Osprey

Appearance

The osprey differs in several respects from other diurnal birds of prey. Its toes are of equal length, its tarsi are reticulate, and its talons are rounded, rather than grooved. The osprey and owls are the only raptors whose outer toe is reversible, allowing them to grasp their prey with two toes in front and two behind. This is particularly helpful when they grab slippery fish.
The osprey is 0.9–2.1 kg in weight and 50–66 cm in length with a 127–180 cm wingspan. It is, thus, of similar size to the largest members of the "Buteo" or "Falco" genera. The subspecies are fairly close in size, with the nominate subspecies averaging 1.53 kg, "P. h. carolinensis" averaging 1.7 kg and "P. h. cristatus" averaging 1.25 kg. The wing chord measures 38 to 52 cm, the tail measures 16.5 to 24 cm and the tarsus is 5.2–6.6 cm.

The upperparts are a deep, glossy brown, while the breast is white and sometimes streaked with brown, and the underparts are pure white. The head is white with a dark mask across the eyes, reaching to the sides of the neck. The irises of the eyes are golden to brown, and the transparent nictitating membrane is pale blue. The bill is black, with a blue cere, and the feet are white with black talons. A short tail and long, narrow wings with four long, finger-like feathers, and a shorter fifth, give it a very distinctive appearance.

The sexes appear fairly similar, but the adult male can be distinguished from the female by its slimmer body and narrower wings. The breast band of the male is also weaker than that of the female, or is non-existent, and the underwing coverts of the male are more uniformly pale. It is straightforward to determine the sex in a breeding pair, but harder with individual birds.

The juvenile osprey may be identified by buff fringes to the plumage of the upperparts, a buff tone to the underparts, and streaked feathers on the head. During spring, barring on the underwings and flight feathers is a better indicator of a young bird, due to wear on the upperparts.

In flight, the osprey has arched wings and drooping "hands", giving it a gull-like appearance. The call is a series of sharp whistles, described as "cheep, cheep" or "yewk, yewk". If disturbed by activity near the nest, the call is a frenzied "cheereek"!

Naming

The genus name "Pandion" derives from "Pandíōn", the mythical Greek king of Athens and grandfather of Theseus, Pandion II. Although Pandion II was not used to name a bird of prey, Nisus, a king of Megara, was used for the genus. The species name "haliaetus" comes from Ancient Greek "haliáetos" from "hali-", "sea-" and "aetós", "eagle".

The origins of "osprey" are obscure; the word itself was first recorded around 1460, derived via the Anglo-French "ospriet" and the Medieval Latin "avis prede" "bird of prey," from the Latin "avis praedae" though the Oxford English Dictionary notes a connection with the Latin "ossifraga" or "bone breaker" of Pliny the Elder. However, this term referred to the bearded vulture.

Distribution

The osprey is the second most widely distributed raptor species, after the peregrine falcon, and is one of only six land-birds with a cosmopolitan distribution. It is found in temperate and tropical regions of all continents, except Antarctica. In North America it breeds from Alaska and Newfoundland south to the Gulf Coast and Florida, wintering further south from the southern United States through to Argentina. It is found in summer throughout Europe north into Ireland, Scandinavia, Finland and Great Britain though not Iceland, and winters in North Africa. In Australia it is mainly sedentary and found patchily around the coastline, though it is a non-breeding visitor to eastern Victoria and Tasmania.

There is a 1,000 km gap, corresponding with the coast of the Nullarbor Plain, between its westernmost breeding site in South Australia and the nearest breeding sites to the west in Western Australia. In the islands of the Pacific it is found in the Bismarck Islands, Solomon Islands and New Caledonia, and fossil remains of adults and juveniles have been found in Tonga, where it probably was wiped out by arriving humans. It is possible it may once have ranged across Vanuatu and Fiji as well. It is an uncommon to fairly common winter visitor to all parts of South Asia, and Southeast Asia from Myanmar through to Indochina and southern China, Indonesia, Malaysia and the Philippines.

The worldwide distribution of the species is unusual for land-based birds, and only recognised in five other species.six of 10000 land based bird species include "Pandion haliaetus" ["sensu lato"] and species: great egret "Ardea alba", the cattle egret "Bubulcus ibis", the glossy ibis "Plegadis falcinellus", the barn owl "Tyto alba" and the peregrine falcon "Falco peregrinus".

Status

The osprey has a large range, covering 9,670,000 km2 in just Africa and the Americas, and has a large global population estimated at 460,000 individuals. Although global population trends have not been quantified, the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List, and for these reasons, the species is evaluated as Least Concern. There is evidence for regional decline in South Australia where former territories at locations in the Spencer Gulf and along the lower Murray River have been vacant for decades.

In the late 19th and early 20th centuries, the main threats to osprey populations were egg collectors and hunting of the adults along with other birds of prey, but osprey populations declined drastically in many areas in the 1950s and 1960s; this appeared to be in part due to the toxic effects of insecticides such as DDT on reproduction. The pesticide interfered with the bird's calcium metabolism which resulted in thin-shelled, easily broken or infertile eggs. Possibly because of the banning of DDT in many countries in the early 1970s, together with reduced persecution, the osprey, as well as other affected bird of prey species, have made significant recoveries. In South Australia, nesting sites on the Eyre Peninsula and Kangaroo Island are vulnerable to unmanaged coastal recreation and encroaching urban development.

Habitat

The osprey is the second most widely distributed raptor species, after the peregrine falcon, and is one of only six land-birds with a cosmopolitan distribution. It is found in temperate and tropical regions of all continents, except Antarctica. In North America it breeds from Alaska and Newfoundland south to the Gulf Coast and Florida, wintering further south from the southern United States through to Argentina. It is found in summer throughout Europe north into Ireland, Scandinavia, Finland and Great Britain though not Iceland, and winters in North Africa. In Australia it is mainly sedentary and found patchily around the coastline, though it is a non-breeding visitor to eastern Victoria and Tasmania.

There is a 1,000 km gap, corresponding with the coast of the Nullarbor Plain, between its westernmost breeding site in South Australia and the nearest breeding sites to the west in Western Australia. In the islands of the Pacific it is found in the Bismarck Islands, Solomon Islands and New Caledonia, and fossil remains of adults and juveniles have been found in Tonga, where it probably was wiped out by arriving humans. It is possible it may once have ranged across Vanuatu and Fiji as well. It is an uncommon to fairly common winter visitor to all parts of South Asia, and Southeast Asia from Myanmar through to Indochina and southern China, Indonesia, Malaysia and the Philippines.

The worldwide distribution of the species is unusual for land-based birds, and only recognised in five other species.six of 10000 land based bird species include "Pandion haliaetus" ["sensu lato"] and species: great egret "Ardea alba", the cattle egret "Bubulcus ibis", the glossy ibis "Plegadis falcinellus", the barn owl "Tyto alba" and the peregrine falcon "Falco peregrinus".

Reproduction

The osprey breeds near freshwater lakes and rivers, 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 five to seven are used in any one year. Many are renovated each season, and some have been used for 70 years. The nest is a large heap of sticks, driftwood, turf or seaweed built in forks of trees, rocky outcrops, utility poles, artificial platforms or offshore islets. As wide as 2 meters and weighing about 135 kg, large nests on utility poles may be fire hazards and have caused power outages.

Generally, ospreys reach sexual maturity and begin breeding around the age of three to four, though in some regions with high osprey densities, such as Chesapeake Bay in the United States, they may not start breeding until 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 are sometimes erected to provide more sites suitable for nest building. In some regions ospreys prefer transmission towers as nesting sites, e.g. in eastern Germany.

The nesting platform design developed by one organization, Citizens United to Protect the Maurice River and Its Tributaries, Inc. has become the official design of the State of New Jersey, U.S. The nesting platform plans and materials list, available online, have been utilized by people from a number of different geographical regions. is the global site for mapping osprey nest locations and logging observations on reproductive success.

Ospreys usually mate for life. Rarely, polyandry has been recorded. The breeding season varies according to latitude; spring in southern Australia, April to July in northern Australia and winter in southern Queensland. In spring the pair begins a five-month period of partnership to raise their young. The female lays two to four eggs within a month, and relies on the size of the nest to conserve heat. The eggs are whitish with bold splotches of reddish-brown and are about 6.2 cm × 4.5 cm and weigh about 65 g. The eggs are incubated for about 35–43 days to hatching.

The newly hatched chicks weigh only 50–60 g, but fledge in 8–10 weeks. A study on Kangaroo Island, South Australia, had an average time between hatching and fledging of 69 days. The same study found an average of 0.66 young fledged per year per occupied territory, and 0.92 young fledged per year per active nest. Some 22% of surviving young either remained on the island or returned at maturity to join the breeding population. When food is scarce, the first chicks to hatch are most likely to survive. The typical lifespan is 7–10 years, though rarely individuals can grow to as old as 20–25 years.

The oldest European wild osprey on record lived to be over thirty years of age. In North America, great horned owls, golden eagles, and bald eagles are the only major predators of ospreys, capable of taking both nestlings and adults. However, kleptoparasitism by bald eagles, where the larger raptor steals the osprey's catch, is more common than predation. The white-tailed eagle, which is very similar to the bald eagle, may harass or prey on the osprey in Eurasia. Raccoons can be a serious threat to nestlings or eggs if they can access the nest. Endoparasitic trematodes have been recorded in wild ospreys.

Food

The osprey is piscivorous, with fish making up 99% of its diet. It typically takes fish weighing 150–300 g and about 25–35 cm in length, but the weight can range from 50 g to 2 kg. Virtually any type of fish in that size range are taken.

Ospreys have vision that is well adapted to detecting underwater objects from the air. Prey is first sighted when the osprey is 10–40 m above the water, after which the bird hovers momentarily then plunges feet first into the water. They catch fish by diving into a body of water, oftentimes completely submerging their entire bodies. As an osprey dives it adjusts the angle of its flight to account for the distortion of the fish's image caused by refraction. Ospreys will typically eat on a nearby perch, but have also been known to carry fish for longer distances.

Occasionally, the osprey may prey on rodents, rabbits, hares, other birds, and small reptiles.

Predators

Swedish ospreys have a significantly higher mortality rate during migration seasons than during stationary periods, with more than half of the total annual mortality occurring during migration. These deaths can also be categorized into spatial patterns: Spring mortality occurs mainly in Africa, which can be traced to crossing the Sahara desert. Mortality can also occur through mishaps with human utilities, such as nesting near overhead electric cables or collisions with aircraft....hieroglyph snipped...

Migration

European breeders winter in Africa. American and Canadian breeders winter in South America, although some stay in the southernmost U.S. states such as Florida and California. Some ospreys from Florida migrate to South America. Australasian ospreys tend not to migrate.

Studies of Swedish ospreys showed that females tend to migrate to Africa earlier than the males. More stopovers are made during their autumn migration. The variation of timing and duration in autumn was more variable than in spring. Although migrating predominantly in the day, they sometimes fly in the dark hours particularly in crossings over water and cover on average 260–280 km per day with a maximum of 431 km per day. European birds may also winter in South Asia, indicated by an osprey tagged in Norway being monitored in western India. In the Mediterranean, ospreys show partial migratory behaviour with some individuals remaining resident, whilst others undertake relatively short migration trips.

Evolution

To date there have been two extinct species named from the fossil record. "Pandion homalopteron" was named by Stuart L. Warter in 1976 from fossils of Middle Miocene, Barstovian age, found in marine deposits in the southern part of California. The second named species "Pandion lovensis", was described in 1985 by Jonathan J. Becker from fossils found in Florida and dating to the latest Clarendonian and possibly representing a separate lineage from that of "P. homalopteron" and "P. haliaetus". A number of claw fossils have been recovered from Pliocene and Pleistocene sediments in Florida and South Carolina.

The oldest recognized family Pandionidae fossils have been recovered from the Oligocene age Jebel Qatrani Formation, of Faiyum, Egypt. However they are not complete enough to assign to a specific genus. Another Pandionidae claw fossil was recovered from Early Oligocene deposits in the Mainz basin, Germany, and was described in 2006 by Gerald Mayr.