The osprey (; Pandion haliaetus), historically known as sea hawk, river hawk, and fish hawk, is a diurnal, fish-eating bird of prey with a cosmopolitan range. It is a large raptor, reaching more than in length and a wingspan of . It is brown on the upperparts and predominantly greyish on the head and underparts.
The osprey is distributed on all continents except Antarctica, but in South America, it occurs only as a nonbreeding migrant. It lives in a wide variety of habitats and nests in locations near a body of water providing an adequate food supply. It has specialised physical characteristics and unique behaviour in hunting its prey, which consists almost exclusively of fish.
Taxonomy The osprey was described in 1758 by Carl Linnaeus under the name Falco haliaetus in his 10th edition of Systema Naturae. Linnaeus specified the type locality as Europe, but in 1761, he restricted the locality to Sweden.
The osprey is the only extant species placed in the genus Pandion that was introduced by French zoologist Marie Jules César Savigny in 1809. The genus is the sole member of the family Pandionidae. The species has always presented a riddle to taxonomists, but here it is treated as the sole living member of the family Pandionidae, and the family listed in its traditional place as part of the order Accipitriformes. Other schemes place it alongside the hawks and eagles in the family Accipitridae. The Sibley-Ahlquist taxonomy has placed it together with the other diurnal raptors in a greatly enlarged Ciconiiformes, but this results in an unnatural paraphyletic classification. Molecular phylogenetic analysis revealed that the family Pandionidae is a sister taxon of the family Accipitridae. The two families diverged an estimated .
The osprey is unusual in that it is a sole living species that occurs nearly worldwide. Even the few subspecies are not unequivocally separable. Generally, four subspecies are recognised, although differences are small, and ITIS lists only the first three. P. h. carolinensis (Gmelin, 1788)– the American or North American osprey occurs from Alaska and Canada to much of Central and South America, except Chile and Patagonia. It is larger and has a darker body and paler breast than the European osprey. P. h. cristatus (Vieillot, 1816) – the Australasian osprey is the smallest and most distinctive subspecies that occurs along the entire marine coastline of Australia and some larger freshwater rivers as well as in Tasmania. It is not migratory. Some authorities have assigned it full species-status as Pandion cristatus, also known as the eastern osprey.
A 2018 genetic study using microsatellite data showed only low genetic divergence between cristatus and the other subspecies. P. h. haliaetus (Linnaeus, 1758) – the Eurasian osprey is the nominate subspecies that occurs across the Palearctic realm and several parts of sub-Saharan Africa from the Azores and the Iberian Peninsula east to Japan and Kamchatka Peninsula, throughout South and Southeast Asia, the Indian subcontinent, Madagascar, and much of the African coastline. P. h. ridgwayi Maynard, 1887 – Ridgway's osprey occurs in the Caribbean islands. It has a very pale head and breast and a weak eye mask. It is nonmigratory. Its scientific name commemorates Robert Ridgway.
Fossil record Three extinct species have been named from the fossil record.
Pandion homalopteron described by Stuart L. Warter in 1976 was found in marine Middle Miocene deposits of the Barstovian age in the southern part of California. Pandion lovensis was described in 1985 and found in Florida; it dates to the Late Clarendonian and possibly represents 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.
The oldest recognized family Pandionidae fossils were recovered from the Oligocene epoch Jebel Qatrani Formation in Faiyum Governorate, Egypt, but they are not complete enough to assign to a specific genus. The remains of another Oligocene species were discovered in Hungary and described as P. pannonicus. Another Pandionidae claw fossil was recovered from Early Oligocene deposits in the Mainz basin, Germany, and was described in 2006 by Gerald Mayr.
Etymology The genus name Pandion derives from Pandíōn , the mythical Greek king of Athens and grandfather of Theseus, Pandion II. The species name haliaetus () comes from Greek haliáetos "sea-eagle" (also haliaietos) from the combining form hali- of hals "sea" and aetos, "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.
Description
The osprey differs in several respects from other diurnal birds of prey. Its toes are of equal length, its tarsi are reticulated, and its talons are rounded, rather than grooved. The osprey and owls are the only raptors whose outer toes are 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 in weight and in length with a 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 , P. h. carolinensis averaging , and P. h. cristatus averaging . The wing chord measures , the tail measures , and the tarsus is .
The upperparts are a deep, glossy brown, while the breast is white, 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. On the underside of the wings, the wrists are black, which serves as a field mark. 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 his slimmer body and narrower wings. The breast band of the male is also weaker than that of the female or is nonexistent, and the underwing coverts of the male are more uniformly pale. Determining the sex in a breeding pair is straightforward, 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!
Distribution and 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 worldwide 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 nonbreeding visitor to eastern Victoria and Tasmania.
A gap, corresponding with the coast of the Nullarbor Plain, occurs 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 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 to Indochina and southern China, Indonesia, Malaysia, and the Philippines.
Behaviour and ecology Diet The osprey is piscivorous, with fish making up 99% of its diet. It typically takes live fish weighing and about in length, but virtually any type of fish from to can be taken. Even larger northern pike (Esox lucius) have been taken in Russia.Adrianova, Olga V. & Boris N. Kashevarov. "Some results of long-term raptor monitoring in the Kostomuksha Nature Reserve." Status of Raptor Populations in Eastern Fennoscandia. Kostomuksha (2005). The species rarely scavenges dead or dying fish.
Ospreys' vision is well adapted to detecting underwater objects from the air. Prey is first sighted when the bird is above the water, after which it hovers momentarily and then plunges feet first into the water. It catches fish by diving into a body of water, oftentimes completely submerging its entire body. 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 mammals, snakes, turtles, small alligators, frogs, birds, salamanders, conchs, and crustaceans.Bierregaard, Richard O., et al. “Osprey (Pandion Haliaetus).” Birds of the World, Mar. 2020, doi:10.2173/bow.osprey.01. Reports of ospreys feeding on carrion are rare, but they have been observed eating dead white-tailed deer and Virginia opossums.
Adaptations The osprey has several adaptations that suit its piscivorous lifestyle. These include reversible outer toes, sharp spicules on the underside of the toes, closable nostrils to keep out water during dives, backward-facing scales on the talons that act as barbs to help hold its catch, and dense, oily plumage to prevent its feathers from getting waterlogged.
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 14 or so similar nesting sites are known, 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 m and weighing about , 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 a shortage of suitable tall structures may exist. If no nesting sites are 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. The nesting platform design developed by 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 used by people from a number of different geographical regions. A global site maps osprey nest locations and logs observations on reproductive success.