Osprey 2007.p65
Utah Division of Wildlife Resources
Wildlife Notebook Series No. 7
Osprey
(Pandion haliaetus)
The Osprey is the only member of the avian Family
Gorge Reservoir currently hosts Utah's largest concentration
Pandionidae. Uniquely adapted to catch and feed almost
of nesting Osprey. Its deep but clear water allows them to
exclusively on fish, it is one of Utah's most specialized
see and catch their prey. And the rocky pinnacles lining the
summer residents. Many also pass through Utah during their
shore provide excellent nesting sites.
spring and fall migrations. Since the mid-1990s, increasing
numbers of Osprey have begun to nest within the state,
While Flaming Gorge Reservoir and Fish Lake
inhabiting areas near lakes, rivers and streams. In a state as
represent historical Osprey nesting strongholds, breeding
dry as Utah, their distribution is closely tied to natural and
pairs of Osprey can now be found at a number of lakes and
man-made water sources.
reservoirs across the state, including Utah Lake, Panguitch
Lake, Pineview Reservoir, Deer Creek Reservoir, Rockport
Habitat
Reservoir, Jordanelle Reservoir, Strawberry Reservoir, Echo
Reservoir, Minersville Reservoir, Starvation Reservoir and
During spring and fall migrations, Osprey may be
Willard Bay.
sighted along many major waterways in the state, though
occasionally they are spotted in habitats miles from water of
Range
any kind such as the Orem Overlook and at Snowbird.
Sightings are more common in areas near the Great Salt Lake
Osprey may be found on almost every continent.
and along the Green and Colorado rivers. They are also seen
Breeding populations can be found in Europe, Asia, North
along the Wasatch Mountains from Zion National Park to the
and Central America, Australia and on many of the Pacific,
Idaho border and in the Uinta Mountains.
Atlantic, Mediterranean and Caribbean islands. Utah's
Osprey migrate south to winter in Mexico, Central America
Construction of reservoirs in Utah has expanded
and South America. Other wintering populations occur in
suitable Osprey habitat for both feeding and nesting. Flaming
the southern areas of Africa and South America.
Description
Osprey catch fish by plunging feet first into the water with
their wings extended high above their head. Their long,
Osprey are large raptors (birds of prey) with
heavy, strong legs and large feet allow them to reach well
distinct dark markings. Adults measure 21 to 24 inches long
under the surface of the water. When either foot touches a
with a wing span from 4 1/2 to 6 feet. They weigh 3 to 4
fish, the Osprey's fast reflexes snap the foot closed, grasp-
pounds. Males have an almost pure white chest and belly,
ing the fish before it has time to escape.
while females have mottled dark brown markings across the
chest that form a "necklace." Both sexes have a white head
To help them grip onto a fish, Osprey also have
with a unique wide brown mask crossing the eye.
ridges of short, sharp spines (spicules) on the bottom of
their feet. In addition they can rotate their toes, which gives
In flight, Osprey are most easily distinguished by
them extra strength, dexterity and stability when catching
their sharply angled wings, which are more narrow than
and holding onto a struggling fish.
those of other large raptors such as hawks and eagles.
Viewed from below, Osprey have dark markings at the
After a successful dive, Osprey may pause briefly
"wrist" where the wings bend, dark wing tips, and dark
on the water before take off. Once in the air, they shake
bands on the tail.
off the water left on their feathers and then position the fish
so its head faces forward. This reduces wind resistance
Juveniles have markings similar to adults but the
and allows them to better control their catch.
feathers on the back, wings and tail are edged with a pale
buff color, resulting in a scaled appearance, and their chests
Reproduction
are slightly mottled.
In late March and early April, the Osprey that nest
Prey and Hunting Behavior
in Utah return from their southern wintering ranges. The
older males return first, followed a few days later by the
Osprey will feed on any medium-sized fish swim-
females and younger males. Usually birds that have nested
ming at or just below the water surface. They often hunt
successfully before, return to the same nest. If one partner
from a perch in order to conserve energy, but are also
does not return, the other partner will seek to mate with
effective aerial hunters. In flight, Osprey may either dive
another bird. Younger birds select new sites for their nests.
directly on their prey or hover in one spot before diving.
Courtship displays are common for all breeding
pairs. Nest site selection and construction are a significant
part of courtship. The male selects the nest site and begins
constructing the nest, usually before the females arrive.
Criteria for good nest sites include security from predators,
protection from high winds and proximity to good fishing
areas.
Osprey courtship displays involve dramatic flying
patterns. Sometimes diving and hovering or swooping up
and diving sharply down, the male will call to the female
while in flight. Then the male carries a fish or nesting
materials to present to the female. When a female accepts
the male as a mate, she helps to finish building the nest he
has selected. The male supplies most of the nesting materi-
als and begins to supply fish for her. By the time the female
is ready to lay eggs in late April or early May, she relies
almost exclusively on the male for food.
Osprey prefer to build their nests in trees, but
readily accept man-made structures such as platforms built
to increase available nesting sites. Artificial nest structures
installed by Division of Wildlife Resources biologists at
selected locations have helped to maintain and increase
Utah's Osprey population. Osprey often build their nests on
power poles, cell phone towers or telephone pole crossarms
as well. At some such sites, they run the risk of death by
electrocution. To reduce this problem, biologists either build
a nest platform above the pole top, or create a nest tower in
proximity to the "selected" power or telephone pole, thus
making the original chosen site less desirable. At Flaming
heavier, coarse grey-colored down within a couple of
Gorge Reservoir, Osprey choose to nest atop rocky pin-
weeks. By the time the chicks are a month old they are
nacles.
almost as large as their parents.
Nests can be quite large and are composed of larger
Young Osprey are entirely dependent on the adults
diameter limbs and branches. Sometimes they even include
for food and shelter. The adult males generally feed them-
such oddities as fishing rods or surveyor stakes. Just before
selves before delivering fish to the females and offspring.
the female lays her eggs, she constructs a nest bowl and
This assures that the males will be in good physical condi-
lines it with downy feathers, moss, shredded bark and other
tion to continue hunting and supplying food for the females
soft materials. She usually lays between one and three eggs,
and chicks. When fishing is poor and there is not enough
although occasionally a female will lay four. The eggs are
food for all the chicks to survive, the chicks compete for
laid one at a time and usually one to three days apart. Both
what fish is brought to the nest. The larger chicks may
parents incubate the eggs, but the female remains on the
push the younger, smaller chicks aside.
eggs for longer periods of time while the male continues to
supply food for both of them.
Approximately nine weeks after hatching, the young
Osprey are ready to "fledge" (fly from the nest). During the
Young Osprey
next month, the young practice flying and learn how to fish.
The males continue to deliver food to the nest or directly to
The chicks hatch five to six weeks after the eggs
the young. By the first of September, most of the females
are laid. They hatch one to three days apart, so the first
have left the area and have begun to migrate south. The
chicks to hatch are developing one to three days ahead of
males and older juveniles follow within a couple of weeks,
the second and third chicks to hatch. The young are born
and by October only the youngest birds and birds that have
helpless and totally dependent on the adults. They have a
migrated from the north are still found here. Osprey are
fine covering of off-white down that is replaced by a
very rarely seen in Utah during the winter.
Management
Osprey are protected by Utah state law and the
federal Migratory Bird Treaty Act. It is illegal to kill
Osprey, disturb nesting Osprey, destroy nests, collect or
have in your possession eggs, feathers, or nests of Osprey.
The Osprey population in Utah continues to in-
crease. When the first population surveys were conducted
in the mid-1970s, biologists found only four active nests
with a total of six young. More recently, the Flaming Gorge
and Green River areas alone host over twenty nesting pairs
of Osprey annually that produce from twenty to forty
young. Substantial increases have also been noted at other
sites across the state.
The Utah Division of Wildlife Resources began
banding Osprey chicks in 1976, and by 1992, over 146
birds had been banded. Bands have been returned from
Colorado, Wyoming, Colombia, Chili, Ecuador, El Salvador,
Bolivia, Peru, and Honduras.
Nesting success depends on several factors. One
Biologists from the Utah Division of Wildlife Re-
factor that may cause nests to fail is human disturbance in
sources will continue monitoring the state's Osprey popula-
the nesting areas. Although Osprey may be tolerant of some
tion to gather additional life history information.
human activities, they are adversely impacted when people
hike or climb too close to their nests. They are also dis-
What You Can Do
turbed by boats or jet skis moving directly toward or
stopping directly under their nests. Other factors that may
• Always view nests from a distance of at least 800
limit nesting success include an increase in predators
to 1,000 yards so as not to disturb nesting birds. If the adult
(especially Great Horned-owls, ravens, Golden Eagles and
birds leave the nest, the chicks, are very susceptible to
falcons), a decline in the available fish populations and
predation, dehydration (from the heat of the sun), or to cold
poaching.
(from the effects of stormy weather).
• If you observe Osprey nesting in other parts of
Utah, report your finding to the nearest Wildlife Resources
office.
• Contribute to wildlife through the Wildlife Tax
Check-off on the Utah State Income Tax form or by making
a contribution to the Watchable Wildlife Program, Utah
Division of Wildlife Resources, 1594 West North Temple,
Suite 2110, Salt Lake City, UT 84116.
Wildlife Notebook Series No. 7 written by Ron Stewart, UDWR
Regional Conservation Outreach Manager, Vernal; edited by
Jim Parrish, UDWR Avian Program Coordinator; illustrated by
Jill Rensel.
The Utah Department of Natural Resources receives federal aid and prohibits discrimination on the basis of race, color, sex, national origin, or disability. For
more information or complaints regarding discrimination, contact Executive Director, Utah Department of Natural Resources, P.O. Box 145610, Salt Lake City,
UT 84116-5610 or Office of Equal Opportunity, U.S. Department of Interior, Washington, D.C. 20240. The Division of Wildlife Resources is funded by the sale
of hunting and fishing licenses and through federal aid made possible by an excise tax on the sale of firearms and other hunting and fishing-related equipment.
Printed on recycled paper.
February 2007
