Great Cormorant Phalacrocorax carbo
Status; International importance;
Population
estimates; Distribution; Annual abundance/
productivity; Phenology/diet/survival
Description
The following was 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:
Not 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
*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 in the same place 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)
|
| UK Population estimate (AON*) |
6,071 |
6,610 |
7,238 |
| % change since previous census |
N/a |
+9 |
+10 |
*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.
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 where colonies are found and how large they are
is provided in the Seabird 2000 great
cormorant 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 great cormorant 1986-2010 with 95%
confidence limits (dotted lines). Based on SMP data; view
the methods
of analysis (PDF 158 kb).
The abundance index for cormorant (which
includes inland and coastal breeders) increased from 1986 to1995
and has since decreased (with a temporary rise in the early 2000s).
In the longer term, census results indicate that the coastal
population increased slightly between 1969-70 (6,100 pairs) and
1985-88 (6,600 pairs). 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) but have declined since
2002. At the last census, in 1999-2002, inland breeders in
the UK comprised about 20% of the total. There is pronounced
regional variation in the trends of abundance in great cormorant;
populations in northern Scotland have declined particularly
severely. Increases in abundance up to 1995 are likely
to have been facilitated by increased legal protection instigated
under the Wildlife and Countryside Act 1981. Factors
responsible for recent declines are likely to include increased
mortality from licensed and unlicensed shooting1,2, as well as possible changes in
food availability.
Productivity
Figure 2: Trend in UK productivity (no. of
chicks fledged per pair) of great cormorant 1986-2010. Based
on SMP data; view the methods
of analysis (PDF 158 kb).
Productivity has declined over the
monitored period and has been relatively low between
2005-2010; the causes of this are unknown.
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 |
| % change since previous
census |
N/a |
-13 |
+21 |
* 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
Between Operation Seafarer and the Seabird Colony Register the
great cormorant population declined by 13% although numbers had
subsequently recovered by Seabird 2000, increasing by 21% since the
previous census. The number of breeding pairs has probably declined
since Seabird 2000 although the SMP annual sample is
relatively small and may not be representative of the national
population, so is not shown. Cormorant colonies can move
location quite quickly so apparent declines at those regularly
monitored may be due to birds moving to nest elsewhere.
These new colonies may not be detected during routine
monitoring by the SMP but will be detected by national censuses,
when coverage is complete.
Productivity
Great cormorants at Scottish colonies on
average fledged approximately 1.80 chicks per pair per year; there
was no statistically significant variation over time.
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 |
| % change since previous
census |
N/a |
+13 |
+8 |
* 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
Figure 1: Trend in abundance index (solid line)
of coastal-nesting great cormorant in England, 1986-2010 with 95%
confidence limits (dotted lines). Based on SMP data; view
the methods
of analysis (PDF 158 kb).
The abundance of great cormorants at coastal colonies in England
peaked in 2003 but has declined again since although there has
been greater fluctuation in the trend in recent years. National
census data too indicate that numbers at coastal colonies
have increased since 1969/70. The current population would
appear to be on a par with that recorded during Seabird 2000.
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) but have declined since 2002. At the last
census, in 1999-2002, the inland breeding population totalled
1,332 pairs - slightly more than recorded on the
coast.
Productivity
Great cormorants at colonies in England
on average fledged approximately 1.68 chicks per pair per year;
there was no statistically significant variation over time.
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 |
| % change since previous
census |
N/a |
+14 |
-2 |
* 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
Figure 1: Trend in abundance index (solid
line) of great cormorant in Wales, 1986-2010 with 95% confidence
limits (dotted lines). Based on SMP data; view
the methods
of analysis (PDF 158 kb).
National census data, together with the trend calculated from
colonies sampled by the SMP, indicate that great cormorant
abundance in Wales has remained fairly stable since 1969/70
although there has been some fluctuation. Abundance peaked in
1989 and 1994 with troughs in 1991, 1999 and 2002. Few inland
colonies exist in Wales.
Productivity
Figure 2: Trend in
productivity (no. of chicks fledged per pair) of great cormorant in
Wales, 1986-2010. Based on SMP data; view the methods
of analysis (PDF 158 kb).
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, recently there
appears to have been a decline in the number of chicks fledged each
year. The cause of this is unknown.
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 |
| % change since previous
census |
N/a |
+581 |
-10 |
* 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
In Northern Ireland, where there are only a few great cormorant
colonies, numbers underwent a large increase between Operation
Seafarer and the Seabird Colony Register when numbers multiplied
almost six-fold. This was followed by a decline with numbers during
Seabird 2000 falling by 10%. Since then the most frequently
surveyed colony, at Strangford Lough (the second largest colony in
the country), increased from 278 pairs in 2000 to 451 pairs in
2010 (with a peak of 490 pairs in 2005). It seems likely the
national population has increased too unless numbers on Sheep
Island (the largest colony in Seabird 2000, holding 344 pairs in
1999) have fallen drastically.
Productivity
No systematic data on the productivity of the great cormorant in
Northern Ireland 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 (AON*) |
1,842 |
3,981 |
4,073 |
| % change since previous
census |
N/a |
+116 |
+2 |
* 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
Great cormorant numbers in the Republic of Ireland more than
doubled between Operation Seafarer and the Seabird Colony Register
to 3,981 pairs. Seabird 2000 found numbers had been stable
since the SCR having increased by fewer than 100 pairs.
Data are received from few colonies each year but the three
largest colonies during Seabird 2000, Lambay, Ireland's Eye and St.
Patrick's Island, were all counted in 2009 and 2010 and held
1,706 and 1,385 pairs in these years respectively (c.f. 1,539 pairs
in 1999). The current status of the national population is,
however, largely unknown as cormorant colonies may move
between years and therefore increases at some colonies may be
offset by decreases elsewhere.
Productivity
Few systematic data on the productivity of the great cormorant
in Republic of Ireland 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 (AON*) |
1,950 |
4,717 |
4,736 |
| % 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 an 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 suggest numbers have been at least stable in the
interim. However, cormorant colonies may move between
years and therefore increases at some colonies may be offset
by decreases elsewhere, so without recent
comprehensive census data the current population
status is uncertain.
Productivity
Few systematic data on the productivity of the great cormorant
have been collected at colonies 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 (AON*) |
35 |
102 |
134 |
| % change since previous
census |
N/a |
+191 |
+40 |
* 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
Great cormorant numbers on the Isle of Man almost trebled
between Operation Seafarer and the Seabird Colony Register to 102
pairs. By the time of Seabird 2000 a further increase had occurred
with numbers rising to 134 pairs. Colonies are few; all were
surveyed in 2008 when a total of 232 pairs were counted,
representing an increase of 73% since 1999.
Productivity
Few data have been collected on the productivity of great
cormorants on the Isle of Man 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 (AON*) |
62 |
113 |
115 |
| % change since previous
census |
N/a |
+82 |
+2 |
* 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
National census data indicate numbers of great cormorants have
almost doubled since Operation Seafarer in 1969/70. However, this
increase occurred before the 1985-88 census as numbers recorded
during the Seabird Colony Register and Seabird 2000 were
virtually identical. No data have been collected since the
1998-2002 census.
Productivity
No systematic productivity data have been collected for
great cormorant in the Channel Islands as part of the SMP.
UK phenology, diet, survival rates
No data have been collected as part of the Seabird Monitoring
Programme.
References
1 Carss, D.N. 1994. Killing of piscivorous
birds at Scottish finfish farms, 1984-1987. Biol. Conserv.
68, 181-8.
2 C.V.Wernham, M.Armitage, S.J.Holloway,
B.Hughes, R.Hughes, M.Kershaw, J.R.Madden, J.H.Marchant, W.J.Peach
and M.M.Rehfisch, 1999, Population, Distribution. Movements and
Survival of Fish-eating Birds in Great Britain, Department of
the Environment, Transport and the Regions Report, London.
Partners
Data have been provided to the SMP by the generous contributions
of its partners, other organisations and volunteers throughout
Britain and Ireland. Partners to the SMP are: BirdWatch Ireland;
The British Trust for Ornithology; Centre for Ecology and
Hydrology; 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 great cormorant appears courtesy of
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not be reproduced in any form whatsoever.