An Osprey has been spotted flying over the tarn at RSPB Geltsdale and landing in a tree nearby this week. It is likely to be a young male checking out the area. This impressive bird of prey is listed as a Schedule 1 species under the Wildlife and Countryside Act 1981 and classified as Amber under UK Birds of Conservation Concern. There are currently approximately 240 breeding Osprey pairs in the UK, but this has not always been the case.
When seen in flight from below, Ospreys have white or mottled underparts and long, angled wings which bend at the ‘wrist joint’. At a distance, their shape could lead them to be mistaken for a large gull. They measure between 52 and 60 cm in length, weigh between 1.2 and 2kg and have a wingspan of 145 to 170 cm. Their upperparts are brown and they have chunky, hooked beaks and blue legs.
Ospreys are mainly seen in the UK in Scotland, but can also be seen in the north of England. They can be seen on large bodies of freshwater during their spring and summer migration. They need a habitat which has a large watercourse, such as a river, lake or coastal area, which provides a plentiful supply of medium-sized fish for them to feed on. They fly high above the water to locate fish and can soar up to 70 metres high before plunging downwards with their wings half folded and feet thrown forward at the last moment. This allows them to catch fish in their talons after diving up to a metre into the water. They are able to close their nostrils while they dive to stoop them inhaling water. They then hold the fish head first to carry it back to their perch or nest.
Young Ospreys may return to the UK, form pairs and build trial nests when they are two years old, but they usually only breed for the first time when they are between three and five years old. They are thought to be largely monogamous, forming a bond with both their mate and nest. The nest, called an eyrie, is usually built on top of a tall tree such as a conifer. They may also nest on cliff edges, coastal rocks and electricity pylons. They generally stick to their nest, adding to it each year with branches, twig, moss, bark and grass, and some nests have even been in use for 20 years. If Ospreys fail to breed successfully, they may start to build a new nest, known as a ‘frustration eyrie’, which they may use the following year.
Male and female Ospreys build the nest together, then the female lays two or three eggs at one to three-day intervals then incubates them for 37 days per egg. The chicks will then hatch a few days apart. Ospreys divide the nesting duties between them, with the female incubating the eggs, then feeding and guarding the chicks, while the male hunts for fish for the female and chicks. The female will share the hunting duties once the chicks are old enough to be left alone, then both parents provide food for them after they fledge at around 53 days after hatching.
Many young birds die before they reach maturity at three years old, but those that survive live an average of eight years, although the oldest known Osprey was 32 years old! Ospreys were once found throughout Europe, but were heavily persecuted, mainly by Victorian egg and skin collectors during the 19th and early 20th centuries. The species became extinct as a breeding bird in England in 1840 and in Scotland in 1916, although it was still seen as a passage migrant. It naturally recolonised in 1954, by birds thought to have come from Scandinavia. Recolonisation was very slow at first – by 1976 there were only 14 nesting pairs. Fifteen years later, in 1991, there were 71 pairs, and in 2001 there were 158, mainly in Scotland. 2001 also saw the first successful nesting of Ospreys in England for 160 years, by both recolonising birds in Bassenthwaite in Cumbria and re-introduced ones at Rutland Water.
Although the future looks more positive, Ospreys are still a rare breeding bird in the UK. Conservation aims to increase the population and range of the species, through including a provision for Ospreys in land use policies of currently occupied habitats and ensuring key feeding and nesting requirements are not compromised. Artificial nest sites are also provided by organisations including the RSPB in strategic locations, to encourage Ospreys to nest, and these organisations also work to protect nesting birds from illegal human disturbance.