Eastern osprey

Eastern osprey
Not evaluated (IUCN 3.1)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Accipitriformes
Family: Pandionidae
Genus: Pandion
Species: P. cristatus
Binomial name
Pandion cristatus
(Vieillot, 1816)

The eastern osprey (Pandion cristatus) is a diurnal, fish-eating bird of prey. It is a large raptor, 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.

Most taxonomic authorities lump this species and the western osprey together (called the osprey), but some (including the International Ornithologists' Union) separate them.

The eastern osprey is found from Sulawesi to Australasia, Solomon Islands, and New Caledonia. It is generally non-migratory.

The eastern osprey tolerates a wide variety of habitats, nesting in any location near a body of water providing an adequate food supply.

As its other common names suggest, the eastern osprey's diet consists almost exclusively of fish. It possesses specialised physical characteristics and exhibits unique behaviour to assist in hunting and catching prey. As an osprey, it is part of the taxonomic genus, Pandion and family, Pandionidae.

Taxonomy and systematics

The genus Pandion was described by the French zoologist Marie Jules César Savigny in 1809.[1]

The eastern 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 eastern and western 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.[2] Some 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 results in an unnatural paraphyletic classification.[3]

Description

The eastern 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 the Buteo or Falco genera. The eastern osprey averages 1.25 kg (2.8 lb). The wing 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).[4][5] 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.[6] 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.[2] A short tail and long, narrow wings with four long, finger-like feathers, and a shorter fifth, give it a very distinctive appearance.[7]

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.[7]

The juvenile eastern 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.[6]

In flight, the eastern 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![8]


Distribution and habitat

In Australia it is mainly sedentary and found patchily around the coastline, though it is a non-breeding visitor to eastern Victoria and Tasmania.[9] There is a 1,000 km (620 mi) 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.[10]

Behaviour and ecology


Diet

Fish make up 99% of the eastern osprey's diet.[11] It typically takes fish weighing 150–300 g (5.3–10.6 oz) and about 25–35 cm (9.8–13.8 in) in length, but the weight can range from 50 g (1.8 oz) to 2 kg (4.4 lb). 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 eastern osprey is 10–40 m (33–131 ft) above the water, after which the bird hovers momentarily then plunges feet first into the water.[12]

Adaptations

The osprey has several adaptations that suit its piscivorous lifestyle :

  • reversible outer toes,[13]
  • sharp spicules on the underside of the toes,[13]
  • closable nostrils to keep out water during dives, and
  • backwards-facing scales on the talons which act as barbs to help hold its catch.
  • dense plumage which is oily and prevents its feathers from getting waterlogged.[14]

Reproduction

The eastern 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.[11][15] Nests can be as wide as 2 meters and weighing about 135 kg.

Generally, eastern ospreys reach sexual maturity and begin breeding around the age of three to four.

Eastern ospreys usually mate for life. Rarely, polyandry has been recorded.[16] 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.[15] 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 (2.4 in × 1.8 in) and weigh about 65 g (2.3 oz).[15] The eggs are incubated for about 35–43 days to hatching.[17]

The newly hatched chicks weigh only 50–60 g (1.8–2.1 oz), 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.[16] 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.

Status and conservation

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.[10]

In South Australia, nesting sites on the Eyre Peninsula and Kangaroo Island are vulnerable to unmanaged coastal recreation and encroaching urban development.[10]

In New South Wales, the osprey is a protected species. For this reason, Conservationists cannot move a nest of ospreys from the bottom left light tower of Central Coast Stadium.

References

  1. ↑ Graves, R. (1955). "The Sons of Pandion". Greek Myths. London: Penguin. pp. 320–323. ISBN 0-14-001026-2.
  2. 1 2 Terres, J.K. (1980). The Audubon Society Encyclopedia of North American Birds. New York, NY: Knopf. pp. 644–646. ISBN 0-394-46651-9.
  3. ↑ Salzman, Eric (1993). "Sibley's Classification of Birds". Birding. 58 (2): 91–98. Retrieved 5 September 2007.
  4. ↑ Ferguson-Lees, J.; Christie, D.A. (2001). Raptors of the World. Houghton Mifflin Company. ISBN 978-0-618-12762-7.
  5. ↑ "Osprey". All About Birds. Cornell Lab of Ornithology. – P. h. carolinensis
  6. 1 2 "Osprey" (PDF). Connecticut Department of Environmental Protection. 1999. Archived from the original (PDF) on 10 June 2012. Retrieved 30 September 2007.
  7. 1 2 Forsman, Dick (2008). The Raptors of Europe & the Middle East: A Handbook of Field Identification. Princeton University Press. pp. 21–25. ISBN 0-85661-098-4.
  8. ↑ Peterson, Roger Tory (1999). A Field Guide to the Birds. Houghton Mifflin Company. p. 136. ISBN 978-0-395-91176-1.
  9. ↑ Simpson, K.; Day, N.; Trusler, P. (1993). Field Guide to the Birds of Australia. Ringwood, Victoria: Viking O'Neil. p. 66. ISBN 0-670-90478-3.
  10. 1 2 3 Dennis, T.E. (2007). "Distribution and status of the Osprey (Pandion haliaetus) in South Australia". Emu. 107 (4): 294–299. doi:10.1071/MU07009.
  11. 1 2 Evans, D.L. (1982). "Status Reports on Twelve Raptors: Special Scientific Report Wildlife" (238). U.S. Department of the Interior, Fish and Wildlife Service.
  12. ↑ Poole, A.F.; Bierregaard, R.O.; Martell, M.S. (2002). Poole, A.; Gill, F., eds. Osprey (Pandion haliaetus). The Birds of North America. Philadelphia, PA: The Birds of North America, Inc.
  13. 1 2 Clark, W.S.; Wheeler, B.K. (1987). A field guide to Hawks of North America. Boston: Houghton Mifflin. ISBN 0-395-36001-3.
  14. ↑ "Pandion haliaetus Linnaeus Osprey" (PDF). Michigan Natural Features Inventory. Retrieved 11 May 2016.
  15. 1 2 3 Beruldsen, G. (2003). Australian Birds: Their Nests and Eggs. Kenmore Hills, Queensland. p. 196. ISBN 0-646-42798-9.
  16. 1 2 Dennis, T.E. (2007). "Reproductive activity in the Osprey (Pandion haliaetus) on Kangaroo Island, South Australia". Emu. 107 (4): 300–307. doi:10.1071/MU07010.
  17. ↑ Poole, Alan F. Ospreys, A Natural and Unnatural History 1989

Further reading

  • Wink, M.; Sauer-Gürth, H.; Witt, H.H. (2004). "Phylogenetic differentiation of the Osprey Pandion haliaetus inferred from nucleotide sequences of the mitochondrial cytochrome b gene" (PDF). In Chancellor, R.D.; Meyburg, B.-U. Raptors Worldwide. Berlin: World Working Group on Birds of Prey and Owls. pp. 511–516. ISBN 963-86418-1-9.
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