5.14. Great Skua
- Present only in the northeast Atlantic, there are approximately 16,000 breeding pairs of great skua worldwide, 60% of which are located in Scotland (Mitchell et al., 2004). Between 1900 and 1990, the Scottish population of great skuas doubled approximately every 12 years, with 80% of breeding birds located within SPAs (Mitchell et al., 2004). They feed on small fish species such as sandeels as well as klepto-parasitising other seabirds although previously they were also known to strongly associate with fishing vessels, preying on discards (Votier et al., 2004; Votier et al., 2008). It is likely that fisheries discards currently make up a much smaller percentage of diet than previously, following the banning of dumping discards at sea which was fully implemented in 2019 (Ulhmann et al., 2019). The species is currently Amber-listed on the UK Birds of Conservation Concern List (Stanbury et al., 2021).
- Great skuas were recorded in low densities in the Offshore Ornithology Study Area, primarily between August and December. The peak estimated population was 72 birds (95%CI 32 – 119) in November 2020, attributed to the passage of birds through the Offshore Ornithology Study Area during southwards post-breeding migration ( Table 5.82 Open ▸ ).
- Berwick Bank Boat-based surveys in 2020-2021 recorded low numbers of great skuas. Most individuals were recorded in August 2020, and these birds were presumed to be birds passing through on their southwards post-breeding migration.
- Great skua distribution was variable, with birds distributed in the east and west of the Offshore Ornithology Study Area, such as in July 2019 and October 2020 respectively ( Figure 5.69 Open ▸ – Figure 5.70 Open ▸ ). Overall, most birds were recorded flying, with only 27% of birds recorded as sitting on the water.
- Flight direction varied between surveys ( Figure 5.71 Open ▸ ).
Table 5.81: Great skua bio-seasons taken from NatureScot (2020a)
Table 5.82: Monthly density and population estimates of all great skuas across Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species.
Figure 5.69: Distribution of great skuas across Offshore Ornithology Study Area between March 2019 and March 2020
Figure 5.70: Distribution of great skuas across Offshore Ornithology Study Area between May S01 2020 and April S01 2021
Figure 5.71: Summarised flight direction of great skuas across Offshore Ornithology Study Area
Figure 5.72: Percentage of flying great skuas per survey across Offshore Ornithology Study Area
5.15. Red-throated diver
- Typically wintering in UK coastal waters, including estuaries and sandy bays, red-throated divers migrate to higher latitudes during the breeding season, breeding on lochs in Scotland (Campbell, 1993). Listed as an Annex 1 species in the EU Birds Directive, red-throated divers are a qualifying species for many UK SPAs in the non-breeding season, with the Outer Firth of Forth and St Andrews Bay Complex SPA being the closest to the Offshore Ornithology Study Area, supporting about 2% of the GB wintering population, estimated at 90 individuals (Scottish Natural Heritage, 2018). The species is currently Green-listed on the UK Birds of Conservation Concern List (Stanbury et al., 2021).
- Red-throated divers were observed across the Offshore Ornithology Study Area in late spring and early winter, with peak density of 0.05 birds/km2 (95%CI 0.02 – 0.09) occurring in November 2020 and equating to an estimated 200 birds (95%CI 72 – 375; Table 5.87 Open ▸ ). Spring peaks in abundance, such as those recorded in May 2019 and May S02 2020 (57 birds (95%CI 22 – 98) and 34 birds (95%CI 0 – 80) respectively), can be attributed to the presence of pre-breeding congregations of the species, which have previously been observed off the east coast of Scotland in late May. Data summed from ESAS surveys conducted between 1980 and 1996 clipped to the Offshore Ornithology Study Area recorded two birds over the 16-year period, with no birds recorded on either the Project or Seagreen boat-based surveys. No red-throated divers were recorded during the WWT waterbird surveys.
- Generally, most observations occurred within the 16 km buffer, with birds recorded within the Project intermittently ( Figure 5.74 Open ▸ to Figure 5.76 Open ▸ ). In November 2020, when abundance of red-throated divers peaked, most birds were recorded in the south and west buffer, with some birds distributed in the south of the Proposed Development Array area.
- Most birds were recorded sitting on the water, but not in large groups; larger counts of birds within 500m transect segments were of 3-5 individuals only ( Figure 5.74 Open ▸ - Figure 5.76 Open ▸ ). No birds were recorded flying.
Table 5.86: Red-throated diver bio-seasons taken from NatureScot (2020a)
Table 5.87: Monthly apportioned density and population estimates of all red-throated divers across Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species
Figure 5.74: Distribution of red-throated divers across Offshore Ornithology Study Area between March 2019 and March 2020
Figure 5.76: Distribution of red-throated divers across Offshore Ornithology Study Area April S02 2021
5.16. Fulmar
- One of the most common seabird species found in the UK, fulmars typically breed on cliffs before moving offshore during the non-breeding period (Mitchell et al., 2004). Over the 20th Century fulmar populations dramatically increased (Fisher, 1952), however this has since stabilised, with declines experienced in some areas (Mitchell et al., 2004). Fulmars are generally long-lived with a low reproductive rate, making them particularly susceptible to environmental variations and anthropogenic impacts (Hatch 1987; Thompson, 2006). Fulmars are a qualifying species for the nearby Fowlsheugh SPA, which supports approximately 157 AOS (NatureScot, 2018; SMP, 2021). The species is currently Amber-listed on the UK Birds of Conservation Concern List (Stanbury et al., 2021).
- Fulmar densities were relatively consistent throughout the first year of aerial survey is with slight increases in March 2019 and between November 2019 and January 2020 during the non-breeding season ( Figure 5.77 Open ▸ ). In Year 2, two large peaks in densities were estimated, occurring in September and December 2020 at 0.77 birds/km2 (95%CI 0.65 – 0.88) and 0.38 birds/km2 (95%CI 0.28 – 0.48), during the breeding and non-breeding seasons ( Table 5.92 Open ▸ ).
- Fulmars were recorded during boat-based surveys of the Project and Seagreen Alpha and Bravo, occurring in regionally important numbers in the latter survey areas. Boat-based surveys conducted throughout the outer Firth of Forth as part of the IMPRESS project (Camphuysen et al., 2004), reported the species as present in low abundances, accounting for 0.6% of total observations. This was also true for WWT waterbird surveys, in which only 25 individuals were recorded.
- The breeding season begins in April, with females exhibiting a pre-laying exodus from coastal colonies a month prior to laying, which may be visible in the slight increase in fulmar abundance in April S02 2021. Egg-laying begins in earnest in May, with birds closely associated to nest sites from May to mid-July. During these months, densities of fulmars were at their lowest in the Offshore Ornithology Study Area, as most birds would be in attendance at colonies. The highest mean seasonal peaks in density were observed during the breeding season ( Table 5.95 Open ▸ ), with a large proportion of birds recorded as sitting on the water, suggesting use of the area for foraging. These results are largely influenced by the relatively high abundance calculated for September 2020, at the end of the breeding season, when birds are dispersing from colonies along the coast.
- Outside of the breeding season, fulmars are highly pelagic, moving further offshore to spend the winter at sea. Few birds were recorded during the non-breeding season, such as in February 2019, suggesting birds are utilising the Offshore Ornithology Study Area most during dispersal periods between colonies and wintering areas ( Table 5.95 Open ▸ ).
- Distribution maps indicate widespread use of the Offshore Ornithology Study Area, with many birds recorded in the south and west during the breeding season, such as in June 2019 and May S01 2020 ( Figure 5.78 Open ▸ to Figure 5.80 Open ▸ ).
- Flight direction of fulmars varied between surveys ( Figure 5.81 Open ▸ ).
Table 5.91: Fulmar bio-seasons taken from NatureScot (2020a)
Table 5.92: Monthly density and population estimates of all fulmars across Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species
Figure 5.77: Estimated densities (birds/km2) of all fulmars across Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species
Table 5.95: Mean seasonal peak (MSP) population and density (birds/km2) of all fulmars in the Offshore Ornithology Study Area in the Offshore Ornithology Study Area across the two years of surveying (March 2019 to April 2021) estimated using design-based analysis. Data include “no-identification” birds apportioned to species
Figure 5.78: Distribution of fulmars across Offshore Ornithology Study Area between March 2019 and March 2020
Figure 5.80: Distribution of fulmars across Offshore Ornithology Study Area April S02 2021
Figure 5.81: Summarised flight direction of fulmars across Offshore Ornithology Study Area
Figure 5.82: Percentage of flying fulmars per survey across Offshore Ornithology Study Area