Lady, oldest osprey in the UK, is preparing to mate in Dunkeld, Scotland, after travelling thousands of miles from the Gambia

One of the world's oldest ospreys, which has already laid 58 eggs and seen 48 chicks leave her nest, has returned to her roost in the Highlands, breaking her own record for longevity.

The osprey known as Lady, pictured on Tuesday, landed back in her eyrie at a wildlife reserve near Dunkeld on Monday after completing her 21st migration, ending a round trip of roughly 6,000 miles to and from her winter home in west Africa. And despite living three times as long as most breeding females, the 26-year-old bird of prey is again by her nest – now grown to the size of a double bed – preparing for her mate.

She is already a global celebrity after a crisis last June when she nearly died from dehydration and starvation after she failed to feed for several days. Tens of thousands of birdwatchers from around the world saw live pictures from the "nest cam" at the Loch of the Lowes reserve which showed Lady weak and listless. She survived and flew off for her 3,000-mile flight to the Gambia; staff at the Scottish Wildlife Trust reserve suspected it would be her last.

Robert Potter, the trust's regional manager, was delighted when her identity was confirmed on Monday by expert ornithologists, thanks to a close-up of one of her eyes, which has a distinctive keyhole shape on its iris. "It's fantastic. It just shows what an amazing bird she is, to make that journey at this age," he said. "She's looking very healthy and is going about her business of tidying up her nest and getting everything ready."

Lady is already confirmed as the oldest wild osprey in Britain and probably the oldest known in the world. The species normally lives to about 10 in the wild, while the oldest recorded osprey in the world reached 32.

But as mother to 48 successful fledglings, Lady's productivity has played a crucial role in the species' survival. Nearly 100 years after it was brought back from near extinction in the UK, there are still only about 200 breeding pairs in Scotland, making the osprey rarer than the golden eagle.

Her arrival home has again provoked worldwide interest. Viewings on Lady's nest cam have been five times higher than usual over the last 24 hours, with fans from as far away as Australia, Canada, Belize and Mauritius logging on.

The key question is whether her mate will return. Several ospreys, including at least one young male, have come close over the last 24 hours but all flew off. If no mate appears in the next week, her breeding chances this year may be over.