Arctic Skua Stercorarius parasiticus
Status; International importance;
Population
estimates; Distribution; Annual abundance/
productivity; Phenology/diet/survival
Description
The following was 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, 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:
Red listed in Birds
of Conservation Concern 3 (2009 update)
UK BAP - priority
species
(further information on Conservation Designations for UK Taxa)
International importance
*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.
UK population estimates and change 1969-2002 (census data)
Although Arctic skuas usually breed every year once they have
been recruited into a colony, and usually return to exactly the
same territory year after year, 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, which may have resulted
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.
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 where colonies are found and how large they are is
provided in the Seabird 2000 Arctic skua
results page (PDF, 1.1 mb).
An
interactive map is available on the NBN Gateway, where you can
filter to display only the Seabird 2000 data. For more
recent, but less comprehensive, coverage view the distribution on
the NBN with all available contributing datasets
The locations sampled during the annual
Seabird Monitoring Programme provide some information on
distribution and are accessible via the Seabird Monitoring Programme
online database.
Annual abundance and productivity by geographical
area
Breeding abundance
Figure 1: Trend in UK
abundance index (solid line) of Arctic skua 1986-2010
with 95% confidence limits (dotted lines). Based on SMP data;
view the methods
of analysis (PDF 158 kb).
Abundance of Arctic skua has probably declined
more than any other seabird in the UK in the period 1986-2009; the
population index in 2008 was 71% lower than in 1986. The index has
increased slightly since then but is still over 50% lower than in
1986. A survey of the Orcadian population in 2010 found just 376
AOT compared to 720 AOT in 2000 so numbers in that
region alone have declined by 47% during the last decade. In
the longer term, the population increased (for unknown
reasons) between 1969-70 (1,000 pairs) to 1985-88 (3,400
pairs), though it is thought that the first census underestimated
numbers somewhat. Contributory factors to the decline include
competition for nesting territories with great skuas1 (which have increased
markedly) and reductions in sandeel stocks, particularly around
Shetland, where over half of the UK (Scotland) population
occurs2.
Productivity
Figure 2: Trend in UK
productivity (no. of chicks fledged per pair) of Arctic
skua 1986-2010. Based on SMP data; view
the methods
of analysis (PDF 158 kb).
Arctic skuas periodically experience years of
very poor productivity, which often coincide with periods
of low sandeel abundance2;
such periods have become more frequent since the late 1990s and
2010 was yet another year of low productivity. Arctic skuas
rely for food by stealing fish caught by other seabirds, especially
black-legged kittiwakes, Arctic terns and Atlantic puffins;
declines in the abundance of these host species has reduced feeding
opportunities for Arctic skuas1.
Within the British Isles this species
breeds only in Scotland. Thus all data and
text displayed for the United Kingdom is
fully relevant for Scotland but is not repeated
here.
This species does not breed in England.
This species does not breed in Wales.
This species does not breed in Northern
Ireland.
This species does not breed in the Republic of
Ireland.
This species does not breed in Ireland.
This species does not breed on the Isle of Man.
This species does not breed on the Channel Islands.
UK Phenology, diet, survival rates
No data have been collected as part of the Seabird Monitoring
Programme.
References
1 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:160-172.
Poyser, London.
2 Phillips, R.A, Caldow, R.W.G. & Furness,
R.W. 1996. The influence of food availability on the breeding
performance and reproductive success of Arctic Skuas.
Ibis. 138, 410-419.
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; Centre for Ecology and
Hydrology; Countryside Council for Wales; Department of
Agriculture, Fisheries and Forestry (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 Environment Agency; 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.