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Guillemot (Uria aalge)

The following has been adapted from original text by Mike P. Harris and Sarah Wanless in Seabird Populations of Britain and Ireland (with permission from A&C Black, London).

 

The guillemot is one of the most abundant seabirds in the temperate and colder parts of the northern hemisphere with very large populations in the Atlantic and the Pacific Oceans and the adjacent areas of the Arctic Ocean. In the northeast Atlantic, its range extends from Portugal in the south to Spitzbergen in the north and includes the Baltic Sea. Two subspecies, not easily separable in the field, breed in our area; the dark-mantled nominate race aalge occurs in most of Europe including Scotland and possibly northern England; the smaller, much browner mantled albionis occurs in England, Wales, Ireland, Helgoland, France and Iberia. A bridled morph, with a striking white eye-ring and spectacle occurs in the Atlantic but not in the Pacific. The frequency of this morph increases with latitude from less than 1% in the south to 20–25% in northern Britain.

Guillemots breed at most places around the coasts where there is suitable cliff habitat. They are extremely gregarious; colonial breeding is the norm and colonies can contain many tens of thousands of individuals. Breeding areas are situated where the birds are safe from mammalian predators. This means that on the mainland, they are confined to sheer cliffs or in among boulders at the bases of cliffs where access is difficult even from the sea. On islands, cliffs and the tops of large stacks are preferred but where such habitat is absent they breed among rocks or even on flat open ground. No nest is built, the single relatively large egg being incubated on the bare rock, guano or soil on a wide variety of breeding sites including large flat, broad ledges where birds are crowded together at average densities of about 20 pairs/m2, narrow ledges, isolated sites that are little more than toeholds, grassy banks, on top of or under boulders and elsewhere, even under bushes. Breeding success is highest where birds breed at high density or where sites are well protected from predators.

 

Conservation status

Guillemot is currently identified as a conservation priority in the following:

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International importance

UK Population

Biogeographic Population

% World Population

1,416,300 IND*

33.3 (N. Atlantic)

12.9

*IND = INDIVIDUALS

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.

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UK population estimates and change 1969–2002 (census data)

Census coverage for this species is likely to have been extremely high during Seabird 2000.

Due to subtle methodological differences within and between the SCR and Seabird 2000 (largely to do with timing of counts and how this affects colony attendance of adults), there is a degree of uncertainty in the calculation of rates of change between the two censuses. However, the general findings are backed up by systematic standardised counts made annually at 15–20 colonies dispersed around Britain.

All counts relating to Seabird 2000 refer to individuals at colonies. Counts of birds can, if required, be converted into an approximate estimate of the number of pairs by multiplying by a correction factor 0.67 to allow for the presence of mates and non-breeders. While this factor has been shown to be generally representative in Britain, more recent debate challenges whether it is still universally applicable1.

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998–2002)

UK Population estimate (Individuals)

611,281

1,081,341

1,416,334

% change since previous census

n/a

+77

+31

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 common guillemot found in different regions, and a map showing the locations and size of colonies, is provided in the Seabird 2000 guillemot 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.

 

United Kingdon

Breeding abundance

guillemot-uk-ab.jpg

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

 

The UK population index for guillemot (Figure 1) was fairly stable in the years immediately following 1986. Between 1990 and 2001, the index increased by 83% and, the trend fluctuated and perhaps even declined thereafter. Since 2007, the trend climbed steadily and in 2014 reached its highest value at 42% above the 1986 baseline. However, trends in each country are markedly different (e.g. see accounts for Scotland and Wales). Over the longer term, national census results show that guillemots increased from 611,000 individuals in 1969-70 to over one million in 1985-88. There is no clear evidence as to why they have increased. While predictions of future population trends are uncertain, observed low productivity in recent years, combined with lowered return rates (see below), may lead to future declines.

Table 1 (below) shows how guillemot numbers have changed at important colonies (those in the SPA network) since they were surveyed for the Seabird 2000 census. The largest declines recorded since Seabird 2000, have been at colonies in Scotland, while important colonies in England, Wales and Northern Ireland have all increased. Fowlsheugh in Scotland is the only colony where numbers have increased since Seabird 2000, however, numbers need to be treated with caution as some SPAs have not been surveyed since 2007 (e.g. Foula, Hoy, and Buchan Ness to Collieston Coast).

Table 1: Recent counts of the number of guillemot (individuals) recorded in SPAs in Britain and Ireland compared to the number recorded during Seabird 2000. The percentage that each colony has changed in size and the per annum change are also provided. (Note: data at Hermaness and St Abb's Head relate to only part of the SPA)

Area

SPA Name

Seabird 2000 (Year)

Count (Year)

Change (%)

per annum

Shetland

Hermaness NNR

10,438 2000

5,808 2016

-44

-3.6

Shetland

Noss

45,777 2001

24,456 2015

-47

-4.4

Shetland

Foula

41,500 2000

24,799 2007

-40

-7.1

Shetland

Sumburgh Head

16,572 1999

7,749 2017

-53

-4.1

Shetland

Fair Isle

39,257 1999

20,924 2015

-47

-3.9

Orkney

West Westray Cliffs

54,718 1999

22,930 2017

-58

-4.7

Orkney

Copinsay

18,675 1999

18,461 2015

-1

-0.1

Orkney

Marwick Head

34,679 1999

11,985 2018

-65

-5.4

Orkney

Hoy

21,777 1999

9,020 2007

-59

-10.4

East Coast

Troup, Pennan and Lion's Heads

45,254 2001

23,626 2017

-48

-4.0

East Coast

Buchan Ness to Collieston Coast

29,389 2001

19,296 2007

-34

-6.8

East Coast

Fowlsheugh

62,330 1999

69,828 2018

+12

+0.6

East Coast

Forth Islands

37,795 2001

26,099 2018

-31

-2.2

East Coast

St Abb's Head NNR

40,720 1998

42,905 2018

+5

+0.3

East Coast

Farne Islands

31,497 2000 49,037 2016

+56

+3.0

East Coast

Flamborough Head and Bempton Cliffs

46,685 2000

84,647 2017

+81

+7.7

The Minch

Handa

112,676 1998

54,664 2016

-51

-3.9

The Minch

Shiant Isles

16,456 1999

9,054 2015

-45

-3.7

The Minch

Mingulay and Berneray

32,590 1998

22,265 2014

-32

-2.4

Irish Sea

Ailsa Craig

9,415 2001

7,040 2018

-25

-1.7

Irish Sea

Rathlin Island

95,117 1999

130,445 2011

+37

+2.7

Irish Sea

Skomer and Skokholm

15,171 2000

29,136 2017

+92

+3.9

Irish Sea

Lambay Island

60,754 1999

59,983 2017

-1

-0.1

 

Productivity

guillemot-uk-prod.jpg

Figure 2. Trend in UK productivity (no. of chicks fledged per pair) of guillemot 1986–2018. Based on SMP data; view the methods of analysis.

 

After remaining stable from 1986 to 2002, guillemot productivity (Figure 2) declined dramatically until 2007, by which time a mean of just 0.23 chicks per pair were fledged. Productivity has improved since then, although values recorded between 2009 and 2018 are still lower than those recorded prior to 2002. Since 2009 fluctuations have been more pronounced compared to 1986–2002. In 2018, productivity was at 0.68 chicks fledged per pair. The reasons behind these changes in productivity are not fully known. Declines in productivity coincided with food shortages and primarily affected colonies in the north and east of the UK, where sandeels (rather than sprats and their relatives) are the main prey. Detailed studies at the Isle of May found reduced energy content in fish brought to chicks at this time2 and that the proportion of sandeels in the diet has decreased at east coast colonies over the last 15–30 years, with sprat mainly fed to chicks since 20003. This would appear to be related to declines in abundance of their sandeel prey which in certain regions is negatively correlated with sea surface temperatures that have risen due to climate change4,5. However, in recent years, sandeels have apparently been abundant at some colonies and this has coincided with increased in productivity, although productivity at colonies where the predominant prey species is sprat has also been high.

Analysis of the SMP dataset found that mean productivity of guillemots between 1986 and 2008 was 0.66 and it declined at a rate of 0.02 chicks per nest per year4. This equated to a decline of 31% over the study period. The quality of the dataset meant such a change (in excess of 10%) would be detected with confidence. Using available life history information (population size, clutch size, age at first breeding and survival rates of different age classes) to parameterise population viability analysis, predicted that were this level of productivity maintained, populations of the guillemot would increase by 75% over 25 years. However, this does not take into account density dependent processes which are known to operate in this species. For the population to decline by 25% over a 25-year period, productivity would have to fall to 0.25 chicks per nest per year.

 

Scotland

Population estimates and change 1969–2002 (census data)

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998–2002)

Population estimate (Individuals)

519,461

943,098

1,167,841

% change since previous census

n/a

+82

+24

 

Breeding abundance

guillemot-scotland-ab.jpg

Figure 3. Trend in abundance index (solid line) of guillemot in Scotland, 1986–2018 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.

 

National census data show an increase an 82% in the Scottish guillemot breeding population between 1969-70 and 1985-88, with a further increase of 24% up to the time of Seabird 2000. The population trend for guillemot in Scotland (Figure 3) was stable up to the early 1990s, after which it climbed slightly over a few years before levelling off. However, since Seabird 2000 (1998–2002), the index has fallen and has been lower than the 1986 baseline since 2004 (maximum 27% below in 2007), although in 2018 it was just 2% below. However, such a broad scale picture masks regional differences. For instance, numbers of guillemots in study plots on mainland Shetland have been falling at a considerable rate since peak figures (as measured post-1986) were recorded in 2000; plots held 85% fewer guillemots in 2018, although numbers have been slowly increasing since 20095. Data from study plots between 2000 and 2018 indicate declines of 41% on Handa and 24% at St. Abb's Head but an increase of 22% at Fowlsheugh. Recent increases in productivity across Scotland, coupled with increased return rates (assuming measurements of this at the Isle of May (Figure 4, below) are typical of what is happening elsewhere), may lead to future increases throughout Scotland. At Sumburgh Head, large gull predation was likely to have been a contributing factor to chick losses in 20177 and 20186.

 

Productivity

guillemot-scotland-prod.jpg

Figure 4. Trend in productivity (no. of chicks fledged per pair) of guillemot in Scotland, 1986–2018. Based on SMP data; view the methods of analysis.

 

Most SMP data on guillemot productivity in the UK have been collected at Scottish colonies so the trend in Figure 4 closely matches that for the UK, although for most years productivity is lower than the national average, except for 1986 to 1988. Productivity was relatively stable until 1996, falling slightly thereafter with a steep decline from 2003 to 2007 when productivity reached its lowest value of 0.19 chicks fledged per pair. Declines in productivity primarily affected colonies in the north and east (e.g. Shetland, Isle of May), coinciding with shortages in sandeels, the main prey for guillemots breeding in those areas. Overall, productivity has improved in the last few years across Scotland, when sandeels were apparently more abundant near some colonies. However, some regions have still recorded very low levels of productivity during the last few years. For example, from 2011 to 2013, the mean productivity in Shetland was 0.14 and in Orkney 0.19, compared to 0.62 in north-west Scotland and 0.72 in south-east Scotland. In 2017 and 2018, guillemots had a relatively successful season, although values recorded were still lower than the years prior to 2000. In 2018, guillemots fledged an average of 0.80 chicks per pair in Shetland; 0.34 in Orkney; 0.83 in north-west Scotland; and 0.71 in south-east Scotland.

At Sumburgh Head, the median laying date in 2018 was two to three days later than in 2017 (Figure 9) and hatching success of first eggs was the lowest since 2011 (63%) when only 11% hatched. However, productivity of 0.54 fledged per laying pair was equal to the long-term mean of 0.54 (1989–2017)5.

 

England

Population estimates and change 1969–2002 (census data)

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998–2002)

Population estimate (Individuals)

29.910

61,070

91,986

% change since previous census

n/a

+104

51

 

Breeding abundance

guillemot-england-ab.jpg

Figure 5. Trend in abundance index (solid line) of guillemot in England, 1986–2018 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.

 

The abundance trend for guillemots in England has generally been upward since the early 1990s. Census results show increases since Operation Seafarer, with numbers doubling by the time of the Seabird Colony Register and increasing by half again by Seabird 2000. It appears from the trend shown above that this increase has continued post Seabird 2000, in contrast to the trend in Scotland. However, the wide confidence intervals associated with the index and the steep increase of the index from 2017 to 2018 (probably due to few colonies being monitored frequently) suggest the results should be treated with some caution.

 

Productivity

guillemot-england-prod.jpg

Figure 6. Trend in productivity (no. of chicks fledged per pair) of guillemot in England, 1986–2018. Based on SMP data; view the methods of analysis.

 

Productivity at the few English colonies studied (Bempton Cliffs, Berry Head, Lundy, Farne Islands and St. Aldhelm’s Head) has been relatively high compared to Scotland. This difference may be due to the food taken at these colonies or be partially due to the intensity of monitoring at the Isle of May, Fair Isle and Sumburgh Head; more northern colonies may be more reliant on sandeels which have been scarce in some recent years (see 'Diet' section). However, low levels of productivity are apparent in several years i.e. 1986, 1997, 2006 and 2007. The reasons for this are not always reported but, in 1997, severe gales at the end of June caused major losses of guillemot eggs and chicks at colonies on the east coast of England.

In 2018, an average of 0.62 and 0.65 chicks per pair fledged at Flamborough Head and Bempton Cliffs, and Lundy Island NNR respectively.

 

Wales

Population estimates and change 1969–2002 (census data)

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998–2002)

Population estimate (Individuals)

17,238

32,126

57.961

% change since previous census

n/a

+86

+45

 

Breeding abundance

guillemot-wales-ab.jpg

Figure 7. Trend in abundance index (solid line) of guillemot in Wales, 1986–2018 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.

 

The abundance index for guillemots in Wales shows a steady increase since the 1990, similar to that for England. The increasing trends for both Wales and England contrast markedly with that of Scotland where abundance has been declining during the past decade. The rate of increase in Wales is greater than England, with an index value in 2018 over two times (267%) that of the 1986 baseline (cf. 4.4% for England and almost equal for Scotland). Over the longer term, national census data for Wales show that guillemots have been increasing since Operation Seafarer. A large proportion of the Welsh population is found on Skomer (24% during Seabird 2000), where previously it was thought that immigration was possibly driving this increase. However, a recent study using 30 years of detailed field observations to estimate key population parameters (productivity, adult survival and juvenile survival) in order to model the population size, showed that the observed rate of increase could be explained by these intrinsic parameters alone without immigration6.



Productivity

There was no statistically significant difference in the productivity of guillemots over the SMP sampling time at colonies in Wales, where an average of 0.73 chicks were fledged per site per year between 1989 and 2018. Average productivity in Wales is slightlylightly higher than recorded in England (0.71 chicks fledged per pair) and far higher than in Scotland (0.59 chicks fledged per pair) in recent years. This is probably due to differences in food taken by guillemots in southern/western colonies compared to eastern/northern colonies. Lower productivity in colonies in north and east Scotland, where sandeels are the main prey, coincided with food shortages. However, guillemots in Welsh colonies are less reliant on sandeels, feeding instead mostly on sprats and gadoids, although more recently there has been an increase in relatively low‐quality prey (Gadids), suggesting a shift in prey availability7.

 

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 (Individuals)

44,672

45,047

98,546

% change since previous census

n/a

<+1

+119

 

Breeding abundance

In Northern Ireland, the largest guillemot colony is on Rathlin Island with smaller colonies at The Gobbins, Muck Island and at scattered cliff faces between Ballycastle and Portrush. Guillemot numbers were stable between Operation Seafarer and the Seabird Colony Register (SCR) censuses, but more than doubled between the SCR and Seabird 2000 to 98,546 individuals. Rathlin Island held 95,117 individuals (96% of the national population) during the last census. In 2007, numbers on Rathlin Island were found to have declined by 14% to 81,303 individuals, but in 2011, a repeat survey recorded 130,445 individuals – an incredible rise of 60% in four years – making it again the largest colony in the UK8. However, numbers of guillemots on Rathlin Island in 2007 were probably low for a number of reasons. Observations at other UK colonies found return rates of birds were amongst the lowest on record that year (see below). Many colonies recorded declines (compared to 2006) and the abundance index for the UK shows a pronounced dip. A detailed study on Canna (Argyll and Bute, Scotland), approximately 120 miles north of Rathlin Island, suggested many returning guillemots had not attempted to breed at some sub-colonies; many adults were occasionally present but very few were incubating eggs or brooding young. Observations of guillemot chicks in early July also found they were less than half-grown, pointing to a late breeding season.

Non-breeding and late-breeding may contribute to lower counts if surveys coincide with periods when birds are absent from, or yet to take up occupancy of, nesting ledges. Only two small colonies, The Gobbins and Muck, have been surveyed in recent years; 2,284 individuals were recorded at The Gobbins and 2,478 individuals at Muck Island in 2018. Both increasing since Seabird 2000 when they held 2,805 individuals combined. Numbers at the other two colonies in Co. Antrim, Carrick-a-rede (185 individuals) and Sheep Island (439 individuals), have not been assessed since 2000. Overall, recent figures suggest the Northern Ireland guillemot population has increased.

 

Productivity

Data submitted to the SMP on the productivity of guillemots in Northern Ireland are sparse; thus, no meaningful average productivity value can be given. The only information in 2018 was from The Gobbins where many guillemot eggs were predated by hooded crows Corvus cornix, carrion crows Corvus corone and herring gulls Larus argentatus (Kerry Leonard pers. comm.).

 

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 (Individuals)

39,643

98,910

138,108

177,388

% change since previous census

n/a

+149

+40

+28

 

Breeding abundance

The table above shows that guillemot numbers in the Republic of Ireland increased considerably after Operation Seafarer and had more than tripled by Seabird 2000. Few colonies are monitored frequently, or in any one year; however, a Republic of Ireland Seabird Census (2015-18) counted 177,388 individuals, an increase of 28% compared to Seabird 20009. This population estimate is the highest ever recorded for the Republic of Ireland, however, it should be treated with caution because different levels of survey effort and methods were applies. Two major colonies, the Cliffs of Moher (+75%) and Great Saltee (+21%), have recorded substantial increases since the Seabird 2000 census, while Lambay Island, the largest colony in Ireland, has remained relatively stable (-1%). This regional variation in colony growth may well be driven by local food availability. Studies have shown that annual variation in guillemot population growth rate can be explained by variation in abundance of their preferred prey species10.

 

Productivity

Data submitted to the SMP on the productivity of guillemots in the Republic of Ireland are sparse; thus, no meaningful average productivity value can be given.

 

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 (Individuals)

84,315

143,957

236,654

% change since previous census

n/a

+71

+64

 

Breeding abundance

National census data show the number of guillemots in the whole of Ireland has increased substantially. The Seabird Colony Register recorded 71% more guillemots than Operation Seafarer and numbers had increased again, by 64%, by Seabird 2000.

In Northern Ireland, Rathlin Island held 130,445 individuals in 2011, and The Gobbins and Muck Island held 2,284 and 2,478 respectively in 2018. A Republic of Ireland Seabird Census (2015-18) counted 177,388 individuals, the highest on record. Overall, these recent figures suggest that the guillemot population in Ireland is likely to have increased since Seabird 2000, although the figure from the Republic of Ireland Census should be treated with caution because different levels of survey effort and methods were applied.

 

Productivity

Very few systematic data on the productivity of guillemots have been collected throughout Ireland as part of the SMP; thus, no meaningful average productivity value can be given.

 

Isle of Man

Population estimates and change 1969–2018 (census data)

 

Operation Seafarer

(1969-70)

Seabird Colony Register

(1985-88)

Seabird 2000

(1998–2002)

Isle of Man Census

(2017-18)

Population estimate (Individuals)

1,050

2,195

4,566

5,217

% change since previous census

n/a

+109

+108

+14

 

Breeding abundance

guillemot-iom-ab.jpg

Figure 8. Abundance of guillemot on the Calf of Man, 1986–2017.

 

The number of guillemots breeding on the Isle of Man increased four-fold between Operation Seafarer and Seabird 2000. Few colonies have been regularly surveyed since Seabird 2000, other than on the Calf of Man, which held c. 15% of the total Isle of Man guillemot population during the SCR (350 individuals) and c. 10% during Seabird 2000 (416 individuals) although both figures could be underestimates as counts were done from land only. A decline appears to have occurred at the colony since Seabird 2000, with recent surveys recording between 25% (e.g. 2009, 2012, 2014, 2015 and 2017) and 50% (e.g. in 2010 and 2013) of the census total. In 2017, a seabird census of the Isle of Man recorded a total of 5,217 individual guillemots, an increase of 14% since Seabird 2000. The most significant increase was found to have occurred at the Anvil-Sugarloaf Chasms, which had increased from 707 individuals in 1985-86 to 3,848 individuals (mean count) by 201711.

 

Productivity

No systematic data on the productivity of guillemots on the Isle of Man have been submitted to the SMP.

 

Channel Islands

Population estimates and change 1969–2015 (census data)

 

Operation Seafarer

(1969-70)

Seabird Colony Register

(1985-88)

Seabird 2000

(1998–2002)

Channel Islands Census
(2015)

Population estimate (Individuals)

201

345

476

496

% change since previous census

n/a

+72

+38

+4

 

Breeding abundance

National census data show that guillemot numbers on the Channel Islands increased between Operation Seafarer and Seabird 2000. In 2015, a seabird census of the Channel Islands was carried out recording a total of 492 individual guillemots, this represents a very slight increase (5%) since Seabird 200012.

 

Productivity

No systematic data on the productivity of guillemots on the Channel Islands have been submitted to the SMP.

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UK phenology, diet, survival rates

Phenology

Phenology (seasonal timing of life cycle events) is not currently monitored within the SMP, but data collected by Professors Tim Birkhead and Ben Hatchwell from the University of Sheffield (Figure 9) show that the median laying date of guillemots on Skomer became almost two weeks earlier over the period 1991–2013. Laying dates in 2009–2012 were the earliest in the time series, being between 9–15 days earlier than the 1991–2008 long-term mean. In contrast, data for Sumburgh Head (Shetland) for the period 2001–2018 (also Figure 9) show median laying date became progressively later initially and, by 2005, guillemots were nesting over three weeks later than in 2001. From 2006 onward, the trend reversed but in more recent years laying date is once again retreating.

guillemot-laying-date.jpg

Figure 9. Median laying date of guillemots on Skomer (blue dots) and Sumburgh Head (red dots), 1991–2018. Skomer data from 1991–2013 reproduced with kind permission of Professors Tim Birkhead and Ben Hatchwell (University of Sheffield/ Countryside Council for Wales13). Sumburgh data reproduced with kind permission of Will Miles (SOTEAG5).

 

Diet

Although local differences in feeding conditions have been suggested as a cause of regional variation in seabird demography actual multi-colony comparisons of diet are rare. In UK waters, the main fish eaten by seabirds during the breeding season belong to three families: Ammodytidae, Clupeidae and Gadidae. Climate change and fishing are affecting these fish stocks and so probably impact on predators such as seabirds. A recent study used standardised observations of prey brought in for chicks to make the first integrated assessment of the diet of guillemot chicks at a UK scale14. Chick diet varied markedly among 23 colonies sampled (spread from Devon to Shetland) between 2006 and 2011. Sandeels (Ammodytidae, probably mostly lesser sandeels Ammodytes marinus), were the commonest prey. Their contribution to the diet varied both latitudinally and among marine regions, with the proportion significantly higher for a given latitude on the west coast compared to the east14. The non-sandeel component of the diet showed latitudinal changes, with small clupeids, probably sprats Sprattus sprattus, predominant at southern colonies whereas juvenile gadids were the main alternative to sandeels in the north. Part of the study period coincided with a brief population explosion of snake pipefish Entelurus aequoreus in the Northeast Atlantic and North Sea. Pipefish were recorded in guillemot chick diet at several northern and north-western colonies in 2006 and 2007 but have been absent since 2009. Spatial and temporal variation in chick diet accorded broadly with patterns expected as a result of rising sea temperatures and impacts of fishing14.

Within the SMP, detailed diet data has been collected annually on the Isle of May. The proportion of sandeels in the diet of young guillemots at the Isle of May fluctuated between 1987 and 2000 before falling steeply and has now been consistently low since 2001 (Figure 10). Those years in which sandeels comprise a low proportion of guillemot's diet on the Isle of May also tend to coincide with low productivity. Alternative energy-rich prey includes clupeids such as sprat, but in 2004 the energy content of these fish (and sandeels) was found to be unusually low, corresponding with very low guillemot productivity2. In 2018, of 1,029 food items delivered to chicks, 89.0% were Clupeids (most thought to be sprat), 5.8% were sandeels and 5.0% were gadoids. This did not appear to impact on the productivity of guillemots as they still managed to fledge an average number (0.70) of chicks during the 2018 breeding season15.

guillemot-sandeel.jpg

Figure 10. Percentage of sandeels (by weight) in the diet of young guillemots at the Isle of May, 1987–2018.

 

Feeding watches at Sumburgh Head (Shetland) throughout the main chick-rearing period (mid-June to mid-July) between 2007 and 2018, have identified the main prey delivered to chicks as gadoids (79.7%) and sandeels (10.9%), which combined account for over 90% of identified food items each year5. This contrasted with 2017, when gadids comprised 50.7% of chick diet and sandeels 46.4%16. As in previous years, the occurrence of clupeids and squid was rare in 2018. Years when few sandeels are delivered to chicks saw an increase in gadids and vice versa. Comparison of chick diet data collected at this colony between 2007-2018 indicates the percentage of sandeels delivered has fallen from 60% to 10%17. At what point this shift from a diet dominated by sandeels took place is unknown, as data at Sumburgh Head have only been collected from 2007; the last year when sandeels made up more than 50% of the chick’s diet. A similar shift in diet at Fair Isle (40 km south-west of Sumburgh Head) seems to have occurred at some time between 2000 and 200212. Since 2003, weights of chicks near fledging at Compass Head (1.3 km north of Sumburgh Head) have been lower than during the 1990s and average productivity at Sumburgh Head has also reduced5.

 

Return rate and survival rate

Important notes on interpretation: Estimation of guillemot adult return rate is currently only undertaken at one site within the Seabird Monitoring Programme - the Isle of May (North-east Fife). Also presented are data from Skomer from a long-term study undertaken by Professors Tim Birkhead and Ben Hatchwell from the University of Sheffield. Return rates are based on sightings of individually colour-ringed birds and are calculated as the proportion of marked birds present in year one that is seen in the following year. Because not every adult alive is seen each year, return rates for 2018 presented here for Isle of May and Skomer need to be treated as minimum estimates of survival of birds seen the previous year. In contrast, survival estimates would take into account birds that are not seen one year but which re-appear in following years.

Guillemot return rate on the Isle of May has declined over time with very low values recorded in 2007 and 2008 (Figure 11). Since then, return rate has improved, with values recorded between 2009, 2014 and 2018 close to average (90%). Figure 12 shows that there is no clear trend in return rate of Skomer guillemots, although a very low value was recorded in 1990. Return rates of guillemots on Skomer were negatively affected by the occurrence of major oil spills on their wintering grounds and by climate (high values of the North Atlantic Oscillation)18.

The winter of 2013/14 saw a succession of severe storms from late January to the beginning of March result in a large 'wreck' of seabirds along Atlantic coasts from England and Ireland to Spain. A minimum of 54,000 seabirds, mostly auks, were washed ashore dead or dying. Examination of many corpses revealed birds were emaciated with empty stomachs indicating starvation as the main cause of death although a small proportion showed signs of oil contamination19. Overall, about 30% of the casualties were guillemots20.

Biometric data from 30 of these corpses indicated birds were typical of the subspecies albionis which breeds from south-west Scotland down to Iberia. Rings recovered from guillemot corpses (from beaches in France) also indicated birds originated from colonies around the UK and Ireland. The majority of birds examined were found to be adults. The total mortality will be much higher than reported because not all beaches were checked, birds were washed ashore over a number of weeks and many birds will be lost unrecorded at sea14.

On Skomer, following the ‘wreck’ of winter 2013/14 the data from 2014 strongly suggested a very high level of mortality among adult birds between 2013 and 2014 and this was consistent with the very high number of guillemot ringing recoveries in the weeks following the ‘wreck’. The data from 2015 reaffirmed that mortality following the ‘wreck’ had been high21. The survival of adult guillemots, based on re-sightings only (not on statistical analyses) suggested that survival was slightly higher in 2016 than in 2015, but lower than in many previous years22. In 2018, survival was (as in 2017) slightly lower than in 201623.

guillemot-return-rate-isle-of-may.jpg

Figure 11. Annual return rate of guillemot breeding on the Isle of May, 1987–2018.

 

guillemot annual return rate Skomer.jpg

Figure 12. Annual return rate of guillemot breeding on Skomer, 1986–2013. Reproduced with kind permission from Professors Tim Birkhead and Ben Hatchwell (University of Sheffield)/Countryside Council for Wales13.

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References

1 Harris, M.P., Heubeck, M., Newell, M.A. and Wanless, S. 2015. The need for year-specific correction factors when converting counts of individual common guillemots Uria aalge to breeding pairs. Bird Study, 62, 276–279.

2 Wanless, S., Harris, M.P., Redman, P. and Speakman, J.R. 2005. Low energy values of fish as a probable cause of a major seabird breeding failure in the North Sea. Marine Ecology Progress Series, 294, 1–8.

3 Heath, M., Edwards, M., Furness, R., Pinnegar, J. and Wanless, S. 2009. A view from above: changing seas, seabirds and food sources in Marine Climate Change Ecosystem Linkages Report Card 2009. eds. Baxter, J.M., Buckley, P.J. and Frost, M.T.), Online science reviews, 24pp. www.mccip.org.uk/elr/view

4 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, British Trust for Ornithology, Thetford.

5 Miles, W. and Mellor, M. 2018. SOTEAG Ornithological Monitoring Programme 2018 Report. The Scottish Oceans Institute, School of Biology, University of St Andrews.

6 Meade, J., Hatchwell, B.J., Blanchard, J.L. and Birkhead, T.R. 2013. The population increase of common guillemots on Skomer Island is explained by intrinsic demographic properties. Journal of Avian Biology, 44, 55–61.

7 Riordan, J. and Birkhead, T. 2018. Changes in the diet composition of Common Guillemot Uria aalge chicks on Skomer Island. Ibis, 160(2), 470–474.

8 Allen, D., Archer, E., Leonard, K. and Mellon, C. 2011. Rathlin Island Seabird Census 2011. Report for the Northern Ireland Environment Agency.6 Meade, J., Hatchwell, B.J., Blanchard, J.L. and Birkhead, T.R. 2013. The population increase of common guillemots on Skomer Island is explained by intrinsic demographic properties. Journal of Avian Biology, 44, 55–61.

9 Cummins, S., Lauder, C., Lauder, A. & 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.

10 Erikstad, K.E., Reiertsen, T.K., Barrett, R.T., Vikebø, F. and Sandvik, H. 2013. Seabird fish interactions: the fall and rise of a common guillemot Uria aalge population. Marine Ecology Progress Series, 475, 267–276.

11 Hill, R.W., Morris, N. G., Bowman, and K. A., Wright, D. 2019. The Isle of Man Seabird Census: Report on the census of breeding seabirds in the Isle of Man 2017-18. Manx BirdLife. Laxey, Isle of Man.

12 Veron, M. and Veron, C. 2016. Seabird Count 2015; monitoring the status of Guernsey’s Seabirds. La Société Transactions, Channel Islands.

13 Birkhead, T.R., Hatchwell, B.J. and Finch, T. 2012. Skomer Island guillemot study 2012. University of Sheffield report to Countryside Council for Wales.

14 Anderson, H.B., Evans, P.G.H., Potts, J.M., Harris, M.P. and Wanless, S. 2014. The diet of common guillemot Uria aalge chicks provides evidence of changing prey communities in the North Sea. Ibis, 156, 23–34.

15 Wanless, S., Harris, M.P., Newell, M.A., Speakman, J.R. and Daunt F. 2018. Community-wide decline in the occurrence of lesser sandeels Ammodytes marinus in seabird chick diets at a North Sea colony. Marine Ecology Progress Series, 600, 193–206.

16 Newell, M., Harris, M.P., Gunn, C.M., Burthe, S., Wanless, S. and Daunt, F. 2014. Isle of May seabird studies in 2014. Unpublished report, JNCC, Peterborough.

17 Heubeck, M., Mellor, M. and Miles, W. 2018. SOTEAG Ornithological Monitoring Programme: 2017 Summary Report. Aberdeen Institute of Coastal Science and Management, University of Aberdeen.

18 Heubeck, M. 2009. Common guillemot Uria aalge chick diet and breeding performance at Sumburgh Head, Shetland in 2007-09, compared to 1990-91. Seabird, 22, 9–18.

19 Votier, S.C., Hatchwell, B.J., Beckerman, A., McCleery, R.H., Hunter, F.M., Pellatt, E.J., Trinder, M. and Birkhead, T.R. 2005. Oil pollution and climate have wide-scale impacts on seabird demographics. Ecology Letters, 8, 1157–1164.

20 Jessop, H. Seabird tragedy in the north-east Atlantic winter 2013/14. Unpublished report, RSPB, Sandy.

21 Sellers, R.S. 2014. Mass mortality of razorbills and other seabirds on the coast of Cumbria in February 2014. Lakeland Naturalist, 2, 63–71.

22 Stubbings, E.M., Büche, B.I., Miquel Riera, E., Green, R.M. and Wood, M.J. 2015. Seabird monitoring on Skomer Island in 2015. Unpublished JNCC Report, Peterborough.

23 Stubbings, E.M., Büche, B.I., Miquel Riera, E., Green, R.M. & Wood, M.J. (2016). Seabird monitoring on Skomer Island in 2016. Unpublished JNCC Report, Peterborough.

24 Stubbings, E.M., Büche, B.I., Riordan, J.A., Baker, B. and Wood, M.J. 2018. Seabird monitoring on Skomer Island in 2018. Unpublished JNCC Report. Peterborough.

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

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SMP Report 1986–2018

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