Ailsa Craig was formed by the heart of an ancient volcano

The island, which sits 12 miles off the south Ayrshire coast, is considered to be one of the most important breeding sites for northern gannets.

The rock is more than 1,000ft high and just over two miles in diameter.

The Royal Society for the Protection of Birds said it hopes to continue the work of encouraging seabirds to return to the island.

About 40,000 pairs of gannet find their home on the island.

Ailsa Craig is also a haven for other seabird species, including guillemot and razorbill.

Since the eradication of rats on the island, puffins have returned, although in smaller numbers than the thousands which once lived there.

RSPB Scotland's regional reserves manager, Alan Lauder, said: "Establishing Ailsa Craig as a reserve is a real coup for the society as the island is internationally renowned for its wildlife and raw beauty.

"We can now continue the work started by others to make sure the puffins and other seabirds re-colonise the island, and the gannets continue to thrive when they return from north west Africa.

"It gives us a fantastic opportunity to tell the UK and the world about our amazing wildlife."

Gannets from north west Africa return to the island

The island is famous as a source of high quality granite, which has been used for the best curling stones.

The RSPB said that granite removed in the past should continue to provide users with high quality stone for many years.

Any further developments, it promised, would be closely monitored to prevent harm to the wildlife or its habitat.

Rat attack

At the end of the 19th century, Ailsa Craig had a human population of 29, working in its granite quarries or the lighthouse, which was completed by the Stevensons in 1836.

It was the human settlement which led to the introduction of brown rats.

These rats attacked the native populations of burrow nesting seabirds such as puffin and Manx shearwater.

Puffins had become extinct as a breeding species on the island by 1934.

Stuart Housden, Director for RSPB in Scotland, said: "The RSPB is very grateful to Lord Ailsa for this exciting opportunity in our Scottish centenary year.

"It is a real boost to establish a reserve at a place with such an interesting history.