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Theospreyor more specifically thewestern osprey(Pandion haliaetus) — also calledsea hawk,river hawk, andfish hawk— is adiurnal,fish-eatingbird of preywith 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 exhibits unique behaviour to assist in hunting and catchingprey. As a result of these unique characteristics, it has been given its owntaxonomicgenus,Pandionandfamily, Pandionidae. Threesubspeciesare usually recognized; one of the former subspecies,cristatus, has recently been given full species status and is referred to as theeastern osprey.
The osprey was one of the many species described byCarl Linnaeusin his 18th-century work,Systema Naturae, and named asFalco haliaeetus.[2]The genus,Pandion, is the sole member of the family Pandionidae, and used to contain only one species, the osprey (P. haliaetus). The genusPandionwas described by the French zoologistMarie Jules César Savignyin 1809.[3][4]
Most taxonomic authorities consider the species cosmopolitan and conspecific. A few authorities split the osprey into two species, thewestern ospreyand theeastern osprey.
The osprey differs in several respects from otherdiurnalbirds of prey. Its toes are of equal length, itstarsiare 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.[5]It has always presented something of a riddle to taxonomists, but here it is treated as the soleliving memberof the family Pandionidae, and the family listed in its traditional place as part of the orderFalconiformes.
The osprey is unusual in that it is a single living species that occurs nearly worldwide. Even the fewsubspeciesare not unequivocally separable. There are four generally recognised subspecies, although differences are small, andITISlists only the first two.[3]
P. haliaetus carolinensis–(Gmelin, 1788):North America. This form is larger, darker bodied and has a paler breast than the type of the first description.[7]
P. haliaetus ridgwayi–Maynard, 1887:Caribbeanislands. This form has a very pale head and breast compared with nominatehaliaetus, with only a weak eye mask.[7]It is non-migratory. Its scientific name commemorates AmericanornithologistRobert Ridgway.[8]
The oldest recognized family Pandionidae fossils have been recovered from the Oligocene ageJebel Qatrani Formation, ofFaiyum,Egypt. However they are not complete enough to assign to a specific genus.[12]Another Pandionidae claw fossil was recovered fromEarly Oligocenedeposits in theMainzbasin,Germany, and was described in 2006 byGerald Mayr.[13]
The osprey is 0.9–2.1 kg (2 lb 0 oz–4 lb 10 oz) in weight and 50–66 cm (191⁄2–26 in) in length with a 127–180 cm (50–71 in) wingspan. It is, thus, of similar size to the largest members of theButeoorFalcogenera. The subspecies are fairly close in size, with the nominate subspecies averaging 1.53 kg (3 lb 6 oz),P. h. carolinensisaveraging 1.7 kg (3 lb 12 oz) andP. h. cristatusaveraging 1.25 kg (2 lb 12 oz). The wing chord measures 38 to 52 cm (15 to201⁄2 in), the tail measures 16.5 to 24 cm (61⁄2to91⁄2 in) and the tarsus is 5.2–6.6 cm (2–25⁄8 in).[20][21]
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.[22]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.[5]A short tail and long, narrow wings with four long, finger-like feathers, and a shorter fifth, give it a very distinctive appearance.[23]
In flight, Northern Territory, Australia
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.[23]
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.[22]
In flight, the osprey has arched wings and drooping "hands", giving it agull-likeappearance. The call is a series of sharp whistles, described ascheep, cheeporyewk, yewk. If disturbed by activity near the nest, the call is a frenziedcheereek![24]
The osprey ispiscivorous, with fish making up 99% of its diet.[33]It typically takes fish weighing 150–300 g (51⁄2–101⁄2 oz) and about 25–35 cm (10–14 in) in length, but the weight can range from 50 g (2 oz) to 2 kg (4 lb 7 oz). 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 (33–131 ft) above the water, after which the bird hovers momentarily then plunges feet first into the water.[34]They catch fish by diving into a body of water, often times 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.[35]
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 Islandoff 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.[33][40]As wide as 2 meters and weighing about 135 kg, large nests on utility poles may befire hazardsand have causedpower outages.[41]
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 Bayin theU.S., 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.[42]In some regions ospreys prefer transmission towers as nesting sites, e.g. in East Germany.[43]
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 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.[44]Osprey-watch.orgis the global site for mapping osprey nest locations and logging observations on reproductive success.[45]
Ospreys usually mate for life. Rarely,polyandryhas been recorded.[46]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.[40]In spring the pair begins a five-month period of partnership to raise their young. The female lays two to foureggswithin 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 (21⁄2 in × 13⁄4 in) and weigh about 65 g (21⁄4 oz).[40]The eggs are incubated for about 35–43 days to hatching.[47]
The newly hatched chicks weigh only 50–60 g (13⁄4–2 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.[46]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(Bubo virginianus),golden eagles(Aquila chrysaetos), andbald eagles(Haliaeetus leucocephalus) are the only major predators of ospreys, capable of taking both nestlings and adults.[37][48][49][50][51]However,kleptoparasitismby bald eagles, where the larger raptor steals the osprey's catch, is more common than predation. Thewhite-tailed eagle(Haliaeetus albicilla), which is very similar to the bald eagle, may harass or prey on the osprey in Eurasia.[52]Raccoons(Procyon lotor) can be a serious threat to nestlings or eggs if they can access the nest.[53]Endoparasitictrematodes(Scaphanocephalus expansusandNeodiplostomumspp.) have been recorded in wild ospreys.[54]
European breeders winter in Africa.[55]American and Canadian breeders winter in South America, although some stay in the southernmost U.S. states such asFloridaandCalifornia.[56]Some ospreys from Florida migrate to South America.[57]Australasianospreys tend not tomigrate.
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 (160–170 mi) per day with a maximum of 431 km (268 mi) per day.[58]European birds may also winter in South Asia, indicated by an osprey tagged in Norway being monitored in western India.[59]In the Mediterranean, ospreys show partial migratory behaviour with some individuals remaining resident, whilst others undertake relatively short migration trips.[60]
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.[61]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 nearelectrical wiringor collisions with aircraft.[62]
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 as Least Concern.[1]There is evidence for regional decline in South Australia where former territories at locations in theSpencer Gulfand along the lowerMurray Riverhave been vacant for decades.[28]
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,[37][63]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 asDDTon reproduction.[64]The pesticide interfered with the bird'scalciummetabolism which resulted in thin-shelled, easily broken or infertile eggs.[25]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 preyspecies, have made significant recoveries.[33]In South Australia, nesting sites on theEyre PeninsulaandKangaroo Islandare vulnerable to unmanaged coastal recreation and encroaching urban development.[28]
The Roman writerPliny the Elderreported that parent ospreys made their young fly up to the sun as a test, and dispatched any that failed.[65]
Another odd legend regarding this fish-eating bird of prey, derived from the writings ofAlbertus Magnusand recorded inHolinshed'sChronicles, was that it had one webbed foot and one taloned foot.[63][66]
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".[67][68]
The Irish poetWilliam Butler Yeatsused a grey wandering osprey as a representation of sorrow inThe Wanderings of Oisin and Other Poems(1889).[65]
There was a medieval belief that fish were so mesmerised by the osprey that they turned belly-up in surrender,[63]and this is referenced byShakespearein 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.
In Buddhism, the osprey is sometimes represented as the "King of Birds", especially in'The Jātaka: Or, Stories of the Buddha’s Former Births', no. 486.
Inheraldry, the osprey is typically depicted as a white eagle,[66]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,[63]and has been featured on more than 50 internationalpostage stamps.[69]
Ospreys are a common feature of First Nations artwork in the Pacific Northwest, such asKwakwakaʼwakw art. They are often used to depict the mythical two-headed Thunderbird.
So-called "osprey" plumes were an important item in theplume tradeof 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.[71]
Bell Boeing V-22 Osprey, an American tiltrotor military aircraft with both vertical takeoff and landing (VTOL), and short takeoff and landing (STOL) capabilities.
During the 2017 regular session of theOregon Legislature, there was a short-lived controversy over thewestern meadowlark's status as state bird versus the osprey. The sometimes-spirited debate included a legislator playing the meadowlark's song on his smartphone over the House microphone.[72]A compromise was reached in SCR 18,[73]which was passed on the last day of the session, designating the western meadowlark as the statesongbirdand the osprey as the stateraptor.
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