All who knew opera-loving Mona Webster during her long and varied life were aware she was a lady of unusual cultural refinement and breadth of interests.

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Widely accomplished in horticulture and needlework, the lighthouse keeper’s daughter's travels in pursuit of rare birds had taken her to the furthest reaches of every continent, often sleeping under canvas in defiance of the advancing years.

So it was with her love of music – a passion which would see her journey to New York well into old age for performances at her favourite opera house.

She died in her adopted city of Edinburgh in August this year aged 96.

It has emerged that the former civil servant left an incredible legacy to her twin passions of music and wildlife, giving away the £10m fortune she had built up through canny investments dating back decades.

Friends and family of the late widow were reported to be stunned at her altruism today when it was revealed that she had left £4.5m to New York’s Metropolitan Opera House and £4.4m to the Wildfowl and Wetlands Trust, the charity established by the naturalist and artist Sir Peter Scott.

She donated £100,000 to the Royal Opera Trust in London’s Covent Garden and the same amount to the Royal National Lifeboat Institution.

Her £550,000 home was left to friends while a further £825,000 was given away in donations and gifts.

A friend of the family described the former Inland Revenue worker as a “very modest person” who would be deeply missed. “Everybody knew about Mona’s love of opera and birdwatching, but the family are stunned at the level of generosity given to these two causes,” the friend said. “Mona was a kind and caring person, and her friends and family I’m sure will be delighted her legacy will live on through her sizeable donations.”

Much of her wealth was tied up in shares, including more than £1m in the American soft drinks maker Dr Pepper.

Among the talks she used to give describing her experiences was one on how to self-manage one’s finances. Her late husband Ted Webster had been the investment manager at Scottish Union and National before his death in 1981.

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The couple had no children and devoted their considerable energies to their many hobbies during 40 years of married life, friends said. She was often heard to tell acquaintances: “There just aren’t enough hours in the day for all my interests.”

Mrs Webster’s love of birds had grown from her childhood living with her parents at Douglas Head Lighthouse in the Isle of Man and later moving to Orkney where she recalled lying on the heather enjoying the distinctive call of the skylarks as they soared in the air above her. She went on to catalogue 5,500 species of bird during her travels.

A head for figures and an impressive memory marked her out for the civil service and she was transferred to wartime London to serve at the tax office then at Somerset House only narrowly surviving the German bombs of the Blitz.

After moving to Edinburgh she and her husband became known for their garden, which was famous for its camelias, roses, azaleas and hydrangeas.

A spokesman for Metropolitan Opera paid tribute to the Scottish benefactor today. “Mrs Webster was a long-time friend of the Met and a generous donor. She did visit the Met occasionally, and she will be greatly missed by those who had the privilege of knowing her,” he said.

David Salmon, from the Wildlife and Wetlands Trust, said: “We are extremely appreciative when this kind of provision is made for us. The donation will go towards preserving wetlands for wildlife and people. It is a remarkable gesture.”