Osprey
Conservation status Least concern |

A North American Osprey preparing to
dive.
|
Scientific classification |
Kingdom: |
Animalia
|
Phylum: |
Chordata
|
Class: |
Aves
|
Order: |
Falconiformes
|
Family: |
Pandionidae
Sclater & Salvin, 1873 |
Genus: |
Pandion
Savigny, 1809 |
Species: |
P. haliaetus
|
|
Binomial name |
Pandion haliaetus
(Linnaeus, 1758) |
The Osprey (Pandion haliaetus) is a medium
large
raptor which is a specialist fish-eater with a worldwide
distribution. It occurs in all continents except
Antarctica, but in South America only as a non-breeding
migrant. It is often known by other
colloquial names such as fishhawk, seahawk
or Fish Eagle.
An unusual bird with no close relatives, it is the only
living species of the genus Pandion, which is in turn
the only genus in the
bird family Pandionidae.
Description
The Osprey is 52-60
centimetres (20.5-23.6 in) long with a 152-167 cm (5-5.5 ft) wingspan. It has mainly white underparts and head, apart
from a dark mask through the eye, and fairly uniformly brown
upperparts. Its short tail and long, narrow wings with four
long "finger" feathers (and a shorter fifth) give it a very
distinctive appearance.
Juvenile birds are readily identified by the buff fringes
to the upperpart plumage, buff tone to the underparts, and
streaked crown. By spring, wear on the upperparts makes
barring on the underwings and flight feathers a better
indicator of young birds. Adult males can be distinguished
from females from their slimmer bodies and narrower wings.
They also have a weaker or non-existent breast band than the
female, and more uniformly pale underwing coverts. It is
straightforward to sex a breeding pair, but harder with
individual birds.
In flight, Ospreys have arched wings and drooping
"hands", giving them a diagnostic
gull-like appearance. The call is a series of sharp
whistles, cheep, cheep, or yewk,
yewk. Near the nest, a frenzied cheereek!
Classification
The Osprey differs in several respects from the other
diurnal birds of prey, and has always presented something of
a riddle to taxonomists. Here it is treated as the sole
member of the family Pandionidae, and the family
listed in its traditional place as part of the order
Falconiformes. Other schemes place it alongside the hawks
and eagles in the family Accipitridae—which itself can be
regarded as making up the bulk of the order Accipitriformes
or else be lumped with the Falconidae into Falconiformes.
The Sibley-Ahlquist taxonomy has placed it together with the
other diurnal raptors in a greatly enlarged Ciconiiformes,
but this has more recently turned out to result in an
unnatural paraphyletic classification.
Subspecies
The Australasian Osprey is the most distinctive
subspecies.
There are four generally recognised
subspecies, although differences are small, and ITIS
only lists the first two.
- P. h. haliaetus (Linnaeus, 1758) Eurasia
P. h. carolinensis (Gmelin, 1788), North America. This
form has a paler breast than nominate haliaetus.
P. h. ridgwayi Maynard, 1887, Caribbean islands. This
form has a very pale head and breast compared to
nominate haliaetus, with only a weak eye mask. It is
non-migratory.
P. h. cristatus (Vieillot, 1816), Australasia. The
smallest subspecies, also non-migratory
Ospreys are unusual insofar as a single species occurs
nearly worldwide. Even the few
subspecies are not unequivocally separable. The reason is
apparently that these birds are usually migratory, enabling
individuals from populations which breed far apart to meet
in the winter quarters, form pairs and thus exchange genetic
information between populations. Furthermore, Ospreys are
long-lived birds which take a considerable time to reach
maturity, which slows down the rate of speciation.
Prehistoric species
There were several prehistoric species of osprey which
have been described from
fossils:
- Pandion sp. (Early Oligocene of Fayyum,
Egypt)
- Pandion homalopteron (Middle Miocene of
California, USA)
- Pandion lovensis (Late Miocene of Florida,
USA)
- Pandion sp. (Late Miocene/Early Pliocene of
Lee Creek Mine, USA)
P. homalopteron was very similar to the living
species and possibly even its direct ancestor. However, the
biogeography of the fossil ospreys has not been
researched well enough to suggest a place where the modern
Osprey originated. The genus apparently first appeared in
the Mediterranean region, but this is not certain.
Behaviour
Diet
The Osprey is particularly well adapted to its
fish diet, with reversible outer toes, closable nostrils
to keep out water during dives, and backwards facing scales
on the talons which act as barbs to help hold its catch. It
locates its prey from the air, often hovering prior to
plunging feet-first into the water to seize a fish. As it
rises back into flight the fish is turned head forward to
reduce
drag. The 'barbed' talons are such effective tools for
grasping fish that, on occasion, an Osprey may be unable to
release a fish that is heavier than expected. This can cause
the Osprey to be pulled into the water, where it may either
swim to safety or succumb to hypothermia and drown.
Nesting
The Osprey breeds by freshwater lakes, and sometimes on
coastal brackish waters. The nest is a large heap of sticks
built in trees, rocky outcrops, telephone poles or
artificial platforms. In some regions with high Osprey
densities, such as Chesapeake Bay, USA, most Ospreys do not start breeding until they are five to
seven years old. Many of the tall structures they need to
build nests on are already taken. If there are no nesting
sites available, young Ospreys may be forced to delay
breeding. To ease this problem, posts may be erected to
provide more sites.
Ospreys usually mate for life. In spring they begin a
five-month period of partnership to raise their young.
Females lay 3–4
eggs within a month, and rely on the size of the nest to
help conserve heat. The eggs are approximately the size of
chicken eggs, and
cinnamon colored; they are incubated for about 5 weeks
to hatching.
The newly-hatched chicks weigh only 50-60 g (2 oz}, but
fledge within eight weeks. When food is scarce, the first
chicks to hatch are most likely to survive. The typical
lifespan is 20-25 years.
European breeders winter in Africa. American and Canadian
breeders winter in South America, although some stay in the
southernmost USA states such as Florida and California.
Australasian Ospreys tend not to
migrate.
Conservation
Twenty to thirty years ago, Ospreys in some regions faced
possible
extinction, because the species could not produce enough
young to maintain the population. Since the banning of
DDT
in many countries in the early 1970s, together with reduced
persecution, the Ospreys, as well as other affected
bird of prey species have made significant recoveries.
Popular culture
The Osprey is the
official bird of Nova Scotia in Canada and Sudermannia in
Sweden. It is the official mascot and team name for the
University of North Florida and the Richard Stockton College
of New Jersey. The bird was depicted on the 1986 series
Canadian $10 note. The Osprey is also the mascot of the
Christian Falangist Party of America
References
- BirdLife International (2004).
Pandion haliaetus. 2006
IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 12 May 2006. Database entry
includes justification for why this species is of least
concern
- Forsman, The Raptors of Europe and the Middle
East,
ISBN 0-85661-098-4
- Mullarney, Svensson, Zetterstrom and Grant,
Collins Bird Guide
ISBN 0-00-219728-6
External links