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Roseate tern (Sterna dougallii)

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

 

The roseate tern population in the UK experienced the most dramatic decline of any seabird species between Operation Seafarer (1969-70) and the SCR Census (1985-88). It also has one of the most restricted ranges of any seabird around the British Isles, with most of the population breeding in just a few colonies. Consequently, the species is of high conservation concern and is one of three red-listed seabirds in the United Kingdom. Roseate terns have probably always been rare and localised in the UK owing to their specialised foraging and nesting habitat requirements. Driven to the brink of extinction by exploitation for the millinery trade during the 19th century, the population recovered through the early 20th century as a result of protective legislation and management. Numbers peaked in the late 1960s, but declined thereafter possibly due to poor immature survival rates, and this may have been partially attributable to deliberate trapping in the Ghanaian wintering grounds. Factors such as predation and nesting habitat loss (due to erosion, competition with gulls and/or disturbance) may have also played a role.

Conservation efforts are directed towards education programmes in the wintering areas in NW Africa and management of breeding sites. However, recovery is evident only at the largest colony, with smaller peripheral colonies declining to low levels or being abandoned despite intensive efforts to maintain them. Movements of birds among colonies within the metapopulation has been an important determinant of regional population trends during the past three decades. Therefore, maintaining or enhancing the species range is likely to depend on conservation efforts to promote growth of relict colonies, restore breeding at abandoned sites, and create new colonies.

Conservation status

Roseate Tern is currently identified as a conservation priority in the following:

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International importance

UK Population

Biogeographic Population

% World Population

56 AON*

2.6 (ssp. dougallii)

<0.1

*AON = Apparently Occupied Nests

The UK population figure 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)

Roseate terns are restricted to a small number of well-known colonies in the UK, all of which have been counted near annually since 1969, such that their populations are monitored in more detail than any other seabird breeding here. Roseate terns were surveyed during Seabird 2000 by systematically counting all nests situated along transect lines set up through colonies. Nests are usually hidden in long vegetation, among boulders, in rabbit burrows or in nest boxes and so counts of AONs from a vantage point will miss a large proportion of nests. The species may move among colonies between years in response to predation or habitat change and so, to avoid double-counting or missing some pairs, all colonies were counted in 2000. During the SCR Census (1985-88) counts were conducted in different years at some colonies. In order to be comparable with Seabird 2000, only counts from the SCR Census conducted in 1986 were used; this was when the most comprehensive survey coverage of colonies was achieved during the period 1985-88.

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998–2002)

UK Population estimate (AON*)

955

323

56

% change since previous census

n/a

-66

-83

*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 roseate tern found in different regions, and a map showing the locations and size of colonies, is provided in the Seabird 2000 roseate 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 estimated reproductive success (hereinafter referred to as productivity) are only shown if data analysis 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. 

 

Overview of all regions

Breeding abundance

An insufficient number of roseate tern colonies are monitored to allow the production of valid annual abundance trends for any of the regions covered by the SMP.

 

Productivity

The number of roseate tern sites monitored frequently are only sufficient to allow meaningful productivity trends to be produced for the UK which is provided in the respective section below.

 

United Kingdom

Breeding abundance

RS UK abundance.jpg

Figure 1. Number of roseate tern AON in the UK, 1986–2019.

 

The UK roseate tern population has undergone considerable long-term decline, decreasing from 950 AON in 1969-70 to 320 in 1985-88, and falling to 56 AON by the Seabird 2000 census (1998–2002). This is most likely to have been due to mortality of immature birds in their wintering grounds in west Africa1, which reduced subsequent recruitment into the breeding population. On the wintering grounds, boys trapped and killed mainly immature birds for food, sport or profit, and while education programmes in the late 1980s and early 1990s reduced mortality rates, these need to be maintained or a resurgence in trapping is likely2.

Food supply in the species’ wintering grounds is also likely to have affected immature survival rates. The above conservation measures (and providing shelter and protection from avian predators in the form of nest boxes at some colonies) have resulted in the UK population starting to recover. By 2019, the UK population had risen to 126 AON. However, recovery has mostly been confined to just Coquet Island and, although numbers are increasing there, full recovery of the UK population is likely to be a long way off.

 

Productivity

RS UK productivity.jpg

Figure 2. Trend in UK productivity (no. of chicks fledged per pair) of roseate tern 1987–2019. Based on SMP data; view the methods of analysis.

 

Although productivity was low in two years in the late 1980s when the population was declining, the number of chicks fledged in UK roseate tern colonies has generally been moderate to high throughout the reporting period. This is partly due to increased conservation effort. Predation of chicks was the likely cause of low productivity in 1987 and 1988, and poor weather affected west coast colonies in 1990, but the cause of low productivity in 2008 was not reported. Since 2010, roseate terns have not bred in Scotland successfully however, in 2019, a roseate tern paired with a common tern on the Forth Islands and produced a chick (Figure 3). In 2019 productivity was 0.8 chicks fledged per pair.

 

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*)

134

18

14

% change since previous census

n/a

-87

-22

*AON = Apparently Occupied Nests

 

Breeding abundance

RS Scor Forth Islands abundance.jpg

Figure 3. Number of roseate tern AON on the Forth Islands, 1986–2019.

 

The three national censuses show a large decline in roseate tern numbers in Scotland, from 134 AON in 1969-70 to 14 AON during Seabird 2000. In the Firth of Forth, the previous stronghold of the species, the decline recorded there since the late 1980s was fairly steady, albeit with some fluctuation (Figure 3). Three islands in the Forth formerly held colonies of roseate terns, although the largest colony had effectively disappeared by the early 1990s, largely due to increased competition for nesting habitat with herring gulls. Elsewhere in Scotland, single pairs occasionally frequent other tern colonies just maintaining its status as a breeding species in the country.

 

Productivity

An average of 0.25 chicks were fledged per pair per year at Scottish colonies between 1986 and 2019. Due to the small number of roseate tern colonies monitored frequently in Scotland, it is not possible to produce a meaningful productivity trend.

 

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*)

355

34

36

% change since previous census   

n/a

-90

+6

*AON = Apparently Occupied Nests

 

Breeding abundance

RS Eng Coquet Island abundance.jpg

Figure 4. Number of roseate tern AON on Coquet Island, 1986–2019.

 

In contrast to Scotland, the one extant roseate tern colony in England, on Coquet Island, has fared better. National census results show that a large decline occurred in England between Operation Seafarer and the Seabird Colony Register, both in terms of the number of birds and number of colonies. Numbers have increased since then, but the species is now confined to Coquet. The rate of increase at this colony was slow at first (from 17 to 33 AON between 1987 and 2000) but then increased more rapidly to 94 AON in 2006. Since then, the population has fluctuated but has increased overall, reaching 122 AON in 2019. Active management on Coquet, via the provision of nest boxes for shelter and protection from avian predators, together with habitat management, has undoubtedly helped the species thrive there, perhaps to the detriment of other nearby colonies as birds abandon them in favour of Coquet.

 

Productivity

Productivity has averaged 0.47 chicks fledged per pair per year between 1986 and 2019. Due to the small number of roseate tern colonies monitored frequently in England, it is not possible to produce a meaningful productivity trend.

 

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*)

202

209

2

% change since previous census   

n/a

+3

-99

*AON = Apparently Occupied Nests

 

Breeding abundance

 

RS Wales abundance.jpg

Figure 5. Number of roseate tern AON at colonies in Wales, 1986–2019.

 

The decline in roseate tern numbers in Wales was steep after the Seabird Colony Register, although prior to this numbers appeared stable in contrast to other populations in Britain and Ireland. By 1991, very few breeding pairs were left and, although there was a slight increase in 1993 and 1994, numbers soon decreased again and have never recovered. Ringing studies have shown the decline was probably due to terns deserting colonies in Wales and emigrating to those in the Republic of Ireland where active management has created sites of higher quality3. Roseate terns have started to nest in Wales again, with two AON being recorded in both 2018 and 2019.

 

Productivity

Roseate terns last bred in Wales in 2006, when a pair fledged one chick. In 2019 and 2019 two chicks have been raised each year. Roseate tern productivity in Wales averaged 0.46 chicks fledged per pair per year between 1987 and 2019.

 

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*)

264

62

4

% change since previous census   

n/a

-76

-94

*AON = Apparently Occupied Nests

 

Breeding abundance

RS NI abundance.jpg

Figure 6. Number of roseate tern AON at three colonies in Northern Ireland, 1986–2019.

 

In common with Scotland and England, the roseate tern population of Northern Ireland declined between Operation Seafarer and the Seabird Colony Register censuses, although the nearby Welsh population remained stable during this period. Then, in conjunction with Welsh colonies, a steep fall in numbers occurred so that few were left breeding by 1991. Emigration of birds to higher quality breeding sites in the Republic of Ireland was at least part of the reason for the decline. From the mid-1990s, the population fluctuated without showing any prolonged recovery and from 2003 declined again. Since 2009, only one AON has been recorded each year, except for 2014 when two AON were recorded. Single non-breeding birds have also been recorded at other sites in recent years.

 

Productivity

In Northern Ireland, roseate tern productivity averaged 0.68 chicks fledged per pair per year between 1991 and 2019. Due to the small number of roseate tern colonies monitored frequently in Northern Ireland, it is not possible to produce a meaningful productivity trend.

 

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*)

1,429

227

734

1,802

% change since previous census   

n/a

-84

+223

+148

*AON = Apparently Occupied Nests

 

Breeding abundance

RS Eire Rockabill abundance.jpg

Figure 7. Number of roseate tern AON at Rockabill in the Republic of Ireland, 1986–2019.

 

After the near ubiquitous decline recorded throughout Britain and Ireland between Operation Seafarer and the Seabird Colony Register, roseate tern numbers in the Republic of Ireland have undergone a healthy increase which continues to the present. However, breeding is now confined to three colonies one of which, Rockabill (Figure 7), holds almost 90% of the Irish population4 and is the largest colony in Europe. As on Coquet Island (England), the provision of nest boxes, in conjunction with other management techniques (e.g. predator control and habitat creation), have benefited the species5. A recent seabird census in the Republic of Ireland (2015–2018)4 recorded 1,820 roseate tern AON, an increase of 148% since Seabird 2000 and 28% higher than recorded during Operation Seafarer.

 

Productivity

RS Eire productivity1.jpg

Figure 8. Trend in productivity (no. of chicks fledged per pair) of roseate tern at Lady’s Island Lake in the Republic of Ireland, 1989–2019.

 

One of the three colonies hosting roseate terns is located at Lady’s Island Lake. Here average productivity was 1.07 chicks fledged per pair between 1989 and 2019 which is higher than the national average of 0.98 during the same time period. In 2019, 1.17 chicks fledged per pair. Due to the small number of roseate tern colonies monitored frequently in the Republic of Ireland, it is not possible to produce a meaningful productivity trend for the country.

 

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*)

1,693

289

738

% change since previous census   

n/a

-83

+155

*AON = Apparently Occupied Nests

 

Breeding abundance

Within Ireland, roseate terns nest predominantly in the Republic of Ireland. Thus, all data and text for the Republic of Ireland are also pertinent to the status of the species in the whole of Ireland.

 

Productivity

Within Ireland, roseate terns nest predominantly in the Republic of Ireland. Thus, all data and text for the Republic of Ireland are also pertinent to the status of the species for the whole of Ireland.

 

Isle of Man

Roseate tern does not breed on the Isle of Man.

 

Channel Islands

Roseate 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 Ntiamoa-Baidu, Y., Nyame, S.K. and Nuah, A.A. 1992. Preliminary report on tern trapping in coastal Ghana. In: Rolland, G. (ed.) Proceedings of the Roseate Tern workshop. SEPNB. Brest.

2 Ratcliffe, N. and Merne, O. 2002. Roseate tern Sterna dougallii. In: Wernham, C.V., Toms, M., Marchant, J., Clark, J., Siriwardena, G. and Baillie, S. eds. The Migration Atlas: Movements of the birds of Britain and Ireland. T and A.D. Poyser, London.

3 https://app.bto.org/ring/countyrec/resultsall/rec6140all.htm

4 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.

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

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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; Department of Agriculture, Environment and Rural Affairs (Northern Ireland); Department of Environment, Food and Agriculture (Isle of Man); Department of the Environment, Climate and Communications (Republic of Ireland); JNCC; Manx Birdlife; Manx National Heritage ; The National Trust; National Trust for Scotland; Natural England; Natural Resources Wales; NatureScot; The Royal Society for the Protection of Birds; Scottish Wildlife Trust; Seabird Group; Shetland Oil Terminal Environmental Advisory Group; States of Guernsey Government; UK Centre for Ecology and Hydrology. More about the SMP partners >>

 

Image of Roseate 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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Categories:

SMP Report 1986–2019

Published: .

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