BIOLOGICAL DATA AND HABITAT REQUIREMENTS
WILDLIFE SPECIES: Pandion haliaetus | Osprey 



TIMING OF MAJOR LIFE HISTORY EVENTS : 
Courtship - Ospreys generally arrive on their breeding grounds in late
March or early April.  Pair bonding persists from one year to the next,
and the same nest site may be used for many years [26].  Most ospreys
are monogamous; occasionally they breed as a polygynous trio (one male
breeding concurrently with two females) [24].

Age at first reproduction - Ospreys generally first breed when they are
between 3 and 4 years old [24,28].  Juveniles spend about 17 months on
the wintering gounds.  At around 2 years of age they return to the
nesting grounds but do not breed until the following year [28].  Age at
first reproduction varies not only among individual ospreys but among
populations, apparently in relation to the availability of nest sites
and other resources.  For example, birds along the eastern shore of
Chesapeake Bay do not start breeding until they are 5 to 7 years old due
to the lack of nest sites [24].

Clutch/incubation/fledging - Most migratory ospreys lay two to four eggs
from late April to early May and incubate them for 5 to 6 weeks [24,28].
An average of 1.1 to 1.3 young per active nest are fledged per year
[28].  Young fledge when they are about 2 months old [4,28].  They
return to the nest for feeding and roosting for another week, and can be
found nearby for sometime after that [4].  Most resident ospreys lay
their clutch in winter.  In southern Florida, for example, ospreys lay
from early December until late February [24].

Life span - On average, out of 100 fledged young, 37 will be alive 4
years after fledging, 17 will be alive 8 years after fledging, and only
six to eight will be alive 12 years after fledging.  The greatest
longevity recorded is 25 years [24].


PREFERRED HABITAT : 
Ospreys occupy a wide range of habitats near water, primarily lakes,
rivers, and coastal waters with adequate supplies of fish [4].  Their
nests are generally built within 6 to 7 miles (9.6-11.2 km) of large
lakes or rivers with slow-moving water [14,30].  Flattened portions of
partially broken off snags, trees, rocks, dirt pinnacles, cacti, and
numerous man-made structures such as utility poles and duck blinds are
used for nests [14,28,30].  The nests consist of a large interwoven pile
of sticks lined with some soft material such as cedar bark or moss
[28,30].  The area around the nest is generally open, giving the birds
clear access when landing.  Ponderosa pine in the western United States,
tupelo (Nyssa sylvatica) in the eastern United States, and mangroves
(Rhizophora spp.) in the subtropics are all favored as nest trees for
this reason [24].


COVER REQUIREMENTS : 
Ospreys typically nest at the extreme tip of a tree or snag with little
or no overhead cover [17].  They prefer tall snags that provide good
visibility and security [5].  Ospreys also prefer to nest over water for
protection against climbing predators.  Islands free of mammalian
predators allow safe nesting in low trees and even on the ground.
Swamps also provide safe nesting [24].


FOOD HABITS : 
The osprey diet consists almost entirely of fish, but they will
occasionally eat frogs, snakes, ducks, crows, and small mammals
[5,6,28,29].  Ospreys can penetrate only about 3 feet (1 m) below the
water surface.  Therefore, they generally catch only surface fish or
those that frequent shallow flats and shorelines.  Ospreys are
opportunists.  If fish are abundant, accessible, and the right size they
seldom go unconsumed [24].  Poole [24] found that along the southern
coast of New England, about one-half of the fish ospreys eat during the
breeding season are winter flounder (Pseudopleuonectes americanus).
White herring (Alosa spp.) and Menhaden (Brevoortia tyrannus) each
supply another 20 percent of the diet.  Inland ospreys are likely to eat
the same species of fish throughout the breeding season, but coastal
populations change prey regularly in response to the seasonal migration
of marine fish [24].  Ospreys in western North America often eat
suckers, carp, bullhead (Ictalurus spp.), and perch (Perca flavescens)
when nesting near warm shallow lakes or reservoirs but eat trout when
nesting near deeper, colder waters [24,29].


PREDATORS : 
Crocodiles (Crocodylus spp.) have been known to eat ospreys roosting on
mudbanks, but only owls (mostly great horned owls [Bubo virginianus])
kill adult ospreys with any regularity.  Raccoons (Procyon lotor) will
eat osprey eggs and chicks.  Predators exert a major impact on the nest
sites ospreys choose.  Most climbing predators like raccoons seem
reluctant to swim far, so only aerial predators such as owls reach
overwater nests easily [24].


MANAGEMENT CONSIDERATIONS : 
In the 1960's osprey populations declined as a result of DDT which were
washed into water courses and ingested by fish.  These DDT residues
affected the estrogen hormone which controls calcium and egg shell
thickness, resulting in thinner shells and broken eggs [4,26].
Following tight restrictions on the use of DDT, pesticide residues
declined, and North American osprey populations increased consistently
between 1968 and 1981.  Ospreys are still vulnerable to contamination
during migration in Central and South America, where DDT continues to be
used to control mosquitos which carry malaria parasites [26].

Some bird species have been observed forming protective nesting
associations with ospreys by building their nests in the sides or
bottoms of the stick nests of ospreys. These include house wrens
(Troglodytes aedon), house sparrows (Passer domesticus), European
starlings (Sturnus vulgaris), common grackles (Quiscalus quiscula),
night-herons (Nycticorax spp.), swallows (Hirundinidae), and jays
(Corvidae) [26].

Artificial nest sites are successfully used by ospreys.  One study
showed that the overall breeding success improved from 45.9 percent in
natural trees to 62.9 percent in man-made platforms [12].

Human disturbance during the critical periods of incubation and early
nesting stages can be fatal to embryos and nestlings if adults are kept
from their nests.  Until an osprey pair becomes habituated to human
activities, human disturbance will jeopardize their nesting success
[29].


REFERENCES : 
NO-ENTRY

Related categories for Wildlife Species: Pandion haliaetus | Osprey