The bird, named NC0, has bucked the breeding trend for younger ospreys, much to the delight of the Scottish Wildlife Trust (SWT).
NC0 laid the egg at SWT’s Loch of the Lowes reserve near Dunkeld, Perth and Kinross, at around 7.40am yesterday.
Ringed as a chick near Loch Ness in 2016, her 13-year-old mate LM12 has been breeding at Loch of the Lowes for ten seasons.
Sara Rasmussen, Scottish Wildlife Trust Perthshire ranger, said: “Younger ospreys tend to be less productive so we thought that NC0 might stop at two eggs this year, but we’re really pleased that she has laid three eggs in her second season on the reserve.
“We can’t wait to see the chicks hatch out next month. Our team of staff and volunteers are monitoring the reserve around the clock to help ensure these ospreys have a safe and secure nesting site.
“I’d like to remind people that accessing the loch can disturb the birds at a critical point in their breeding season.
“We’d encourage members of the public to follow the Scottish Outdoor Access Code and pay attention to any warning signs that are in place to help protect wildlife.”
Osprey eggs are the same size as large hen eggs and hatch around five to six weeks after they are laid. NC0’s eggs are expected to hatch in mid to late May.
Ospreys were extinct in Britain for much of the 20th century but began to recover in the 1960s.
Today, an estimated 300 pairs breed in the UK each summer.
The recovery of NC0’s latest egg is thanks to the efforts of conservation charities including SWT, whose osprey protection programme is supported by the players of People’s Postcode Lottery.
A live osprey webcam run by SWT ensures people from around the world can follow events as they happen.
Will Humpington, People's Postcode Lottery advisor for climate change and environment, said: “I’m thrilled to learn that NC0 has laid a full clutch of three eggs under the watchful eyes of the Scottish Wildlife Trust’s team.
“Our players are proud to support the Trust’s Osprey Protection Programme and we’re looking forward to seeing the chicks hatch out in a few weeks’ time.”