And the RSPB is delighted with the news since just 20 breeding pairs were recorded nationwide in 1980.

Ospreys became a protected species as persecution led to decline in the 19th century. The birds became a popular target for taxidermists, and collectors stole eggs from their nests resulting in extinction as the last recorded breeding took place in Scotland in 1916. Benefiting from protective legislation, ospreys returned to Scotland in 1954 and settled in Aberdeenshire in 1977.

RSPB East Scotland North east Area Manager said: "Ospreys are a fantastic bird and extremely popular. Their increasing numbers are great for the species and it also means that more people can enjoy the chance to see them."

There is only one species of osprey, a specialised fish-eating bird of prey with white or pale mottled underparts and most akin to eagles and buzzards in appearance with a long hook on its bill for tearing fish apart, and specially adapted legs and feet for grasping muscular fish head first, like a torpedo.

Osprey feed on medium sized marine and fresh water fish, catching their prey by gliding and soaring above the water's surface until a near vertical plunge dive with feet thrown forward and wings half folded, results in a catch.

By and large, ospreys are strongly faithful to their lifelong mate and to their eyrie, or nest, which is usually built on top of a large tree though nests also exist on top of man made structures and cliff ledges in coastal areas. Male and female birds share nest duties between them.

The female does most of the incubating, brooding and direct feeding of the young and guards them throughout the nesting period though she will share hunting duties with her mate at the later stages when the chicks have grown. The male provides most of the fish for the female and their young.

The male and female join forces to build their nest, which can be as large as 120-150cm wide and 50-60cm and takes between two and three weeks to build, from materials such as branches, twigs, moss, bark and grass. Returning to the site, and their nest, year after year, these long-lived birds add to the nest, which, over the years, can grow to a depth of 150-200cm.

Incredibly, some nests have been in use for 20 years, though, if a pair of birds fail to breed successfully one year, they often start to build a new nest, and this may then be used again the following year.

The birds arrive from Africa in late March and April. Two or three eggs are laid at one to three day intervals and hatch a few days apart after a 37-day incubation period. After fledging at about 53 days, the male and female both provide the food. The young stay close to the nest for a further two months prior to the flight back to Africa in August or September.

Weather conditions, food shortage, inexperienced parents, nest disturbance and occasional stolen eggs are the most common causes of nest failure and many juvenile birds die before the age of three.

Immature ospreys may return to the UK, pair up and build trial nests at two years though they don't normally breed until at least their third year, and sometimes their fourth or fifth.

One of the most popular places to see ospreys in Scotland is at RSPB Scotland's nature reserve at Loch Garten. The site was specifically purchased for the conservation of ospreys and live CCTV pictures of the nest there can be seen at the centre or via the RSPB website, www.rspb.org.uk/birdsofprey/lochgartenospreynest.asp.

In Aberdeenshire, the best spots are Aboyne Loch, the Ythan Estuary, Lochter Fishery at Oldmeldrum and around the River Don near Inverurie and Kintore. Scottish Natural Heritage supports the work of RSPB Scotland in Aberdeenshire.