Download Breeding seabirds - Scottish Natural Heritage

Scottish Natural Heritage
BIODIVERSITY INDICATOR
S005 – Dec 2016
The numbers and breeding success of seabirds
Scotland’s twenty four species of breeding seabirds are of
international importance. Seabirds are useful and important
indicators for assessing the state of the marine environment. They
rely on the sea, but breed on land making them relatively easy to
monitor. They respond to a range of factors such as changes in
food availability, weather, predation and pollution. Being relatively
long lived the numbers of breeding seabirds usually changes
slowly over time. Breeding success (the number of chicks
produced) provides an indication of food availability (generally fish
and other marine species) and other factors such as predation
during the breeding season. Breeding success typically varies
far more from year to year than breeding numbers.
Northern gannet © Lorne Gill, SNH
Evidence
The indicators of breeding numbers for 12 species, and breeding success for 12 species, out of the 24
seabird species that breed in Scotland, are based on estimates from a representative sample of
seabird colonies around Scotland. These are monitored as part of the UK Seabird Monitoring
Programme, which started in 1986.
The numbers and breeding success of seabirds in Scotland, 1986-2015
Breeding numbers
120
100
60
2015
2014
2013
2012
2011
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
40
Breeding success
120
100
80
60
NOTE: The axes are not scaled to zero
Year
Assessment
From the start of the time series in 1986 to the most recent estimate in 2015:
• The mean numbers of 12 species of breeding seabirds in Scotland declined. By 2015,
breeding numbers was 50% of the 1986 level.
• Mean breeding success of 12 breeding seabird species has declined.
TREND
Decreased
DATA CONFIDENCE
http://www.snh.gov.uk/indicators/
Medium
2015
2014
2013
2012
2011
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
40
1986
Index 1986 = 100%
80
Commentary
Included in this indicator are 16 i of the 24 species of seabird that regularly breed in Scotland.
All seabird species included in this indicator are either Red or Amber listed as Birds of
Conservation Concern (Eaton et al., 2015). Five are Red listed (European shag; Arctic skua;
Atlantic puffin; black-legged kittiwake; and herring gull) and the remaining eleven are Amber
listed.
Out of the 12 species assessed for breeding numbers, Arctic skua has declined the most
(-76%). The Northern Isles are their breeding stronghold and there have been declines in
the availability of sandeels, which they obtain from other seabirds, such as kittiwake, by
chasing to make them release their food. Increased predation from great skua has also
been linked to their decline (Meek et al., 2011). No species show an overall increase in
the indicator, though the numbers of common guillemot, common tern, Arctic tern and
Sandwich tern have shown a slight increase from 2011 to 2015.
Breeding success varied amongst the 12 species assessed. In 2015, it was higher than the
long-term (1986 to 2014) average for six species: Arctic skua; black-legged kittiwake;
common tern; common guillemot; northern gannet; and Sandwich tern. Three species had
breeding success lower than the long-term average: herring gull; little tern; and northern
fulmar. Three species had breeding success in 2015 around the long-term average:
Arctic tern; Atlantic puffin; and great skua. A recent survey of northern gannet (Murray
et al., 2015), has shown a large increase in their breeding numbers. Good breeding
success and improved survival of immature and adult birds has helped boost populations
and led to an expansion of their range.
Source data and updates
The indicator has been updated with data up to and including 2015. Breeding numbers
trends are based on 12 species and the breeding success trend on the 12 species for which
sufficient data are available ii. Data are derived from the UK Seabird Monitoring Programme
(SMP) and its partners. The SMP collects and collates data on breeding numbers,
demographic parameters (including breeding success and survival rate), and diet from a
sample of colonies around the UK. The data confidence has been reduced to medium as it
is over fifteen years since the last national census. The census provides an accurate
snapshot of seabird breeding numbers and allows us to benchmark the annual colony
counts.
Updates are provided annually and the data are available from JNCC.
UK Indicators
JNCC
reports
on
seabird
population
trends
as
an
Official
Statistic
(see http://jncc.defra.gov.uk/page-4235). As Scotland supports the majority of UK breeding
seabirds, the UK trend is greatly influenced by trends in Scotland. Seabird abundance in the
UK increased between 1970 and 1999, and has since declined.
References
Eaton, M., Aebischer, N., Brown, A. et al. 2015. Birds of Conservation Concern 4: the population status of birds in
the UK, Channel Islands and Isle of Man. British Birds, 108, 708-746.
Meek, E.R., Bolton, M., Fox, D. and Remp, J. 2011. Breeding skuas in Orkney: a 2010 census indicates densitydependent population change driven by both food supply and predation. Seabird, 24, 1-10.
Murray, S., Harris, M.P. and Wanless, S. 2015. The status of the gannet in Scotland in 2013-14. Scottish Birds,
35, 3-18.
i
Data available for 1 = Breeding Numbers 2= Breeding Success
Arctic skua1,2; Arctic tern1,2; Atlantic puffin2;black guillemot1;black-legged kittiwake1,2;common gull1;common tern1,2;European
shag1; great black-backed gull1; great skua2; common guillemot1,2; herring gull1,2;little tern1; northern fulmar1,2; northern gannet2;
Sandwich tern1,2
ii
Note: No data were available for lesser black-backed gull in 2015 and this has been removed from the indicator
http://www.snh.gov.uk/indicators/