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Arctic tern (Sterna paradisaea)

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

 

Arctic terns are the commonest tern breeding in the UK, but their northerly distribution means they are less familiar to most observers. The population is concentrated in the Northern Isles, with 73% occurring there. In common with other tern species, Arctic terns were probably reduced to low levels by hunting for the millinery trade and egging, but have probably increased since the 1930s owing to legal protection. Increasing sandeel stocks in waters around Shetland through the 1970s and early 1980s, improving food availability, may have also contributed to population growth. However, a collapse of the sandeel stock around Shetland between 1984 and 1990 resulted in a reversal of fortunes.

In western Scotland and the Western Isles, declines and redistribution of the population have resulted from predation by introduced American mink Neovison vison. Future population trends depend on the success of mink eradication and control projects being implemented in these areas. Many Arctic tern colonies at the southern range of the UK population are increasing, probably in response to site management for breeding terns.

Conservation status

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

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International importance

UK Population

Biogeographic Population

% World Population

53,400 AON*

4.7 (Europe and N Atlantic)

3.1

*AON = Apparently Occupied Nests

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.

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

All terns show a low degree of site faithfulness from one year to the next. In response to predation or habitat change, especially in areas where islands and other suitable habitat are plentiful, terns often move en masse between different sites. This is such a problem that in order to gain an accurate national estimate of tern numbers, a simultaneous census was planned to cover all colonies in Britain within a single year. Hence in 2000, the majority of British tern colonies were surveyed including extensive surveys of Orkney and Shetland. The main exception was in the Western Isles, where most tern colonies in Lewis and Harris were surveyed in 1999, while those in the south of the Sound of Harris to Barra Head were surveyed in 2002. For Northern Ireland, it was decided to make the most of limited resources and utilise results from the All-Ireland tern survey conducted in 1995. More recent counts (with those from 2000 given priority) were included for some colonies. Movements among these regions are unlikely to have caused severe bias in trend estimation. Thus, Seabird 2000 is likely to have included counts from the vast majority of Arctic tern colonies, with comprehensive coverage within their UK range. During the SCR, coverage of the Northern Isles was poor, but this was overcome by inclusion of data from the 1980 survey of terns in Orkney and Shetland. There is also debate concerning the degree to which survey coverage, changes in methods and survey timing have contributed to changes in status since Operation Seafarer, and so long-term changes should be treated with caution.

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

UK Population estimate (AON*)

51,411

76,886

53,380

% change since previous census

n/a

+50

-31

*AON = Apparently Occupied Nests

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

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Distribution/abundance

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

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

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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-tern-uk-ab.jpg

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

 

There is uncertainty, due to questions of compatibility of methods between censuses, of the magnitude of changes in Arctic tern population size between 1969-70 and 1985-88, though numbers probably increased over this period. The Arctic tern abundance index, based on the SMP sample, showed a rapid increase, followed by a decrease, during 1986 to 1990 (influenced by changes at a few large colonies in the Northern Isles of Scotland during those years). Between 1990 and 2009, the index fluctuated between 100 and 130, excluding 2002–2004 when a dip was noticeable. Abundance fell steeply between 2009 and 2011 but rose again to 2014, when it was higher than in any year (excluding 1988 and 1989) probably due to increased numbers at colonies in England and Wales. In 2015 and 2016, the index fell again but was still above the 1986 baseline. After a rise in the abundance index in 2017, it decreased to 11% below the 1986 baseline in 2018. Declining abundance up to and including 2004 was in part caused by poor breeding seasons in the Northern Isles, which were attributed to sandeel Ammodytes spp. shortages linked to oceanographic changes (see below). Declines in the Arctic tern population have also been caused (in western Scotland) by American mink Neovison vison predation, a non-native invasive species. A successful mink eradication programme on the Western Isles and other control measures1 are contributing towards conservation initiatives aimed at increasing the population.

 

Productivity

arctic-tern-uk-prod.jpg

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

 

The productivity of Arctic terns is consistently the lowest of any of the seabirds breeding in the UK. Since 1986, the annual average productivity has only risen above 0.40 chicks per pair once, in 2000, and in most years lies below 0.30. Especially unproductive years occurred from 1988 to 1990, in 2004 and in two of the last four breeding seasons, associated with marked shortages in prey (especially sandeels around the Northern Isles, where most Arctic terns breed). The effects of this may have been exacerbated by poor weather hampering foraging and chilling eggs and chicks, together with increased predation by gulls seeking alternative food sources. Sandeel shortages in Shetland have probably been caused by oceanographic changes that affected larval sandeel transport and recruitment from spawning stock in Orkney2,3. From 2015 to 2017, sandeel prey appeared to be plentiful and unseasonable weather conditions, strong tides and predation were the more likely causes of fewer chicks fledging than in 20144,5,6.

 

Scotland

Population estimates and change 1969–2002 (census data)

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

Population estimate (AON*)

46,385

71,178

47,306

% change since previous census

n/a

+53

-34

*AON = Apparently Occupied Nests

 

Breeding abundance

arctic-tern-scotland-ab.jpg

Figure 3. Trend in abundance index (solid line) of Arctic tern in Scotland, 1986–2018 with 95% confidence limits (dotted lines; drawing of upper limit restricted to preserve detail in the abundance index). Based on SMP data; view the methods of analysis.

 

The rapid increase and subsequent fall in the abundance of Arctic terns in Scotland between 1986 and 1990 is probably influenced by changes at a few large colonies in the Northern Isles during those years. Thereafter, the index declined to a low point in 2004, with a short period of recovery before further declines from 2009 to 2011. The index has risen slightly in recent years and, in 2014, was just 15% below the 1986 baseline, although by 2018 had declined to almost 50% below. Declines are likely to have been caused by a combination of factors. In the Northern Isles, very low productivity (below 0.30) is evident in 29 years between 1986 and 2018, driven by sandeel shortages linked to oceanographic changes3. In western Scotland, declines have been caused by American mink taking adults, eggs and chicks from near-shore nesting islands1,7, although successful mink eradication programmes on the west coast have led to increases at many sites8. Scotland's Arctic tern population appears not have changed significantly since Operation Seafarer, although there is some uncertainty over this due to questions concerning the compatibility of methods between the national censuses.

 

Productivity

arctic-tern-scotland-prod.jpg

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

 

Productivity of Arctic terns is consistently lower than common terns, and indeed the lowest of any seabird species breeding in Scotland. Annual average productivity has risen above 0.40 chicks per pair only twice in 30 years. Very low productivity (below 0.20) is evident in 17 years, including six years in the last decade, associated with food shortages (especially sandeels around the Northern Isles, where most Arctic terns breed), exacerbated by poor weather and increased predation by gulls seeking alternative food sources. Sandeel shortages in Shetland have probably been caused by oceanographic changes that affected larval sandeel transport and recruitment from spawning stock in Orkney2,3. At colonies in Lochaber, and in Argyll and Bute, detailed studies into the effects of predation by American mink revealed that colonies where mink were controlled fledged an average of 0.65 chicks per nesting pair compared to 0.50 at colonies with no, or unsuccessful, mink control8.

 

England

Population estimates and change 1969–2002 (census data)

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

Population estimate (AON*)

4,469

4,544

3,602

% change since previous census   

n/a

+2

-21

*AON = Apparently Occupied Nests

 

Breeding abundance

arctic-tern-england-ab.jpg

Figure 5. Trend in abundance index (solid line) of Arctic tern in England, 1986–2018 with 95% confidence limits (dotted lines). Based on SMP data; view the methods of analysis.

 

Arctic tern numbers in England appear to have been stable between the first two censuses (1969-70 and 1985-88), however, this should be viewed with caution as there is uncertainty regarding how compatible the different methods used in each census were. Between the SCR census and Seabird 2000, numbers declined by one-fifth. However, since 2000 (when all Arctic tern colonies were surveyed for Seabird 2000), numbers appear to have increased. With the addition of missing data from Long Nanny, Figure 5 now shows the abundance trend since 1986 (previous reports only showed numbers at five main colonies). Abundance declined from 1986 to 1991 before recovering in 1992 then falling again until 1999. Since then, numbers have increased and the baseline has been crossed in recent years, reaching a new high point in 2014. Three colonies monitored in 2018 (Farne Islands, Coquet, Long Nanny) which contained over 95% of Arctic terns nesting in England, held 6,370 AON. This is more than has been recorded during any of the national censuses and is a 77% increase to what was recorded from all colonies (c. 16 are known) during Seabird 2000.

 

Productivity

arctic-tern-england-prod.jpg

Figure 6. Trend in productivity (no. of chicks fledged per pair) of Arctic tern in England, 1986–2018. Based on SMP data; view the methods of analysis.

 

Productivity of Arctic terns in England has fluctuated widely over the 32 years it has been monitored. However, it has not been as consistently low as that recorded at Scottish colonies. Until recently, the lowest recorded productivity was in 2004 (0.18), however, in 2016 it reached 0.02, the lowest year since records began. During 2015 and 2016, Arctic terns at Long Nanny nested in large numbers but, out of 3,000 AON, only 40 chicks fledged. While productivity has remained low at most reported colonies, Coquet Island achieved reasonably high productivity in 2017 and 2018, with 1.13 and 1.39 chicks fledged per pair respectively.

 

Wales

Population estimates and change 1969–2002 (census data)

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

Population estimate (AON*)

436

732

1,705

% change since previous census   

n/a

+68

+133

*AON = Apparently Occupied Nests

 

Breeding abundance

arctic-tern-wales-ab.jpg

Figure 7. Abundance of Arctic tern on The Skerries, Isle of Anglesey, 1986–2018.

 

There are only a few Arctic terns colonies in Wales, all situated on the island of Anglesey. National census data show numbers increased from 436 AON in 1969-70 to 1,705 AON in 1998–2002. This increase has continued; for example, in 2008, over 2,800 AON were found at four colonies and in 2018 there were 3,017 in three colonies, so the Welsh population has almost doubled over the last 18 years. By far the largest colony, holding at least 95% of the Welsh population, is on The Skerries which held 3,500 AON each year between 2013 and 2015. Numbers dropped to 2,770 AON briefly in 2017 but were at 3,435 AON in 2018 (Figure 7).

 

Productivity

In Wales, productivity of Arctic terns increased during the 1990s, after which there were a few years of relatively consistent high productivity. However, since 2003, productivity has fluctuated widely, possibly due to food shortage in some years. Insufficient data in recent years does not allow a trend to be generated. The Cemyln breeding seasons in 2016 and 2017 were particularly poor, with no chicks fledging from 60 and 20 AON respectively, due to some predation, but mostly repeated disturbance, by otters Lutra lutra (Chris Wynne pers. comm.). In 2018 productivity at Cemlyn was 0.71 chicks per pair, much higher than the 1986 to 2018 average of 0.33 chicks fledged per pair.

 

Northern Ireland

Population estimates and change 1969–2002 (census data)

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

Population estimate (AON*)

121

432

767

% change since previous census   

n/a

+257

+78

*AON = Apparently Occupied Nests

 

Breeding abundance

arctic-tern-ni-ab.jpg

Figure 9. Abundance of Arctic tern at Strangford and Carlingford Loughs, and Cockle Island, 1986–2018.

 

In Northern Ireland, Arctic terns breed in just a few colonies, including the Copeland Islands, Strangford Lough, Belfast Harbour, Bird Island, Green Island, and Cockle Island. During Operation Seafarer, 121 Arctic tern AON were recorded in Northern Ireland. Numbers then increased in each subsequent census, with Seabird 2000 recording 767 AON. Counts from three regularly monitored colonies, Strangford and Carlingford Loughs, and Cockle Island, show how numbers there have changed over time, reaching a peak in 2006 (926 AON) but declining steeply afterward with just 178 pairs present at the three sites in 2012 (Figure 9). Since then, numbers have fluctuated but are currently increasing again, with 604 AON recorded in 2018. The Copeland Islands, the largest colony of Arctic terns in Northern Ireland, held between 800 and 1,000 AON each year from 2003 to 2012, with a new peak of 1,250 AON being recorded in 2013. No full survey has taken place on all three islands of the Copeland Islands in the past five years, however, Arctic terns were counted on Lighthouse Island in 2018, when 150 AON were recorded. In 2018, numbers still compared favourably against the total figure from the last census with 769 AON recorded at five of eight colonies, especially as the largest, Big Copeland Island, is not included in this total.

 

Productivity

Arctic terns in Northern Ireland fledged an average of 0.31 chicks per pair per year between 1991 and 2018; there was no statistically significant variation over time. Productivity has been extremely low in some years, especially between 2007 and 2011, when the main colonies on the Copeland Islands failed due to a combination of adverse weather and predation by gulls and otters Lutra lutra. Productivity was again very low in 2018, due to the effects of Storm Hector and significant predation by large gulls and otters at Carlingford and Strangford Lough (five chicks fledged from 263 AON).

 

Republic of Ireland

Population estimates and change 1969–2018 (census data)

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

Republic of Ireland Census

(2015-18)

Population estimate (AON*)

848

1,856

2,735

2,778

% change since previous census   

n/a

+119

+47

+2

*AON = Apparently Occupied Nests

 

Breeding abundance

arctic-tern-ireland-ab.jpg

Figure 10. Abundance of Arctic tern at Rockabill and Lady's Island Lake, 1986–2018.

In the Republic of Ireland, Arctic tern numbers increased between every national census, with Seabird 2000 recording a population three times higher than Operation Seafarer. The Rockabill and Lady's Island Lake (Figure 10) colonies increased to combined peak of 1,102 AON in 2010 but, by 2014 numbers had fallen to 808 AON. The majority of these (787 AON) were at Lady's Island Lake with the colony at Rockabill decreasing considerably since 2009. In 2018, 59 AON were counted at Rockabill and 693 AON at Lady’s Island Lake8,9. A recent seabird census of the Republic of Ireland recorded 2,778 Arctic tern AON, a slight increase since Seabird 200010.

 

Productivity

Arctic terns in the Republic of Ireland on average fledged approximately 0.28 chicks per pair per year between 1991 and 2013; there was no statistically significant variation over time. No productivity data have been submitted to the SMP since 2014.

 

All Ireland

Population estimates and change 1969–2002 (census data)

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998–2002)

Population estimate (AON*)

969

2,288

3,502

% change since previous census   

n/a

+136

+53

*AON = Apparently Occupied Nests

 

Breeding abundance

Seabird 2000 found Arctic terns numbers throughout Ireland had increased by 261% since Operation Seafarer. Since Seabird 2000, numbers in Northern Ireland had been increasing, and in 2006, numbers at monitored colonies were double that recorded by Seabird 2000. No full survey has taken place on all three islands of the Copeland Islands in the past five years, however, Arctic terns were counted on Lighthouse Island in 2018, when 150 AON were recorded. In 2018, numbers still compared favourably against the total figure from the last census with 769 AON recorded at five of eight colonies, especially as the largest, Big Copeland Island, was not included in the total. A recent seabird census of the Republic of Ireland has counted 2,778 AON, a 2% increase since Seabird 200010. These recent count data suggest that it is very likely that the Irish Arctic tern population is increasing.

 

Productivity

arctic-tern-all-ireland-prod.jpg

Figure 11. Trend in productivity (no. of chicks fledged per pair) of Arctic tern throughout Ireland, 1986–2015. Based on SMP data; view the methods of analysis.

 

Productivity of Arctic terns from colonies throughout Ireland appears to have been declining over the last decade, with very few chicks fledged in 2005, 2006, 2013 and 2015. Prior to 1998, data are lacking for several years, so no clear trend is evident over the whole period.

No Arctic tern productivity data have been submitted to the SMP from the Republic of Ireland since 2014.

 

Isle of Man

Population estimates and change 1969–2018 (census data)

 

Operation Seafarer

(1969-70)

Seabird Colony Register

(1985-88)

Seabird 2000

(1998–2002)

Isle of Man Census

(2017-18)

Population estimate (AON*)

29

22

8

56

% change since previous census

n/a

-24

-64

+600

*AON = Apparently Occupied Nests

 

Breeding abundance

The small population of Arctic tern breeding on the Isle of Man nest almost entirely near The Ayres or Rue Point. A total of 29 AON were recorded during Operation Seafarer and 22 during the Seabird Colony Register. This had declined somewhat by Seabird 2000 when only 8 AON were recorded, although numbers had been lower during the early 1990s. Immediately after Seabird 2000, numbers increased slightly, but a decline began in 2005 and continued until 2012 when only AON were recorded. In contrast, the Isle of Man Seabird Census in 2017 recorded 56 AON, the highest number since monitoring began11.

 

Productivity

Data submitted to the SMP on the productivity of Arctic terns on the Isle of Man are sparse; thus, no meaningful average productivity value can be given.

 

Channel Islands

Arctic tern does not breed on the Channel Islands.

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UK phenology, diet, survival rates

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

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References

1 Craik, J.C.A. 1997. Long-term effects of North American Mink Mustela vison on seabirds in western Scotland. Bird Study, 44, 303–309.

2 Wright, P.J. 1996. Is there a conflict between sandeel fisheries and seabirds? A case study at Shetland. In: Greenstreet, S.P.R. and Tasker, M.L. eds. Aquatic predators and their prey. Fishing News Books, Oxford, pp. 154–165.

3 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. SOAFD Marine Laboratory, Aberdeen, Scotland.

4 Wright, D. and Wilde, D. 2015. Cemlyn wardens report 2015. Unpublished NWWT Report, North Wales Wildlife Trust.

5 Short, D. and Watts E. 2016. Breeding of four species of tern and Black-headed Gull at Forvie National Nature Reserve, 2015. Unpublished SNH Report, Scottish Natural Heritage, Edinburgh.

6 Rendell-Read, S. 2016. Little Tern Newsletter 2015. Unpublished RSPB Report, Royal Society for the Protection of Birds, Sandy.

7 Craik, J.C.A. 2015. Results of the mink-seabird project in 2014. Unpublished SAMS Report, Scottish Association for Marine Science, Oban.

8 Acampora, H., Ní Dhonnabháin, L., Miley, D. and Newton, S. 2018. Rockabill Tern Report 2018. Unpublished BirdWatch Ireland Seabird Conservation Report. BirdWatch Ireland.

9 Daly, D., Murphy, B., O’Connor, B. and Murray, T. 2018. Lady’s Island Lake Tern Report 2018. NPWS report. National Parks and Wildlife Service, Department of Culture, Heritage and the Gaeltacht, Ireland.

10 Cummins, S., Lauder, C., Lauder, A. and Tierney, T. D. 2019. The Status of Ireland’s Breeding Seabirds: Birds Directive Article 12 Reporting 2013 – 2018. Irish Wildlife Manuals, No. 114. National Parks and Wildlife Service, Department of Culture, Heritage and the Gaeltacht, Ireland.

11 Hill, R.W., Morris, N. G., Bowman, K. A. and Wright, D. 2019. The Isle of Man Seabird Census: Report on the census of breeding seabirds in the Isle of Man 2017-18. Manx BirdLife. Laxey, Isle of Man.

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

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SMP Report 1986–2018

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