Hermaness Bonxie

Bird of the Month July 2024: Great Skua

When it comes to birds, my favourite one tends to be the one I’ve just seen so inevitably changes all the time. However, if pushed to name an all-time top five, the great skua has to be one of my absolute favourites. Bolshie, brutish and beautiful, bonxies, as they are known in the Orkney and Shetland dialects, are true pirates of the sea, letting others catch their food before taking it from them. Yet with a small and localised population, they are also vulnerable. This is something that has become increasingly apparent with the recent outbreaks of avian influenza, or bird flu, in the UK’s wild bird populations. So, with bonxies only visiting our shores in summer, July is a good month to look out for this bruiser of a bird if you are lucky enough to live in or visit Scotland’s northern coasts.

Beautiful Brutes

Great skuas are large, bulky, herring gull-sized seabirds with powerful beaks. Their superficially plain brown colouration is deceptively beautiful being flecked with hints of gold throughout. There is also variation between individuals with some a rich deep brown, others almost blonde. The head has a slightly darker cap. Each wing has a large white wing panel used to good effect during territorial displays on the breeding grounds. As ground nesting birds, albeit without many obvious threats, their plumage helps them blend into the browns and golds of their moorland nesting sites.

Great skua or bonxie
Great skuas blend in well on their moorland nesting grounds

Bonxies are the largest of the Northern Hemisphere’s four skua species. The region’s three smaller species (Arctic, pomarine and long-tailed skuas) are all somewhat daintier in flight. They also have protruding central tail feathers of varying lengths, something bonxies lack. This, and the great skua’s obvious white wing panels makes them fairly easy to distinguish, even from a distance. In fact, bonxies are much more similar in appearance to the Southern Hemisphere’s three species: Chilean, south polar and brown skua. Their call, meanwhile, is perhaps their most surprising feature as it seems far too high-pitched and comical for such a brutish bird.

Great skua or bonxie
Some birds are a deep, chocolate brown

Like all skuas, bonxies rely to some extent on a feeding behaviour called kleptoparasitism. This means that instead of always catching their own food, they will chase other species, such as auks and terns, to make them give up theirs. Due to their large size, they will even chase gannets and force them to regurgitate their catch. Bonxies also directly predate smaller birds and mammals such as puffins and rabbits. Incredibly, research from St Kilda found that one population had learnt to hunt the rare Leach’s storm petrel, even though they only return to the islands at night. Like their distant gull relatives, bonxies are opportunists. This means they have also learnt to follow fishing vessels to take advantage of discards. During the breeding season, they sometimes eat berries growing in their moorland colonies, as well.

Piracy in the Scottish Isles

Great skuas have a smaller breeding range than their three Northern Hemisphere relatives. While the latter all have more or less circumpolar distributions, bonxies are restricted to pockets of the northeast Atlantic. There are breeding colonies in the Faroe Islands, Iceland, northern Norway, Svalbard, Scotland, Northern Ireland and Ireland. Until recent range expansions, they have also traditionally been more southerly breeders than Arctic, pomarine and long-tailed skuas, although there is some overlap with Arctic skua populations in places. While these breed on Arctic tundra, bonxies do so more on coastal moorland as a result of that more southerly range. In Britain, they only breed in northern Scotland, predominantly in Orkney, Shetland and St Kilda. The island of Handa of the west coast is another stronghold.

Bonxies or great skuas
A typical bonxie territorial display, clearly showing the white wing patches

Bonxies arrive back on their breeding grounds in April or May. Where populations are low, pairs nest on their own. In other places, such as Hermaness in Shetland, they form large, if loose, colonies. The nests are shallow depressions in heather or grass. Colonies are often close to seabird breeding cliffs so that there is not far to travel for food. Females typically lay two eggs and the pair defends them and the resulting chicks aggressively by dive bombing any intruders.

Large aggregations of bathing bonxies often form at freshwater pools, perfect for cleaning off sea water

During this period, large groups often gather at suitable freshwater pools and lochs to bathe and clean sea water from their feathers, a wonderful spectacle if you are able to see it. Birds leave again in August and September to head out to sea. At this time they can turn up pretty much anywhere around coastal Britain and Ireland. Winter is spent roaming the north Atlantic, anywhere between West Africa and eastern parts of Canada and the US.

Bonxie Boom or Bust?

Although only numbering approximately 16,000 pairs globally in 2004 (compare this to the Arctic skua which numbers around 140,000 pairs in Europe alone), the great skua’s population had been growing over the last one hundred years. Increased numbers meant it also expanded its range northeast to the Svalbard archipelago in the 1970s. Ringing recoveries show that many birds breeding in Svalbard were born in Scotland. Expanding Scottish colonies also pushed birds south and west to form new colonies in Ireland in the 1990s and Northern Ireland in 2010. In the UK alone, there was a 111% range increase between 1968 and 2011. Numbers more than trebled over this same period and the last count of 1998 – 2002 recorded 9650 pairs. This dramatic rise is almost certainly related to high levels of fishing discards in the region. Population rises did slow somewhat, though, with the EU’s discard ban, introduced in 2015.

Bonxie and Muckle Flugga
A bonxie at one of Scotland’s largest colonies: Hermaness on Unst, Shetland

All this changed in the summer of 2021, however when avian influenza, or bird flu, killed a number of great skuas, predominantly on St Kilda. The following year, the disease devastated seabird populations around Britain, with bonxies again affected. Recent research from the RSPB found that by the 2023 breeding season, the UK’s population had fallen by 76% as a result of bird flu. At some sites, declines were estimated as being up to 90%. As the UK holds 60% of the world’s breeding population of the species, these losses are incredibly worrying for a bird that numbers less than 20,000 pairs worldwide. The only silver lining is that they remained largely unaffected in 2023. This is possibly due to the fact those huge losses meant there weren’t enough birds to collect at communal bathing spots and colonies were even more spread out. This perhaps made it harder for any infected birds to affect others. Remaining adults may also have developed some level of immunity, something seen in small numbers of gannets and shags.

Bonxie in flight
A bonxie in flight

Perfectly Piratical

Although having less of an impact here now than in the 2022 breeding season, the avian flu outbreak is far from over. Worryingly, the bonxie’s Southern Hemisphere relatives are now increasingly at risk. Indeed, the disease was detected in brown skuas in South Georgia last autumn. There have also been likely cases in this species and south polar skua on mainland Antarctica this year. Hopefully our own skuas will have a successful breeding season, however, and escape further outbreaks of avian influenza. The events of the last few years are a reminder, though, that for all its bulk and swagger, even the bonxie is vulnerable to the devastating effects of our climate and nature emergencies.

Great skua
Great skuas regularly patrol seabird cliffs in summer

Thanks for reading! If you like my writing and would like to leave me a tip, you can do so below.

Leave a Comment