Guillemot Uria aalge

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

 

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Description

Common Guillemot vignette

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:

EC Birds Directive - migratory species

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

(further information on Conservation Designations for UK Taxa)

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

 


International importance

 

UK Population % Biogeographic Population % World Population
1,416,300 Individuals 33.3 (N Atlantic) 12.9

 

The UK population figure (rounded to the nearest hundred) was derived from data in Mitchell, P.I., Newton, S.F., Ratcliffe, N. and Dunn, T.E. (eds.) 2004. Seabird Populations of Britain and Ireland. Poyser, London. This was also the source of figures for the Biogeographic and World populations.

 


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

 

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.

 


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 (PDF, 2.0 mb).

 

An interactive map is available on the NBN Gateway, where you can filter to display only the Seabird 2000 data.  For more recent, but less comprehensive, coverage view the distribution on the NBN with all available contributing datasets.

 

The locations sampled during the annual Seabird Monitoring Programme provide some information on distribution and are accessible via the Seabird Monitoring Programme online database.

 


Annual abundance and productivity by geographical area

 

With reference to the regional accounts below please note the following.

Breeding abundance: graphs of abundance index with 95% confidence linits are only shown for a region where the trend produced has been deemed accurate (see methods of analysis). Where a trend was thought to be inaccurate, graphs of abundance at major colonies in a region may be shown instead, particularly if such colonies hold greater than 10% of the regional population, are monitored frequently and may thus help illustrate regional population fluctuations outwith national censuses. Occasionally, too few data have been collected regionally to produce either of these.

Productivity: graphs of productivity are only shown if analysis of breeding success data produced a significant result for regional and/or year effects (again see methods of analysis). If results were not significant, then a regional mean productivity value is given. However, on some occasions, too few data are available from which to provide a meaningful average. Furthermore, for 11 species where the quality of monitoring data available was considered high, population viability analysis was undertaken at the UK level and the results of this are also reported.   

 



 

Breeding abundance

 

UK common guillemot abundance trend

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

 

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 has climbed steadily and in 2014 has reached its highest value at 60% 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 good evidence as to why they increased. While predictions of future population trends are uncertain the observed low productivity in recent years, combined with lowered return rates (see below), may lead to future declines.

 

Table 1 below shows how numbers of guillemots have changed at some of the most important UK colonies (those in the SPA network) in the period since they were surveyed for Seabird 2000. The largest declines recorded since Seabird 2000, have been in colonies in Scotland while important colonies in England, Wales and Northern Ireland have all increased.

 

Area SPA Name Seabird 2000 Count (Year) Change (%) % per annum
Shetland Hermaness NNR 10,439 2000 3,658 2015 -65 -6.8
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 6,957 2015 -58 -5.3
Shetland Fair Isle 39,257 1999 20,924 2015 -47 -3.9
Orkney West Westray Cliffs 54,718 1999 50,613 2007 -8 -1.0
Orkney Copinsay 18,675 1999 18,461 2015 -1 -0.1
Orkney Marwick Head 34,679 1999 16,562 2012 -52 -5.5
Orkney Hoy 21,777 1999 9,020 2007 -59 -10.4
East Coast Troup, Pennan and Lion's Heads 45,254 2001 14,896 2007 -67 -16.9
East Coast Buchan Ness to Collieston Coast 29,389 2001 19,296 2007 -34 -6.8
East Coast Fowlsheugh 62,330 1999 55,507 2015 -11 -0.7
East Coast Firth of Forth Islands 37,795 2001 25,533 2015 -32 -2.8
East Coast St Abb's Head NNR 40,720 1998 32,990 2013 -19 -1.4
East Coast Farne Islands 31,497 2000 53,461 2015 +70 +3.6
East Coast Flamborough Head and Bempton Cliffs 46,685 2000 59,166 2008 +27 +3.0
West Coast Handa 112,676 1998 56,706 2011 -50 -5.1
West Coast Shiant Isles 16,456 1999 7,684 2008 -53 -8.1
West Coast Mingulay and Berneray 32,590 1998 22,265 2014 -32 -2.4
West Coast Ailsa Craig 9,415 2001 5,675 2015 -40 -3.6
West Coast Rathlin Island 95,117 1999 130,445 2011

+37

+2.7
West Coast Skomer and Skokholm 15,171 2000 27,349 2015 +80 +4.0

Table 1: Recent counts of the number of guillemot (IND) recorded in SPAs in the UK compared to the number recorded in them during Seabird 2000. The percentage that each colony has fallen by, and the per annum change, is also provided. (Note: data for Hermaness and St Abb's Head relate to only part of the SPA).

 

Productivity

 

UK Common guillemot productivity trend

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

 

After remaining stable from 1986 to 1996, guillemot productivity (Figure 2) declined dramatically between 2004 and 2008, by which time a mean of just 0.23 chicks per pair was fledged. Productivity has improved since then, although values recorded between 2009 and 2015 are still lower than those recorded prior to 2004. 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 study at the Isle of May found reduced energy content in fish brought to chicks at this time2. The association between years of low guillemot productivity and years of high sea surface temperatures (SST) due to climate change isuncertain, though indications are that a decline in sandeel productivity is linked to warming sea temperatures3. In recent years, sandeels have apparently been abundant at some colonies, coincident with improved success, although productivity at colonies where the predominant prey species is sprat has also been high.

 

Analysis of the SMP dataset found the mean breeding success of guillemot 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 breeding success 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, breeding success would have to fall to 0.25 chicks per nest per year.

 

 

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

 

Scotland common guillemot abundance trend

Figure 1: Trend in abundance index (solid line) of guillemot in Scotland, 1986-2015 with 95% confidence limits (dotted lines; drawing of upper limit restricted to preserve detail in the abundance index). Based on SMP data; view the methods of analysis (PDF 158 kb).

 

National census data show an increase of 82% 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 1) was stable up to the early 1990s, after that 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 in nine of the last 10 years (maximum 25% below in 2007). 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 59% fewer guillemots in 20155. Data from study plots between 2000 and 2015 indicate declines of 42% on Handa (Sutherland) and 29% at St. Abb's Head (Berwickshire) but an increase of 22% at Fowlsheugh (Kincardine and Deeside). It is thought that decreased attendance by off-duty adults or non- and failed breeders has contributed substantially to the decline in Shetland, where former breeding ledges are now deserted at many colonies. Measures of attendance in a single plot used to follow breeding success at Sumburgh Head have been falling over the last decade5. Recent low breeding productivity across Scotland coupled with low return rates (assuming measurements of this at the Isle of May are typical of what is happening elsewhere) may lead to future declines throughout Scotland.

 

 

Productivity

 

Scotland Common guillemot productivity trend

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

 

Most data on the productivity of guillemots in the UK have been collected at Scottish colonies so the trend in Figure 2 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 up to 1996, falling slightly thereafter with a steep decline from 2003 to 2007 when productivity had fallen below 0.25 chicks 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 breeding success during the last few years. For example, from 2011 to 2013, the mean breeding success 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 2014 and 2015, guillemots had a relatively successful season, although values recorded were still lower than the years prior to 2000. In 2015 guillemots fledged an average of 0.55 chicks per site in Shetland; 0.57 in Orkney; 0.65 in north-west Scotland; and 0.79 in south-east Scotland.

 

At Sumburgh Head, the median laying date in 2015 was two days earlier than in 2014 (Figure 3) and hatching success of first eggs was relatively high (70%). This consequence of good colony attendance by adults aided chick survival. However, breeding success of 0.52 fledged per laying pair was slightly lower than the 1989-2014 colony average of 0.545.

 

 

 

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

 

England common guillemot abundance trend

Figure 1: Trend in abundance index (solid line) of guillemot in England, 1986-2015 with 95% confidence limits (dotted lines; drawing of upper limit restricted to preserve detail in the abundance index). Based on SMP data; view the methods of analysis (PDF 158 kb).

 

The 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 (probably due to few colonies being monitored frequently) suggest the results should be treated with some caution.

 

Productivity

 

England Common guillemot productivity trend

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

 

Productivity at the few English colonies studied (Bempton Cliffs (Humberside), Berry Head (Devon) Lundy (North Devon), Farne Islands (Northumberland) and St. Aldhelm’s Head (Dorset)), and at colonies in Wales, has generally been relatively high compared with Scotland. These differences in productivity 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. Reasons as to why 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 2015, an average of 0.72 and 0.32 chicks per pair fledged at Flamborough Head and Bempton Cliffs SPA and Lundy Island NNR, respectively, slightly lower than 2014 at Flamborough Head and Bempton Cliffs SPA (0.79) but markedly lower at Lundy (0.50).

 

 

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

 

Wales common guillemot abundance trend

Figure 1: Trend in abundance index (solid line) of guillemot in Wales, 1986-2015 with 95% confidence limits (dotted lines; drawing of upper limit restricted to preserve detail in the abundance index). Based on SMP data; view the methods of analysis (PDF 158 kb).

 

The 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 2015 over two times (243%) that of the 1986 baseline (cf. 2.4 for England and 0.8 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 (Dyfed, 24% during Seabird 2000) where guillemot numbers have been increasing at an almost constant rate of 5% per annum for the last three decades. 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 0.68 chicks were fledged per site per year between 1989 and 2015. Average productivity in Wales is similar to that recorded in England, but far higher than in Scotland in recent years. This is probably due to differences in food taken by guillemots in southern/western colonies compared to eastern/northern colonies. Lowered 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, so have an alternative food source for their chicks not only in years when sandeels are in short supply (see 'Diet' section).

 

 

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

 

Guillemot numbers in Northern Ireland 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. There are only five guillemot colonies in the country, with the greatest numbers found on Rathlin Island (Co. Antrim) which 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 UK. However, the 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); the abundance index for the UK shows a pronounced dip. 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 lowered counts if surveys coincide with periods when birds were absent from, or yet to take up occupancy of, nesting ledges. Only two small colonies, The Gobbins and Muck (both Co. Antrim), have been surveyed in recent years; 3,255 individuals were recorded at these in 2014 and 4,207 in 2015. Both have increased since Seabird 2000 when they held 2,805 individuals. 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 common 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 2015 was from The Gobbins where an entire section of guillemot nests was wiped out by two herring gulls predating eggs. In previous breeding seasons hooded crows, carrion crows, and herring gulls were responsible for the predation of many guillemot eggs at The Gobbins.

 

 

Population estimates and change 1969-2002 (census data)

 

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

Population estimate (Individuals) 39,643 98,910 138,108
% change since previous census    N/a +149 +40

 

 

Breeding abundance

 

The table above shows that guillemot numbers in the Republic of Ireland increased considerably after Operation Seafarer, more than tripling by Seabird 2000. Few colonies are monitored frequently, or in any one year; however, in 2015, 26 guillemot colonies were counted7. At these a total of 170,608 individuals were recorded compared to 137,491 individuals during Seabird 2000, an increase of 24%. The majority of individuals (35%) were recorded on Lambay Island (Co. Dublin), one of the largest colonies in the country where the population has declined very slightly since Seabird 2000 (60,754 individuals). During Seabird 2000, 34 colonies were counted holding 138,108 individuals. Ten of these colonies were not counted in 2015 but only held less than 1% of the national population (311 individuals). Hence, the numbers counted in 2015 suggest that guillemot numbers in the Republic of Ireland have increased since the last census. 

 

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.

 

 

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. Since then, numbers in Northern Ireland at the most important colony (Rathlin Island) initially declined but have now increased again. In the Republic of Ireland, a survey of 26 guillemot colonies in 2015 resulted in an increase of 24% compared to 27,749 recorded during Seabird 2000. Some smaller islands were not counted which held c. 300 individuals during Seabird 2000. Hence, a large proportion of the national population was surveyed suggesting an increase of guillemot numbers for the whole of Ireland.. 

 

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.

 

 

Population estimates and change 1969-2002 (census data)

 

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

Population estimate (Individuals) 1,050 2,195 4,566
% change since previous census    N/a +109 +108

 

 

Breeding abundance

 

guillemot Calf of Man abundance 2015

Figure 1: Abundance of guillemot on the Calf of Man (Isle of Man), 1986-2015.

 

The number of guillemots breeding on the Isle of Man had increased four-fold between Operation Seafarer and Seabird 2000. Few colonies have been surveyed since Seabird 2000, other than on the Calf of Man, which held c.15% of the total Isle of Man guillemots 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 and 2015) and 50% (e.g. in 2010 and 2013) of the census total. Many species at this colony have declined since Seabird 2000, but it is not known whether these declines are representative of the whole of the Isle of Man..

 

Productivity

 

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

 

 

Population estimates and change 1969-2002 (census data)

 

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

Population estimate (Individuals) 201 345 476
% change since previous census    N/a +72 +38

 

 

Breeding abundance

 

National census data show that guillemot numbers on the Channel Islands increased between Operation Seafarer and Seabird 2000 in with other regions of the British Isles. No data have been collected since Seabird 2000, so the current status of guillemots on the Channel Islands cannot be assessed. 

 

Productivity

 

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

 

 


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 3) show that the median laying date of guillemots on Skomer became almost two weeks earlier over the period 1991-2013 (no data are available for 2014 and 2015). Laying dates in 2009-2012 were by far 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 2001-2015 (also Figure 3) show median laying date became progressively later initially; 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 median laying date Skomer Sumburgh head 2015

Figure 3: Median laying date of guillemots on Skomer (Dyfed, blue dots) and Sumburgh Head (Shetland, red dots), 1991-2015. Skomer data reproduced with kind permission of Professors Tim Birkhead and Ben Hatchwell (University of Sheffield/ Countryside Council for Wales8). Sumburgh data reproduced with kind permission of Martin Heubeck (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 scale9. 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 east9. 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. Comparison of guillemot chick diet between 2006 and 2011 with data collected 15–30 years earlier also suggested that the proportion of sandeels in the diet had decreased at colonies bordering the North Sea9. 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 northwestern 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 fishing9.

 

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 4). 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 2015, of 770 food items delivered to chicks, 90.9% were clupeids (most thought to be sprat), 8.8% were sandeels and 0.3% were gadoids. This did not appear to impact on the breeding success of guillemots as they still managed to fledge an average number (0.78) of chicks during the 2015 breeding season10.

 

guillemot Isle of May Sandeels 2015

Figure 4: Percentage of sandeels (by weight) in the diet of young guillemots at the Isle of May (North-east Fife), 1987-2015.

 

Feeding watches at Sumburgh Head (Shetland) throughout the main chick-rearing period (mid-June to mid-July) between 2007 and 2015, have identified the main prey delivered to chicks as sandeels and gadoids, which combined account for over 90% of identified food items each year. Years when few sandeels are delivered to chicks see an increase in gadids and vice versa. Comparison of chick diet data collected at this colony between 1990-1991 with 2007-2012 indicates the percentage of sandeels delivered has fallen from 80% to 52%11,12. At what point this shift from a diet dominated by sandeels took place is unknown, but a similar shift in diet at Fair Isle (40km 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 (1.3km north of Sumburgh Head) have been lower than during the 1990s and average breeding success at Sumburgh Head has also been reduced12. In contrast, on Skomer (Dyfed), clupeids are still the main component of guillemot chick diets (Tim Birkhead, pers. comm.). This fiding has varied little over time, and supports generally high productivity. 

 

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 (Dyfed) 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 2015 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 5). Since then, return rate has improved with values recorded between 2009 and 2015 close to average. Figure 6 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)13. No data were available from Skomer for 2014 and 2015.

 

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 contamination14. Overall, about 30% of the casualties were guillemots15.

 

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 high16. The effect of this 'wreck' on the guillemot populations of the UK and Ireland is not yet known but the large estimated mortality is of potentially great concern with regard to future impacts on breeding numbers.

guillemot Isle of May returns 2015

Figure 5: Annual return rate of guillemot breeding on the Isle of May (North-east Fife), 1987-2015.

guillemot Skomer returns 2015

Figure 6:  Annual return rate of guillemot breeding on Skomer (Dyfed), 1986-2013.  Reproduced with kind permission of Professors Tim Birkhead and Ben Hatchwell (University of Sheffield)/Countryside Council for Wales8..

 


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, BTO, Thetford.

5 Heubeck, M. and Mellor, M. 2016. SOTEAG Ornithological Monitoring Programme: 2015 Summary Report. Aberdeen Institute of Coastal Science and Management, University of Aberdeen.

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 Newton, S.  Lewis, L. and  Trewby, M. 2015. Results of a Breeding Survey of Important Cliff‐Nesting Seabird Colonies in Ireland 2015. National Parks and Wildlife Service Ireland.

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

9 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.

10 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.

11 Heubeck, M. and Mellor, M. 2014. SOTEAG Ornithological Monitoring Programme: 2013 Summary Report. Aberdeen Institute of Coastal Science and Management, University of Aberdeen.

12 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.

13 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.

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

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

16 Stubbings, E.M., Büche, B.I., Miquel Riera, E., Green, R.M. and Wood, M.J. 2015. Seabird monitoring on Skomer Island in 2015.


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