Roseate Tern Sterna dougallii

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

 

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Description

Roseate Tern vignette

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:

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

Wildlife and Countryside Act 1981 - protected under Schedule 1

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

UK BAP - priority species

(further information on Conservation Designations for UK Taxa)

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

OSPAR List of Threatened and/or Declining Species and Habitats

 


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.

 


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

(1986)

Seabird 2000

(2000)

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.

 


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 (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% CLs 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 abundance graph 1986-2015

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

 

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, mostly due to mortality of immature birds in their winter quarters in west Africa, 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 likely1. 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 this has now risen so that the UK population numbered 113 AON in 2015. However, declines occurred at all colonies, whilst recovery has mostly been confined to just one main colony and, although numbers are increasing there, full recovery of the UK population remains a long way off.

 

Productivity

 

UK roseate tern productivity trend

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

 

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 other years, e.g. 2008, 2010, 2013 and 2015 was not reported.

 

 

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 Forth Islands abundance 2015

Figure 1: Abundance of roseate tern on the Forth Islands, 1986-2015.

 

The three national censuses show a large decline in roseate numbers from 134 pairs in 1969-70 to a mere 14 pairs 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 1). 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. No records were submitted to the SMP for 2015.

 

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 (the last year for which the SMP has data).

 

 

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 Coquet abundance 2015

Figure 1: Abundance of roseate tern on Coquet Island (Northumberland), 1986-2015.

 

In contrast to Scotland, the one extant roseate tern colony in England, on Coquet Island (Northumberland), has fared better. National census results show that a large decline occurred throughout 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 pairs between 1986 and 2000) but increased rapidly from 2000 onward, with numbers reaching 94 pairs in 2006. However, the increase appears to have halted; numbers between 2007 and 2015 varied between 70 and 111 pairs. Active management on Coquet, via the provision of nestboxes 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

 

England roseate tern productivity trend

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

 

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 in England had been increasing (Figure 1), although breeding roseate terns are now confined to just one colony (c. five colonies known during 1985-88), with sporadic sightings at others during the summer months.

 

 

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 abundance 2015

Figure 1: Abundance of roseate tern at colonies in Wales, 1986-2015.

 

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 the populations of other countries in the British Isles. 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 apparently 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 during nine of the last 10 years although one pair was present at a colony in 2014 and 2015 and bred successfully.

 

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).

 

 

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 Ireland abundance 2015

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

 

In common with Scotland and England, the roseate tern population of Northern Ireland declined between Operation Seafarer and the Seabird Colony Register, 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. Since the mid 1990s, the population has fluctuated without showing any prolonged recovery, but, as of 2003, has once more declined toward zero with just a single pair recorded nesting each year from 2009 to 2013, with two pairs present in 2014 and one in 2015. 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 0.56 chicks fledged per pair per year between 1991 (the first year in the SMP with data) 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*) 1,429 227 734
% change since previous census    N/a -84 +223

 

* AON = Apparently Occupied Nests

 

Breeding abundance

 

Roseate tern republic Ireland abundance 2015

Figure 1: Trend in abundance index (solid line) of roseate tern in the Republic of Ireland, 1986-2014 with 95% confidence limits (dotted lines). Based on SMP data; view the methods of analysis (PDF 158 kb).

 

After the near ubiquitous decline recorded throughout the British Isles 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 holds almost 90% of the population with only a few pairs at another. As on Coquet (England), the provision of nestboxes, in conjunction with other management prescriptions (e.g. predator control and habitat creation) have been of benefit to the survival of the species. Over 1,400 roseate terns were recorded nesting in 2014. Numbers in 2014 were well above those recorded by Seabird 2000, and the SCR census before it, and were approaching levels recorded by Operation Seafarer in 1969/70. No data from the Republic of Ireland were submitted to the SMP for the 2015 breeding season.

 

Productivity

 

Republic of Ireland roseate tern productivity trend

Figure 2: 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 (PDF 158 kb).

 

Roseate terns at colonies in the Republic of Ireland have generally been quite 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 data from the Republic of Ireland were submitted to the SMP for the 2015 breeding season.

 

 

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

 

Counting roseate terns only takes place at a small number of colonies, limited data is therefore available for produce a reliable abundance trend for Ireland. Within Ireland, the roseate tern nests mainly 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 were submitted to the SMP for the 2015 breeding season.

 

Productivity

 

All-Ireland roseate tern productivity trend

Figure 2: 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 (PDF 158 kb).

 

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.

 

 

Roseate tern does not breed on the Isle of Man.

 

 

Roseate 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. 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 & A.D. Poyser, London.

 


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