Sandwich Tern Sterna sandvicensis

StatusInternational importancePopulation estimates;  DistributionAnnual abundance/ productivityPhenology/diet/survival

 

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Description

Sandwich 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).

 

Sandwich terns exhibit the most erratic population trends and distribution of any seabird breeding in the UK. The population fluctuates dramatically among years due to large variations in the proportion of mature birds attempting to breed and distribution varies owing to mass movements between colonies. The species is distributed widely but patchily around the coasts of the British Isles, broadly reflecting the availability of favoured nesting habitat: low-lying offshore islands, islets in bays or brackish lagoons, spits or remote mainland dunes. Despite frequent changes in the sites used, the broad distribution in the UK has changed little over the last 30 years. Sandwich terns are among the most gregarious of all seabirds, with the population confined to a small number of relatively large colonies in which birds nest at very high densities.

 

Tern populations in NW Europe were brought to the brink of extirpation at the end of the 19th century by egg collection for food and hunting of adults for the millinery trade, but recovered in response to protective legislation in the early 20th century. Sandwich terns in the UK increased from the 1920s to the mid 1980s, with protection from increasing recreational disturbance on beaches as well as from persecution probably facilitating this recovery. Annual counts of the main colonies demonstrated that there was a sustained increase between the first two national surveys, but that the population fluctuated erratically around this trend.

 


Conservation status

 

Sandwich 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
12,500 AON* 16.9 (ssp. sandvicensis) 9.6

 

*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)

 

Coverage of Sandwich tern colonies was comprehensive during all three of the national surveys, and so long-term trends will be real rather than artifacts of survey coverage. However, the size of the breeding population fluctuates erratically from year to year so trends based on comparison of two widely spaced surveys must therefore be viewed with caution, since one of them may have coincided with a year of temporarily depressed population size. Because whole colonies may move site within a year or two in response to changing conditions, such movements have the potential to produce severe bias in national population estimates that rely on summing counts from colonies surveyed in different years. To minimise this, all Sandwich tern colonies in the UK (except for one) were surveyed in 2000. During the SCR census, counts of colonies within regions were often taken from different years so, if colonies moved, some pairs may have been double counted and others omitted.

 

 

Operation Seafarer

(1969-70)

Seabird Colony Register

(1985-88)

Seabird 2000

(2000-2001)

UK Population estimate (AON*) 11,068 14,766 12,490
% change since previous census N/a +33 -15

 

*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 Sandwich tern found in different regions, and a map showing the locations and size of colonies, is provided in the Seabird 2000 Sandwich tern results page (PDF, 1.0 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 Sandwich tern abundance trend

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

 

Between censuses in 1969-70 and 1985-88, the United Kingdom population increased from 10,500 pairs to 14,800, probably as a result of increased legal protection, helping to reduce disturbance from recreation. The breeding abundance of Sandwich terns in the UK peaked in 1988, declining thereafter until the mid-90s when the index reached its lowest point. Since then, an increase is evident up to 2002 after which abundance appears to be declining again toward 2013. In 2015, the index was based at 5% above the 1986 baseline. The spike in the index in 2009 is due to an influx of Sandwich terns - apparently from continental Europe -nesting at Minsmere (Suffolk); 550 AON were recorded there in 2009, compared to only one pair the year before and in 2014, and none several years before and after 2009, including 2015.

 

Productivity

 

Sandwich tern Productivity UK 2015

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

 

A marked decline in productivity is obvious since 2000 when Sandwich terns fledged a record number of chicks. In the 14 years prior to 2000 it could be argued that productivity showed no clear trend, although in 1991 and between 1997 and 1999 it was particularly low. Few chicks fledged in these years due to bad weather, predation and disturbance by a variety of mammals and gulls; food shortage was implicated at only one colony. Predation on eggs and chicks by foxes Vulpes vulpes is probably the most prevalent factor determining productivity, and abandonment of a colony is often the result of predation1. Fox populations are thought to have increased during the past few decades due to less intensive management by gamekeepers. Nature reserve managers use electric fences to exclude foxes, which are not always successful. As Sandwich terns nest on low-lying ground close to the tide edge, their nests are vulnerable to tidal inundation; predictions of increased storminess and sea-level change under climate change scenarios may lead to increased prevalence of such events.

 

Analysis of the SMP dataset found breeding success of Sandwich terns averaged 0.66 chicks per nest per year between 1986 and 2008 and remained relatively stable2. The quality of the dataset meant any change of 10% or more could be detected with confidence. Using existing life history information (population size, clutch size, age at first breeding and survival rates of different age classes) to parameterise population viability analysis, it was predicted that, if this level of breeding performance were to remain unchanged, the population of Sandwich terns would decline by 62% over 25 years. Such a decline could be averted, and the population could be stabilised, if breeding success rose to 1.10. In 2015, UK productivity was 0.43 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*) 2,465 2,286 1,068
% change since previous census    N/a -7 -53

 

* AON = Apparently Occupied Nests

 

Breeding abundance

 

Scotland Sandwich tern abundance trend

Figure 1: Trend in abundance index (solid line) of Sandwich 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 Scottish population of Sandwich terns changed little between the national censuses in 1969-70 and 1985-88 but a large decline occurred as numbers fell by 53% by the Seabird 2000 census. The majority of the Scottish population nests at the Sands of Forvie (Gordon), a well monitored colony, which held almost half of Scotland's Sandwich terns during Seabird 2000. The trend between 1987 and 1998 is largely governed by the decline observed at Sands of Forvie, caused by several years of predation by foxes3. Since 1999, numbers have increase at Sands of Forvie, fluctuating between 1008 and 565 AON. However, other large colonies became extinct during this period, most by the mid to late 1990s (e.g. Loch of Strathbeg (Banff and Buchan), Inchmickery (City of Edinburgh), McDermott's (Inverness), while at others (e.g. Long Craig (Dunfermline), Isle of May (North-east Fife)) nesting has only been sporadic. Gulls extirpated the colony on Inchmickery but causes of decline or extinction have not been ascertained for other colonies. Since 2010, the trend has been relatively stable with an index between 47-60% below the baseline however, in 2015, the index increased to 39%.

 

Productivity

 

Scotland Sandwich tern productivity trend

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

 

The productivity of Sandwich terns at colonies monitored in Scotland has fluctuated considerably since recording began. 2000 and 2001 were the only years on record with relatively high levels of productivity, with the average being 0.67 chicks fledged per pair. In 2015, Sandwich terns at Sands of Forvie again occupied a breeding colony among Black-headed gulls. Productivity at this colony rose slightly to 0.50 chick per pair (440 chicks from 874 pairs). Numbers of breeding pairs and productivity were higher than 2014 (0.33 chicks fledged per pair) and overall have been increasing since 2006 (0.16 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*) 7,392 9,844 9,018
% change since previous census    N/a +33 -8

 

* AON = Apparently Occupied Nests

 

Breeding abundance

 

England Sandwich tern abundance trend

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

 

In contrast to Scotland, Sandwich tern numbers in England have generally fared better, with an increase between Operation Seafarer and the Seabird Colony Register. Numbers have since been fairly stable, although since 2002 there is some evidence of a slight decline. The index spikes in 2009 when over 500 pairs nested at Minsmere, possibly as a result of birds abandoning a colony on the continent. This colony had been effectively abandoned in 1977 and has been deserted again from 2010 to 2013, with one pair attempting to breed there in 2014 and none in 2015. Several other former colonies now hold no breeding Sandwich terns (e.g. Dungeness (Kent), Foulness (Essex), Foulney (Cumbria), Havergate (Suffolk), Chichester (West Sussex), North Solent (Hampshire)). The main colonies are on the Farne Islands and Coquet (both Northumberland) and Blakeney Point and Scolt Head (both Norfolk) where over 6,800 Sandwich terns nested in 2015. These colonies now probably hold over 70% of the English population.

 

Productivity

 

England Sandwich tern productivity trend

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

 

Annual average productivity at English colonies is usually higher than that recorded in Scotland but is very variable due to the influences of predation and tidal inundation. However, since peak productivity was recorded in 2000, there has been a downward trend culminating in very low levels of chick production in recent years. For example, in both 2012 and 2013, three of six colonies where breeding success was recorded failed completely, with losses of eggs and chicks to various predators highlighted as a problem at some colonies. No reasons were provided to the SMP for the low productivity in 2014. In 2015, Scolt Head Island NNR had a very successful breeding season with 3,200 chicks fledged from 3,550 nests. In contrast Blakeney Point only fledged 8 chicks from 1,113 nests. A similar scenario happened in 2000, when all nests at Blakeney Point failed and neighbouring Scolt Head showed one of the highest breeding success records for the last 15 years.

 

 

Population estimates and change 1969-2002 (census data)

 

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

Population estimate (AON*) 0 450 450
% change since previous census    N/a N/a 0

 

* AON = Apparently Occupied Nests

 

Breeding abundance

 

Sandwich tern Cemlyn abundance 2015

Figure 1: Abundance of Sandwich tern at Cemlyn Lagoon (Gwynedd), 1986-2015.

 

Sandwich terns are confined to just one location in Wales, at Cemlyn Lagoon on Anglesey (Gwynedd). No birds were recorded there during Operation Seafarer although an influx of 50 pairs mid season in 1970 possibly related to birds displaced from elsewhere. By the time of the Seabird Colony Register 450 pairs were nesting at the lagoon and, aside from a peak of short duration from 1987-1989, numbers there remained relatively stable until Seabird 2000. Numbers have increased substantially from 2001 onward, with the colony now regularly holding over 2,000 pairs (although only 409 pairs nested in 2008). The last five breeding seasons have all seen new peaks recorded at the colony, with 2,650 pairs nesting during 2015, the highest number since monitoring began4.  

 

Productivity

 

Sandwich tern Wales productivity 2015

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

 

Sandwich terns nesting at Cemlyn have been relatively successful compared with other British colonies. Over one chick per pair has been fledged in several years since 1996 (1997, 2003 and 2006), which may also explain the increased numbers nesting at the site since 2002 as young from successful breeding seasons themselves return to nest at the colony. In 2007 and 2008, there was almost complete failure with very few young fledged due to predation and desertion of nests. Since 2009, the average breeding success has been 0.73 chicks fledged per pair, however, during the last four years this has been between 0.45 and 0.55 chicks per pair. 2015 proved to be a similar season with at least 1,200 chicks fledged from a total of 2,650 estimated breeding pairs (average of 0.45 chicks per pair) which was lower than 2014. Delayed hatching due to very poor weather in late May may have caused the failure of many early nests. High predation also impacted on the colony with an adult peregrine falcon visiting regularly in July and killing at least 19 fledglings and seven adults. This was in addition to a ‘mustelid’ predator (e.g. Otter, Stoat or Weasel) killing at least 101 juveniles and 8 adult terns4.

 

 

Population estimates and change 1969-2002 (census data)

 

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

Population estimate (AON*) 1,211 2,186 1,954
% change since previous census    N/a +80 -11

 

* AON = Apparently Occupied Nests

 

Breeding abundance

 

Sandwich tern Northern Ireland abundance 2015 

Figure 1: Abundance of Sandwich tern at five colonies in Northern Ireland, 1986-2015.

 

Sandwich tern has the most complete monitoring record over the longest period of any seabird species in Northern Ireland. National census data show that numbers of Sandwich terns nesting in Northern Ireland increased between Operation Seafarer and the Seabird Colony Register by 80%, but fell by 11% up to Seabird 2000. This later decline, between 1987 and 2000 (years when the majority of tern colonies were counted in the SCR and Seabird 2000, respectively), can be broadly seen by data from five well monitored colonies (Cockle Island (Co. Down), Carlingford Lough (Co. Down), Strangford Lough (Co. Down), Larne Lough (Co. Antrim) and Lower Lough Erne (Co. Fermanagh)), presented above (Figure 1). Previous reports stated that Strangford Lough (Co. Down) was abandoned in 1986 and 1988 but this appears to be in error; in actual fact, 1,418 nested in 1986 and 2,228 in 1988. Comprehensive monitoring of these five colonies between censuses suggest total numbers in Northern Ireland declined after the SCR until the early 1990s, before increasing steadily until 2005, reaching a peak of 3,300 AON. Numbers are once again falling at a steep rate. Five of six extant colonies in Northern Ireland were surveyed in 2015, with a total of 1,663 pairs recorded, indicating that  numbers are currently slightly less than that recorded during Seabird 2000 (1,954 AON), as the sixth colony, where nesting is sporadic, holds only a few tens of pairs at most.

 

Productivity

 

Few systematic data on the productivity of Sandwich terns in Northern Ireland have been collected as part of the SMP. On average, 0.34 chicks have been fledged per pair per year between 1990 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*) 1,005 1,281 1,762
% change since previous census    N/a +27 +38

 

* AON = Apparently Occupied Nests

 

Breeding abundance

 

Sandwich tern Lady’s Lake Island abundance graph 1986-2015

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

 

Operation Seafarer recorded 1,005 pairs of Sandwich tern in the Republic of Ireland. This number has increased during each subsequent census with 1,762 pairs counted during Seabird 2000. The largest colony of the eight known is at Lady's Island Lake (Co. Wexford, Figure 1), which held approximately 60% of the population during the last census. Numbers there have increased substantially during the last decade with a peak of 1,958 pairs nesting in 2009. There has been a slight decline since then with 1,799 nesting pairs recorded in 2015. With Inch Islet, the next largest colony, known to hold 397 pairs when last surveyed in 2010, the current national population is likely to exceed 2,000 breeding pairs.  

 

Productivity

 

Sandwich tern Republic of Ireland Productivity 2015

Figure 2: Trend in productivity (no. of chicks fledged per pair) of Sandwich tern in the Republic of Ireland, 1986-2014. Based on SMP data; view the methods of analysis (PDF 158 kb).

 

Sandwich terns breeding in the Republic of Ireland also show the typical fluctuating fortunes found in the other countries of the British Isles. Particularly low productivity was recorded in 1994, 1999 and 2008, but in most years since 2000 Sandwich terns have been relatively productive. No productivity data have been submitted since 2008.

 

 

Population estimates and change 1969-2002 (census data)

 

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

Population estimate (AON*) 2,216 3,467 3,716
% change since previous census    N/a +56 +7

 

* AON = Apparently Occupied Nests

 

Breeding abundance

 

Sandwich tern all Ireland abundance 2015

Figure 1: Abundance of Sandwich tern at six colonies throughout Ireland, 1986-2015.

 

National census data show a 56% increase in Sandwich tern numbers between Operation Seafarer and the Seabird Colony Register. Seabird 2000 recorded similar numbers to the SCR census. Over the decade since the last census the five main colonies in Northern Ireland and at Lady's Island Lake in Republic of Ireland have all increased in numbers and in 2015 these colonies alone held close to 3,500 pairs but as recently as 2009 held almost 5,000 pairs. Taking smaller colonies and those not counted recently (of which there are at least nine in total) into account, the total Irish population at present probably lies between 4,000-4,500 breeding pairs.

 

Productivity

 

All-Ireland Sandwich tern productivity trend

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

 

The trend in breeding performance shown for the whole of Ireland closely matches that shown for the Republic of Ireland where most of the data have been collected but with slightly lowered average values. Particularly low levels of productivity were recorded in 1994, 1999 and 2008, but in most years since 2000 Sandwich terns have been relatively productive. No productivity data have been submitted by the Republic of Ireland since 2008 and by Northern Ireland since 2013.

 

 

Sandwich tern does not breed on the Isle of Man.

 

 

Sandwich tern 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 Ratcliffe, N., Pickerell, G. and Brindley, E. 2000. Population trends of Little and Sandwich Terns Sterna albifrons and S. sandvicensis in Britain and Ireland from 1969 to 1998. Atlantic Seabirds 2: 211-26.

2 Cook, A.S.C.P. and Robinson, R.A. 2010. How representative is the current monitoring of breeding success in the UK? BTO Research Report No. 573, BTO, Thetford.

3 Short, D. 2014. Breeding of four species of tern and Black-headed Gull at Forvie National Nature Reserve, 2013. Unpublished report, Scottish Natural Heritage.

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

 


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