Osprey (pandion haliaetus)
Life History
The osprey, or fish hawk, feeds exclusively on live fish.
Its toes and talons (claws) are long and sharp for holding onto slippery
fish. Ospreys are mostly brown on their backs, white below, and have long
narrow wings in the shape of a stretched out “M.” They have distinctive
dark brown patches at the bend of each wing and dark brown stripes through
the eyes. Ospreys are fairly large birds,with a body length of about 21-24
inches and a wing span from 4 1/2 to 5 1/2 feet. Females are larger than
males, as is true of most birds of prey. Their habitats include shallow
water estuaries, lakes, and rivers.
Foraging
During spring and summer, ospreys find an abundance
of medium-sized fish on the Chesapeake to feed their young. Males typically
forage far and wide for food, whereas females stay on the nest, or nearby.
Ospreys hunt by soaring over water, periodically hovering on beating wings
to scan for surface schooling or spawning fish. On breezy days, they let
the wind keep them aloft as they search for fish. Cloudy conditions with
rippled water lessen the osprey's fishing success, which can jeopardize
hungry nestlings.
Upon sight of its prey, the osprey makes a spectacular
dive. Folding its wings tightly, it descends swiftly and plunges feet
first into the water, often submerging completely. Another technique is
a shallow scoop for fish at the surface of the water and the osprey hardly
gets wet. Clasping the twisting fish, the osprey takes flight and labors
to climb ever higher. Successful early season hunts often end with a beautiful
courtship flight, an undulating display of the male's flight power to
its mate.
Nesting
Ospreys three years or older usually mate for life,
and return to the same nest site year after year. Spring courtship marks
the beginning of a five month period when the pair works together to raise
their young.
A clutch of three or four eggs are laid by the third
week of April. The bulk of the nest and its depressed center helps conserve
heat. The eggs, usually mottled cinnamon brown, are about the size of
jumbo chicken eggs, and must be incubated for nearly 5 weeks.
The eggs finally yield their treasures, nearly 2-ounce
helpless chicks that can barely beg for food. Amazingly, with a plentiful
supply of fish, these balls of fluff will become soaring acrobats in just
eight weeks. However, if food is scarce, the chick that hatches from the
first laid egg stands the best chance of survival since it can outcompete
its smaller siblings and may even push them out of the nest.
Osprey abundance in the Bay region is partially determined
by favorable nesting sites. Offshore structures offer protection from
terrestrial predators (such as raccoons) and human activity, permit rapid
detection and escape from danger, and place the birds near their food
supply. Ospreys may choose sites over the water such as duck blinds, navigation
markers, or manmade nesting platforms or high trees and utility poles
on land.
Fortunately, ospreys, if not harassed, are reasonably
tolerant of human beings. When these raptors are respected as interesting,
though noisy neighbors, they will nest close to people, and can be enjoyed
at many sites around the Bay. An Eastern Shore river such as the Tred
Avon has constant summer boating traffic, but also supports over 30 nests
which fledge large numbers of young. Ospreys are also nesting successfully
on heavily used western shore rivers like the South, Severn, Magothy,
and Back. In recent years, there has even been a nest on the Potomac within
the limits of Washington, D.C.
Migration
Ospreys return to the Chesapeake every spring, usually
around the beginning of March. By late July, most young Chesapeake ospreys
are on the wing. The young and adults begin their southern migration by
the end of August to wintering grounds in the Caribbean, Central America
and South America. Throughout September ospreys and many other birds of
prey from the northeastern U.S. funnel through coastal Virginia just north
of the Bay Bridge Tunnel near the Eastern Shore of Virginia National Wildlife
Refuge. More than 100 osprey sail over the mouth of the Chesapeake during
many of these "flight days" along with numerous other raptors ranging
in size from bald eagles to kestrels.
Threats to Survival
Although ospreys are now a common sight on Chesapeake
Bay, two to three decades ago they faced possible extinction along much
of the Atlantic coast. For years, they were unable to produce enough young
to maintain the population. Production was down because of egg failures
caused by extremely thin and easily broken eggshells.
Years of research led to the discovery that their eggshell
thinning was caused by the pesticide DDT, which had been in heavy use
since World War II for spraying mosquitoes and crop pests. DDT was banned
from use in the U.S. in the early 1970s and the osprey and some other
affected birds of prey have made remarkable recoveries.
The help of people in constructing thousands of artificial
nest platforms has also benefitted the osprey. However, intensive human
development along shorelines still can harm the aquatic environment which
ospreys depend upon. Formerly, active nests were routinely removed from
buoys and channel markers, reducing the number of young produced. Now,
this can be done only with a permit and if safety is affected.
Some areas of the Bay are low in fish abundance and cannot
support highly productive osprey colonies. In these areas, perhaps one
young will survive for every nest whereas other areas with more fish can
produce two or three fledglings per nest. The osprey's high visibility
and position at the top of the aquatic food chain make it a valuable indicator
species for detecting future habitat destruction, dwindling fish populations,
and contamination of the environment.
The Future
The story of the osprey on Chesapeake Bay is one of beauty
and promise. The beauty is in their spectacular flights and vociferous
calls heard throughout the spring and summer. The promise arises from
the resurgence of osprey abundance following the ban on harmful pesticides.
And the promise can extend to the entire Bay and its living resources
if people take strong measures to restore the Chesapeake's aquatic habitats.
With our perseverance and determination, the osprey will remain a beautiful
symbol of the Chesapeake and an environmental indicator for the future.
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