Scientific name: Pandion haliaetus
Identification
Photo by Laurie Campbell
Ospreys are relatively large, growing to 55-62cm in length, with exceptionally long wings that extend to a span of 145-180cm. The wings are often held in a characteristic ‘W’ shape, making the bird unmistakeable in flight. When compared with other birds of prey in Britain, it appears larger than a buzzard but obviously smaller than a golden eagle. They are dark brown above and white below, and in Britain can sometimes be confused with some of our larger gulls. The breast has a variable brown band, more pronounced in females than males. The head is white with a dark brown band across the eyes. The eyes are yellow, although orange in young ospreys. They weigh 1.2-2kg and males are 5-10% smaller than females.
Habitat and Distribution
Ospreys inhabit a vast array of habitats, including marine, freshwater and brackish. The main requirement is a good supply of medium-sized fish which can be caught from the surface of the water. They are very widely distributed and are found on all five continents. There are thought to be 40-50,000 pairs worldwide.
Global distribution of the osprey (IUCN 2011)
Diet
The osprey’s diet consists solely of fish. The outer toe of their talons is reversible, meaning that prey can be gripped firmly between two talons in front and two behind, and the strong black bill is curved into a hook for tearing up fish. They have a fleshy nostril that closes as it dives into water and their feathers do not have an aftershaft, meaning they can shed droplets of water more easily. On arrival at a fishing site, an osprey will circle the water, usually at a height of 100ft or more. It flies steadily above the surface, with the head swivelling and looking intently at the water. When a fish is spotted, it stops and hovers, then drops halfway to the water and continues to look at the fish. If satisfied, it closes its wings and carries out a most spectacular plunge into the water, at the last moment throwing its outstretched talons directly in front of its head to grab the fish. Experienced ospreys are successful in one out of every four dives.
Ospreys eat any available species of fish but prefer those in the 150-300g weight range. An osprey needs to consume 300-400g of fish per day. They fish in all types of environments, including lakes, rivers, estuaries and coastal waters.
Reproduction
Ospreys are a migratory species, with British ospreys spending the breeding season (March-September) in the UK, then migrating to Africa for the winter. Breeding pairs do not spend the winter together, but meet up once back at the nest site. Ospreys generally build nests at the top of prominent trees, normally conifers, and as they tend to be added to every year, can become quite large. The female lays a clutch of 2-4 eggs, normally 3. Eggs are incubated for 35-37 days, predominantly by the female, with the male hunting for the both of them. Once the chicks hatch the female only leaves the nest for very short periods of time, and the male catches fish for the whole family. The chicks grow quickly and fledge after 51-56 days. About 3 weeks later the female departs for Africa and the male continues to feed the chicks for a further 1-2 weeks. The rest of the family then follow suit, all departing within a few days of each other. The adults return to their breeding quarters the following spring, but juveniles remain in Africa for a year and don’t return to the UK until the spring of their second year.
Status and threats
Globally, the species is listed by the World Conservation Union (IUCN) as ‘Least Concern’. Within Britain they are doing well but remain absent from many of their historic territories. They have difficulty breeding in new areas and are slow to recolonise places where they once thrived, with approximately 60% of adults dying before breeding. Sadly, ospreys are still persecuted and this remains one of the major threats to their survival. Collision with overhead power lines and entanglement in fishing nets are also big dangers.
Within the UK ospreys are strictly protected under Schedule 1 of the Wildlife and Countryside Act 1981 and The Nature Conservation (Scotland) Act 2004. They are also included on the Amber List of conservation concern. It is an offence to intentionally take, injure or kill an osprey or to take, damage or destroy its nest, eggs or young. It is also an offence to intentionally or recklessly disturb the birds close to their nest during the breeding season. Violation can result in a fine of up to £5000 and/or a prison sentence of up to 6 months.
