The leading bird charity has been recruited to the fight to save Scotland's red squirrel population, as signs grow of a fragile recovery of this threatened species which is native to Britain.

RSPB Scotland has joined has joined forces with five other charitable, government and landowning bodies in a bid to secure the future of the iconic woodland mammal, through the pioneering Saving Scotland's Red Squirrels (SSRS) project launched in 2009.

The red squirrel is the UK's only native squirrel and numbers have declined rapidly since the introduction of grey squirrels from North America in the 19th Century.

Since 1952, 95% of red squirrels in England and Wales have been wiped out, and today 75% of the UK's remaining population is found in Scotland, around 120,000. However, greys still threaten the existence of the native reds because they compete for food and habitat, and transmit the deadly squirrelpox virus.

The SSRS project aims to continue to prevent the spread northwards of grey squirrels and squirrelpox via a programme of grey squirrel control in a zone running coast to coast along the Highland Boundary Fault. It is also mapping priority areas for red squirrel conservation in south Scotland, and co-ordinating the control of grey squirrels.

Over 2013 the Scottish Wildlife Trust (SWT), one of the project partners, analysed records collected by staff, landowners and volunteers.

This data revealed that the collapse in Scottish red squirrel numbers had been halted and there were numerous examples of red squirrels returning to areas from which they had been absent for many years.

But there was a welcome for new arrival to the campaign from SSRS Project Manager Mel Tonkin: "Saving Scotland's Red Squirrels has already been successful in beginning to reverse the downward trend for red squirrels in Scotland, but our work will need to continue for many years to really secure the future of the species. We are therefore delighted with this new partnership with RSPB Scotland."

Dr Aileen McLeod, Minister for Environment, Climate Change and Land Reform, said: "The numbers of red squirrels in Scotland are increasing and are now returning to their former habitats. This has been most notably in the Borders, Dumfries and Galloway, Ayrshire, and the north-east of Scotland where people are once again seeing red squirrels visiting the bird feeders in their gardens."

She said it was due to the important work being carried out by stakeholders such as the SWT, landowners, Forestry Commission Scotland and volunteers who had been undertaking targeted control of grey squirrels.

She was delighted that RSPB Scotland were now involved bringing a wealth of knowledge to the project.

Stuart Housden, Director of RSPB Scotland, said: "We are in the privileged position of owning and managing more than 80 nature reserves across Scotland, and we already posses a huge responsibility for delivering on the conservation of our native red squirrels."

He said RSPB had been impressed by the work of the SSRS project, as it represented the best chance of preventing the extinction of this species on the British mainland.

"We are really pleased not only to be joining forces with the member organisations to help contribute to this important work, but also to commit hard-won charitable funds to this excellent project. We are looking forward to a very productive and constructive partnership," he said.