5.6. Common scoter
- Typically present in coastal environments, common scoters spend much of their time at sea in large flocks, migrating inland to freshwater environments to breed, such as those located in Caithness and Sutherland between May and July (del Hoyo et al., 1992). Outwith the breeding season, scoters typically utilise shallow marine environments, feeding on various invertebrate, mollusc and gastropod species (Fox, 2003). The species is currently Red-listed on the UK Birds of Conservation Concern List (Stanbury et al., 2021).
- Common scoters were present in June 2019 (technically in the breeding period) and presumably non-breeding birds were encountered in January 2020 ( Table 5.35 Open ▸ ; Figure 5.31 Open ▸ ). There are no breeding locations for common scoter within mean max foraging range of Berwick Bank. Estimated densities from design-based analysis were low, with population estimates for the Offshore Ornithology Study Area ranging between 9 birds (95%CI 0 – 28) in January 2020 and 16 birds (95%CI 0 – 48) in June 2019.
- Within the two surveys in which common scoter were observed in the Offshore Ornithology Study Area, all birds were recorded as flying. In June 2019, all birds flew in a southeast direction while in January 2020 all birds flew north ( Figure 5.33 Open ▸ ). It is likely that the species primarily pass through the Offshore Ornithology Study Area during passage to other areas.
- Common scoters were detected in similar parts of the Offshore Ornithology Study Area, in the western buffer ( Figure 5.32 Open ▸ ). Since the west of the Offshore Ornithology Study Area is closer to the coast, this distribution is not unexpected.
- The apparent higher estimates for flying birds compared to all birds (see Table 5.35 Open ▸ and Table 5.36 Open ▸ ) are simply due to different iterations of the bootstrapping analysis process and rounding.
Table 5.34: Common scoter bio-seasons taken from NatureScot (2020a)
Table 5.35: Monthly density and population estimates of all common scoter across the Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species
Table 5.36: Monthly density and population estimates of flying common scoter only across the Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species
Figure 5.31: Estimated densities (birds/km2) of all common scoter across the Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species
Figure 5.32: Distribution of common scoter across the Offshore Ornithology Study Area in June 2019 and January 2020
Figure 5.33: Summarised flight direction of common scoter across the Offshore Ornithology Study Area
5.7. Black-headed gull
- Black-headed gulls are distributed throughout Scotland, primarily on the east and south-west coasts (Forrester et al., 2007). As well as birds arriving from elsewhere in the UK, many black-headed gulls migrate from northern and eastern Europe (Horton et al., 1983). Relatively large flocks of wintering birds have been observed within the Firth of Forth, such as at Skinflats and the Isle of May, located to the west of the survey area (Forrester et al., 2007). The species is currently Amber-listed on the UK Birds of Conservation Concern.
- Black-headed gulls were uncommon in Offshore Ornithology Study Area, and were only recorded during the non-breeding season ( Table 5.40 Open ▸ ) with a mean seasonal peak population estimated at 9 birds (95%CI 1 – 24) and a density of 0.00 birds/km2 ( Table 5.43 Open ▸ ).
- Digital aerial survey data presented here is consistent with existing data from the outer Firth of Forth region which suggests the species is typically present in low numbers in the non-breeding season. Data summed from ESAS surveys conducted between 1980 and 1996 clipped to the Offshore Ornithology Study Area recorded only two black-headed gulls in the 16-year period. In addition, boat-based surveys of Seagreen only recorded one individual.
- Most black-headed gulls identified within the Offshore Ornithology Study Area were recorded as flying, with mean peak population estimates for the non-breeding season estimated at 8 birds (95%CI 0 – 20) and 2 birds (95%CI 0 – 4) for flying and sitting birds respectively ( Table 5.41 Open ▸ and Table 5.42 Open ▸ ).
- Black-headed gulls were distributed to the west of the Offshore Ornithology Study Area, in the south and west buffer in September and December 2020 respectively ( Figure 5.35 Open ▸ ).
- As so few birds were present in the Offshore Ornithology Study Area, it was difficult to draw reliable conclusions regarding flight direction ( Figure 5.36 Open ▸ )
Table 5.39: Black-headed gull bio-seasons taken from NatureScot (2020a)
Table 5.40: Monthly density and population estimates of all black-headed gulls across the Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species
Table 5.41: Monthly density and population estimates of flying black-headed gulls only across the Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species
Table 5.42: Monthly density and population estimates of sitting black-headed gulls only across Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species
Table 5.43: Mean seasonal peak (MSP) population and density (birds/km2) of all black-headed gulls 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 5.35: Distribution of black-headed gulls across the Offshore Ornithology Study Area in September and December 2020
Figure 5.36: Summarised flight direction of black-headed gulls across the Offshore Ornithology Study Area
5.8. Little gull
- As passage migrants, little gulls spend part of the year in UK waters as they move between summer and wintering grounds (Stone et al., 1995). The smallest gull species in the UK (Dunning, 1992), they generally migrate to UK coastal environments for the non-breeding period (Forrester et al., 2007). Post-breeding adult birds usually arrive in Scotland from Europe between late July and August, followed by juvenile birds, observed in the highest concentrations along the Angus and Dundee coast (Forrester et al., 2007), which is to the north of the Offshore Ornithology Study Area. A secondary influx generally occurs between October and November, mainly consisting of adult and first-winter birds (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, suggesting the presence of suitable habitat within the SPA area.
- Little gulls were observed in the Offshore Ornithology Study Area during the breeding and non-breeding seasons, with no records between March and June in either Year 1 or Year 2 ( Table 5.46 Open ▸ ). Peak abundances were recorded in August 2019 and 2020 with a lesser peak occurring in both years, in February 2020 and December 2020 respectively. Design-based density estimates ranged between 0.00 birds/km2 and 0.03 birds/km2 (95%CI 0.01 – 0.06) in 2019/20 compared to 0.00 birds/km2 and 0.11 birds/km2 (95%CI 0.06 – 0.16) in 2020/21.
- Boat-based surveys of Berwick Bank in 2019-2020 recorded one little gull, present in the June 2021 survey.
- During the non-breeding season, most birds were recorded as flying, with only 15% of birds recorded as sitting on the water. Feeding strategy adopted by little gulls is variable, with individuals either feeding while inflight, or picking food items from the water’s surface (Vittery, 2001). The presence of sitting birds within the Offshore Ornithology Study Area suggests the area may be utilised during foraging.
- Little gulls were distributed throughout the Offshore Ornithology Study Area. In some months, birds were distributed only in the buffer, such as in July 2019 and September 2020 ( Figure 5.38 Open ▸ to Figure 5.40 Open ▸ ). Many little gulls were recorded within the Proposed Development Array area in August 2020 and April S02 2021. Birds were recorded in the south of the Offshore Ornithology Study Area in September 2020 and January 2021 compared to the northwest in December 2020.
- No flight direction data were available for this species.
Table 5.45: Little gull bio-seasons taken from NatureScot (2020a)
Table 5.46: Monthly density and population estimates of all little gulls across the Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species
Figure 5.38: Distribution of little gulls across the Offshore Ornithology Study Area between March 2019 and March 2020
Figure 5.40: Distribution of little gulls across the Offshore Ornithology Study Area in April S02 2021
Table 5.50: Mean count, SD and proportion of little gulls in each age class averaged across bio-season
Figure 5.42: Percentage of flying little gulls per survey across the Offshore Ornithology Study Area
5.9. Common gull
- Common gulls are relatively abundant throughout Europe, with over 50% of the global breeding population concentrated in the northern regions of Europe (Tasker, 1994). 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). Generally, lower numbers of common gulls are present during the breeding period, distributed in inland areas (Bukaciński and Bukacińska, 2003). The species is generally long-lived, with recruits starting to breed after 2-5 years (Rattiste, 2006). The species is currently Amber-listed on the UK Birds of Conservation Concern List (Stanbury et al., 2021).
- Common gulls were primarily recorded in the Offshore Ornithology Study Area during the non-breeding season in both years, with abundance peaking in December 2020 at 982 birds (95CI 232-1934) ( Table 5.52 Open ▸ ). During the breeding season, abundance peaked in July 2019 and August 2020, equating to design-based population estimates for the Offshore Ornithology Study Area of 33 birds (95%CI 1 – 70) and 180 birds (95%CI 112 – 261) respectively (Table 5.60). Design-based density estimates ranged between 0.00 birds/km2 and 0.13 birds/km2 (95%CI 0.05 – 0.22) in 2019/20 compared to 0.00 birds/km2 and 0.25 birds/km2 (95%CI 0.06 – 0.49) in 2020/21.
- Boat-based surveys of Berwick Bank recorded low numbers of common gulls between July and August 2019 and April and June 2020. The species was not highlighted as a key species in any of the other data sources included in the desktop study, with the species expected to be present in low numbers during the non-breeding season.
- Although some birds were recorded in the Offshore Ornithology Study Area during the breeding season, this only comprised around 16% of the total common gulls recorded during the two-year period. This is to be expected, since the species is known to breed in inland areas such as moorland and heaths, utilising coastal areas during the winter (Tasker et al., 1991). Across the entire survey programme, most birds were recorded as flying, with only 23% of birds recorded as sitting on the water. In October 2019 and December 2020 when abundance peaked, 94% and 70% of birds were recorded as flying respectively. The relatively low proportion of birds recorded as sitting on the water suggests that the area is not utilised much during foraging, but instead used during passage to and from wintering areas.
- Flight direction was variable, with birds recorded flying in easterly and westerly directions in November 2019 and December 2020 ( Figure 5.47 Open ▸ ).
- Generally, common gulls were distributed to the northwest of the Offshore Ornithology Study Area, with many birds in the western buffer, such as between October and December 2019. Very low abundances were also recorded within the Proposed Development array area. In December 2020, when abundances peaked, many birds were recorded in the northwest and west of the buffer, with a few also present in the south.
Table 5.51: Common gull bio-seasons taken from NatureScot (2020a)
Table 5.52: Monthly density and population estimates of all common gulls across the Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species
Figure 5.46: Distribution of common gulls across the Offshore Ornithology Study Area April S02 2021
Figure 5.47: Summarised flight direction of common gulls across the Offshore Ornithology Study Area
Figure 5.48: Percentage of flying common gulls per survey across the Offshore Ornithology Study Area