St Kilda: a seabird sanctuary without parallel
St Kilda in summer can be a raucous place. Strange, you’d say, for an uninhabited island over 40 miles away from the nearest settlement. But it’s not people causing the clamour, it’s birds.
Each summer, the remote St Kilda archipelago, cared for by the National Trust for Scotland, is home to around half a million breeding seabirds. At our last count, 17 seabird species nest and raise young here, including one of the world’s largest northern gannet colonies and significant populations of Leach’s storm petrel, northern fulmars and a huge Atlantic puffin colony. ‘If you stand on Dún on a busy day,’ says St Kilda Seabird Ranger Craig Nisbet, ‘you may see tens of thousands of puffins wheeling around your head. It’s just the most incredible sight.’
Other breeding seabirds on St Kilda include Manx shearwaters, guillemots, razorbills, great skuas, Arctic skuas and shags, with UNESCO describing St Kilda World Heritage Site as ‘a seabird sanctuary without parallel in Europe’. Its importance for seabird colonies stems from its position in the North Atlantic – close to food sources and away from human activity – and its vertiginous landscape of stacs, cliffs, scree and grassy slopes, ideal for nests and burrows. It’s also free of land-based predators, such as rats and mink, which eat seabird eggs and chicks.
Until the last St Kildans were evacuated in 1930, seabirds – and especially fulmars – were integral to the islanders’ lives. ‘For thousands of years, seabirds were everything to the St Kildans, providing them with meat, oil, eggs and feathers,’ explains Susan Bain, the Trust’s Manager for the Western Isles. ‘Seabirds’ importance in the islands’ cultural heritage is evident in the few traditional St Kilda songs we still have – there are choruses imitating seabird calls, songs lamenting young men fallen to their death during fowling expeditions, and a song showing a young woman’s frustration with a suitor who’s not yet brought her a gift of seabird eggs to demonstrate his bravery!’
The sounds of St Kilda
For today’s summer visitors to St Kilda, the seabirds create a magnificent soundscape. Depending on where you are, you may hear a polyphonic babble of razorbills, guillemots, kittiwakes, gannets, skuas and puffins cackling, jabbering or croaking, or even the whirring wings of circling fulmars, wonderfully described by one ornithologist as ‘like the fizzing, whizzing noise, the crescendo of clockwork, that goes on inside a grandfather clock just before it strikes’.
And that’s just the seabirds. St Kilda’s soundscape also features numerous other bird species, says Susan, including the drumming and ‘squeaking-bed’ call of snipe, the comical ooh-ing and cooing of eider ducks, and the warbling of the St Kilda wren.
At night-time, the sounds become eerier. ‘On St Kilda, at night, when you see and hear the Leach’s storm petrels and Manx shearwaters returning to their colony, St Kilda has a different persona. It’s like two seabird cities in one, and you don’t get that in many colonies,’ says Craig.
Seabird population declines
Sadly, the soundscape of St Kilda is almost certainly quieter than it used to be, with some species’ numbers plummeting here (and elsewhere) in recent decades. In 2023, we carried out a full census of cliff-nesting birds on St Kilda – an incredible achievement which took over 1,400 hours – and found steep declines in fulmars, guillemots, razorbills and kittiwakes since the previous comparable survey in 1999. For example, there were just over 20,000 fulmar nests counted in 2023, less than a third of the 67,000 recorded in 1999.
One factor in seabirds’ declining populations and productivity (the number of chicks they fledge) is climate change. Warming sea temperatures, along with some fishing practices, are likely affecting food resources in the North Atlantic, and changing currents could compound this further, according to the Climate Vulnerability Index (CVI) Assessment for St Kilda, published in 2024.
Pollution is also a threat to marine life, including seabirds, while avian flu hit St Kilda hard in 2021–22. Around two-thirds of its great skuas (or ‘bonxies’ as they’re often called in Scotland) were wiped out by avian flu, though numbers have recovered slightly since then.
The power of data
In order to identify and better understand these declines and trends in seabird populations, the Trust’s seabird specialists and volunteers are rigorous in capturing data – not just through archipelago-wide censuses but through regularly monitoring population plots and breeding success. In summer 2024, our rangers and volunteers also mapped, ringed and took samples from bonxies and puffins on St Kilda to monitor their response to avian flu and understand more about where they forage and breed.
You can see more about this in Trust ambassador Cal Major’s fascinating St Kilda video diaries.
The findings from all this data-gathering and other research on St Kilda inform our work to care for, protect and share the seabird colonies, and to speak up to policymakers and others on behalf of wildlife. They also give us a deeper understanding of what’s happening in the wider marine environment.
If you ask seabird ranger Craig Nisbet why he’s now chosen to spend four summers in this isolated archipelago, where the living conditions and weather can be far from ideal, he’ll talk about the sights, sounds and abundance of St Kilda’s seabird colonies, but also about something bigger.
St Kilda’s seabird colonies may be remote, but what they tell us is essential for our understanding of the wider world – as well as being one of Scotland and Europe’s greatest nature spectacles.