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Painting
by Leigh Gillette
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One evening last week, I watched my favorite
bird arrive for the season. The great blue heron crossed the sunset sky
on slowly beating wings, its head and neck drawn close to its shoulders,
its graceful legs trailing behind it.
Banking, the heron turned a few descending
circles, and touched down on the shore of the Animas River for a dusk
feeding session. The great blue heron is a gorgeous bird, but I appreciate
it as much for the environmental challenges it faces as for its stately
appearance.
The great blue heron (Ardea herodias) is one of the
most widely recognizable wading birds in North America, and can be found
from southern Canada to Mexico. Poised on long, slender legs, it stands
four feet high, boasts a seven-foot wing span, and weighs five to eight
pounds.
Aptly named, the great blue’s plumage
is primarily blue-gray, accented by a white face and distinctive black
eye stripe. During mating season, the adult heron grows elaborate plumes
on the head, neck and back.
It was for these plumes that the heron
population was decimated one hundred years ago, when fashion demanded
hats adorned with sprays of heron feathers. Thankfully, pressure from
conservationists and changing fashion saved the heron from extinction.
The heron’s sharp, sturdy beak is used to spear
its diet of fish, amphibians, reptiles, and small mammals. A hunting
heron wades in water no deeper than its chest, slowly pacing the shallows.
Becoming motionless when it senses its prey, the heron stabs with its
beak when the prey is within reach. The impaled prey is then swallowed
whole.
Herons also hunt rodents on dry land, but
must dip the furred prey in water to ease swallowing. Because their food
is largely aquatic in nature, great blue herons require freshwater or
saltwater wetland habitat. In Colorado, they primarily feed and nest
along river courses found between 4,000 and 9,000 feet.
Great blue herons are migratory birds. In our area,
a few remain year-round, but many migrate to southern New Mexico, Arizona
and northern Mexico in fall. The birds return to their nesting sites
in February and March, with courtship and nest building following soon
after.
Herons nest in communal groups called
rookeries, which can contain from a few pairs of birds to several hundred
pairs. A word of caution to birdwatchers hoping to observe great blues
on the nest: the herons flee easily, leaving the eggs and chicks exposed
to the elements and to predation from eagles, owls, crows, vultures,
and raccoons. Experts recommend limiting human activity within 300 yards
of the nesting sites, especially during courtship and incubation.
In the rookery, herons generally build their nests 30-70
feet above the ground, in mature trees near water. The nests are large
platforms of interwoven sticks lined with softer materials. Eggs are
laid in April or May, and hatch after a 28-day incubation.
In the 1960’s, the widespread use
of the pesticide DDT caused poisoning in the herons’ food supply,
leading to eggshell thinning and high chick mortality. The timely ban
on DDT allowed the heron population to rebound. Today, the greatest challenge
to the great blue heron is riparian habitat destruction.
In Colorado, only the smallest fraction
of viable river bank habitat remains, threatening this bird and all wildlife
dependent upon riparian habitat.
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