Unique
among North American raptors for its diet of live fish and ability
to dive into water to catch them, Ospreys are common sights soaring
over shorelines, patrolling waterways, and standing on their huge
stick nests, white heads gleaming. These large, rangy hawks do well
around humans and have rebounded in numbers following the ban on
the pesticide DDT. Hunting Ospreys are a picture of concentration,
diving with feet outstretched and yellow eyes sighting straight
along their talons.
Keys to identification
Size & Shape
Ospreys are very large, distinctively shaped hawks. Despite their
size, their bodies are slender, with long, narrow wings and long
legs. Ospreys fly with a marked kink in their wings, making an M-shape
when seen from below.
Color Pattern
Ospreys are brown above and white below, and overall they are whiter
than most raptors. From below, the wings are mostly white with a
prominent dark patch at the wrists. The head is white with a broad
brown stripe through the eye. Juveniles have white spots on the
back and buffy shading on the breast.
Behavior
Ospreys search for fish by flying on steady wingbeats and bowed
wings or circling high in the sky over relatively shallow water.
They often hover briefly before diving, feet first, to grab a fish.
You can often clearly see an Osprey's catch in its talons as the
bird carries it back to a nest or perch.
Habitat
Look for Ospreys around nearly any body of water: saltmarshes, rivers,
ponds, reservoirs, estuaries, and even coral reefs. Their conspicuous
stick nests are placed in the open on poles, channel markers, and
dead trees, often over water.
At a Glance
Habitat
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Food
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Nesting
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Behavior
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Conservation
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Lake/Pond
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Fish
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Tree
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Aerial Dive
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Least Concern
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Measurements
Both Sexes
Length
21.322.8 in
5458 cm
Wingspan
59.170.9 in
150180 cm
Weight
49.470.5 oz
14002000 g
Relative Size
Smaller than a Bald Eagle; larger and longer-winged than
a Red-tailed Hawk.
Other Names
Balbuzard pêcheur (French)
Gavilán pescador (Spanish)
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Cool Facts
- An Osprey may log more than 160,000 migration miles during its
15-to-20-year lifetime. Scientists track Ospreys by strapping
lightweight satellite transmitters to the birds backs. The
devices pinpoint an Osprey's location to within a few hundred
yards and last for 2-3 years. During 13 days in 2008, one Osprey
flew 2,700 milesfrom Martha's Vineyard, Massachusetts, to
French Guiana, South America.
- Ospreys are unusual among hawks in possessing a reversible outer
toe that allows them to grasp with two toes in front and two behind.
Barbed pads on the soles of the birds' feet help them grip slippery
fish. When flying with prey, an Osprey lines up its catch head
first for less wind resistance.
- Ospreys are excellent anglers. Over several studies, Ospreys
caught fish on at least 1 in every 4 dives, with success rates
sometimes as high as 70 percent. The average time they spent hunting
before making a catch was about 12 minutessomething to think
about next time you throw your line in the water.
- The Osprey readily builds its nest on manmade structures, such
as telephone poles, channel markers, duck blinds, and nest platforms
designed especially for it. Such platforms have become an important
tool in reestablishing Ospreys in areas where they had disappeared.
In some areas nests are placed almost exclusively on artificial
structures.
- Osprey eggs do not hatch all at once. Rather, the first chick
emerges up to five days before the last one. The older hatchling
dominates its younger siblings, and can monopolize the food brought
by the parents. If food is abundant, chicks share meals in relative
harmony; in times of scarcity, younger ones may starve to death.
- The name "Osprey" made its first appearance around
1460, via the Medieval Latin phrase for "bird of prey"
(avis prede). Some wordsmiths trace the name even further back,
to the Latin for "bone-breaker"ossifragus.
- The oldest known Osprey was 25 years, 2 months old.
Unable to dive to more than about three feet below the water's
surface, Ospreys gravitate toward shallow fishing grounds, frequenting
deep water only where fish school near the surface. Ospreys nest
in a wide variety of locations, from Alaska to New England, Montana
to Mexico, Carolina to California; their habitat includes almost
any expanse of shallow, fish-filled water, including rivers, lakes,
reservoirs, lagoons, swamps, and marshes. Whatever the location,
Osprey nesting habitat must include an adequate supply of accessible
fish within a maximum of about 12 miles of the nest; open, usually
elevated nest sites free from predatory mammals such as raccoons,
and a long enough ice-free season to allow the young to fledge.
The Osprey is the only hawk on the continent that eats almost exclusively
live fish. In North America, more than 80 species of live fresh-
and saltwater fish account for 99 percent of the Ospreys diet.
Captured fish usually measure about 613 inches in length and
weigh one-third to two-thirds of a pound. The largest catch on record
weighed about 2.5 pounds. On very rare occasions, Ospreys have been
observed feeding on fish carcasses or on birds, snakes, voles, squirrels,
muskrats, and salamanders. Ospreys probably get most of the water
they need from the flesh of their prey, although there are reports
of adults drinking on hot days.
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Osprey nests are built of sticks and lined with bark,
sod, grasses, vines, algae, or flotsam and jetsam. The
male usually fetches most of the nesting materialsometimes
breaking dead sticks off nearby trees as he flies pastand
the female arranges it. Nests on artificial platforms,
especially in a pairs first season, are relatively
smallless than 2.5 feet in diameter and 36
inches deep. After generations of adding to the nest year
after year, Ospreys can end up with nests 1013 feet
deep and 36 feet in diametereasily big enough
for a human to sit in. |
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Ospreys require nest sites in open surroundings for
easy approach, with a wide, sturdy base and safety from
ground predators (such as raccoons). Nests are usually
built on snags, treetops, or crotches between large branches
and trunks; on cliffs or human-built platforms. Usually
the male finds the site before the female arrives. |
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Adept at soaring and diving but not as maneuverable
as other hawks, Ospreys keep to open areas, flying with
stiff wingbeats in a steady, rowing motion. Primarily
solitary birds, they usually roost alone or in small winter
flocks of six to ten. Nesting Ospreys defend only the
immediate area around their nest rather than a larger
territory; they vigorously chase other Ospreys that encroach
on their nesting areas. In breeding season, males perform
an aerial "sky-dance," sometimes called "fish-flight."
With dangling legs, often clasping a fish or nesting material
in his talons, the male alternates periods of hovering
with slow, shallow swoops as high as 600 feet or more
above the nest site. Sustaining this display for 10 minutes
or more, he utters repeated screaming calls while gradually
descending in an undulating fashion to the nest. |
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Nesting Facts
Clutch Size
14 eggs
Number of Broods
1 broods
Egg Length
2.22.7 in
5.56.8 cm
Egg Width
1.72 in
4.25 cm
Incubation Period
3642 days
Nestling Period
5055 days
Egg Description
Cream to pinkish cinnamon; wreathed
and spotted with reddish brown.
Condition at Hatching
Capable of limited motion. Covered
with down and with eyes open.
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Conservation
status via IUCN
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Least Concern
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Ospreys are a conservation success story and their populations
are still growing, aided by pesticide bans and the construction
of artificial nest sites. Osprey numbers crashed in the early 1950s
to 1970s, when pesticides poisoned the birds and thinned their eggshells.
Along the coast between New York City and Boston, for example, about
90 percent of breeding pairs disappeared. Osprey studies provided
key support for wider legal arguments against the use of persistent
pesticides. After the 1972 U.S. DDT ban, populations rebounded,
and the Osprey became a conservation success symbol. But Ospreys
are still listed as endangered or threatened in some statesespecially
inland, where pesticides decimated or extirpated many populations.
As natural nest sites have succumbed to tree removal and shoreline
development, specially constructed nest platforms and other structures
such as channel markers and utility poles have become vital to the
Ospreys recovery. Sadly, a growing cause of death for Ospreys
is entanglement at the nest: the adults incorporate baling twine
and other discarded lines into their nests; these can end up wrapped
around a chick's feet and injure it or keep it from leaving the
nest.
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