barbecue tongs.
Using
the second technique, the heron slowly wades around in 6-12
inches of water until it drives a fish out from its hiding
place. The heron then stops and slowly stretches its neck.
When the prey is within range, the bird uncoils its body and
thrusts its head into the water after it. After eating the
catch, the heron resumes its walk. Should the bird fail to
find sufficient fish in an area, it flies a short distance
away and resumes fishing.
When its
catch is too large to be gulped down immediately or has dangerous
spines, the heron drops it back into the water and grabs hold
of it repeatedly and violently with its beak until it is dazed
or the spines snap. Then it can be swallowed more easily.
Sometimes two fish are caught simultaneously.
Other
techniques are observed more rarely: for example, great blue
herons in flight sometimes dive underwater to catch fish;
others hover over the water and submerge their heads to catch
fish; and some swim in deep water and feed on fish found near
the surface.
Tips
for Viewing Great Blue Herons and Signs of Them
People
most often observe great blue herons as the birds fly slowly
and steadily, wings arching gracefully down with each beat,
neck bent back, and feet trailing behind. They are also seen
feeding-standing motionless and staring into shallow water,
or walking with measured steps as they search for prey.
Herons
are great birds to watch if you are a beginning birder. Their
large size and interesting behaviors will provide you with
many hours of enjoyable viewing. In urban areas, these birds
have acclimated to people so you can get a close view of them
hunting without disturbing them.
The nesting
behavior of great blue herons is not often witnessed since
they nest in colonies in fairly isolated areas. Heron rookeries
should not be disturbed during the nesting season (Feb. 15
to July 31). Several studies have shown that human disturbance
during the breeding season can cause adult herons to abandon
the entire rookery. Herons are least tolerant of disturbance
during the pre-nesting and courtship periods, becoming progressively
less likely to abandon nests after laying eggs.
Even if
you can't see great blue herons in their rookeries, they are
fascinating to watch on their feeding grounds. Great blue
herons often congregate at mudflats and ell grass beds during
low tides from June to December where they feed on small fish.
Here you may have the opportunity to view many herons at once.
To prevent
problems from occurring, use high-powered binoculars or spotting
scopes to observe herons. Nesting herons should be left alone
and follow area regulations and closures to protect colonies.
Many designated viewing areas have been set up by naturalists.
Things
to listen and look for include:
- Tracks
and trails: Great blue heron tracks are easily found
in the mud or sand next to a feeding site. Their tracks
show four toes and the webbing may or may not appear, depending
on the hardness of the surface.
Great
blue heron tracks and trail. The track from front to back
is about 6 inches long and a claw imprint shows clearly
at the end of each toe. The hind toe is well-developed for
standing and walking. The walking stride is about 10 inches.
The trail is fairly straight, and feet point forward.
- Droppings
and pellets: Great blue heron droppings are
semi-liquid and mostly white. Solid droppings vary from
2-3 inches in length, and contain signs of fish, frogs,
small rodents, and other prey. The ground beneath nests
can become coated with droppings. Undigested material may
also be coughed up as pellets.
- Calls:
The normal call of a great blue heron is a deep, hoarse
fraaaahnk or braak. In aggressive situations or when frightened,
the call is a short, harsh frank frank frank taaaaaw. Herons
call in flight and on the ground, during the day and at
night.
An adult arriving at the rookery usually gives a dull guttural
cry. The young cry constantly and grab at each others' bills.
Tips
for Attracting Herons
If you put out a bird feeder, you have to expect the birds
to come and eat. A pond full of fish makes a wonderful heron
(and kingfisher) feeder. Keep the pond stocked with cheap
feeder goldfish, give the heron a good place to stalk them,
and enjoy the show. In order to give fish a place to hide,
one or two areas can be kept as hunting spots for herons and
the other areas can be heavily planted to block access into
the pond. Because kingfishers tend to dive from a perch to
catch fish, a simple perch can be built for them if a dead
tree or large bare branch doesn't exist nearby.
To
help preserve heron habitat:
- Preserve
shoreline trees.
- Protect
eelgrass beds because they provide great habitat for herring.
Herring is a major food source for herons, kingfishers,
salmon, seals, and other marine mammals.
- Protect
wetlands.
- Keep
pets under control and away from great blue herons.
- While
visiting the beach or boating, give herons and heron rookeries
plenty of space.
- Minimize
development near heron colonies.
For detailed
management recommendations for great blue herons and their
colonies, http://wdfw.wa.gov/hab/phs/vol4/gbheron.htm.
Why
do Birds Nest in Colonies?
Why do some birds nest in colonies? The habit is widespread-Brewer's
blackbirds, great blue herons, and gulls all nest in such
a way.
In eastern
Washington, Brewer's blackbirds forage for insects in short
vegetation around ponds and streams, mostly close to the colony
nest site, but sometimes a mile or more away. The birds appear
to concentrate their feeding in areas where prey is most abundant.
This habit apparently developed because it allows less adept
birds to follow more successful foragers when they leave the
colony to feed, and perhaps also because it provides some
protection against predation.
Cliff
swallows exhibit similar behavior. Cliff swallows that have
been unsuccessful in finding food (flying insects) return
to the colony and follow a successful forager to a food source.
Most seabirds that nest together also forage for fish together,
suggesting that they too can benefit from each other's good
fortune on the hunt.
Some birds
such as the great blue heron, however, nest colonially and
generally forage alone. So is it less likely that the colony
serves as an "information-center" for its members?
Among
herons, young birds may benefit from the learning opportunities
presented by colony living. Older, more experienced herons
are better able to find food. However, if their younger colony
mates follow them to the feeding grounds they are likely to
have less success at foraging, because of the increased competition.
Why, then,
do older herons live in colonies? One hypothesis is that the
older birds benefit through protection from predation. Being
more dominant birds, they are able to acquire the safest nesting
sites, located in the center of the colony. Adapted from "The
Birder's Handbook."
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