Skip to Content

Arctic skua (Stercorarius parasiticus)

The following has been adapted from original text by Robert W. Furness and Norman Ratcliffe in Seabird Populations of Britain and Ireland (with permission from A&C Black, London).

 

In Britain, the Arctic skua is confined to breeding in north and west Scotland, at the southern extremity of its circumpolar, high latitude breeding range. In Scotland, most nest in moorland colonies close to aggregations of auks (common guillemots, razorbills and Atlantic puffins), black-legged kittiwakes and Arctic terns from which they obtain food by piracy. In a few places, such as the extensive moors of Caithness, the species can be found further inland in rather scattered breeding territories, where feeding on berries, insects and small birds may be more important. Unlike the larger great skua, Arctic skuas do not normally scavenge behind fishing boats or feed as members in multi-species flocks of seabirds on surface shoals of fish, as their smaller size means they cannot compete in such situations. Although numbers nesting in Scotland increased in the 1970s and 1980s, most of their breeding sites have been established for many decades or centuries with few new colonies formed, resulting in a remarkably static breeding range.

Conservation status

Arctic skua is currently identified as a conservation priority in the following:

Top

International importance

UK Population

Biogeographic Population

% World Population

2,100 AOT*

8.4 (NE Atlantic)

1.0

*AOT = Apparently Occupied Territories

The UK population figure (rounded to the nearest hundred) was derived from data in Mitchell, P.I., Newton, S.F., Ratcliffe, N. and Dunn, T.E. (eds.) 2004. Seabird Populations of Britain and Ireland. Poyser, London. This was also the source of figures for the Biogeographic and World populations.

Top

UK population estimates and change 1969–2002 (census data)

Once they have been recruited into a colony, Arctic skuas usually breed every year returning to the same territory year after year. However, in seasons when food supply is particularly poor, birds may fail to lay. This appears to have been the case during surveys of Arctic skua in Shetland in 2000 and 2001 which may have resulted in an underestimate of the number that would normally be breeding under more favourable conditions. Breeding success in Shetland was also poor in 2000 and 2001, and birds that lost eggs early on may have shown low attendance in the territory, possibly resulting in some territories being missed. Counts in Shetland in 2002 were affected by poor weather conditions in some parts, with a considerable area surveyed in fog which may also have contributed to an underestimate of numbers.

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998–2002)

UK Population estimate (AOT*)

1,039

3,388

2,136

% change since previous census   

n/a

+226

-37

* AOT = Apparently Occupied Territories

For census results for individual countries and Ireland, the Channel Islands and the Isle of Man see under relevant sections below.

Top

Distribution/abundance

The Seabird 2000 census provides the most comprehensive recent assessment of the distribution and abundance of breeding seabirds. Numbers of Arctic skua found in different regions, and a map showing the location and size of colonies, is provided in the Seabird 2000 Arctic skua results.

The locations sampled during the annual Seabird Monitoring Programme provide some information on distribution and are accessible via the Seabird Monitoring Programme online database.

Top

Annual abundance and productivity by geographical area

With reference to the regional accounts below please note the following:

Breeding abundance: graphs of abundance index with 95% confidence limits are only shown for a region where the trend produced has been deemed accurate (see methods of analysis). Where a trend was thought to be inaccurate, graphs of abundance at major colonies in a region may be shown instead, particularly if such colonies hold greater than 10% of the regional population, are monitored frequently and may thus help illustrate regional population fluctuations outwith national censuses. Occasionally, too few data have been collected regionally to produce either of these.

Productivity: graphs of productivity are only shown if analysis of breeding success data produced a significant result for regional and/or year effects (again see methods of analysis). If results were not significant, then a regional mean productivity value is given. However, on some occasions, too few data are available from which to provide a meaningful average. Furthermore, for 11 species where the quality of monitoring data available was considered high, population viability analysis was undertaken at the UK level and the results of this are also reported.

 

United Kingdom

Breeding Abundance

arctic-skua-uk-ab.jpg

Figure 1. Trend in UK abundance index (solid line) of Arctic skua 1986–2018 with 95% confidence limits (dotted lines). Based on SMP data; view the methods of analysis.

 

National census data show the population of Arctic skuas increased between 1969-70 (1,000 AOT) and 1985-88 (3,400 AOT) although some of this increase was due to greater coverage during the SCR census. However, Seabird 2000 only recorded 2,100 AOT, 37% fewer than the preceding census. Figure 1 shows the trend was stable until the early 1990s but has declined steadily since; the Arctic skua has probably declined more than any other seabird in the UK during the period from 1986 to 2018, with the lowest population index in 2013 estimated to be 82% lower than in 1986. The current breeding seabird census, Seabirds Count, will provide a more comprehensive assessment of the scale of the decline.

A recent study in 2015 estimated that Artic skuas had declined to approximately 200 AOT in Orkney, Shetland and Handa combined, an 81% decline since 1992 and 71% since Seabird 20001. Arctic skuas in Shetland had already declined by 42% between the SCR and Seabird 2000 censuses, and a small number of well monitored colonies suggest a further fall in the population; (Foula, Fair Isle, Fetlar, Mousa, Hermaness, North Hill, Noss, and Hoy held 78 AOT between them in 2018, 81% fewer than was recorded by Seabird 2000 (403 AOT)). In the west of Scotland, only 15 AOT were recorded on Handa in 2018, a decline of 64% since a peak of 42 AOT in 2001.

In Scotland, Arctic and great skuas breed sympatrically, usually beside large colonies of cliff-nesting seabirds2. One of the main factors contributing towards this national decline is likely to be the continuous decrease in their annual productivity (no. chicks fledged per pair) and that of their host species from which they kleptoparasitise food (Arctic tern, kittiwake, common guillemot and puffin). Recent observed alterations in the marine food web in the northeast Atlantic, strongly influenced by fisheries management and climate change, are driving the decline of lesser sandeels Ammodytes marinus, a main food source of Arctic skuas and their host species3,4,5,6. Another factor contributing to their decline is likely to be competition for nesting territories and predation by great skuas which have increased markedly2,7,8,9,10.

 

Productivity

Arctic skua UK productivity.jpg

Figure 2. Trend in UK productivity (no. of chicks fledged per pair) of Arctic skua 1986–2018. Based on SMP data; view the methods of analysis.

 

Arctic skuas periodically experience years of very poor productivity (chicks fledged per pair), which often coincide with periods of presumed low sandeel abundance2; such periods have become more frequent since the late 1990s, with several years of very low productivity since 2003, although 2015 was the most productive breeding seasons since 1999.

Annual data from the six most frequently monitored Arctic skua colonies in Shetland (85 data points between 2003–2018 from Fair Isle, Fetlar, Foula, Hermaness, Mousa and Noss) illustrate just how bad breeding seasons have become. Complete failure was recorded 43 times, with productivity below 0.20 chicks fledged per pair on a further 16 occasions; only on ten occasions did productivity climb above 0.80. Arctic skuas rely on stealing fish caught by other seabirds, especially Arctic terns, black-legged kittiwakes, common guillemots and Atlantic puffins; declines in the abundance and chick provisioning of these host species has reduced feeding opportunities for Arctic skuas1,2. Recent sandeel scarcity around Shetland is attributed to low recruitment in most years since the mid-1980s, linked to hydro-climatic changes affecting hatching dates, survival and transport of larvae from major spawning areas north and west of Orkney11,12. More significantly, environmental conditions for sandeels appear to be worsening, with sea temperature increases and oceanographic changes affecting their physiology, food supply, phenology and survival, leading to trophic mismatch and less food for seabirds13,14,15. Predation of Arctic skua chicks, and sometimes displacement or killing of adults during territory disputes by great skuas (also ultimately linked to a scarcity of alternative fish prey for great skuas), is also known to be reducing productivity in some regions3,9,11.

Scotland

Breeding abundance

arctic-skua-scotland-ab.jpg

Figure 3. Trend in abundance index (solid line) of Arctic skua in Scotland, 1986–2018 with 95% confidence limits (dotted lines). Based on SMP data; view the methods of analysis.

 

National census data show the Scottish Arctic skuas population increased between 1969-70 (1,000 AOT) and 1985-88 (3,400 AOT) although some of this increase was due to greater coverage during the SCR census. However, Seabird 2000 only recorded 2,100 AOT, 37% fewer than the preceding census. Figure 3 shows the trend was stable until the early 1990s but has declined steadily since; the Arctic skua has probably declined more than any other seabird in the UK during the period from 1986 to 2018, with the lowest population index in 2013 estimated to be 82% lower than in 1986.

A survey of the Orkney population in 2010 found just 380 AOT compared to 720 AOT in 2000, so numbers there alone declined by 47% during that decade (and by 64% since 1992 when 1,043 AOT were recorded). In addition, a study in 2015 estimated Artic skua to have declined to approximately 200 AOT in Orkney, Shetland and Handa combined, a 81% decline since 1992 and a 71% decline since Seabird 20001. However, to fully ascertain the scale of the current decline, extensive survey work is still needed in Shetland where over half of the UK (and Scottish) population has bred in the past. Arctic skuas in Shetland had already declined by 42% between the SCR and Seabird 2000, and a small number of well monitored colonies suggest a further large fall in numbers; (Foula, Fair Isle, Fetlar, Mousa, Hermaness, North Hill, Noss, and Hoy held 78 AOT between them in 2018, 81% fewer than was recorded by Seabird 2000 (403 AOT)). In the west of Scotland, only 15 AOT were recorded on Handa in 2018 with numbers there having declined fairly steadily since 2001 when a peak of 42 AOT was recorded.

In Scotland, Arctic and great skuas breed sympatrically, usually beside large colonies of cliff-nesting seabirds2. One of the main factors contributing towards this national decline is likely to be the continuous decrease in their annual productivity (no. chicks fledged per pair) and that of their host species from which they kleptoparasitise food (Arctic tern, kittiwake, common guillemot and puffin). Recent observed alterations in the marine food web in the northeast Atlantic, strongly influenced by fisheries management and climate change are driving the decline of lesser sandeels Ammodytes marinus, a main food source of Arctic skuas and their host species3,6,7,8,9,10. Another factor contributing to their decline is likely to be competition for nesting territories and predation by great skuas which have increased markedly2,9,11,12,13.

 

Productivity

arctic-skua-scotland-prod.jpg

Figure 4. Trend in productivity (no. of chicks fledged per pair) of Arctic skua in Scotland, 1986–2018. Based on SMP data; view the methods of analysis.

 

Arctic skuas periodically experience years of very poor productivity (no. of chicks fledged per pair), which often coincide with periods of presumed low sandeel abundance2; such periods have become more frequent since the late 1990s, with several years of very low success since 2003, although 2015 was the most productive breeding seasons since 1999. A recent study found that annual productivity declined, from a five-year mean of 0.91 in 1992 to 1996 to 0.29 in 2011 to 2015. During 1992–2000, it fell below 0.5 fledged per pair just once (1998), whereas it reached this level only three times since (2006, 2014, 2015)1.

Annual data from the six most frequently monitored Arctic skua colonies in Shetland (85 data points between 2003-2018 from Fair Isle, Fetlar, Foula, Hermaness, Mousa and Noss) illustrate just how bad breeding seasons have become. Complete failure was recorded 43 times, with productivity below 0.20 chicks fledged per pair on a further 16 occasions; only on 10 occasions did productivity climb above 0.80. Arctic skuas rely on stealing fish caught by other seabirds, especially Arctic terns, black-legged kittiwakes, common guillemot and Atlantic puffins; declines in the abundance and chick provisioning of these host species has reduced feeding opportunities for Arctic skuas1,2. Recent sandeel scarcity around Shetland is attributed to low recruitment in most years since the mid-1980s, linked to hydro-climatic changes affecting hatching dates, survival and transport of larvae from major spawning areas north and west of Orkney14,15. More significantly, environmental conditions for sandeels appear to be worsening, with sea temperature increases and oceanographic changes affecting their physiology, food supply, phenology and survival, leading to trophic mismatch and less food for seabirds6,7,8. Predation of Arctic skua chicks and sometimes displacement or killing of adults during territory disputes by great skuas (also ultimately linked to a scarcity of alternative fish prey for great skuas) is also known to be reducing productivity in some regions3,9,11,12.

 

England

Arctic skua does not breed in England.

 

Wales

Arctic skua does not breed in Wales.

 

Northern Ireland

Arctic skua does not breed in Northern Ireland.

 

Republic of Ireland

Arctic skua does not breed in the Republic of Ireland.

 

All Ireland

Arctic skua does not breed in Ireland.

 

Isle of Man

Arctic skua does not breed on the Isle of Man.

 

Channel Islands

Arctic skua does not breed on the Channel Islands.

Top

UK phenology, diet, survival rates

No data have been collected as part of the Seabird Monitoring Programme.

Top

References

1 Perkins, A., Ratcliffe, N., Suddaby, D., Ribbands, B., Smith, C., Ellis, P., Meek, E. and Bolton, M. 2018. Combined bottom-up and top-down pressures drive catastrophic population declines of Arctic skuas in Scotland. Journal of Animal Ecology, 87(6), 1573–1586.

2 Furness, R.W. and Ratcliffe, N. 2004. Arctic Skua Stercorarius parasiticus. In: Mitchell, P.I., Newton, S.F., Ratcliffe, N. and Dunn, T.E. eds. 2004. Seabird Populations of Britain and Ireland, pp. 160–172. Poyser, London.

3 Phillips, R.A., Caldow, R.W.G. and Furness, R.W. 1996. The influence of food availability on the breeding performance and reproductive success of Arctic Skuas. Ibis, 138, 410–419.

4 Frederiksen, M., Edwards, M., Richardson, A.J., Halliday, N.C. and Wanless, S. 2006. From plankton to top predators: bottom-up control of a marine food web across four trophic levels. Journal of Animal Ecology, 75, 1259–1268.

5 Régnier, T., Gibb, F.M. and Wright, P.J. 2017. Importance of trophic mismatch in a winter-
hatching species: evidence from lesser sandeel. Marine Ecology Progress Series, 567, 185–197.

6 Wanless, S., Harris, M.P., Newell, M.A., Speakman, J.R., and Daunt, F. 2018. Community-wide decline in the occurrence of lesser sandeels Ammodytes marinus in seabird chick diets at a North Sea colony. Marine Ecology Progress Series, 600, 193–206.

7 Furness, R. 1977. Effects of Great Skuas on Arctic Skuas in Shetland. British Birds, 70, 96–107.

8 Phillips, R.A., Furness, R.W. and Stewart, F.M. 1998. The influence of territory density on the vulnerability of Arctic skuas Stercorarius parasiticus to predation. Biological Conservation, 86, 21–31.

9 Jones, T., Smith, C., Williams, E. and Ramsay, A. 2008. Breeding performance and diet of Great Skuas Stercorarius skua and Parasitic Jaegers (Arctic Skuas) Stercorarius parasiticus on the west coast of Scotland. Bird Study, 55, 257–266.

10 Phillips, R.A., Caldow, R.W.G. and Furness, R.W. 1996. The influence of food availability on the breeding effort and reproductive success of Arctic Skuas Stercorarius parasiticus. Ibis, 138, 410–419.

11 Wright, P.J. and Bailey, M.C. 1993. Biology of Sandeels in the Vicinity of Seabird Colonies at Shetland. Fisheries Research Report, No. 15/93. Aberdeen: SOAFD Marine Laboratory.

12 Poloczanska, E.S., Cook, R.M., Ruxton, G.D. and Wright, P.J. 2004. Fishing vs. natural
recruitment variation in sandeels as a cause of seabird breeding failure at Shetland: a modelling approach. Journal of Marine Science, 61, 788–797.

13 Frederiksen, M., Furness, R.W. and Wanless, S. 2007. Regional variation in the role of bottom-up and top-down processes in controlling sandeel abundance in the North Sea. Marine Ecology Progress Series, 337, 279–286.

14 Burthe, S., Daunt, F., Butler, A., Elston, D., Frederiksen, M., Johns, D., Newell, M., Thackeray, S.J. and Wanless, S. 2012. Phenological trends and trophic mismatch across multiple levels of a North Sea pelagic food web. Marine Ecology Progress Series, 454, 119–133.

Top

Partners

Data have been provided to the SMP by the generous contributions of its partners, other organisations and volunteers throughout Britain and Ireland. Partners to the SMP are: BirdWatch Ireland; The British Trust for Ornithology; UK Centre for Ecology and Hydrology; Natural Resources Wales; Department of Environment, Food and Agriculture (Isle of Man); Department of Environment, Heritage and Local Government (Republic of Ireland); States of Guernsey Government; JNCC; Manx Birdlife; Manx National Heritage; The National Trust; National Trust for Scotland; Natural England; Northern Ireland Department of Agriculture, Environment and Rural Affairs; The Royal Society for the Protection of Birds; Scottish Natural Heritage; Seabird Group; Shetland Oil Terminal Environmental Advisory Group; Scottish Wildlife Trust. More about the SMP partners >>

 

Image of Arctic skua appears courtesy of Ian Rendall ©, is subject to international copyright law and may not be reproduced in any form whatsoever.

Top

Categories:

SMP Report 1986–2018

Published: .

Back to top