page_title: Osprey
section_title: Reproduction
hierarchical_section_title: Osprey / Behaviour and ecology / Reproduction
caption_attribution_description: English: Osprey with its nest. Photographed from a tiny island near to Abu Dhabi City.
context_page_description: The osprey or more specifically the western osprey — also called 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 60 cm in length and 180 cm across the wings. It is brown on the upperparts and predominantly greyish on the head and underparts.
  The osprey tolerates a wide variety of habitats, 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-breeding migrant.
  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 catching prey. As a result of these unique characteristics, it has been given its own taxonomic genus, Pandion and family, Pandionidae. Three subspecies are usually recognized; one of the former subspecies, cristatus, has recently been given full species status and is referred to as the eastern osprey.
context_section_description: 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 U.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. In some regions ospreys prefer transmission towers as nesting sites, e.g. in East Germany.
  The 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 platform plans and materials list, available online, have been utilized by people from a number of different geographical regions. Osprey-watch.org 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 (September–October) in southern Australia, April to July in northern Australia and winter (June–August) 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 (2.4 in × 1.8 in) and weigh about 65 g (2.3 oz). The eggs are incubated for about 35–43 days to hatching.
  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. 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), and bald eagles (Haliaeetus leucocephalus) 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 (Haliaeetus albicilla), which is very similar to the bald eagle, may harass or prey on the osprey in Eurasia. Raccoons (Procyon lotor) can be a serious threat to nestlings or eggs if they can access the nest. Endoparasitic trematodes (Scaphanocephalus expansus and Neodiplostomum spp.) have been recorded in wild ospreys.
caption: Osprey standing next to its nest showing their relative sizes
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