Theosprey (/ˈɒspri,-preɪ/;[2]Pandion haliaetus), historically known assea hawk,river hawk, andfish hawk, is adiurnal,fish-eatingbird of prey with acosmopolitan range. It is a largeraptor, reaching more than 60 cm (24 in) in length and 180 cm (71 in) across the wings. It is brown on the upperparts and predominantly greyish on the head and underparts.
The osprey tolerates a wide variety ofhabitats, nesting in any location near a body of water providing an adequate food supply. It is found on all continents except Antarctica, although in South America it occurs only as a non-breedingmigrant.
As its other common names suggest, the osprey's diet consists almost exclusively of fish. It possesses specialised physical characteristics and unique behaviour in hunting itsprey. Because of its unique characteristics it is classified in its owntaxonomicgenus,Pandion, andfamily, Pandionidae.
The osprey was described in 1758 by the Swedish naturalistCarl Linnaeus under the nameFalco haliaetus in his landmarktenth edition of hisSystema Naturae.[3][4] Linnaeus specified thetype locality as Europe, but in 1761 he restricted the locality to Sweden.[4][5] The osprey is the only species placed in thegenusPandion that was introduced by the French zoologistMarie Jules César Savigny in 1809.[6][7] The genus is the sole member of the family Pandionidae.[7] The species has always presented a riddle to taxonomists, but here it is treated as the soleliving member of the family Pandionidae, and the family listed in its traditional place as part of the orderAccipitriformes. Other schemes place it alongside the hawks and eagles in the familyAccipitridae.[4] TheSibley-Ahlquist taxonomy has placed it together with the other diurnal raptors in a greatly enlargedCiconiiformes, but this results in an unnaturalparaphyletic classification.[8]Molecular phylogenetic analysis has found that the family Pandionidae issister to the family Accipitridae. It is estimated that the two families diverged around 50.8 million years ago.[9]
Australasian osprey (P. h. cristatus), inAustralia
The osprey is unusual in that it is a sole living species that occurs nearly worldwide. Even the fewsubspecies are not unequivocally separable. There are four generally recognised subspecies, although differences are small, andITIS lists only the first three.[10]
P. haliaetus carolinensis(Gmelin, 1788)– the American or North American osprey occurs from Alaska and Canada to much ofCentral andSouth America, except Chile and Patagonia. It is larger, darker bodied and has a paler breast than the European osprey.[11]
P. haliaetus ridgwayiMaynard, 1887 – Ridgway's osprey occurs in theCaribbean islands. It has a very pale head and breast and a weak eye mask.[11] It is non-migratory. Its scientific name commemoratesRobert Ridgway.[12]
P. haliaetus 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 inTasmania. It is not migratory.[11] Some authorities have assigned it full species-status[13] asPandion cristatus, also known as theeastern osprey.[14] A 2018 genetic study usingmicrosatellite data showed only lowgenetic divergence betweencristatus and the other subspecies.[15]
Twoextinct species were named from the fossil record.[16]Pandion homalopteron described by Stuart L. Warter in 1976 was found in marineMiddle Miocene deposits of theBarstovian age in the southern part ofCalifornia. The second speciesPandion lovensis was described byJonathan J. Becker in 1985 and found inFlorida; it dates to the LateClarendonian and possibly represents a separate lineage from that ofP. homalopteron andP. haliaetus. A number of claw fossils have been recovered from Pliocene and Pleistocene sediments in Florida andSouth Carolina.[citation needed]
The oldest recognized family Pandionidae fossils were recovered from the Oligocene ageJebel Qatrani Formation inFaiyum Governorate,Egypt. However, they are not complete enough to assign to a specific genus.[17] Another Pandionidae claw fossil was recovered fromEarly Oligocene deposits in theMainz basin, Germany, and was described in 2006 byGerald Mayr.[18]
The genus namePandion derives fromPandíōnΠανδίων, themythical Greekking of Athens and grandfather ofTheseus,Pandion II. The species namehaliaetus (Latin:haliaeetus)[19] comes fromGreekἁλιάετοςhaliáetos "sea-eagle" (alsoἁλιαίετοςhaliaietos) from the combining formἁλι-hali- ofἅλςhals "sea" andἀετόςaetos, "eagle".[20][21]
Osprey atCootes Paradise, Hamilton, OntarioEurasian osprey in flight, Northern Territory, Australia
The osprey differs in several respects from otherdiurnal birds of prey. Its toes are of equal length, itstarsi arereticulate, 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.[26]The osprey is 0.9–2.1 kg (2.0–4.6 lb) in weight and 50–66 cm (20–26 in) in length with a 127–180 cm (50–71 in) wingspan. It is, thus, of similar size to the largest members of theButeo orFalco genera. The subspecies are fairly close in size, with the nominate subspecies averaging 1.53 kg (3.4 lb),P. h. carolinensis averaging 1.7 kg (3.7 lb) andP. h. cristatus averaging 1.25 kg (2.8 lb). Thewing chord measures 38 to 52 cm (15 to 20 in), the tail measures 16.5 to 24 cm (6.5 to 9.4 in) and the tarsus is 5.2–6.6 cm (2.0–2.6 in).[27][28]
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.[29] The irises of the eyes are golden to brown, and the transparent nictitating membrane is pale blue. The bill is black, with a bluecere, and the feet are white with black talons.[26] On the underside of the wings the wrists are black, which serves as afield mark.[30] A short tail and long, narrow wings with four long, finger-like feathers, and a shorter fifth, give it a very distinctive appearance.[31]
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.[31]
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.[29]
In flight, the osprey has arched wings and drooping "hands", giving it agull-like appearance. The call is a series of sharp whistles, described ascheep, cheep, oryewk, yewk. If disturbed by activity near the nest, the call is a frenziedcheereek![32]
The osprey is the second most widely distributed raptor species, after theperegrine falcon, and is one of only six land-birds with a worldwide distribution.[33] It is found in temperate and tropical regions of all continents, exceptAntarctica. In North America it breeds fromAlaska andNewfoundland south to theGulf Coast andFlorida, wintering further south from the southern United States through to Argentina.[34] It is found in summer throughout Europe north into Ireland, Scandinavia, Finland and Great Britain though not Iceland, and winters inNorth Africa.[35] In Australia it is mainlysedentary and found patchily around the coastline, though it is a non-breeding visitor to easternVictoria andTasmania.[36]
The osprey ispiscivorous, with fish making up 99% of its diet.[41] It typically takes live fish weighing 150–300 g (5.3–10.6 oz) and about 25–35 cm (9.8–13.8 in) in length, but virtually any type of fish from 50 g (1.8 oz) to 2 kg (4.4 lb) can be taken.[27] Even larger 2.8 kg (6.2 lb)northern pike (Esox lucius) has been taken inRussia.[42] The species rarely scavenges dead or dying fish.[43]
Ospreys have a vision that is well adapted to detecting underwater objects from the air. Prey is first sighted when the osprey is 10–40 m (33–131 ft) above the water, after which the bird hovers momentarily and then plunges feet first into the water.[44] 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 byrefraction. Ospreys will typically eat on a nearby perch but have also been known to carry fish for longer distances.[45]
The osprey has severaladaptations that suit its piscivorous lifestyle. These include reversible outer toes,[49] sharpspicules on the underside of the toes,[49] closable nostrils to keep out water during dives, backward-facing scales on the talons which act as barbs to help hold its catch and dense plumage which is oily and prevents its feathers from getting waterlogged.[50]
Eurasian osprey standing next to its nest showing their relative sizes
The osprey breeds near freshwater lakes and rivers, and sometimes on coastal brackish waters. Rocky outcrops just offshore are used inRottnest Island off the coast ofWestern 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.[41][51] As wide as 2 meters and weighing about 135 kg (298 lb), large nests on utility poles may befire hazards and have causedpower outages.[52]
Generally, ospreys reach sexual maturity and begin breeding around the age of three to four, though in some regions with high osprey densities, such asChesapeake 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.[53] The nesting platform design developed by the organizationCitizens United to Protect the Maurice River and Its Tributaries, Inc. has become the official design of theState 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.[54] There is a global site for mapping osprey nest locations and logging observations on reproductive success.[55]
Ospreys usually mate for life. Rarely,polyandry has been recorded.[56] The breeding season varies according to latitude: spring (September–October) in southern Australia, April to July in northern Australia, and winter (June–August) in southern Queensland.[51] In spring, the pair begins a five-month period of partnership to raise their young. The female lays two to foureggs 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 (2.4 in × 1.8 in) and weigh about 65 g (2.3 oz).[51] The eggs are incubated for about 35–43 days to hatching.[57]
The newly hatched chicks weigh only 50–60 g (1.8–2.1 oz), but fledge in 8–10 weeks. A study onKangaroo 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.[56] 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.[citation needed] The oldest European wild osprey on record lived to be over thirty years of age.[citation needed]
European breeders winter in Africa.[58] American and Canadian breeders winter in South America, although some stay in the southernmost U.S. states such asFlorida andCalifornia.[59] Some ospreys from Florida migrate to South America.[60]Australasian ospreys tend not tomigrate.
Studies of Swedish ospreys showed that females tend to migrate to Africa earlier than 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 during the day, they sometimes fly in the dark hours, particularly in crossings over water and cover on average 260–280 km (160–170 mi) per day with a maximum of 431 km (268 mi) per day.[61] European birds may also winter in South Asia, as indicated by an osprey tagged in Norway being monitored in western India.[62] In the Mediterranean, ospreys show partial migratory behaviour with some individuals remaining resident, whilst others undertake relatively short migration trips.[63]
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.[64] These deaths can also be categorized into spatial patterns: Spring mortality occurs mainly in Africa, which can be traced to crossing theSahara desert. Mortality can also occur through mishaps with human utilities, such as nesting near overhead electric cables or collisions with aircraft.[65]
Adult American ospreys on a man-made nest in New Jersey, US
The osprey has a large range, covering 9,670,000 km2 (3,730,000 sq mi) 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 (i.e., declining more than 30% in ten years or three generations), and for these reasons, the species is evaluated asLeast Concern.[1] There is evidence for regional decline in South Australia where former territories at locations in theSpencer Gulf and along the lowerMurray River have been vacant for decades.[37]
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,[66][67] 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 asDDT on reproduction.[68] The pesticide interfered with the bird'scalcium metabolism which resulted in thin-shelled, easily broken or infertile eggs.[34] Possibly because of the banning of DDT in many countries in the early 1970s, together with reduced persecution, the osprey, as well as other affectedbird of prey species, have made significant recoveries.[41] In South Australia, nesting sites on theEyre Peninsula andKangaroo Island are vulnerable to unmanaged coastal recreation and encroaching urban development.[37]
The Roman writerPliny the Elder reported that parent ospreys made their young fly up to the sun as a test, and dispatched any that failed.[69]
Another odd legend regarding this fish-eating bird of prey, derived from the writings ofAlbertus Magnus and recorded inHolinshed'sChronicles, was that it had one webbed foot and one taloned foot.[67][70]
The osprey is mentioned in the famous Chinese folk poem "guan guan ju jiu" (關關雎鳩); "ju jiu" 雎鳩 refers to the osprey, and "guan guan" (關關) to its voice. In the poem, the osprey is considered to be an icon of fidelity and harmony between wife and husband, due to its highly monogamous habits. Some commentators have claimed that "ju jiu" in the poem is not the osprey but themallard duck, since the osprey cannot make the sound "guan guan".[71][72]
The Irish poetWilliam Butler Yeats used a grey wandering osprey as a representation of sorrow inThe Wanderings of Oisin and Other Poems (1889).[69]
There was a medieval belief that fish were so mesmerised by the osprey that they turned belly-up in surrender,[67] and this is referenced byShakespeare in Act 4 Scene 5 ofCoriolanus:
I think he'll be to Rome As is the osprey to the fish, who takes it By sovereignty of nature.
Inheraldry, the osprey is typically depicted as a white eagle,[70] often maintaining a fish in its talons or beak, and termed a "sea-eagle". It is historically regarded as a symbol of vision and abundance; more recently it has become a symbol of positive responses to nature,[67] and has been featured on more than 50 internationalpostage stamps.[73]
In 1994, the osprey was declared the provincial bird ofNova Scotia, Canada.[74]
The osprey pictured in the coat of arms ofSääksmäki
"Seahawks", another term for osprey, is also common among sports teams. TheSeattle Seahawks, a professionalAmerican football team in theNational Football League, received their identity from a naming contest, defeating 1,740 others.[76] According to team general managerJohn Thompson, the name "shows aggressiveness, reflects our soaring Northwest heritage and belongs to no other major league team."[77]
So-called "osprey" plumes were an important item in theplume trade of the late 19th century and used in hats including those used as part of the army uniform. Despite their name, these plumes were actually obtained fromegrets.[78]
During the 2017 regular session of theOregon Legislature, there was a short-lived controversy over thewestern meadowlark's status as the state bird versus the osprey. The sometimes-spirited debate included state representativeRich Vial playing the meadowlark's song on his smartphone over the House microphone.[79] A compromise was reached in SCR 18,[80] which was passed on the last day of the session, designating the western meadowlark as the statesongbird and the osprey as the stateraptor.
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