Scottish Biodiversity Indicator – The Numbers and Breeding Success of Seabirds (1986 to 2019)

Published: 2021

Scotland’s breeding seabirds are of international importance. Seabirds are useful and important indicators for assessing the state of the marine environment (Parsons et al. 2008). Although they rely on the sea, breeding on land makes 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.

Monitoring Scotland’s Seabirds

The indicators of breeding numbers for 11 species, and breeding success for 11 species, (totalling 15 species, out of the 24 that breed in Scotland). The results are estimates from a representative sample of seabird colonies around Scotland, monitored as part of the UK Seabird Monitoring Programme, which started in 1986.

Indicator Assessment

From the start of the time series in 1986 to the most recent estimate in 2019:

The mean numbers of 11 species of breeding seabirds in Scotland declined. By 2019, breeding numbers were 49% of the 1986 level.
Mean breeding success of 11 breeding seabird species has fluctuated. In 2019, it was 6 percentage points higher than the long-term average of 75%.

The full description for accessibility is linked below this image. — Figure 1: Seabird breeding numbers (1986 to 2019).

Click for a full description

The dashed line shows the 95% confidence limits.

Reasons for Change

Overall Scotland’s seabirds have declined since 1986. The key drivers of change are fisheries, climate change and invasive non-native species. To a lesser extent, pollutants and offshore renewables may present some threats to seabirds. Work to develop the Scottish Seabird Conservation Strategy has provided information on the pressures and threats that Scotland’s seabirds face. This work is in progress and as it develops, it will help secure the future for Scotland’s seabirds.

Breeding Numbers

Out of the 11 species assessed for breeding numbers from 1986 to 2019, Arctic skua continues to show the largest declines (81%). Reductions in the availability of sandeels and the effects this has upon species such as black-legged kittiwake is understood to be one to the main factors affecting Arctic skua. Increased predation from great skuas has also been linked to their decline (Perkins et al. 2018). Common terns have shown a sharp decline in 2019 to 48%. The number of terns attempting to breeding at sites can vary markedly from year to year (Ratcliffe, 2004), so to understand whether this is a trend future years of results are required. Guillemot numbers are increasing 17% since 2016. They are now at a similar level to the early 2000s. A number of our seabirds appear to be stabilising at lower levels than the 1986 baseline year. Early research indicates that for some species, for example herring gull, this may be reverting to typical levels prior to 1986 (Foster et al. 2017).

Breeding success

Breeding numbers typically change more slowly than breeding success and looking at breeding success helps us understand some of the immediate factors that cause changes in seabird numbers, such as food availability, weather events and predation. The 2019 results show that breeding success was higher than the long-term average. There was a mixed picture across the 11 species assessed. Arctic skua, Atlantic puffin, black-legged kittiwake and herring gull breeding success was higher in 2019 compared to their long-term averages. Great skua and Arctic tern breeding success was lower than the long-term average. For the remaining species, breeding success was around the long-term average.

Source data and updates

The indicator has been updated with data up to and including 2019. The trend for breeding numbers is based on 11 species and the breeding success trend on the 11 species for which sufficient data are available. 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. Due to restricted fieldwork undertaken in 2020, the next update will be available in 2022 using data from 2021.

UK Indicators

JNCC reports on seabird population trends as an Official Statistic. As Scotland supports the majority of UK breeding seabirds, the UK trend is heavily influenced by trends in Scotland. Seabird abundance in the UK increased between 1970 and 1999 and has since declined.

References

Foster, S., Swann, R.L., and Furness, R.W. 2017. Can changes in fishery landings explain long-term population trends in gulls? Bird Study, 64, 90-97.

Parsons, M., Mitchell, I., Butler, A., Ratcliffe, N., Frederiksen, M., Foster, S., and Reid, J. B. 2008. Seabirds as indicators of the marine environment. ICES Journal of Marine Science, 65, 1520-1526.

Perkins, A., Ratcliffe, N., Suddaby, D. Ribbands, B., Smith, C., Ellis, P., Meek, E., and Bolton, M. 2018.Combined bottom‐up and top‐down pressures drive catastrophic population declines of Arctic skuas in Scotland. Journal of Animal Ecology. 87, 1573-1586.

Ratcliffe, N. 2004. Common Tern in Seabird Populations of Britain and Ireland: results of the Seabird 2000 Census (1998-2002). P. Ian Mitchell, Stephen F. Newton, Norman Ratcliffe and Timothy E. Dunn (Eds.). Published by T and A.D. Poyser, London.

Table 1: List of species contributing to the Indicators
Species (link to JNCC SMP)	Breeding Numbers	Breeding Success
Arctic Skua	Yes	Yes
Arctic Tern	Yes	Yes
Atlantic Puffin	No	Yes
Black Guillemot	Yes	No
Black-legged Kittiwake	Yes	Yes
Common Gull (coastal)	Yes	No
Common Tern	Yes	Yes
European Shag	Yes	No
Great Black-backed Gull	Yes	No
Great Skua	No	Yes
Guillemot	Yes	Yes
Herring Gull (natural-nesting)	Yes	Yes
Little Tern	No	Yes
Northern Fulmar	Yes	Yes
Northern Gannet	No	Yes

The data for the graph on Arctic Skua - breeding numbers is provided in table 2 — Figure 3: Arctic Skua - Breeding Numbers (1986-2018)

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The graph shows the declining trend in Arctic skua breeding numbers.

Table 2: Arctic Skua Key Pressures and Threats (source Scottish Conservation Strategy (in development))
Key Pressures and threats	Arctic Skua
Bycatch surface	Low
Bycatch pelagic	Medium
Bycatch demersal	Low
Bycatch aqua-culture	Low
Wind turbine collision mortality	Medium
Displacement by wind turbines	Medium
Wind turbines as a barrier to species movement	Low
Mortality by collision with underwater turbines etc	Low
Habitat loss from coastal infrastructure	Low
Marine litter	High
invasive predatory mammals	High
Reduction in prey by fishing	High
Disturbance from recreation, tourism and transport	Medium
Intentional taking of adults/eggs	Low
synthetic contaminants	Medium
Mortality from oil contamination	High
non-synthetic contaminants)	Medium

The data for the graph on Arctic tern - breeding numbers is provided in table 3 — Figure 5: Arctic Tern – Breeding numbers and success (1986-2019)

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Graph showing Arctic tern breeding numbers.

Table 3: Arctic Tern Key Pressures and Threats (source Scottish Conservation Strategy (in development))
Key pressures and threats	Arctic Tern
Bycatch surface	Low
Bycatch pelagic	Low
Bycatch demersal	Low
Bycatch aqua-culture	Low
Wind turbine collision mortality	Medium
Displacement by wind turbines	Medium
Wind turbines as a barrier to species movement	Low
Mortality by collision with underwater turbines etc	Low
Habitat loss from coastal infrastructure	Low
Marine litter	High
invasive predatory mammals	High
Reduction in prey by fishing	High
Disturbance from recreation, tourism and transport	Medium
Intentional taking of adults/eggs	Medium
synthetic contaminants	High
Mortality from oil contamination	High
non-synthetic contaminants)	Medium

The data for the graph on Atlantic Puffin - breeding numbers is provided in table 4 — Figure 7: Atlantic Puffin - breeding success Average (1986-2018)

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Graph showing the trend in Atlantic puffin breeding success.

Table 4: Atlantic Puffin Key Pressures and Threats (source Scottish Conservation Strategy (in development))
Key pressures and threats	Atlantic Puffin- breeding	Atlantic Puffin – non breeding
Bycatch surface	High	High
Bycatch pelagic	High	High
Bycatch demersal	Medium	Medium
Bycatch aqua-culture	Low	Low
Wind turbine collision mortality	Low	Low
Displacement by wind turbines	Medium	Medium
Wind turbines as a barrier to species movement	High	High
Mortality by collision with underwater turbines etc	High	High
Habitat loss from coastal infrastructure	High	Medium
Marine litter	High	High
invasive predatory mammals	High	NA
Reduction in prey by fishing	Low	Low
Disturbance from recreation, tourism and transport	Medium	Low
Intentional taking of adults/eggs	Low	Low
synthetic contaminants	High	High
Mortality from oil contamination	High	NA
non-synthetic contaminants)	High	High

The data for the graph on Black-legged Kittiwake - breeding numbers is provided in table 5 — Figure 8: Black-legged Kittiwake - breeding numbers Average (1986-2018)

The data for the graph on Black-legged Kittiwake is provided in table 5 — Figure 9: Black-legged Kittiwake - breeding success average (1986-2018)

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Graph showing trend of black-legged kittiwake breeding success.

Table 5: Black-legged Kittiwake Key Pressures and Threats (source Scottish Conservation Strategy (in development))
Key pressures and threats	Black-legged Kittiwake – breeding	Black-legged Kittiwake – non-breeding
Bycatch surface	Medium	Medium
Bycatch pelagic	Medium	Medium
Bycatch demersal	Low	Low
Bycatch aqua-culture	Low	Low
Wind turbine collision mortality	Medium	Medium
Displacement by wind turbines	High	High
Wind turbines as a barrier to species movement	Low	Low
Mortality by collision with underwater turbines etc	High	High
Habitat loss from coastal infrastructure	High	High
Marine litter	High	High
invasive predatory mammals	Low	NA
Reduction in prey by fishing	High	High
Disturbance from recreation, tourism and transport	High	High
Intentional taking of adults/eggs	Low	Low
synthetic contaminants	High	Medium
Mortality from oil contamination	High	High
non-synthetic contaminants)	Medium	Medium

The data for the graph on Black Guillemot - breeding numbers is provided in table 6 — Figure 10: Black Guillemot - breeding numbers

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Graph showing trend in black guillemot numbers.

Table 6: Black Guillemot Key Pressures and Threats (source Scottish Conservation Strategy (in development))
Key pressures and threats	Black Guillemot
Bycatch surface	High
Bycatch pelagic	Low
Bycatch demersal	Medium
Bycatch aqua-culture	High
Wind turbine collision mortality	Low
Displacement by wind turbines	Low
Wind turbines as a barrier to species movement	Medium
Mortality by collision with underwater turbines etc	Medium
Habitat loss from coastal infrastructure	Medium
Marine litter	Medium
invasive predatory mammals	High
Reduction in prey by fishing	NA
Disturbance from recreation, tourism and transport	Medium
Intentional taking of adults/eggs	NA
synthetic contaminants	NA
Mortality from oil contamination	High
non-synthetic contaminants)	High

A graph on Common gull - breeding numbers — Figure 11: Common Gull - breeding numbers

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Graph showing trend in coastal breeding common gull numbers.

The data for the graph on Common tern - breeding numbers is provided in table 7 — Figure 12: Common tern - breeding numbers

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Graph showing trend in common tern breeding numbers.

Table 7: Common Tern Key Pressures and Threats (source Scottish Conservation Strategy (in development))
Key pressures and threats	Common Tern
Key pressures and threats	Common Tern
Bycatch surface	Low
Bycatch pelagic	Low
Bycatch demersal	Low
Bycatch aqua-culture	Low
Wind turbine collision mortality	Medium
Displacement by wind turbines	Medium
Wind turbines as a barrier to species movement	Low
Mortality by collision with underwater turbines etc	High
Habitat loss from coastal infrastructure	High
Marine litter	High
invasive predatory mammals	High
Reduction in prey by fishing	Low
Disturbance from recreation, tourism and transport	Medium
Intentional taking of adults/eggs	Low
synthetic contaminants	NA
Mortality from oil contamination	NA
non-synthetic contaminants)	High

The data for the graph on European Shag - breeding numbers is provided in table 8 — Figure 14: European Shag - breeding numbers

Click for a full description

Grahps showing the trend in European shag breeding numbers.

Table 8: European Shag Key Pressures and Threats (source Scottish Conservation Strategy (in development))
Key pressures and threats	European Shag - breeding	European Shag – non-breeding
Bycatch surface	High	High
Bycatch pelagic	Low	Low
Bycatch demersal	High	High
Bycatch aqua-culture	High	High
Wind turbine collision mortality	Low	Low
Displacement by wind turbines	Low	Low
Wind turbines as a barrier to species movement	Low	Low
Mortality by collision with underwater turbines etc	Medium	Medium
Habitat loss from coastal infrastructure	High	High
Marine litter	High	High
invasive predatory mammals	Medium	NA
Reduction in prey by fishing	High	High
Disturbance from recreation, tourism and transport	Low	Low
Intentional taking of adults/eggs	Low	Low
synthetic contaminants	High	High
Mortality from oil contamination	High	High
non-synthetic contaminants)	High	High

A full description for this image can be found directly below — Figure 15: Great Black-backed Gull - breeding numbers

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Graph showing trend in breeding numbers for Great black-backed gull.

Table 9: Great Black-backed Gull Key Pressures and Threats (source Scottish Conservation Strategy (in development))
Key pressures and threats	Great Black-backed Gull - breeding	Great Black-backed Gull – non-breeding
Bycatch surface	Medium	Medium
Bycatch pelagic	Medium	Medium
Bycatch demersal	Low	Low
Bycatch aqua-culture	Low	Low
Wind turbine collision mortality	Medium	Medium
Displacement by wind turbines	Low	Low
Wind turbines as a barrier to species movement	Low	Low
Mortality by collision with underwater turbines etc	Low	Low
Habitat loss from coastal infrastructure	Low	Low
Marine litter	High	High
invasive predatory mammals	Medium	NA
Reduction in prey by fishing	Medium	Medium
Disturbance from recreation, tourism and transport	Low	Low
Intentional taking of adults/eggs	Low	Low
synthetic contaminants	High	High
Mortality from oil contamination	High	High
non-synthetic contaminants)	High	High

Table 10: Great skua Key Pressures and Threats (source Scottish Conservation Strategy (in development))
Key pressures and threats	Great skua – breeding	Great skua – non-breeding
Bycatch surface	Medium	Medium
Bycatch pelagic	Medium	Medium
Bycatch demersal	Low	Low
Bycatch aqua-culture	Low	Low
Wind turbine collision mortality	Low	Low
Displacement by wind turbines	Medium	Low
Wind turbines as a barrier to species movement	Low	Low
Mortality by collision with underwater turbines etc	Low	Low
Habitat loss from coastal infrastructure	Low	Low
Marine litter	High	High
invasive predatory mammals	High	NA
Reduction in prey by fishing	Medium	Medium
Disturbance from recreation, tourism and transport	Medium	Low
Intentional taking of adults/eggs	Low	Low
synthetic contaminants	High	High
Mortality from oil contamination	High	High
non-synthetic contaminants)	High	High

Table 11: Commom Guillemot Key Pressures and Threats (source Scottish Conservation Strategy (in development))
Key pressures and threats	Commom Guillemot – breeding	Common Guillemot – non-breeding
Bycatch surface	High	High
Bycatch pelagic	High	High
Bycatch demersal	High	High
Bycatch aqua-culture	Low	Low
Wind turbine collision mortality	Low	Low
Displacement by wind turbines	Medium	Medium
Wind turbines as a barrier to species movement	High	High
Mortality by collision with underwater turbines etc	High	High
Habitat loss from coastal infrastructure	High	Medium
Marine litter	Medium	Medium
invasive predatory mammals	High	NA
Reduction in prey by fishing	High	High
Disturbance from recreation, tourism and transport	Medium	Medium
Intentional taking of adults/eggs	Low	NA
synthetic contaminants	High	NA
Mortality from oil contamination	High	High
non-synthetic contaminants)	High	High

Table 12: Herring Gull Key Pressures and Threats (source Scottish Conservation Strategy (in development))
Key pressures and threats	Herring Gull - breeding	Herring Gull – non-breeding
Bycatch surface	Low	Low
Bycatch pelagic	Medium	Medium
Bycatch demersal	Low	Low
Bycatch aqua-culture	Low	Low
Wind turbine collision mortality	Medium	Medium
Displacement by wind turbines	Low	Low
Wind turbines as a barrier to species movement	Low	Low
Mortality by collision with underwater turbines etc	Low	Low
Habitat loss from coastal infrastructure	Medium	Medium
Marine litter	High	High
invasive predatory mammals	High	NA
Reduction in prey by fishing	High	High
Disturbance from recreation, tourism and transport	Low	Low
Intentional taking of adults/eggs	High	High
synthetic contaminants	High	High
Mortality from oil contamination	High	High
non-synthetic contaminants)	High	High

Table 13: Little Tern Key Pressures and Threats (source Scottish Conservation Strategy (in development))
Key pressures and threats	Little Tern
Bycatch surface	Low
Bycatch pelagic	Low
Bycatch demersal	Low
Bycatch aqua-culture	Low
Wind turbine collision mortality	Low
Displacement by wind turbines	Low
Wind turbines as a barrier to species movement	Low
Mortality by collision with underwater turbines etc	Low
Habitat loss from coastal infrastructure	High
Marine litter	High
invasive predatory mammals	High
Reduction in prey by fishing	High
Disturbance from recreation, tourism and transport	Medium
Intentional taking of adults/eggs	Low
synthetic contaminants	Medium
Mortality from oil contamination	High
non-synthetic contaminants)	NA

Table 14: Northern Fulmar Key Pressures and Threats (source Scottish Conservation Strategy (in development))
Key pressures and threats	Northern Fulmar - breeding	Northern Fulmar - non-breeding
Bycatch surface	High	High
Bycatch pelagic	Medium	Medium
Bycatch demersal	Low	Low
Bycatch aqua-culture	Low	Low
Wind turbine collision mortality	Medium	Medium
Displacement by wind turbines	Medium	Medium
Wind turbines as a barrier to species movement	Low	Low
Mortality by collision with underwater turbines etc	Low	Low
Habitat loss from coastal infrastructure	Low	Low
Marine litter	Medium	Medium
invasive predatory mammals	High	NA
Reduction in prey by fishing	Medium	Medium
Disturbance from recreation, tourism and transport	Medium	Medium
Intentional taking of adults/eggs	Low	Low
synthetic contaminants	Low	Low
Mortality from oil contamination	Medium	Medium
non-synthetic contaminants)	Low	Low

Key pressures and threats	Northern Gannet - breeding	Northern Gannet - non-breeding
Bycatch surface	High	High
Bycatch pelagic	High	High
Bycatch demersal	Low	Low
Bycatch aqua-culture	Low	Low
Wind turbine collision mortality	Medium	Medium
Displacement by wind turbines	Medium	Medium
Wind turbines as a barrier to species movement	Medium	Medium
Mortality by collision with underwater turbines etc	Low	Low
Habitat loss from coastal infrastructure	Low	Low
Marine litter	Medium	Medium
invasive predatory mammals	High	NA
Reduction in prey by fishing	High	High
Disturbance from recreation, tourism and transport	Medium	Medium
Intentional taking of adults/eggs	Low	Low
synthetic contaminants	NA	High
Mortality from oil contamination	High	High
non-synthetic contaminants)	High	High

Last updated:19/08/2021

Scottish Biodiversity Indicator – The Numbers and Breeding Success of Seabirds (1986 to 2019)

Monitoring Scotland’s Seabirds

Indicator Assessment

Reasons for Change

Breeding Numbers

Breeding success

Source data and updates

UK Indicators

References

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