Osprey

Osprey
	A North American Osprey preparing to dive.
Conservation status
	Least Concern
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.

The Osprey is a species with many unique characteristics, and therefore has been given its own taxonomic genus, Pandion, and family, Pandionidae.

Description

The Osprey is 1400-2000 grams (3-4.4 pounds) and 52-60 centimetres (20.5-24 inches) long with a 150-180 cm (5-5.9 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!

Pandion haliaetus call

Bird call of the Osprey (Pandion haliaetus)

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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

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 is larger, darker bodied and 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), found around the coastline of, and along some large rivers within, Australia and Tasmania. 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.

Behaviour

Diet

File:Ospreyfood.jpg

An Osprey holding its meal

Fish comprise almost the whole diet. Fish they capture are generally 150–300 g (5.3-10 oz) and measure about 25–35 cm (10-12 in) in length, but can range from 50 to 2000 g (1.7-68 oz). The Osprey is particularly well adapted to this 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 (fish heavier than the Osprey itself are hazardous in this way). Rarely, Ospreys may prey on other wetland animals, such as reptiles (up to the size of young alligators), aquatic rodents, salamanders and other birds.

Nesting

The osprey breeds by freshwater lakes, and sometimes on coastal brackish waters. Rocky outcrops just offshore are used in Rottnest Island off the coast of Western Australia, where there are 14 or so similar nesting sites of which 5-7 are used in any one year. Some have been used for 70 years. 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, and there may be a shortage of suitable tall structures. 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 suitable for nest building.

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 cinnamon-colored eggs are about 60 x 45 mm (2.4 x 1.8 in) and weigh about 65 g (2.4 oz). The eggs 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. Bubo owls and Bald Eagles (and possibly other eagles of comparable size) are the only major predators of both nests and adults. Ospreys have rarely been known to be preyed on by crocodiles when they dive into the water.

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. Possibly because of 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 Södermanland in Sweden.
It is the official mascot and team name for the Minor League Baseball team the Missoula Osprey, University of North Florida, Richard Stockton College of New Jersey, and the University of North Carolina Wilmington.
It is the official mascot and team name (known by the alternative 'seahawk') for the Seattle Seahawks US football team, St. Mary's College of Maryland, and Salve Regina University Salve Seahawks
The bird was depicted on the 1986 series Canadian $10 note.
The Osprey is the mascot of the Christian Falangist Party of America.
The Ospreys is the registered name of the Neath and Swansea regional Rugby Union team in South Wales, UK.
The osprey is the namesake of the V-22 Osprey tilt-rotor aircraft.

References

Template:IUCN2006 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
Gessner, David, Return of the Osprey, ISBN 1565122542
Gessner, David, Soaring with Fidel, ISBN 0807085782

External links