Common Guillemot Uria aalge
Status; International importance;
Population
estimates; Distribution; Annual abundance/
productivity; Phenology/diet/survival
Description
The following was 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 common 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. 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.
Common 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
Common guillemot is currently identified as a conservation
priority in the following:
Amber listed in Birds
of Conservation Concern 3 (2009 update)
(further information on Conservation Designations for UK Taxa)
Amber listed in
Birds of Conservation Concern in Ireland 2 (2007
update)
International importance
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. This factor has been shown to be generally
applicable in Britain.
| |
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 where colonies are found and how large they are
is provided in the Seabird 2000 common
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
Breeding abundance
Figure 1: Trend in UK abundance index (solid
line) of common guillemot 1986-2010 with 95% confidence
limits (dotted lines). Based on SMP data; view
the methods
of analysis (PDF 158 kb).
The UK population index for common guillemot
(Figure 1) was fairly stable in the years immediately following
1986. Between 1990 and 2001 the index increased by 83%
and, although it fluctuated thereafter, in 2010 has again
reached an abundance index comparable with 2001; so common
guillemots would appear to be almost 50% more abundant now than in
the late 1980s. Over the longer term, census results show that
common guillemots increased from 0.61 million individuals in
1969/70 to 1.08 million in 1985-88. There is no good evidence as to
why they increased. The apparent stabilisation since 2001 may
be a result of so-called 'density-dependent' effects,
where growth at the densest colonies slowed
or reversed when competition for space and food reached
critical levels. While predictions of future population
trends are uncertain, the observed low productivity combined
with low return rate at the sampled colony (see below) may
lead to future declines.
Productivity
Figure 2: Trend in UK productivity (no. of
chicks fledged per pair) of common guillemot 1986-2010.
Based on SMP data; view the methods
of analysis (PDF 158 kb).
Common guillemot productivity (Figure 2)
was stable from 1986 to 1996, but thereafter
declined, dramatically so between 2002 and 2007, by which time a
mean of just 0.30 chicks per pair was fledged. This
decline coincided with food shortages and, at one colony, a
decrease in the energy content of fish brought to chicks1. Declines
in productivity primarily affected colonies in the north and
east of the UK, where sandeels (rather than sprats and their
relatives) are the main prey; indeed the sample of colonies for
which productivity data is available is somewhat biassed to these
regions. The association of years of low guillemot
productivity with rising sea surface temperatures (SST) due to
climate change is uncertain,
though there are indications that declines in the productivity
of sandeels may be linked in complex ways to warming sea
temperatures2. Mean guillemot
productivity was higher in 2008-2010, though it
remains below the long-term mean. The reasons for
increased productivity are not known. Although sandeels were
apparently abundant at some colonies recently (when they had been
scarce in immediately preceding years), common guillemots in
areas where the prey is predominantly sprat have
also experienced higher productivity.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (Ind*) |
519,461 |
943,098 |
1,167,841 |
| % change since previous
census |
N/a |
+82 |
+24 |
* Ind = Individuals
Breeding abundance
Figure 1: Trend in abundance index (solid
line) of common guillemot in Scotland, 1986-2010 with 95%
confidence limits (dotted lines). Based on SMP data; view
the methods
of analysis (PDF 158 kb).
The population index for common guillemot
in Scotland (above) was fairly stable up to the early 1990s
then increased slightly over a few years before levelling off.
However, since 2001 the index has declined and has been
lower than the 1986 baseline in six of the last seven
years (maximum 25% below in 2007). Over the longer term, census
results show an increase of 82% between 1969/70
and 1985-88 so there are still far more common guillemots than
recorded during Operation Seafarer. Recent low breeding
productivity coupled with low return rate at the one sampled
colony (see below) may lead to future declines.
Productivity
Figure 2: Trend in productivity (no. of
chicks fledged per pair) of common guillemot in Scotland,
1986-2010. Based on SMP data; view the methods
of analysis (PDF 158 kb).
Most data on the productivity of common guillemots in the UK
have been collected at Scottish colonies so the trend shown above
closely matches that for the UK although values obtained for 2009
and 2010 are lower. Productivity was relatively stable up
to 1996, falling slightly thereafter with a steep
decline from 2002 onward. In 2007 and 2008, a mean
of just 0.21 chicks per pair was fledged. Declines in
productivity primarily affected colonies in the north and
east, coinciding with shortages in sandeels, the main
prey for common guillemots breeding in those
areas. Productivity improved in 2009 and 2010, although was
still well below the long-term average, when
sandeels were apparently more abundant near some colonies.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (Ind*) |
29,910 |
61,070 |
91,986 |
| % change since previous
census |
N/a |
+104 |
+51 |
* Ind = Individuals
Breeding abundance
Figure 1: Trend in abundance index (solid
line) of common guillemot in England, 1986-2010 with 95%
confidence limits (dotted lines). Based on SMP data; view
the methods
of analysis (PDF 158 kb).
The trend for common guillemots in England has
generally been upward since the early 1990s, albeit with a slight
dip between 1997 and 2000 followed by apparent stability from 2005
onward. 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. Although the at times wide confidence intervals in the
index impart some uncertainty in the data, it appears this
increase continued post Seabird 2000, in contrast to the trend
in Scotland.
Productivity
There was no statistically significant year effect in the
productivity of common guillemots at colonies in England, where an
average of 0.70 chicks were fledged per pair per year. Productivity
at the few English colonies studied is relatively high
compared with Scotland.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (Ind*) |
17,238 |
32,126 |
57,961 |
| % change since previous
census |
N/a |
+86 |
+45 |
* Ind = Individuals
Breeding abundance
Figure 1: Trend in abundance index (solid
line) of common guillemot in Wales, 1986-2010 with 95%
confidence limits (dotted lines). Based on SMP data; view
the methods
of analysis (PDF 158 kb).
The abundance index for common guillemots in Wales
shows a steady increase since the early 1990s so is similar to
that for England, with both in contrast to Scotland.
The slope of the trend for Wales is steeper than that for
England with the index value in 2010 three times that of the
1986 baseline (c.f. 2.4 for England and 0.8 for Scotland). Over the
longer term national census results for Wales show that common
guillemots have been increasing since Operation Seafarer.
Productivity
There was no statistically significant difference in the
productivity of common guillemots over time at colonies
in Wales, where an average of 0.72 chicks were fledged per
pair per year. Average productivity in Wales is similar
to that recorded in England, and far higher than that for
Scotland in recent years.
Population estimates and change 1969-2002 (census data)
| |
Operation Seafarer
(1969-70)
|
Seabird Colony Register
(1985-88)
|
Seabird 2000
(1998-2002)
|
| Population estimate (Ind*) |
44,672 |
45,047 |
98,546 |
| % change since previous
census |
N/a |
<+1 |
+119 |
* Ind = Individuals
Breeding abundance
Common guillemot numbers in Northern Ireland more than doubled
between the Seabird Colony Register and Seabird 2000 to 98,546
individuals. Most of these are found on Rathlin Island which held
95,117 individuals (96% of the national population) during the
last census. In 2007, numbers on Rathlin had declined by 14%
to 81,303 individuals. Clearly, with few other sizeable common
guillemot colonies in the country, the national population
will have fallen too, although it will still be well
above that recorded by the Seabird Colony Register, or by Operation
Seafarer.
Productivity
Few systematic data on the productivity of common guillemots
have been collected in Northern Ireland as part of 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 (Ind*) |
39,643 |
98,910 |
138,108 |
| % change since previous
census |
N/a |
+149 |
+40 |
* Ind = Individuals
Breeding abundance
The table above shows common guillemot numbers in the Republic
of Ireland increased considerably after Operation Seafarer,
more than tripling by Seabird 2000. Few colonies in the
country are monitored frequently enough to allow accurate
conclusions about the current population status, but recent
counts are available for some colonies. On Lambay, the largest
colony, 67,314 individuals were recorded in 2009 compared with
60,754 during Seabird 2000, an increase of 11%. Several smaller
colonies have also increased in size since the last census; in
2010, Bray Head, Ireland's Eye and Great Skellig held 5,462
individuals compared to 3,899 in 1999. These recent figures all
suggest numbers in the Republic of Ireland will have increased
substantially since Seabird 2000. However, at Cliffs of Moher, the
third largest colony in the region, numbers in 2005 had
seemingly decreased from 19,962 individuals at the time of
Seabird 2000 to 7,250 apparently incubating birds (which would
equate to approximately 10,875 individuals). Given these
conflicting changes, especially at two major colonies, it
is unwise to draw conclusions about the national population
trend over the previous decade without other data.
Productivity
Very few systematic data on the productivity of common
guillemots have been collected in the Republic of Ireland as part
of 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 (Ind*) |
84,315 |
143,957 |
236,654 |
| % change since previous
census |
N/a |
+71 |
+64 |
* Ind = Individuals
Breeding abundance
National census data show the number of common 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 have declined, due to a fall on
Rathlin Island which holds the majority of the national population,
but changes in the Republic of Ireland are less clear given
contrasting fortunes of the species at Lambay (increase) and Cliffs
of Moher (decrease) and in the absence of data from other major
colonies in this country.
Productivity
Very few systematic data on the productivity of common
guillemots have been collected throughout Ireland as part of
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 (Ind*) |
1,050 |
2,195 |
4,566 |
| % change since previous
census |
N/a |
+109 |
+108 |
* Ind = Individuals
Breeding abundance
Figure 1: Abundance of common guillemot on
the Calf of Man, 1986-2010.
Common guillemots on the Isle of Man have doubled
in number during each subsequent national
census. Few colonies have been surveyed since Seabird
2000 although on the Calf of Man (Figure 1), where numbers
have fluctuated over the years, a decline appears to have
occurred. Counts in 2005, 2006 and 2010 have all been in the range
of 200-260 individuals. 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 productivity have been collected as part
of 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 (Ind*) |
201 |
345 |
476 |
| % change since previous
census |
N/a |
+72 |
+38 |
* Ind = Individuals
Breeding abundance
National census data show that common guillemot
numbers on the Channel Islands increased between Operation
Seafarer and Seabird 2000 in common with other regions of
the British Isles. No data have been
collected over the last decade.
Productivity
No systematic data on productivity have been collected as part
of 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 at
University of Sheffield (Figure 3) show that the median laying date
of common guillemots on Skomer (SW Wales) became about 10 days
earlier over the period 1991-2010. Laying date in 2009 and 2010
were by far the earliest in the time series, being 15 and 8 days
earlier than the long-term mean respectively.
Figure 3. Median laying date
of common guillemots on Skomer (SW Wales), 1991-2010. Reproduced
with kind permission of Professors Tim Birkhead and Ben
Hatchwell (University of Sheffield)/ Countryside Council for
Wales3.
Diet
Figure 4 shows that the proportion of sandeels in the diet
of young guillemots at the Isle of May has fluctuated, but was
consistently low since 2001. 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 include clupeids such as sprat, but in 2004 the energy density
of these fish (and sandeels) was found to be unusually low,
corresponding with very low guillemot
productivity1. In contrast,
on Skomer (SW Wales) sprat is by far (>90%) the
largest component of guillemot diet, having varied little
over time, and supports generally high productivity (Tim
Birkhead, pers comm).
Figure 4. Percentage of sandeels (by weight) in
the diet of young common guillemots at the Isle of May
(SE Scotland), 1987-2010.
Return rate and survival rate
Important notes on
interpretation: Estimation of common guillemot
adult return rate is currently only undertaken
at one site within the Seabird Monitoring Programme -the Isle
of May in the Firth of Forth, SE Scotland. Also presented are
data from Skomer from a long term study undertaken by Professors
Tim Birkhead and Ben Hatchwell at 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 2010 presented here for Isle of May and
Skomer need to be treated as minimum estimates of survival of
birds seen in 2009. In contrast, survival estimates do take
into account birds that are not seen one year but which re-appear
in following years.
Figure 5 shows that guillemot return rate on the Isle of
May declined from around 1998 and very low values occurred in 2007
and 2008. Return rate was then around average in 2009 and in 2010.
Figure 6 shows that there is no clear trend in return rate of
Skomer guillemots, though low rates occurred in 1990 and in 2008.
Like birds from the Isle of May, return rate was around average in
2009 but was the highest on record in 2010 at 98%. Survival
rates 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)4. The declining
return rates seen on Isle of May appear not to have had a marked
effect on the UK abundance index (Figure 1) though the latter has
shown a levelling off or slight decline during the last decade.
Figure 5. Annual return rate of common
guillemot breeding on the Isle of May (SE Scotland),
1987-2010.
Figure 6. Annual return rate
of common guillemot breeding on Skomer (SW Wales),
1986-2010. Reproduced with kind permission of Professors Tim
Birkhead and Ben Hatchwell (University of Sheffield)/
Countryside Council for Wales3.
References
1 Wanless, S., Harris, M. P., Redman, P. & Speakman, J. R.
2005. Low energy values of fish as a probable cause of a major
seabird breeding failure in the North Sea. Mar. Ecol. Prog. Ser.
294: 1-8.
2 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 JM, Buckley PJ and Frost MT), Online
science reviews, 24pp. www.mccip.org.uk/elr/view
3 Birkhead, T.R., Hatchwell, B.J. and,
Patrick, S. (2009) Skomer Islands guillemot study 2009. University
of Sheffield report to Countryside Council for Wales.
4 Votier, S.C., Hatchwell, B.J., Beckerman, A., McCleery,
R.H., Hunter, F.M., Pellatt, E.J., Trinder, M. & Birkhead,
T.R. (2005) Oil pollution and climate have wide-scale
impacts on seabird demographics. Ecology
Letters 8 1157-1164
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; Countryside Council for Wales; Department of
Agriculture, Fisheries and Forestry (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.