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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 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

roseate-tern-uk-ab.jpg

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

 

The UK roseate tern population has undergone a long-term decline, decreasing from 950 pairs in 1969-70 to 320 in 1985-88 and falling further between 1986 and 1991. 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. Just 56 AON were recorded by Seabird 2000 but by 2018 the UK population had risen to 120 AON. However, recovery has mostly been confined to just Coquet Island and, although numbers are increasing there, full recovery of the UK population remains a long way off.

 

Productivity

roseate-tern-uk-prod.jpg

Figure 2. Trend in UK productivity (no. of chicks fledged per pair) of roseate tern 1987–2018. 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. In 2017, productivity was at the second highest value ever recorded, 1.17 chicks fledged per pair, while in 2018 the index decreased to 0.74.

 

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

roseate-tern-scotland-ab.jpg

Figure 3. Abundance of roseate tern on the Forth Islands, 1986–2018.

 

The three national censuses show a large decline in roseate numbers from 134 AON in 1969-70 to 14 AON during Seabird 2000. In the Firth of Forth, the stronghold of the species in Scotland, 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 due to increased competition for nesting habitat with herring gulls and breeding at another isle was sporadic. Only one colony has been active in recent years, but it too has disappeared due to flooding, predation and disturbance. Elsewhere in Scotland, single pairs occasionally frequent other tern colonies just maintaining its status as a breeding species in the country.

 

Productivity

Productivity data at Scottish colonies showed no statistically significant variation over time, although was low, averaging 0.34 chicks fledged per pair per year between 1992 and 2007.

 

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

roseate-tern-england-ab.jpg

Figure 4. Abundance of roseate tern on Coquet Island, 1986–2018.

 

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 38 AON between 1986 and 2000) but increased rapidly from 2000 onward, with numbers reaching 94 AON in 2006. Since then, the population has been fluctuating between 71 and 94 AON until 2015 when it increased steeply to 111. In 2018, there were 118 AON at the colony. 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

roseate-tern-england-prod.jpg

Figure 5. Trend in productivity (no. of chicks fledged per pair) of roseate tern at colonies in England, 1988–2018. Based on SMP data; view the methods of analysis.

 

The productivity of roseate terns at colonies in England shows no definitive trend. Mean productivity usually lies below 0.90 chicks fledged per pair, in contrast to the colonies in the Republic of Ireland which seldom fledge less than 1.00 chick per pair per year. Despite the low success, numbers have been increasing (Figure 5), although breeding roseate terns are now confined in England to just one colony (c. five colonies known during 1985-88), with sporadic sightings at others during the summer months.

 

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

 

roseate-tern-wales-ab.jpg

Figure 6. Abundance of roseate tern at colonies in Wales, 1986–2018.

 

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 showed the decline was probably due to terns deserting colonies in Wales (and Northern Ireland) and emigrating to those in the Republic of Ireland where active management had created sites of higher quality. No roseate terns have nested in Wales since 2006.

 

Productivity

Productivity data at Welsh colonies showed no statistically significant variation over time, averaging 0.68 chicks fledged per pair per year between 1987 and 2006 (the last year for which the SMP has data).

 

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

roseate-tern-ni-ab.jpg

Figure 7. Abundance of roseate tern at three colonies in Northern Ireland, 1986–2018.

 

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 was 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 some other sites in recent years.

 

Productivity

There is no statistically significant variation over time in productivity data collected at colonies in Northern Ireland which were slightly more successful than Scottish colonies. Roseate tern productivity averaged 0.66 chicks fledged per pair per year between 1991 (the first year in the SMP with data) and 2018.

 

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

roseate-tern-roi-rockabill-ab.jpg

Figure 8. Abundance of roseate tern at Rockabill in the Republic of Ireland, 1986–2018.

 

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 8) which holds almost 90% of the population3. As on Coquet (England), the provision of nest boxes, in conjunction with other management techniques (e.g. predator control and habitat creation), have been of benefit to the species4. A recent seabird census in the Republic of Ireland recorded 1,820 AON, an increase of 148% since Seabird 2000 and 28% higher than recorded during Operation Seafarer.

Productivity

roseate-tern-roi-prod.jpg

Figure 9. Trend in productivity (no. of chicks fledged per pair) of roseate tern in the Republic of Ireland, 1986-2014. Based on SMP data; view the methods of analysis.

 

Roseate terns at colonies in the Republic of Ireland have generally been productive over the years, usually fledging more than one chick per pair each year. However, in 1997, 1998, 2008, 2012 and 2014 productivity was lower than this, largely as a result of losses of eggs and chicks due to poor weather. No productivity data from the Republic of Ireland have been submitted to the SMP since 2015.

 

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, the roseate tern nests predominantly in the Republic of Ireland. Thus, all data and text for the Republic of Ireland is also pertinent to the status of the species for the whole of Ireland. No data from the Republic of Ireland have been submitted to the SMP since 2015.

 

Productivity

roseate-tern-all-ireland-prod-1986-2015.jpg

Figure 10. Trend in productivity (no. of chicks fledged per pair) of roseate tern throughout Ireland, 1986-2015. Based on SMP data; view the methods of analysis.

 

Unsurprisingly, the trend shown above for All-Ireland closely matches that shown for the Republic of Ireland, where the majority of data have been collected over the years, albeit with slightly lower average annual values. Losses of eggs and chicks due to poor weather were responsible for at least some of relatively low values recorded (e.g. in 1998 and 2008). No data from the Republic of Ireland have been submitted to the SMP since 2015.

 

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 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.

4 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; 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 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 1986–2018

Published: .

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