The survival of seabirds including puffins and kittiwakes on St Kilda – the island archipelago home to one of the world’s most important seabird populations – is being threatened by climate change, striking new evidence shows.
Naturalists have discovered that the kittiwake, a small migratory gull with ink-black wing tips, is on the brink of disappearing from St Kilda. The remote cluster of Scottish islands in the eastern Atlantic is the UK’s only place with two Unesco world heritage site listings – for its culture and natural history – and one of only 24 sites with a dual listing worldwide.
The kittiwake did not breed in St Kilda this season, with just one chick born there this year after a 99% decrease in occupied nests since the 1990s. Its adult population has since halved. The number of fulmar chicks has plunged by 33% since 2005, while St Kilda’s puffin population is in persistent decline.
Warming seas to the west of the Hebrides are believed to have driven the marine life the birds rely on further north into colder seas or deeper into the water, starving the birds of food.
The findings from the annual bird survey by the National Trust for Scotland, the charity which owns St Kilda, have alarmed conservationists.
“This data from St Kilda is really extremely worrying,” said Dr Paul Walton, head of habitats and species in Scotland for the Royal Society for the Protection of Birds. “We are losing whole colonies of these birds now and it’s a very serious issue. Frankly, it breaks my heart, it really does.”
With crucial UN climate talks approaching their halfway point in Paris, the data underscored the case for urgent action on climate change, he said. Capping the growth in global temperatures at 2C – the target for policymakers – could be enough to allow the marine environment to adapt over time, Walton added.
“There’s a very strong climate change link here that needs to go straight to Paris: what they decide there is going to determine the future of our seabirds,” he said. “We are clear on what the science is saying, that really big ecology effects of climate change are unfolding in the marine environment around Scotland right now. It’s not coming, it’s here now.”
St Kilda – now regarded as one of the world’s most significant bird sanctuaries – was once inhabited by an isolated and beleaguered community whose songs and poetry heavily featured the seabirds they subsisted on before moving off the archipelago in 1930.
It lies about 41 miles (66km) west of the Hebrides. When bird populations are at their highest, about 1 million birds perch on the island’s high, precipitous cliffs, sea stacs and rocky crags, hosting the world’s largest gannet colony and nearly a third of the charismatic Atlantic puffins that live around the UK and Ireland.
In 1987, the National Trust for Scotland (NTS) counted 7,829 kittiwakes on the islands. Now that number stands at 3,886. When routine monitoring began 21 years ago, there were 513 occupied kittiwake nests there, with 56 chicks born. This year, researchers found just four nests, a 99.2% decrease, and a single chick.
The number of fulmar nests has declined by 37% since 2002, with productivity rates well below normal levels, averaging 0.28 chicks per nest compared with 0.42 in 2005.
Puffin numbers are also struggling. At 0.59 chicks per burrow, the NTS says puffin breeding is “still below the long-term average and, set against the longtime scale of the decline, suggests conditions are becoming less suitable for breeding”.
Susan Bain, who manages the island for the NTS, has ruled out windfarms and overfishing as other causes for the birds’ decline. Studies of dead kittiwakes found they had not been eating their normal diet, suggesting fish had moved to follow the cooler waters.
Lighter and more buoyant than their neighbouring gannets, the birds struggled to dive to the necessary depths. As a result, dead chicks were found having digested non-nutritious pipefish.
“We’re seeing significant declines in the number of species, which suggests that there’s something changing in the seas,” Bain said. “We know the sea temperature is getting warmer, so the fish are moving or are at greater depths.”
Bain says the headline figures are worrying, given the island’s exceptional biological significance. But she is not concerned for its Unesco status, yet. “At the moment, no, I’m not worried, but I wouldn’t want to be complacent about that either,” she said. “If these declines continue, then maybe.”
Regular, long-term visitors had noticed the kittiwake’s absence, she added. “We were seeing a couple of hundred nests around the village bay in the past. Now there are four, which is devastating. It’s very noticeable. They’re statistically extinct, although we will continue to look for them next year.
“It is normally a noisy place. You walk up to the cliffs and put your head over and it’s constant noise of fulmars, guillemots and razorbills. When they leave and go out to sea it’s silent, you really do notice. It would change the nature of the place significantly if that soundtrack was gone.”