The mission is almost bordering on the impossible: how to save the pirate of the seas from the brink of being lost forever? Two thirds of the world’s population of great skuas nest in Scotland but their numbers have been decimated by avian flu, driving the large seabirds, also known as bonxies, to the brink. Now, with three quarters of the Scottish population lost to the virus, an epic effort to save them has been played out in remote St Kilda involving exhausting legwork, trickery, fake eggs, a plastic tub and some tin foil. Great skua chicks on St Kilda have been given tags to help monitor them throughout their lives (Image: National Trust for Scotland) Despite their aggressive reputation, a tendency to divebomb humans who approach their nests and to attack other birds and steal their food, great skuas have been highly vulnerable to avian flu, which has caused mass fatalities among Scotland’s seabirds since it emerged in 2021.
As it took hold, nature rangers across its traditional northern islands nesting sites faced the distressing task of gathering carcasses of great skua and other birds which littered nest sites and coastlines. Now some of the same National Trust for Scotland nature teams have been at the forefront of the desperate effort to save the great skua that remain, and give their offspring a fighting chance to reach maturity. Over recent months they have trekked miles over wild St Kilda landscape to carry out a massive mapping exercise aimed at identifying the remaining birds’ territories.
With the sites identified came the difficult task of scrambling up hills in sometimes grim weather to reach their nests in order to carefully trap the adult birds – defying the risk of being divebombed - and to take samples from them and to tag them. To add to the challenge, they faced a race against time. For to capture the birds, they first had to trick them, by removing their precious grey-blue speckled eggs from the nest, keeping them warm so as not to interfere with their incubation, and returning them without damaging them or distressing the parent bird.
To solve the problem of how to keep the eggs warm in such a remote location, they used a simple insulated tub – not unlike a lunchbox – with an extra tin foil layer. With the precious nest empty, the space was filled with two almost identical fake eggs to trick the adult into returning. Great skua eggs are replaced with fake ones to enable important tests and tagging of adult birds (Image: National Trust for Scotland) Once caught, the adult bird was swabbed to check for signs of avian flu, and fitted with tiny identification rings before being released and the eggs returned to the nest.
The team later also tagged the chicks, enabling them to follow their progress for years to come. Read more by Sandra Dick: What next for Scotland's ice climbing centre? Oasis Britpop style meets Harris Tweed - definitely maybe. The delicate task – carried out under strict controls and fully licenced - is the first time great skuas have been tagged on that scale and is being seen as crucial: before avian flu struck, the St Kilda archipelago harboured 183 great skua nests, the number has now slumped to 70.
It’s a similar picture on other islands in the Trust’s care, which were once strongholds for the charismatic ‘pirates of the seas’. On Mingulay, nest numbers before avian flu sat at 129, but have dropped to just 44. Neighbouring Pabbay has just 24 nests and on Bernerary there are only nine nesting pairs.
Unst and Yell, meanwhile, has only a handful of pairs. Great skua eggs are kept warm in an insulated tub (Image: National Trust for Scotland) According to bird organisation RSPB, great skua numbers across the UK plunged from 9,088 to 2,160, with signs of a 76% decline in breeding numbers across its range. The birds are thought to be particularly vulnerable due to their kleptoparasitic behaviour: they often chase down other seabirds such as gannets and bully them into regurgitate their meals.
If the attacked bird is infected with avian flu, the food emerges coated in saliva likely to be loaded with the deadly H5N1 virus. With great skua numbers now desperately low, they are among five seabird species just added to the UK red list of birds at most need of conservation. The St Kilda NTS bird team during the great skua project (Image: National Trust for Scotland) The new list includes the Arctic Tern, which breeds mainly in Orkney and Shetland and then embarks on an epic journey to the Antarctic for winter, Leach’s storm petrel which tends to nest on the north-west coast, the great black-backed gull and the deceptively named common gull.
The recent effort to help support St Kilda’s few remaining great skua has been captured in a short NTS film presented by Trust ambassador and vet Cal Major, who joined the daunting task of trekking to the nest sites. She said: “The colour rings applied to the birds' legs means we can identify individual birds all their life and follow their stories over many years. Great skua in flight over St Kilda (Image: National Trust for Scotland) “We can see (the rings) through binoculars, we don’t have to catch the birds to be able to identify them.
“It’s an exciting way of being able to see what happens to the bird, how long it lives, whether it has chicks, whether it comes back to St Kilda or ends up somewhere else in the world . “This research has never been more important,” she adds. Read more by Sandra Dick: How shipwreck sleuths helped solve the century old mystery A monstrous design: The beauty of Glasgow's Brutalist buildings “After a few very tough years I’m really rooting for them and hoping that the beautiful sight of their chicks hatching on St Kilda is the start of their population’s rebounding retaining their global stronghold on the islands of Scotland.
” Similar tagging of great skuas has been carried out by government agency NatureScot on the Shetland islands of Hermaness and Foula. Before avian flu, Foula had around 1,800 pairs of great skua. There are now thought be less than 1,400 individual birds.
NTS ambassador Cal Major took part in the St Kilda great skua project (Image: National Trust for Scotland) Craig Nisbet, NTS Seabird Ranger on St Kilda recalled the rapid impact of avian flu on the bonxies. “In 2021, I found my first dead great skua around about early July. It was when I found a few more that alarm bells started ringing.
“By end of the season we reported 66 dead adults found on the island. The following year things got a lot worse,” he added. “That was really hard.
In 2022 it felt like a very big part of my job was overseeing the demise of one of our most fantastic seabird species that breed on the island.” Great skuas are one of St Kilda and Shetland’s iconic birds, migrating north from their wintering grounds in Spain and Africa in April and remaining until September. Adult great skua with its colour rings in summer 2024 (Image: National Trust for Scotland - Craig Nisbet) Roughly the size of a herring gull, they are bold and aggressive: seemingly unafraid of humans, they will repeatedly divebomb in order to protect their nests.
Ellie Owen, NTS Senior Seabird Officer says the work on St Kilda is part of a series of measures under the banner Flufix. “This work sees us increasing the number of counts we are doing so that species at risk are being counted more frequently to alert us to any sudden population drops, and hopefully, eventually evidence of recovery. “We are also actively researching why this disease hit seabirds so badly, how it arrived here, and how we might help birds if it, or a similar disease reaches outbreak proportions that HPAI has.
” Swabs and samples are taken from the birds are checked for signs of virus, and dead birds are also analysed. Read more by Sandra Dick: Cancelled and forgotten: the fight to restore hero's reputation The end of an era for Mull's iconic eagles The final element of the Flufix project has been pushing for improved funding and better policies to keep seabirds safe while they recover from flu. But while it’s hoped the species may be over the worst, birds are still being affected.
So far this summer swabbing of dead birds has revealed two skuas, on the NTS managed island of Fair Isle, and one on St Kilda, both died of avian flu. The effort to tag great skua is part of a National Trust for Scotland series of short films, St Kilda Diaries with Cal Major , that explore nature on the archipelago.
