Age at first breeding

3-5 years

Number of eggs

Usually 3

Size of eggs (mm)

Incubation period

Fledging period

Chicks

A young Osprey spends the first seven or eight weeks of its life confined within the nest (or eyrie), a huge pile of sticks lined with moss, bark and grass. It will be fed primarily by the female who tears pieces from a fish and passes them into the nest.

By two weeks the youngsters can move around the nest and after a month they are very active, preening and exercising their wings. Gradually the wing-flapping increases until they are able to lift a little off the nest and then take their hesitant first flight.

The young Ospreys on the right are about five weeks old and have been brought down from their nest to be ringed.

Juveniles

For at least two weeks after fledging, the young Ospreys return to their nest for food brought in by the adults.

Usually the young stay in the area near the nest as they improve their skill in the air and then begin to make attempts to catch fish for themselves.

Returning to breed

Experienced adult birds leave West Africa and head north to the breeding areas again in March. However, younger birds do not reappear at the sites from which they fledge for several years. Sometimes they return when they are 2 years old, but do not usuaslly begin to breed until they are 3 to 5 years old. Often a pair will build a nest and establish a territory in the first year, returning to breed the following year.

Ospreys, especially the males, usually return to breed in the area in which they fledged. This explains the relatively slow expansion of range in Scotland and is why translocation of young birds before they fledge has proved so successful.

Ospreys generally mate for life and the older, experienced birds usually arrive back in the nesting area first with established pairs nearly always returning to their previous nest sites. New pairs must find new sites when thay arrive and often have difficulty finding a suitable natural site to hold the nest, which will often be over a metre wide. They usually choose a site within 3-5 kilometres of water and prefer to have an open area around the future nest so as to have easy access when landing. Flat-topped trees are the most likely natural site but Ospreys take readily to man-made structures such as pylons, as well as artificial nests like those at Rutland Water

Eggs and incubation

Female Ospreys begin to lay their eggs in late April. The eggs are beautifully blotched reddish-brown and are about the same size as a large hen's egg. They are produced at two-day intervals. Novice breeders will usually lay two eggs; more experienced birds lay three and, just occasionally four.

Both adults will take part in the long incubation process but the female takes the major part with the male providing her with food and chasing away any potential predators.

Until fledging the female stays on or close to the nest site but after the young have fledged she joins the male in bringing food back to the nest site. Ultimately the young become independent hunters and the adults' role as parents and providers is finished.