Arctic Tern Sterna paradisaea

Status;  International importance;  Population estimates;  Distribution;  Annual abundance/ productivity; Phenology/diet/survival

 

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Description

Arctic Tern vignette

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:

Amber listed in Birds of Conservation Concern 4 (2015 update)

EC Birds Directive - listed in Annex 1 and as a migratory species

(further information on Conservation Designations for UK Taxa)

Amber listed in Birds of Conservation Concern in Ireland 2014-2019 (2014 update)

 


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.

 


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.

 


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 (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

 

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.   

 



 

Breeding abundance

 

UK Arctic tern abundance trend

Figure 1: Trend in UK abundance index (solid line) of Arctic tern 1986-2015 with 95% confidence limits (dotted lines). Based on SMP data;  view the methods of analysis (PDF 158 kb).

 

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 during those years). Between 1990 and 2009, the index fluctuated between 100 and 130, excluding 2004 when a dip was noticeable. Abundance fell steeply between 2009 and 2011 but is rising again and, in 2014, was higher than in any year (excluding 1988 and 1989) probably due to increased numbers at colonies in England and Wales. In 2015, trend index fell again but abundance was still 18% above the 1986 baseline. Declining abundance up to and including 2004 was in part caused by a period of poor breeding seasons in the Northern Isles, which was in turn attributable to sandeel shortages linked to oceanographic changes (see below). Declines in the Arctic tern population have also been caused (in western Scotland) by American mink 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

 

UK Arctic tern productivity trend

Figure 2: Trend in UK productivity (no. of chicks fledged per pair) of Arctic tern 1986-2015. Based on SMP data; view the methods of analysis (PDF 158 kb).

 

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 it lies below 0.30. Especially unproductive years occurred from 1988 to 1990 and in four of the last eight 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. In 2015, prey seemed to be plentiful in the form of sandeels however, unseasonable weather conditions, strong tides and likely predators resulting in fewer chicks fledging than the previous year4,5,6.

 

 

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

 

Scotland Arctic tern abundance trend

Figure 1: Trend in abundance index (solid line) of Arctic tern in Scotland, 1986-2015 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 (PDF 158 kb).

 

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 afterward before further declines from 2009 onward. The index has risen slightly in recent years and, in 2015, sits 66% lower than in 1986. Declines have been caused by a combination of factors. In the Northern Isles, a period of poor breeding seasons were recorded, driven by sandeel shortages linked to oceanographic changes. In western Scotland, declines have been caused by American mink taking adults, eggs and chicks from near-shore nesting islands. Successful mink eradication programmes on the west coast are contributing towards conservation measures at many sites. Over the longer term, Scotland's Arctic tern population may have changed much since Operation Seafarer, although there is some uncertainty over this due to questions of compatibility of census methods between the national surveys.

 

Productivity

 

Scotland Arctic tern productivity trend

Figure 2: Trend in productivity (no. of chicks fledged per pair) of Arctic tern in Scotland, 1986-2015. Based on SMP data; view the methods of analysis (PDF 158 kb).

 

Compared with their conspecific, the common tern, the productivity of Arctic terns is consistently lower and indeed the lowest of any seabird species breeding in Scotland. Annual average productivity has risen above 0.40 chicks per pair only once in 30 years. Very low productivity (below 0.20) is evident in 21 years, including nine years in the last decade, associated with marked 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 Orkney 2,3. At colonies in Lochaber and in Argyll and Bute detailed studies into the effects of predation by American mink revealed some losses to this animal in 2014. 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 control.

 

 

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

 

England Arctic tern abundance trend

Figure 1: Trend in abundance index (solid line) of Arctic tern in England, 1986-2015 with 95% confidence limits (dotted lines). Based on SMP data; view the methods of analysis (PDF 158 kb).

 

Although Arctic tern numbers in England appear to have been stable between the first two censuses, questions of compatibility of methods between censuses, introduces uncertainty in the magnitude of changes in the population size between 1969-70 and 1985-88. 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 have increased. With the addition of some missing data from Long Nanny, Figure 1 now shows the abundance trend since 1986 (previous reports only showed numbers at five main colonies). Abundance declined up to 1991 before recovering, then fell again until 1999. Since that time, numbers have increased and the index has been crossed in recent years, but in 2014 it reached a new high point although dipped slightly to 18% above the 1986 baseline in 2015. Six colonies monitored in 2015 (Farne Islands, Coquet, Long Nanny (all Northumberland), Blakeney Point, Scolt Head (both Norfolk) and Seaforth (Merseyside)), which contain over 95% of Arctic terns nesting in England, held 5,122 AON. This is more than has been recorded during any of the national censuses and is a 41% increase to what was recorded from all colonies (c.16 are known) during Seabird 2000.

 

Productivity

 

England Arctic tern productivity trend

Figure 2: Trend in productivity (no. of chicks fledged per pair) of Arctic tern in England, 1986-2015. Based on SMP data; view the methods of analysis (PDF 158 kb).

 

The productivity of Arctic terns in England has fluctuated widely over the 30 years it has been recorded by the SMP. However, it has not been as consistently low as that recorded at Scottish colonies.  Until recently, productivity was lowest in 2004 (0.18) however, 2015 is now the lowest year since recording began with only 0.10 chicks fledged per pair.

 

 

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 Abundance, Skerries

Figure 1: Abundance of Arctic tern on The Skerries (Gwynedd), 1986-2015.

 

There are only a few breeding sites for Arctic terns in Wales, all situated on the island of Angelsey. National census data show numbers have increased, from 436 pairs in 1969-70 to 1,705 pairs in 1998-2002. This increase has continued; for example, in 2012, over 3,900 pairs were found in four colonies, so the national population has more than doubled over the last decade. By far the largest colony, holding over 80% of the Welsh population, is on The Skerries (Gwynedd) where over 3,500 pairs have nested each year between 2013 and 2015.

 

Productivity

 

Wales Arctic tern productivity trend

Figure 1: Trend in productivity (no. of chicks fledged per pair) of Arctic tern in Wales, 1986-2015. Based on SMP data; view the methods of analysis (PDF 158 kb).

 

In Wales, the trend in productivity of Arctic terns was upward during the 1990s, after which there was a few years of relatively consistent high productivity. However, since 2003 productivity has fluctuated widely, possibly due to food shortage in some years. Detailed monitoring at Cemlyn (Gwynedd) in 2015 indicated another poor breeding season with only 15 chicks fledging from 47 AON (15 chicks from only 39 nests in 2014) although it was not clear why breeding success was so low4.   

 

 

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 Ireland abundance 2015

Figure 1: Abundance of Arctic tern at Strangford and Carlingford Loughs and Cockle Island (all Co. Down), 1986-2015.

 

During Operation Seafarer, only a few hundred Arctic terns nested in Northern Ireland. Numbers increased in each subsequent national census, with Seabird 2000 recording 767 pairs. Counts from three of the more regularly monitored colonies, Strangford and Carlingford Loughs and Cockle Island (all Co. Down), 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, and 284 nesting pairs in 2015. However, the Copeland Islands (Co. Down), the main concentration of nesting Arctic terns, held between 800 and 1,000 pairs each year from 2003-2012, with a new peak of 1,250 AON recorded there in 2013 (no survey took place in 2014 or  2015). In 2006, numbers at monitored colonies reached c.2,000 pairs (a few known colonies were not visited), well above that recorded by Seabird 2000. Despite declines at some colonies since 2006 numbers still compare favourably against the total figure from the last census.

 

Productivity

 

Arctic terns in Northern Ireland on average fledged approximately 0.35 chicks per pair per year between 1991 and 2015; there was no statistically significant variation over time. Breeding success 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. In 2015, 50 chicks fledged from 85 nests monitored at Carlingford Lough..

 

 

Population estimates and change 1969-2002 (census data)

 

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

Population estimate (AON*) 848 1,856 2,735
% change since previous census    N/a +119 +47

 

* AON = Apparently Occupied Nests

 

Breeding abundance

 

Arctic Tern Abundance, Republic of Ireland

Figure 1: Abundance of Arctic tern at Rockabill (Co. Dublin) and Lady's Island Lake (Co. Wexford), 1986-2015.

 

In the Republic of Ireland, Arctic tern numbers also increased in each subsequent national census. Counts during Seabird 2000 were three times higher than that recorded by Operation Seafarer. Since Seabird 2000, fewer Arctic tern colonies have been monitored. Counts at Rockabill (Co. Dublin) and Lady's Island Lake (Co. Wexford), both sites with regular survey coverage, had been increasing over the last decade, peaking at 1,102 pairs in 2010 (combined), but numbers in 2014 had fallen to 808 pairs. The majority of these (787) are now found at Lady's Island Lake with the colony at Rockabill decreasing considerably since 2009. However, without a comparison of the data from the other 20 colonies known during Seabird 2000, the current status of the population is unknown.

 

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 data were submitted to the SMP in 2014 and 2015.

 

 

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 that Arctic terns numbers throughout Ireland had increased by 261% since Operation Seafarer. In the years since Seabird 2000, numbers in Northern Ireland had been increasing, and in 2006, numbers at monitored colonies were double that recorded by Seabird 2000. Numbers have fallen since that peak year; e.g. just 400 pairs were present at three monitored colonies in 2014 compared to over 900 pairs at the same colonies nine years previously. However, the Copeland Islands, the main concentration of nesting Arctic terns, have held between 800 and 1,000 pairs each year from 2003-2012, with a new peak of 1,250 AON recorded there in 2013 (no surveys were done in 2014 and 2015). The few colonies regularly monitored in the Republic of Ireland held just over 800 pairs in 2014, but had also declined recently from a peak of c.1,000 pairs in 2010. Combining data for both 2013 and 2014 gives a total of over 2,400 pairs at sampled colonies. However, with only a few recent counts from 20 other colonies in the Republic of Ireland for comparison the current All-Ireland population is unknown although is greater than that recorded during the SCR.

 

Productivity

 

All-Ireland Arctic tern productivity trend

Figure 1: 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 (PDF 158 kb).

 

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.

 

 

Population estimates and change 1969-2002 (census data)

 

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

Population estimate (AON*) 29 22 8
% change since previous census    N/a -24 -64

 

* AON = Apparently Occupied Nests

 

Breeding abundance

 

Arctic Tern Abundance, Isle of Man

Figure 1: Abundance of Arctic tern at The Ayres (Isle of Man), 1986-2015.

 

The small population of Arctic tern breeding on the Isle of Man nest almost entirely near The Ayres or Rue Point. Twenty-nine pairs were recorded during Operation Seafarer and 22 pairs by the Seabird Colony Register. This had declined somewhat by Seabird 2000 when only five pairs 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 three pairs built nests. In contrast, 2015 recorded over 37 AON - the highest number since monitoring began.

 

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.

 

 

Arctic tern does not breed on the Channel Islands.

 

 


UK phenology, diet, survival rates

 

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

 

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 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 report, Scottish Natural Heritage, Aberdeen.

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

 


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