5.17. Manx shearwater

  1. Manx shearwaters are highly pelagic and migratory, coming to coastal colonies to breed between April and October, before migrating south away from the UK during the non-breeding season (Guilford et al., 2009; NatureScot, 2020a). Approximately 89% of the world population breeds in Great Britain and Ireland (Mitchell et al., 2004), with around 40% of these birds breeding on Rum, off the west coast of Scotland (Newton et al., 2004). The species is vulnerable to predation by other seabird species such as great black-backed gulls and great skuas (Newton et al., 2004). As pursuit divers, they mainly target small shoaling fish, molluscs and crustaceans (JNCC, 2016). The species is currently Amber-listed on the UK Birds of Conservation Concern List (Stanbury et al., 2021).
  2. Manx shearwater densities were generally low with birds primarily observed during the breeding season, peaking in June in both Year 1 and Year 2 ( Figure 5.84   Open ▸ ). In these months, peak densities were calculated at 0.02 birds/km2 (95%CI 0.00 0.04) and 0.04 birds/km2 (95%CI 0.02 – 0.07) respectively, equating to population estimates of 72 birds (95%CI 16 – 150) and 153 birds (95%CI 63 – 268; Table 5.97   Open ▸ ). Mean peak population estimates for both years of surveys were calculated at 113 birds (95%CI 40 – 209) during the breeding season ( Table 5.100   Open ▸ ).
  3. Berwick Bank boat-based surveys of in 2020-2021 recorded low numbers of Manx shearwaters across the survey period, with the species also not listed as a key species in the Seagreen Alpha or Bravo boat-based surveys. Site-specific digital aerial video pre-construction monitoring surveys of the same area suggested the species may be present in low numbers.
  4. Distribution of Manx shearwaters was variable, with birds distributed to the south and west, such as in June 2019, and July and September 2020 ( Figure 5.84   Open ▸ and Figure 5.85   Open ▸ ). In June 2020, many birds were also distributed in the northwest buffer.
  5. Generally, Manx shearwater were mostly recorded in flight on surveys (67%). Higher proportions of sitting birds recorded during the breeding season may be due to the presence of rafting or foraging birds (Richards et al., 2019). The species is a qualifying species for the Outer Firth of Forth and St Andrews Bay Complex SPA since the area hosts one of only five known at-sea aggregations in Great Britain and the only east coast aggregation (JNCC, 2016).  
  6. Flight direction was variable ( Figure 5.86   Open ▸ ).

 

Table 5.96:
 Manx shearwater bio-seasons taken from NatureScot (2020a)

Table 5.96:  Manx shearwater bio-seasons taken from NatureScot (2020a)

 

Table 5.97:
 Monthly density and population estimates of all Manx shearwaters across Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species

Table 5.97:  Monthly density and population estimates of all Manx shearwaters across Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species

 

Table 5.98:
 Monthly density and population estimates of flying Manx shearwaters only across Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species

Table 5.98:  Monthly density and population estimates of flying Manx shearwaters only across Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species

Table 5.99:
 Monthly density and population estimates of sitting Manx shearwaters only across Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species

Table 5.99:  Monthly density and population estimates of sitting Manx shearwaters only across Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species

Figure 5.83:
 Estimated densities (birds/km2) of all Manx shearwaters across Offshore Ornithology Study   Area using design-based analysis. Data include “no-identification” birds apportioned to species

Figure 5.83:  Estimated densities (birds/km2) of all Manx shearwaters across Offshore Ornithology Study   Area using design-based analysis. Data include “no-identification” birds apportioned to species

 

Table 5.100:
Mean seasonal peak (MSP) population and density (birds/km2) of all Manx shearwaters in the Offshore Ornithology Study Area across the two years of surveying (March 2019 to April 2021) estimated using design-based analysis

Table 5.100: Mean seasonal peak (MSP) population and density (birds/km2) of all Manx shearwaters in the Offshore Ornithology Study Area across the two years of surveying (March 2019 to April 2021) estimated using design-based analysis

 

 

 

Figure 5.84:
 Distribution of Manx shearwaters across Offshore Ornithology Study Area in June, August and September 2019 and June to August in 2020

Figure 5.84:  Distribution of Manx shearwaters across Offshore Ornithology Study Area in June, August and September 2019 and June to August in 2020

Figure 5.85:
 Distribution of Manx shearwaters across Offshore Ornithology Study Area September 2020

Figure 5.85:  Distribution of Manx shearwaters across Offshore Ornithology Study Area September 2020

Figure 5.86:
  Summarised flight direction of Manx shearwaters across Offshore Ornithology Study Area

Figure 5.86:   Summarised flight direction of Manx shearwaters across Offshore Ornithology Study Area

 

Figure 5.87:
 Percentage of flying Manx shearwaters per survey across Offshore Ornithology Study Area

Figure 5.87:  Percentage of flying Manx shearwaters per survey across Offshore Ornithology Study Area

 

5.18. Shag

  1. Distributed throughout the northeast Atlantic and Mediterranean, the UK supports approximately 34% of the global shag population (Wanless and Harris, 1997; JNCC 2016).  Pursuit divers, they primarily feed on small fish species, such as saithe and sandeel (Harris and Wanless, 1991; Lorentsen et al., 2018). Shags are a qualifying species for the nearby Forth Islands, Outer Firth of Forth and St. Andrews Bay Complex and St. Abb’s Head to Fast Castle SPA’s. Colonies at the Isle of May and St. Abb’s National Nature Reserve were estimated to support approximately 404 and 133 AON respectively in 2018 and 2015 (SMP, 2021). The species is currently Red-listed on the UK Birds of Conservation Concern List (Stanbury et al., 2021).
  2. Shags were only recorded twice in the Offshore Ornithology Study Area, on the June 2019 and December 2020 surveys ( Figure 5.88   Open ▸ ). Design-based density estimates for June 2019 were 0.01 birds/km2 (95%CI 0.00 – 0.02), equating to a population estimate of 25 birds (95% CI 0 –72). The mean seasonal peak population estimate for the breeding season was 12 birds (95% CI 0 – 36; Table 5.105   Open ▸ ) compared to the non-breeding season, where 5 birds (95%CI 0 – 12) were estimated to be present.
  3. Shags were not an abundant species during the Berwick Bank boat-based surveys in 2020 and 2021 or on the Seagreen boat-based surveys. 
  4. Birds were distributed in the south of the Offshore Ornithology Study in both June 2019 and December 2020, present in the buffer. All shags were recorded flying northwest ( Figure 5.91   Open ▸ ).

 

Table 5.101:
 Manx shearwater bio-seasons taken from NatureScot (2020a)

Table 5.101:  Manx shearwater bio-seasons taken from NatureScot (2020a)

Table 5.102:
Monthly density and population estimates of all shags across Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species

Table 5.102: Monthly density and population estimates of all shags across Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species

 

Table 5.103:
Monthly density and population estimates of flying shags only across Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species

Table 5.103: Monthly density and population estimates of flying shags only across Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species

 

Table 5.104:
Monthly density and population estimates of sitting shags only across Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species

Table 5.104: Monthly density and population estimates of sitting shags only across Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species

Figure 5.88:
Estimated densities (birds/km2) of all shags across Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species

Figure 5.88:  Estimated densities (birds/km2) of all shags across Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species

 

Table 5.105:
Mean seasonal peak (MSP) population and density (birds/km2) of all shags in the Offshore Ornithology Study Area across the two years of surveying (March 2019 to April 2021) estimated using design-based analysis

Table 5.105:  Mean seasonal peak (MSP) population and density (birds/km2) of all shags in the Offshore Ornithology Study Area across the two years of surveying (March 2019 to April 2021) estimated using design-based analysis

 

Figure 5.89:
 Distribution of shags across Offshore Ornithology Study Area in June 2019

Figure 5.89:  Distribution of shags across Offshore Ornithology Study Area in June 2019

 

Figure 5.90:
  Distribution of shags across Offshore Ornithology Study Area in December 2020

Figure 5.90:   Distribution of shags across Offshore Ornithology Study Area in December 2020

 

Figure 5.91:
  Summarised flight direction of shags across Offshore Ornithology Study Area

Figure 5.91:   Summarised flight direction of shags across Offshore Ornithology Study Area

6 Summary

  1. The proposed Berwick Bank Wind Farm is located in the outer Firth of Forth, adjacent to the consented Firth of Forth offshore wind farms (OWFs) Seagreen, Inch Cape and Neart na Gaoithe. Berwick Bank is proposed for development by SSE Renewables.
  2. The proposed Berwick Bank development will, if consented, provide an estimated 4.1 GW of renewable energy and turbine capacity may range from 14 – 24 MW with a maximum number of turbines on site ranging between 179 – 307. Importantly, the minimum lower blade tip height is 37 m (LAT) as an embedded design measure to reduce collision risk to seabirds.
  3. This technical report, and its Annexes (A-L) provide the baseline ornithological characterisation for the Project. The report provides baseline information on the seasonal distribution, density, and abundance of seabirds in the Proposed Development Array area and a 16 km buffer (the Offshore Ornithology Study Area) based on:
  • available reports and literature (“Desktop study” Section 22), and
  • analysis of data from a series of digital aerial surveys 2019 – 2021 (“Berwick Bank digital aerial surveys” Section 33).
    1. There are several at-sea seabird survey datasets relevant to the baseline of Berwick Bank, including boat-based surveys undertaken at the site, boat and aerial surveys at adjacent sites (e.g., Seagreen) and the studies on gannet and auk foraging, survival and population dynamics, based on telemetry data (Lane and Harmer, 2021; Bogdanova et al., in prep.). Other data related to research projects (e.g., Camphuysen, 2005) and broader scale monitoring programmes (e.g., WWT aerial surveys and ESAS boat-based surveys) are also available.
    2. There are numerous breeding seabird colonies within the region, many of which are designated seabird Special Protection Areas (SPAs) that include the Forth Islands SPA, Fowlsheugh SPA, and St Abb’s Head to Fast Castle SPA. The Seabird Monitoring Project provides the most up-to-date estimates of the abundance of breeding seabirds at UK colonies.
    3. The Offshore Ornithology Study Area constituting an area of 3,975km2 was surveyed between March 2019 and April 2021 to collect seabird and marine mammal data suitable for site characterisation. The survey design consisted of 35 strip transects, spaced 2km apart, extending roughly north-west to south-east, across the survey area.
    4. The surveys were conducted by HiDef Digital Aerial Surveying Ltd. using aerial digital video methods. Survey aircraft were equipped with four HiDef Gen II cameras with sensors set to a resolution of 2 cm Ground Sample Distance (GSD). Each camera sampled a strip of 125m width, separated from the next camera by ~20m, providing a combined sampled width of 500m within a 575m overall strip.
    5. Surveys were flown at a height of approximately 550 m above sea level to ensure the altitude of the aircraft is always above that recommended to avoid disturbance to seabirds. Thaxter et al. (2016) recommends a minimum flight altitude of 460-500 m Above Sea Level (ASL).
    6. Position data for the aircraft was captured from a Garmin GPSMap 296 receiver with differential GPS enabled to give 1 m accuracy for the positions and recording updates in location at one second intervals for later matching to observations.
    7. Data from the cameras were processed to achieve a minimum target coverage of 12.5%. All camera data were viewed by HiDef’s trained reviewers and further analysis by the identification team. At least 20% of all birds were selected at random and subjected to a separate ‘blind’ QA process. If less than 90% agreement was attained for any individual camera then corrective action was initiated: if appropriate, the failed identifier’s data were discarded, and the data re-identified. Any disputed identifications were passed to a third-party expert ornithologist for a final decision. Birds were assessed for behaviour (flying, sitting) and, where possible, approximate age and sex.
    8. Survey data were primarily analysed using design to generate estimates of density and abundance per species /species group within the Offshore Ornithology Study Area and the Proposed Development array area. This report provides estimates and accounts for 18 of the most abundant species.
    9. The design-based analysis approach used a non-parametric bootstrap method with replacement (Buckland et al., 2001) on strip transect data to estimate the density of animals at the site, the standard deviation, the 95% Confidence Intervals (CIs) and coefficient of variance (CV). Estimates for guillemot, razorbill and puffin were corrected for availability bias following Barlow et al. (1988) to provide absolute abundance estimates. This could only be calculated for three auk species due to limited information currently available on diving rates of other seabird species. Monthly density and abundance estimate for flying birds, sitting birds and “all birds” were estimated. These estimates were used to generate mean-peak population estimates for all appropriate bio-seasons based on NatureScot guidance (2020a).
    10. Distribution maps for all species from design-based analysis were created as cent-count maps. Observations were aggregated within 500 m bins of transect using a nearest neighbour technique. The aggregated observations were presented per unit area of each bin (500 m x surveyed strip width).
    11. MRSea was used to generate model-based estimates of abundance. However, whilst the estimates were largely comparable to those from design-based estimates for many surveys, use of MRSea did not confer the expected advantage of greater precision of point estimates and for some surveys, estimates were unacceptably inflated. MRSea did not perform well in surveys where transects were missed. HiDef invested considerable time and work with the author of MRSea in order to be able to run it on the survey data. HiDef raised some of these issues during the Marine Scotland Ornithology Impact Assessment workshop in February 2022.
    12. Over the 25-month survey period, 41 species were observed. During Year 1 of the survey programme (March 2019 to February 2020; comprised of 11 surveys), a total of 88,624 individuals of 31 species were recorded. In Year 2 (March 2020 to April 2021; comprised of 14 surveys), 32 species were recorded over 192,376 observations. A further 21,618 observations identified to species groups were made over the course of the surveys. The number of flights flown in Year 2 were greater and this contributes to the larger number of detections in this year compared to Year 1; however, as seabirds are mobile species, interannual variation in abundance of species is expected.
    13. Guillemots were the most abundant species, with peaks present in April, May and August and/or September in both years, coinciding with the start of the breeding season and the post-breeding flightless moult stage. April/May peaks coincide with the onset of egg-laying and incubation (Harris and Wanless, 2004). During this time, most birds were recorded as sitting on the water, which is to be expected considering their feeding strategy, in which they dive for prey from the water surface. When accounting for animals diving at the time of the survey, estimates of density were higher during the breeding season, with mean peak densities for the region of 46.91 birds/km2 (95%CI 37.98 – 57.83), compared to 34.88 birds/km2 (95%CI 27.41 – 43.02) during the non-breeding season. Peak population estimates in April S02 2021 equated to 242,168 birds (95%CI 190,509 – 305,941). The local SPA total for guillemots is estimated at 280,972 breeding adults, with another 148,805 breeding adults at North Caithness Cliffs SPA also likely to have connectivity with the Project. The relatively high abundance estimated for the site in April S02 2021 is likely to be explained by a good breeding season in 2020 (supported by our data for September 2020 and NatureScot, 2021), which as a consequence will lead to a high number of birds returning to the area ahead of the following 2021 breeding season.
    14. The highest mean seasonal peak of kittiwakes was estimated during the non-breeding season at approximately 50,958 birds (95%CI 35,530 – 69,349) likely attributed to the movement of birds between colonies and wintering areas. Behaviour differed between seasons with the largest proportions of flying birds generally occurring between April and June, and October and December dependent on year. Large proportions of birds were recorded as sitting on the water in all surveys, suggesting the Offshore Ornithology Study Area is used for foraging year-round.  
    15. Razorbills were present in relatively high abundances, with birds recorded most frequently in October and September in Year 1 and Year 2 respectively. Throughout the year, most birds were recorded as sitting on the water. This is to be expected when considering the feeding strategy adopted by the species, in which they dive from the surface of the water for prey (Shoji et al., 2015). The highest mean seasonal peak for all razorbills occurred during the non-breeding season, calculated at 35,589 birds (95%CI 25,185 – 46,150).
    16. Puffins were relatively abundant throughout the Offshore Ornithology Study Area, with density and population estimates suggesting the species utilises the area most frequently between March and September during the breeding season. Mean seasonal peaks were estimated as 12,290 birds (95%CI 9,857 – 14,997) in the breeding season and 20,667 birds (95%CI 17,298 – 24,031) in the non-breeding season. High abundances between May and August suggest birds at nearby colonies use the Offshore Ornithology Study Area to forage during chick rearing, with widespread dispersal towards the end of this period suggesting movement offshore to at-sea wintering areas.
    17. Gannets were most abundant in the breeding season with a mean seasonal peak for this period estimated at 14,581 birds (95%CI 12,528 – 16,840) and comprised in almost equal proportions of flying and sitting birds; suggesting the area is used during foraging and during passage to foraging grounds further afield. High densities are to be expected within the survey area, due to the proximity to Bass Rock where breeding success of gannets has been consistently high, despite fluctuations in breeding success for other seabird species in the vicinity (Nelson, 2006; Hamer et al., 2007).
    18. Common scoter occurred in very low numbers, recorded during the June 2019 and January 2020 surveys only. All birds were recorded as flying, with abundance estimates for these months calculated at 16 birds (95%CI 0 - 48) and 9 birds (95%CI 0 - 28), respectively.
    19. Black-headed gulls were only recorded within the Offshore Ornithology Study Area in the non-breeding season. The mean seasonal peak population estimate for the Offshore Ornithology Study Area was estimated at 9 birds (95%CI 1 - 24) during the non-breeding season.
    20. Little gulls were observed during the non-breeding and breeding seasons. Low numbers of birds are known to be present along the Fife and Lothian coasts, with the Firth of Forth being one of the only areas where birds are consistently seen in low numbers between December and March (Forrester et al., 2007). The Outer Firth of Forth and St Andrews Bay Complex SPA, which overlaps the southwest corner of the Offshore Ornithology Study Area, was designated to support non-breeding populations of little gulls among other seabird species. The mean seasonal peak population occurred during the non-breeding season, calculated at 279 birds (95%CI 150 - 426).
    21. Common gulls were primarily recorded during the non-breeding season in both years. Over winter, the UK hosts almost half the European population of common gulls (European Commission, 2009), with many of these birds occurring in Scottish coastal areas (Burton et al., 2013). The mean seasonal peak abundance estimates were 146 birds (95%CI 81 - 218) and 745 birds (95%CI 218 – 1,408) in the breeding and non-breeding season, respectively.
    22. Herring gulls were the most abundant large gull species encountered during the survey period, present in greater numbers from mid to late summer and again in winter. Very few birds were present throughout the rest of the year. Mean-peak population estimates were highest in the non-breeding season estimated at 3,382 birds (95%CI 957 – 6,294), and the proportion of flying to sitting birds was similar. A mean-peak population of 3,356 birds (95%CI 2,246 – 4,733) was estimated in the breeding season.
    23. Lesser black-backed gulls were recorded intermittently throughout the survey programme, mainly recorded during the breeding season. Specific to the Offshore Ornithology Study Area, lesser black-backed gulls are a qualifying species for the Forth Islands SPA, with 1,684 AON, 131 AOT and 97 AOT in 2018 on the Isle of May, Fidra and Craigleith respectively (NatureScot, 2018; SMP, 2021). Between years, peaks in abundance varied considerably, with nearly three times as many birds recorded in the July 2020 peak compared to that in July 2019. No birds were recorded in January and February in both years. The mean seasonal peak abundance during the breeding season was 580 birds (95%CI 427 – 741) compared to 17 (95%CI 1 - 43) during the non-breeding season.
    24. Common terns return to UK waters between April and September to breed, spending their winters across the southern hemisphere. Birds were observed in both the 2019/20 and 2020/21 survey periods, with over 10 times more observations occurring in Year 2 compared to Year 1. In the breeding season, the mean seasonal peak abundance was estimated to be 3,225 birds (95%CI 2,224 – 4,332). Lower abundances at the start of the breeding season, such as between May and June can be attributed to birds beginning egg-laying and nest attendance, in which they are more closely associated with their nest sites until chicks have fledged. Densities of birds during these months in the survey area are expected to be low, as many birds remain close to colonies. A few birds were recorded during the non-breeding season.
    25. Arctic terns spend a shorter period in UK waters than common terns, returning to the UK to breed between late April and early September. The species was present during the breeding period in both years of surveying. During the breeding and non-breeding seasons, the mean seasonal peak population was estimated to be 4,074 birds (95%CI 3,188 – 5,088) and 163 (95%CI 45 – 325) respectively.
    26. Great skua were recorded in low densities in the Offshore Ornithology Study Area, primarily between August and December. The peak estimated population estimate was calculated at 72 birds (95%CI 32 – 119) in November 2020. It is likely this peak in abundance can be attributed to the passage of birds through the area during southwards post-breeding migration.
    27. Red-throated diver were predominately detected within the buffer, with birds recorded within the Proposed Development Array intermittently. The highest mean seasonal peak was estimated during the non-breeding season at 105 birds (95%CI 36 – 204).
    28. Fulmar densities were relatively consistent throughout the first year of surveying, with slight increases in March 2019 and between November 2019 and January 2020 during the non-breeding season. 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. Mean seasonal peak abundance was highest during the breeding season with an estimated 1,776 birds (95%CI 1,469 – 2,100), although this was largely influenced by the September peak. The mean seasonal peak for the non-breeding period was estimated at 1,071 birds (95%CI 787 – 1,365).
    29. Densities of Manx shearwaters were generally low, with birds primarily observed during the breeding season, peaking in June in Year 1 and Year 2. Mean peak estimates for both years of surveying of 113 birds (95%CI 40 – 209) in the breeding season, compared to 0 birds in the non-breeding season. A higher proportion of birds were recorded as flying compared to other behaviours (e.g. sitting or diving) however, higher proportions of sitting birds recorded during the breeding season may be due to the presence of rafting or foraging birds (Richards et al., 2019).
    30. Shags were only recorded twice in the Offshore Ornithology Study Area, on the June 2019 and December 2020 surveys. The mean seasonal peak population estimate for the breeding season was calculated at 12 birds (95% CI 0 – 36). Birds were distributed in the south of the Offshore Ornithology Study Area in both June 2019 and December 2020, present in the buffer. All shags were recorded flying northwest.

 

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Camphuysen, C.J. (2013). A historical ecology of two closely related gull species (Laridae): multiple adaptations to a manmade environment. PhD Thesis, University of Groningen.

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