Great Skua (Stercorarius skua)

Pre- and post-outbreak population figures are drawn from a comprehensive RSPB survey conducted in May–July 2023, compared against a prior major census spanning 2015–2021. Scotland's share of the UK and global population, range expansion figures, and predatory behaviour are drawn from the British Trust for Ornithology's published assessment. The longer-term, population-level consequences of the avian flu outbreak are treated as genuinely unresolved, reflecting researchers' own stated position that these remain unclear beyond the measured short-term collapse. The early history, the origin of the name and the 2005 population figures come from Mark Cocker and Richard Mabey's Birds Britannica (2005); its figures are given as history, not as current counts.

The spread of colonies, the survey totals, ringing and tracking results and the breeding biology come from Robert W. Furness's account in the Scottish Ornithologists' Club's The Birds of Scotland (2007). Those figures end in 2003 and are history beside the post-2021 avian flu counts. The 2023 figures of 9,088 and 2,160 refer to breeding numbers at the colonies surveyed, not to every great skua in the UK.

A global significance worth stating precisely

This article names Scotland's importance to the great skua with its real documented weight: the UK holds over half the world's population of the species, and almost the entire UK population breeds in Scotland, concentrated at specific named sites including Shetland, Orkney, Handa, Sutherland, and St Kilda. This article states this directly because it clarifies that the species' recent crisis in Scotland is not simply a national concern but one with genuine global conservation significance, given how disproportionately the world population depends on this single country's breeding colonies.

A collapse stated with its full, catastrophic scale

This article does not soften the documented impact of the 2021–23 avian flu outbreak: a comprehensive 2023 survey found breeding numbers at the colonies surveyed had fallen from 9,088 to 2,160, a 76% decline, with over 2,500 deaths recorded in 2022 alone and a substantial share concentrated at a single Shetland colony. This article states these figures directly because they represent one of the most severe documented single-event population collapses recorded for any Scottish seabird species, not a vague description of disease impact.

A predator, honestly described

This article names the great skua's predatory and kleptoparasitic behaviour directly rather than presenting the species in softer terms: bonxies actively hunt small birds, rodents, and rabbits, and are well known for chasing other seabirds in flight specifically to steal food they have already caught. This article states this because an honest ecological account of the species includes its genuine role as an aggressive coastal predator, not only its current status as a species of conservation concern.

A genuine prior success, credited alongside the current crisis

This article presents the great skua's substantial pre-outbreak range expansion — 111% growth in breeding range since 1968–72, and 138.2% growth in winter distribution since 1981–84 — as a real, documented conservation success story in its own right, stated directly alongside rather than displaced by the current avian flu crisis. This article names both facts together because an honest account of the species' recent history includes both its genuine prior expansion and its current severe, documented setback.

A decline whose longer-term consequences remain genuinely unresolved

This article states the confirmed 76% population collapse directly while noting honestly that researchers themselves describe the longer-term, population-level consequences of the outbreak as not yet fully established beyond this measured short-term figure. This article presents this distinction because asserting a confident long-term population trajectory — whether recovery, further decline, or stabilisation — would overstate what the current evidence, focused primarily on the severe initial collapse, actually supports.

Bunxie: a name from Shetland

established Mark Cocker and Richard Mabey, in Birds Britannica (2005), call "bonxie" the best example of a local name overtaking the official one across the country; few birdwatchers say "great skua" aloud. They trace it, probably, to the Old Norse bunki, which gave the Shetland word "bunksi" for a dumpy, untidy or heavily dressed person. The name fits the bird's barrel-chested build. The genus name Stercorarius comes from the Latin for dung, from an old belief that skuas chased other seabirds to eat their droppings, when in fact they are after the food. The book still used the older scientific name Catharacta skua.

Welcomed, eaten, then protected

established Bonxies are relatively recent colonists. The first colonies, on Unst and Foula, were described by the Rev. George Low in 1774 and probably did not predate the mid-eighteenth century. At first Shetland crofters valued them because they drove ravens and white-tailed eagles away from the sheep. Low wrote that the "Bunxies" were "cherished by them with the greatest veneration and kindness". The welcome faded when bonxies were found to take lambs. Islanders then caught young birds and tethered them round the croft to fatten for the table, and bonxies were eaten into the twentieth century; illegal egg-eating carried on on Foula until the 1970s.

established Together with taxidermists and trophy hunters, this pressure pushed the species to the edge of extinction in Britain. Legal protection in the early twentieth century began a steady recovery, with numbers doubling in some decades. In 2005 Birds Britannica put the British population at 8,500 pairs, almost two-thirds of the world total, with about 3,000 pairs on Foula, then the largest colony on earth.

shared Those figures were already slightly dated. The Birds of Scotland (2007) reports about 9,650 territories in Scotland in 2000, and Foula down from over 3,000 pairs in 1977 to about 2,300 by 2003.

Discards, sand-eels and kittiwakes

established Part of that increase was fuelled by fishing waste: between 1976 and 1986 trawlers dumped enough offal and unwanted fish to support around 200,000 seabirds. When sand-eel stocks crashed in the 1980s, bonxies, which had robbed sand-eels from other seabirds, turned to killing the seabirds themselves. Robert Furness estimated that by 1996 British bonxies were killing around 200,000 kittiwakes, half of them adults, and the book links this to a halving of Shetland's kittiwakes since 1981.

established The SOC account, written by Furness himself, puts the balance carefully. In Shetland bonxies feed mainly on sandeels and whitefish discards, and only to a much smaller extent on seabirds they kill. Bird-killing matters more where colonies are small or other food is scarce, as on St Kilda. Falling sandeel stocks and smaller discards in the north-western North Sea have pushed many birds towards predation.

The Scottish record to 2007

established Spread. Robert W. Furness's account in the Scottish Ornithologists' Club's The Birds of Scotland (2007) traces the recovery colony by colony. Up to 75 pairs bred in Shetland in the 1880s and only about 20 around 1900. Under protection numbers rose by about 7% a year until the 1970s, and more slowly after that. Orkney was colonised in 1914, the Outer Hebrides in 1959, St Kilda in 1963, Handa in 1964, the Summer Isles in 1980 and the Shiants in 1982, with new colonies in the 1990s on Canna, the Flannans, Barra, the Uists, Coll and the Treshnish Isles. Shetland's share fell from 96% of territories in 1969 to 71% in 2000 as Orkney grew; Hoy went from 72 pairs to 1,973 and became the second largest Scottish colony.

established A bird of the cool north. Scotland is the southern limit of the breeding range, and the account suggests that temperature may set it, since these cold-adapted birds find sunshine and warm days stressful while incubating. Most of the range expansion has been northwards into the Arctic. Chicks ringed on Foula have been found breeding in nearly all the new high-latitude colonies, including north Russia, and in the new western Scottish ones.

established Breeding. Birds gather at non-breeding "club" sites from two to eight years old and first breed at four to twelve. Adults survive at about 90% a year. They arrive in late March, lay in mid- to late May and fledge chicks around the end of July. Territories are usually 30–100 m apart. Off-duty birds stand on a favourite raised mound, which turns bright green from droppings and trampling. Breeding success reaches 1.3 chicks per pair in good years but has often been cut by food shortage in Shetland since the mid-1980s.

established Migration. Ringing recoveries of first-winter birds range from Russia and Norway to Tunisia, the Cape Verde Islands, New England and Brazil. Older birds move less, those over four years old wintering mostly off Iberia. Satellite tracking of Foula adults in 2002–03 showed most going south through the North Sea and English Channel to winter off north-west Africa. Some cross Scotland overland, from the Moray Firth and the Forth by the Great Glen and the Clyde.

established Threats in 2007. The account names human persecution, protection from exploitation and changes in food supply caused by fisheries as the main factors. Contaminants build up in the birds but showed no effect on survival. Some drown in nets and on long lines and some are shot on migration. Furness warned that falling discards could reduce numbers and noted that illegal persecution was clearly implicated in sudden drops on Fair Isle. Avian flu was not on the list; it arrived 14 years later.

• "Bonxie" probably comes from a Shetland word for a dumpy, untidy person.
• Shetland crofters first welcomed bonxies for chasing ravens and sea eagles away from their sheep.
• Young bonxies were once tethered round Shetland crofts and fattened for the pot.
• The UK holds over half the world's great skua population, almost all of it breeding in Scotland.
• Great skuas are known locally as "bonxies" and are aggressive predators, hunting small birds, rodents, and rabbits.
• They are also kleptoparasites, chasing other seabirds in flight to steal their caught food.
• Great skua breeding numbers at the colonies surveyed fell by 76% between a pre-outbreak baseline and a 2023 survey, from 9,088 to 2,160.
• Around 1900 only about 20 pairs of great skuas bred in Scotland, all in Shetland.
• Great skuas are cold-adapted, and Scotland is the southern edge of their breeding range; incubating birds find sunshine and warm days stressful.
• Off-duty bonxies keep a favourite lookout mound in the territory, which turns bright green from their droppings and trampling.
• Over 2,500 great skua deaths were recorded in 2022 alone, with a substantial share at a single Shetland colony.
• Before the avian flu crisis, the species' UK breeding range had expanded by 111% since 1968–72.
• The great skua is globally classified as Least Concern despite being UK Red-listed, reflecting its concentrated but currently severely affected Scottish breeding population.

• Clarification: This article does not claim a confirmed longer-term population trajectory following the measured 76% decline; researchers describe the outbreak's longer-term, population-level consequences as not yet fully established.
• Do not say the name "bonxie" refers to the bird's aggression; it probably comes from a Shetland word for a dumpy, untidy person.
• Do not describe the 9,088 and 2,160 figures as counts of individual birds across the UK; they are breeding numbers at the colonies surveyed.
• Do not call Foula a 3,000-pair colony in the 2000s; it held over 3,000 pairs in 1977 and about 2,300 by 2003.
• Note: This article does not present the species' current crisis as its entire recent history; the substantial pre-outbreak range expansion represents a genuine, separate conservation success stated honestly alongside the current severe decline.