The following has been adapted from original text by Robin M. Sellers in Seabird Populations of Britain and Ireland (with permission from A&C Black, London).
Historically, great cormorants have been regarded as primarily coastal birds in Britain and Ireland, but during the last 40 years there has been a gradual shift of wintering quarters inland, to the extent that almost every lowland lake and river has some. In England, the number nesting inland in trees has increased from just 151 pairs at one colony in 1986 to 1,334 pairs at 35 colonies in 1999–2002. This growth of inland colonies has been fuelled by the immigration of the sub-species P. c. sinensis from continental Europe. P. c. carbo nests predominantly on the coast and constitutes most of the UK population, which accounts for 13% of the world population that is restricted to the northern Atlantic coasts.
Conservation status
Great cormorant is currently identified as a conservation priority in the following:
- Green 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 2020–2026
- EC Birds Directive – migratory species
International importance
|
UK Population |
% Biogeographic Population |
% World Population |
|
8,900 AON* |
2.4 (ssp. carbo/sinensis) |
1.5 |
* AON = Apparently Occupied Nests
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.
Note: The UK population figure above includes data from both inland and coastal colonies hence differs from that tabled below.
UK population estimates and change 1969–2002 (census data)
Great cormorants build large conspicuous nests with coastal colonies normally situated on stacks, rocky islets, cliffs or rocky promontories. Many colonies persist at the same location for long periods, but others come and go or suddenly shift location – the presence of a colony in one year is no guarantee that there will be one there the following year. This introduces uncertainty in population size when counts from a number of years have to be combined, as was the case during all three national censuses. To limit this problem, an effort was made during Seabird 2000 to reduce the number of years over which counts were obtained. However, the timing of breeding by different pairs of great cormorants within the same colony is not always synchronous resulting in no guarantee that a single count of the nests will reflect precisely the true number of breeding attempts. Seabird 2000, like previous censuses, conducted a single count at an optimum time within a given year (1 May–25 June), so population estimates are comparable although the absolute size of the breeding population is probably underestimated.
|
|
Operation Seafarer (1969-70) |
Seabird Colony Register (1985-88) |
Seabird 2000 (1998–2002) |
|
Population estimate (AON*) |
6,071 |
6,610 |
7,238 |
|
Inland numbers |
- |
- |
1,646 |
|
Total Figure |
- |
- |
8,884 |
|
% change since previous census |
n/a |
+9 |
+10 |
*AON = Apparently Occupied Nests
Note: Inland colonies were not counted during the first two national censuses, so, to enable direct comparison, the percentage change refers to coastal colonies only.
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 Great cormorant found in different regions, and a map showing the location and size of colonies, is provided on the Seabird 2000 great cormorant 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.
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 estimated reproductive success (hereinafter referred to as productivity) are only shown if data analysis 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.
Note: for clarity, the Figure 1 ‘Overview of all regions’ abundance graph does not include confidence limits. These can be found in the respective regional accounts below.
Overview of all regions
Breeding abundance
Figure 1. Trends in abundance index of great cormorant 1986–2019 for UK (red), England (black) and Wales (orange). Further details, including 95% confidence limits, can be found in the sections below.
There has been pronounced regional variation in great cormorant abundance trends since monitoring began in 1986 (Figure 1). In England, an overall increase has been recorded, whereas in Wales the index has been more stable. More detailed information can be found in the individual country sections below.
An insufficient number of great cormorant colonies are monitored in Scotland, Northern Ireland, Republic of Ireland, Isle of Man and the Channel Islands, to allow the production of valid annual abundance trends.
Productivity
An insufficient number of great cormorant colonies are monitored in Scotland, England, Wales, Northern Ireland, Republic of Ireland, Isle of Man and the Channel Islands, to allow the production of valid annual productivity trends.
United Kingdom
Breeding abundance
Figure 2. Trend in UK abundance index (solid line) of great cormorant 1986–2019 with 95% confidence limits (dotted lines). Based on SMP data; view the methods of analysis.
The UK abundance index for great cormorant (which includes inland and coastal breeders) has fluctuated over the reporting period with several periods of increase followed by declines. The lowest value was recorded in 2013, when the index was approximately 10% below the baseline, although, since then, it has increased markedly and in 2019 was almost 30% above the baseline.
In the UK, inland breeding cormorants are largely confined to England and increased markedly during the 1990s (helped in part by immigration of birds from continental Europe of subspecies P. c. sinensis)1. At the last census, in 1998–2002, inland breeders in the UK comprised approximately 18% of the total breeding population (c. 1,646 of 8,884 AON).
Productivity
In the UK, first-year survival and productivity are higher for inland breeding cormorants, which is linked to earlier and greater food availability at these sites2. Productivity declined significantly between 1997 and 2009, although the number of nests and sites monitored each year has fluctuated considerably so this trend may not be representative of the population as a whole. Great cormorants at UK colonies fledged approximately 1.84 chicks per nest per year between 1989 and 2019.
Scotland
Population estimates and change 1969–2002 (census data)
|
|
Operation Seafarer (1969-70) |
Seabird Colony Register (1985-88) |
Seabird 2000 (1998–2002) |
|
Population estimate (AON*) |
3,438 |
2,986 |
3,626 |
|
Inland numbers |
- |
- |
0 |
|
Total Figure |
- |
- |
3,626 |
|
% change since previous census |
n/a |
-13 |
+21 |
*AON = Apparently Occupied Nests
Note: Inland colonies were not counted during the first two national censuses, so, to enable direct comparison, the percentage change refers to coastal colonies only.
Breeding abundance
Between Operation Seafarer and the Seabird Colony Register, the great cormorant population in Scotland declined by 13%, although numbers had recovered by Seabird 2000, increasing by 21% since the previous census. Although the SMP annual sample is not thought to be representative of the Scottish population (e.g. the derived trend from SMP data indicates a decline between SCR and Seabird 2000 in contrast to the above table), the number of breeding pairs may have remained relatively stable since the last national census. For example, compared with data collected during Seabird 2000, 10 colonies counted in 2019 held 738 AOS, an increase of just 1%.
Productivity
Great cormorants at Scottish colonies on average fledged approximately 1.79 chicks per nest per year between 1991 (no productivity data were submitted before then) and 2019; there was no statistically significant variation over time.
England
Population estimates and change 1969–2002 (census data)
|
|
Operation Seafarer (1969-70) |
Seabird Colony Register (1985-88) |
Seabird 2000 (1998–2002) |
|
Population estimate (AON*) |
1,057 |
1,220 |
1,315 |
|
Inland numbers |
- |
- |
1,581 |
|
Total Figure |
- |
- |
2,896 |
|
% change since previous census |
n/a |
+13 |
+8 |
*AON = Apparently Occupied Nests
Note: Inland colonies were not counted during the first two national censuses, so, to enable direct comparison, the percentage change refers to coastal colonies only.
Breeding abundance
Figure 3. Trend in abundance index (solid line) of great cormorant in England, 1986–2019 with 95% confidence limits (dotted lines). Based on SMP data; view the methods of analysis.
National census data indicate that numbers of great cormorants at coastal colonies in England increased between 1969-70 and 1998–2002. In conjunction with this, inland breeding cormorants (in the UK largely confined to England) increased markedly during the 1990s, helped in part by immigration of birds from continental Europe of the subspecies P. c. sinensis1. During Seabird 2000, the inland breeding population was 1,581 AON – slightly more than recorded on the coast2. In 2012, the inland population was estimated at 2,362 AON breeding at 48 sites3. Figure 3 shows how abundance at colonies (both coastal and inland) has increased overall since 1986. In 2019, the trend index fell slightly and is now 51% above the baseline. However, the confidence intervals over the last three years are much wider due to less monitoring being undertaken during this period.
Productivity
The productivity of great cormorants at colonies in England showed no statistically significant variation over time; approximately 1.68 chicks were fledged per pair per year between 1986 and 2019.
Wales
Population estimates and change 1969–2002 (census data)
|
|
Operation Seafarer (1969-70) |
Seabird Colony Register (1985-88) |
Seabird 2000 (1998–2002) |
|
Population estimate (AON*) |
1,468 |
1,668 |
1,634 |
|
Inland numbers |
- |
- |
65 |
|
Total Figure |
- |
- |
1,699 |
|
% change since previous census |
n/a |
+14 |
-2 |
*AON = Apparently Occupied Nests
Note: Inland colonies were not counted during the first two national censuses, so, to enable direct comparison, the percentage change refers to coastal colonies only.
Breeding abundance
Figure 4. Trend in abundance index (solid line) of great cormorant in Wales, 1986–2019 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, together with the trend calculated from colonies sampled by the SMP, indicate that great cormorant abundance in Wales has remained relatively stable since 1969-70, albeit with some fluctuation. The trend peaks in 1988, 1994 and 2019, with troughs in 1991, 1999, 2002 and 2018. Few inland colonies exist in Wales and no recent information is available for these. The largest two colonies of great cormorant in Wales, at Puffin Island and Little Orme, increased by 50% and 33% respectively between 2010 and 2019.
Productivity
Collection of productivity data at colonies in Wales has been sporadic, especially in the first half of the recording period, such that no clear trend is evident. However, there appears to have been a decline in the number of chicks fledged each year, although the cause is unknown. Great cormorants no longer breed on Skomer, with the colony moving from the Mew Stone to Midland Island in 2017, where 18 AON were counted in 2019.
Northern Ireland
Population estimates and change 1969–2002 (census data)
|
|
Operation Seafarer (1969-70) |
Seabird Colony Register (1985-88) |
Seabird 2000 (1998–2002) |
|
Population estimate (AON*) |
108 |
736 |
663 |
|
Inland numbers |
- |
- |
0 |
|
Total Figure |
- |
- |
663 |
|
% change since previous census |
n/a |
+581 |
-10 |
*AON = Apparently Occupied Nests
Note: Inland colonies were not counted during the first two national censuses, so, to enable direct comparison, the percentage change refers to coastal colonies only.
Breeding abundance
Figure 5. Number of great cormorant AON at Strangford Lough (Co. Down), 1986–2019.
In Northern Ireland, there are only six known great cormorant colonies4. These held 663 AON during Seabird 2000, which was 10% fewer than that recorded during the SCR Census (736 AON) but six-times more than recorded by Operation Seafarer (108 AON). However, from 2017 to 2018, five colonies (Strangford Lough, Burial Island, Gobbins, Little Skerries and Sheep Island) held 673 AON, a very similar number to the Seabird 2000 count. At Strangford Lough, the most frequently surveyed colony (and also one of the largest colonies in the country), numbers increased substantially after Seabird 2000, from 125 AON to a peak of 490 AON in 2005 (Figure 5). Since then numbers fell to 245 AONs in 2015 but had recovered to 388 AON in 20194. Numbers of cormorants at Sheep Island have fluctuated annually but have shown an overall decrease in size, from 380 AON in 1985 to 88 AON in 2018, when they were last counted. The colony at Gobbins has fluctuated in numbers, dropping as low as two AON in 2007, increasing to 33 AON in 2008, but falling to 0 AON in 2019.
Productivity
Data submitted to the SMP on the productivity of great cormorants in Northern Ireland are sparse; thus, no meaningful average productivity value can be given.
Republic of Ireland
Population estimates and change 1969–2018 (census data)
|
|
Operation Seafarer (1969-70) |
Seabird Colony Register (1985-88) |
Seabird 2000 (1998–2002) |
Republic of Ireland Census (2015-18) |
|
Population estimate (AON*) |
1.842 |
3,981 |
4,073 |
4,688** |
|
Inland numbers |
- |
- |
475 |
- |
|
Total Figure |
- |
- |
4,548 |
- |
|
% change since previous census |
n/a |
+116 |
+2 |
+3 |
*AON = Apparently Occupied Nests
** Combination of inland and coastal. Information on the exact split was not provided5.
Note: Inland colonies were not counted during the first two national censuses, so, to enable direct comparison, the percentage change refers to coastal colonies only.
Breeding abundance
Great cormorant numbers in the Republic of Ireland more than doubled between Operation Seafarer and the Seabird Colony Register (SCR) to 3,981 AON. Seabird 2000 found numbers had been relatively stable since the SCR, having increased by fewer than 100 AON. A total of 65 sites were counted during the recent Republic of Ireland Seabird Census (2015–2018)5, 21 more sites than Seabird 2000. At these, a total of 4,688 AON were recorded compared to 4,548 AON during Seabird 2000, an increase of 3%. Less than 10% of the estimated breeding population of great cormorant occurred at inland sites5. There were insufficient data from the Republic of Ireland to allow annual trends to be generated for the period 1986 to 2019.
Productivity
Data submitted to the SMP on the productivity of great cormorants 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 (AON*) |
1,950 |
4,717 |
4,736 |
|
Inland numbers |
- |
- |
475 |
|
Total Figure |
- |
- |
5,211 |
|
% change since previous census |
n/a |
+142 |
<+1 |
*AON = Apparently Occupied Nests
Note: Inland colonies were not counted during the two earlier national censuses, so, to enable direct comparison, the Seabird 2000 figure refers to the coastal population only.
Breeding abundance
For the whole of Ireland combined, national censuses show a considerable increase between Operation Seafarer and the Seabird Colony Register, but numbers between the SCR and Seabird 2000 were similar. Since then, data from a few of the largest colonies in Northern Ireland suggest numbers may have been stable in the interim. In addition, the recent Republic of Ireland Seabird Census (2015–2018)5 recorded 4,688 AON, a 3% increase to the 4,548 AON counted during Seabird 2000, indicating that the all-Ireland great cormorant population is relatively stable.
Productivity
Data submitted from colonies in Northern Ireland and the Republic of Ireland are sparse. Thus, no meaningful average productivity value can be given for the whole of Ireland.
Isle of Man
Population estimates and change 1969–2018 (census data)
|
|
Operation Seafarer (1969-70) |
Seabird Colony Register (1984-88) |
Seabird 2000 (1998–2002) |
Isle of Man Census (2017-18) |
|
Population estimate (AON*) |
35 |
102 |
134 |
251 |
|
Inland |
- |
- |
0 |
0 |
|
Total Figure |
- |
- |
134 |
251 |
|
% change since previous census |
n/a |
+191 |
+40 |
+87 |
*AON = Apparently Occupied Nests
Note: Inland colonies were not counted during the first two national censuses, so, to enable direct comparison, the percentage change refers to coastal colonies only.
Breeding abundance
Great cormorant numbers on the Isle of Man almost trebled between Operation Seafarer and the Seabird Colony Register to 102 AON. By the time of Seabird 2000 a further increase had occurred with numbers rising to 134 AON. All colonies were surveyed in 2011 and 2017 when totals of 206 and 251 AON were counted, respectively. The most recent data from 2017 indicate an increase of 87% since 1999 when all colonies were counted for Seabird 2000. The increase does not reflect that for Britain and Ireland as a whole, but does reflect the St Bee’s Head trend, indicating a possible regional increase in the north east of the Irish Sea6.
Productivity
Data submitted to the SMP on the productivity of great cormorants in the Isle of Man are sparse; thus, no meaningful average productivity value can be given.
Channel Islands
Population estimates and change 1969–2015 (census data)
|
|
Operation Seafarer (1969-70) |
Seabird Colony Register (1984-85) |
Seabird 2000 (1998–2002) |
Channel Islands Census (2015) |
|
Population estimate (AON*) |
62 |
113 |
115 |
185 |
|
Inland numbers |
- |
- |
0 |
0 |
|
Total Figure |
- |
- |
115 |
185 |
|
% change since previous census |
n/a |
+82 |
+2 |
+61 |
*AON = Apparently Occupied Nests
Note: Inland colonies were not counted during the first two national censuses, so, to enable direct comparison, the percentage change refers to coastal colonies only.
Breeding abundance
National census data show that the number of great cormorants on the Channel Islands doubled between Operation Seafarer and the Seabird Colony Register censuses. The population had barely changed by the time of the Seabird 2000 census, although had increased by a further 61% when counted again during the 2015 census7.
Productivity
No systematic data on the productivity of great cormorants on the Channel Islands have been submitted to the SMP.
UK phenology, diet, survival rates
No data have been collected as part of the Seabird Monitoring Programme.
References
1 Newson, S., Marchant, J., Sellers, R., Ekins, G., Hearn, R. and Burton, N. 2013. Colonisation and range expansion of inland-breeding cormorants in England. British Birds, 106, 737–743.
2 Newson, S.E., Hughes, B., Hearn, R. and Bregnballe T. 2005. Breeding performance and timing of breeding of inland and coastal breeding Cormorants Phalacrocorax carbo in England and Wales. Bird Study, 52(1), 10–17.
3 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.
4 Booth Jones, K. and Wolsey, S. 2019. Northern Ireland Seabird Report 2018. British Trust for Ornithology, Thetford.
5 Cummins, S., Lauder, C., Lauder, A. and Tierney, T. D. 2019. The Status of Ireland’s Breeding Seabirds: Birds Directive Article 12 Reporting 2013–2018. Irish Wildlife Manuals, No. 114. National Parks and Wildlife Service, Department of Culture, Heritage and the Gaeltacht, Ireland.
6 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.
7 Veron, M. and Veron, C. 2016. Seabird Count 2015; monitoring the status of Guernsey’s Seabirds. La Société Transactions, Channel Islands.
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; Department of Agriculture, Environment and Rural Affairs (Northern Ireland); Department of Environment, Food and Agriculture (Isle of Man); Department of the Environment, Climate and Communications (Republic of Ireland); JNCC; Manx Birdlife; Manx National Heritage; The National Trust; National Trust for Scotland; Natural England; Natural Resources Wales; NatureScot; The Royal Society for the Protection of Birds; Scottish Wildlife Trust; Seabird Group; Shetland Oil Terminal Environmental Advisory Group; States of Guernsey Government; UK Centre for Ecology and Hydrology. More about the SMP partners >>
Image of Great cormorant appears courtesy of Ian Rendall ©, is subject to international copyright law and may not be reproduced in any form whatsoever.
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