Pairs of white-tailed sea eagles in Scotland produced more young during 2010 than in any other year since they were reintroduced 35 years ago.
RSPB Scotland said 46 young birds fledged which was 10 more than the previous year.
Scotland also has 52 adult pairs, an increase of six on 2009 figures, according to the charity.
The birds were first reintroduced to Rum in 1975, but can now also be found in Fife.
And last year, a sea eagle was spotted over Cumbria and Dumfries and Galloway after it flew down from Fife.
It was seen over the Solway coast near Carlisle and later above Annan in southern Scotland.
The UK's largest bird of prey was hunted to extinction over the 19th and 20th Centuries and new birds had to be taken from countries such as Norway for release in Scotland.
Environment Minister Roseanna Cunningham said the record increase in numbers was fantastic.
She said: "2010 is a significant year in that it is the 25th anniversary of the first young to be reared in Scotland since its extinction in the early 20th Century, and it is also the Year of International Biodiversity.
"I have no doubt that the successful reintroduction of this magnificent bird can continue, and along with the East Coast Sea Eagle Project, ensures that this species can establish territories right across Scotland, restoring a strong Scotland-wide population."
The east coast project involves the RSPB, Scottish Natural Heritage and Forestry Commission Scotland.
Stuart Housden, director of RSPB Scotland, said a huge number of people had helped with the reintroduction programme.
He added: "Achieving the milestone of 50 pairs puts the species well on track to reaching pre-Victorian population levels - and this has only been possible due to the invaluable support of farmers, crofters, foresters and countless others in communities up and down Scotland."
Ron Macdonald, from Scottish Natural Heritage, said it was a joy to see the large birds in flight.
In May this year the results of a study on sea eagles and their link to the deaths of young lambs were released.
It suggested the birds have a "minimum impact" on lambs' chances of survival.
The fortunes of selected lambs in three flocks in Wester Ross were monitored to help determine whether large numbers of livestock fall prey to the raptors.
Crofters in the area and on Skye had claimed the birds fed on their stock.
Scottish Natural Heritage, which commissioned the study, said less than 2% of lambs' deaths were directly linked to the birds.