Helicopters have become a common sight in the skies above Scotland's mountains as they fly in to rescue stricken hillwalkers.

Now the aircraft are being hired by conservationists as part of a major new bid to help save the country's most popular munros from the thousands of hikers whose feet have been causing severe erosion to high level paths.

The National Trust for Scotland launched the new initiative at Ben Lomond where around 100 tonnes of stone has just been winched to the summit and other badly scarred areas along the ridgeway.

More than 30,000 people walk up to the summit of the iconic hill beside Loch Lomond each year, including growing numbers of fundraisers on group sponsored walks, whose efforts combined with wind and rain can be hugely damaging to fragile hilltop vegetation.

The day-long £12,000 airlift, which was done last week, will enable the Trust's footpath repair team to triple the speed at which they can restore the mountain tops in future by saving them from the time-consuming task of searching for sufficient rocks and gravel among dwindling natural resources on the slopes.

It is the first key work to be carried out under the charity's new £150,000 Footpath Fund campaign to help preserve more than 400 miles of paths across dozens of Scotland's highest peaks.

Bob Brown, the Trust’s upland path manager, said: “Hiring a helicopter for a day is expensive but it is cost-effective because it means our footpath team can spend more time on repairs, rather than transporting materials around the hill.

“It could take two people all day at least to dig out a single tonne of stone on the hillside and then one person another day to shift that stone to the repair site.

“The team could usually do a metre a day of path repairs if they were gathering stone in this way. Flying it in means they can do around three metres per day instead."

The Trust owns more land in Scotland than any other conservation body, with 188,000 acres of key countryside including more than 40 munros - peaks of 3000 feet or more.

Helicopters have been used to deliver stone for high altitude path repairs before but only for short term projects. The amount dropped on Ben Lomond is expected to be enough to provide material for ongoing repairs for at least the next decade.

Maintenance of the mountain path network costs the charity £200,000 annually, most of which comes from fundraising and membership fees.

Just over £63,000 has been raised since the Foothpath Fund was launched in August. The campaign includes a landscape version of selfies, dubbed landsies, where supporters are urged to take pictures of their favourite views and make donations.

Further work will be carried out at Glencoe and Torridon next year under the initiative.

The Ben Lomond airlift was jointly funded by Scottish Natural Heritage which said it was “crucial” for preserving the much-walked mountain.

Fiona Cuninghame, SNH recreation and access officer, said: “Ben Lomond is one of Scotland’s most popular mountain paths, heavily used by many people in the central belt and visitors to the Loch Lomond & The Trossachs National Park.”