Scotland’s puffin population is feared to have been decimated as post mortems on hundreds of birds washed up in Spain have confirmed they died from starvation.

Experts are now warning that puffin numbers during this year’s migration onshore will have collapsed and even threaten the future survival of the species. 

More than 1,000 dead puffins have been discovered on the shores of the Canary Islands and the regions of Cantabria and Asturias in the past few weeks.

The Spanish Ornithological Society estimates the actual mortality rate is much higher, representing just 20 per cent of the total number of puffins that have died at sea. 

READ MORE: Fears for Scotland’s puffins as hundreds wash up dead on Spanish coastline

Dead puffins or puffins in very frail condition have also been discovered on the shores of Bilbao and Galicia in northern Spain and in Portugal in places such as Peniche and Madeira. 

Last week, the Spanish Ornithological Society confirmed to The Herald that, of the puffins discovered on the Spanish coastline with leg rings, “more” had been ringed in Scotland than in any other location.

This has led to calls by British ornithologists for urgent research to establish what is causing the deaths amid concerns that storms or changes in oceanography linked to climate change could be responsible. 

Some of the recently-discovered ringed birds were traced to Sule Skerry, a remote islet 40 miles west of Orkney, and Garbh Eilean in the Shiant Islands off the coast of Lewis, according to the bird conservation society.

The Herald: The coastline of Spain has turned into a cemetery for Atlantic puffins in recent weeksThe coastline of Spain has turned into a cemetery for Atlantic puffins in recent weeks (Image: Sarah Kelman/BTO)

New analysis by the University Institute of Animal Health And Food Safety of the University of Las Palmas de Gran Canaria has confirmed the probable cause of the mass die-off of puffins to be starvation. 

Professor Antonio Fernandez, who led an autopsy study of 20 puffins that died on the coastline of the Canary Islands, told Canarias7: “There has been an unusual mortality of puffins…everything indicates they have not been able to eat”. 

The veterinary pathologist added his team had observed the dead puffins had suffered a weight loss of between 20% and 30%, as well as a loss of fat and muscle deposits. In scientific terms, he said the birds suffered “a total destabilisation of the homeostatic balance”. 

Mr Fernandez also sought to discount any suggestions that avian influenza was behind the mass deaths, noting none of the puffins that were analysed had tested positive for the disease.

While Atlantic puffin populations still number in the millions, their numbers have been in decline for decades, as rises in sea temperatures threaten the extinction of their most common prey, the sand eel. 

The decline has been such that in 2015, their conservation status was changed from “least concern” to “vulnerable”, where it still remains. 

Puffins feed by diving up to almost 200ft from the surface of the water in search of small fish such as herring, hake and sand eels. 

The birds spend most of their lives at sea, coming ashore in Scotland from late April until the middle of August to form breeding colonies in places such as Shetland, Orkney, the Isle of May, Fair Isle and the Treshnish Isles.

The Isle of May, the UK’s third largest colony, lost nearly 30% of all puffins in the mid-2000s, and since then the population has slowly increased, but not compared to what it used to be. 

Dawn Balmer, head of surveys at the British Trust for Ornithology said: “Puffins and other seabirds have been found in the Canaries, Portugal, north west Spain and Morocco. Some birds in Portugal have been tested for avian influenza and have tested negative.

“The cause of death is not yet known but some birds were in poor condition and the most likely cause will be difficulty feeding due to bad weather.”