Kittiwake numbers on St Kilda have plummeted to their lowest level, with experts fearing warning the population is at risk of collapse.

Over the last season there was just one kittiwake nest discovered across seven monitoring sites in the isolated archipelago, and the only hatched chick later died.

Seabird populations are rapidly falling after a century of growth, and puffins, fulmars, guillemots and razorbills are also under threat, according to the National Trust for Scotland.

Senior nature conservation adviser Dr Richard Luxmoore said the decline signalled changes to the local environment, particularly in the plankton vital to marine life in the region.

He said: "Seabirds are essentially part of the marine ecosystem. Although they breed on land they spend most of their life out at sea and they can tell us a lot about its health.

"In the last 30 years plankton communities have shifted northward by 1000 kilometres, more than the distance from Edinburgh to Paris, and it's having huge impact.

"If vegetation shifted by a similar distance there would be pandemonium but because it's happening in the sea we tend not to notice."

Seven of the seabird species found on St Kilda are geographically significant and four - the northern gannet, Atlantic puffin, great skua and Leach's storm-petrel - are important globally.

Dr Luxmoore added: "If the inhabitants of St Kilda were to come back now nearly 90 years after their evacuation and see the cliffs that were once teeming with seabirds now almost empty, they would be horrified to see what has happened on the island where they once lived."