5.3. Razorbill
- Common around the UK, razorbills are distributed at coastal colonies between April and August during the breeding season, usually found in mixed species assemblages with other seabirds such as guillemots and kittiwakes (Mitchell et al., 2004). The northwest North Sea provides important habitat for razorbills year-round, especially between July and September during the flightless moult period (Stone et al., 1995). Several large breeding colonies are present along the east coast of Scotland, such as the Isle of May, St Abb’s Head and Fowlsheugh which respectively supported an estimated 4,867, 2,683 and 11,750 birds in 2018 (SMP, 2021). The total count of razorbills within the foraging range (mean max distance +1 sd from Woodward et al.2019) of the Project approximates the regional population and is estimated at 84,501 breeding adults. The species is currently Amber-listed on the UK Birds of Conservation Concern List (Stanbury et al., 2021).
- Razorbills were present in relatively high abundances in the Offshore Ornithology Study Area, with birds recorded most frequently in October and September in Year 1 and Year 2 respectively, during the non-breeding season ( Table 5.16 Open ▸ ). When accounting for availability bias. Design-based estimates gave densities ranging from 0.37 birds/km2 (95%CI 0.22 – 0.56) to 3.21 birds/km2 (95%CI 1.51 – 5.39) in 2019/20 and 0.50 birds/km2 (95%CI 0.34 – 0.66) to 13.77 birds/km2 (95%CI 9.66 – 17.91) in 2020/21 ( Table 5.16 Open ▸ ).
- Boat-based surveys of Berwick Bank in 2020-2021 identified razorbill as one of the key five species, which collectively accounted for 87% of all observations, of which razorbill accounted for 9.68% of all records. Data from the IMPRESS project (Camphuysen et al., 2004) reported that razorbills accounted for 11% of all observations. However, razorbills were not identified as a predominant species in Seagreen boat-based surveys.
- Mean seasonal peaks were higher during the non-breeding period with an estimated population of 35,589 birds (95%CI 25,185 – 46,150; Figure 5.13 Open ▸ ). Estimates during the breeding season were much lower, calculated at 11,280 birds (95%CI 8,395 – 14,646). During the non-breeding season when abundance of razorbills peaked, their distribution was towards the west of the Offshore Ornithology Study Area ( Figure 5.14 Open ▸ - Figure 5.16 Open ▸ ).
- Low abundances during the summer suggests most birds at nearby colonies do not venture into the Offshore Ornithology Study Area to forage during chick-rearing but do disperse through the Offshore Ornithology Study Area in the post-breeding period, as indicated by increases in abundance towards the end of the breeding season, such as in August and September 2020 ( Figure 5.13 Open ▸ ). Adults usually undergo a post-breeding moult around July and August, prior to movement offshore into the North Sea, which is estimated to support around 100,000 wintering razorbills (Furness, 2015). Younger age classes generally disperse further than older birds, with adults returning to colonies sooner than immature birds prior to the start of the breeding period (Furness, 2015).
- Across all seasons, most razorbills were recorded as sitting on the water, with few birds recorded as flying during the 25 months of surveys. This is to be expected considering their feeding strategy which involves diving from the surface of the water (Shoji et al., 2015). In Year 1, the highest percentage of flying birds was recorded in March during the return migration period, with a similar peak occurring in Year 2 (although to a lesser extent; Figure 5.18 Open ▸ ). In Year 2, the percentage of flying birds peaked in October and April S01, in the non-breeding and breeding seasons respectively.
- The paucity of flying birds during the programme presented difficulties when assessing trends in flight direction, although many birds were recorded flying west in March 2019 and a large proportion also flew south in April S01 2021 ( Figure 5.17 Open ▸ ). It is possible that this may be the migration of birds back to breeding colonies to the west and south of the survey area, such as the Isle of May and St. Abb’s Head.
- Ages of razorbills are not presented since adults can only be aged when in the presence of a juvenile for size comparison and they almost exclusively occur as single adult-chick pairs.
Table 5.15: Razorbill bio-seasons taken from NatureScot (2020a)
Table 5.16: Monthly absolute density and population estimates of all razorbills across the Offshore Ornithology Study Area using design-based analysis, adjusted for availability bias. Data include “no-identification” birds apportioned to species
Figure 5.13: Estimated absolute densities (birds/km2) of all razorbills across the Offshore Ornithology Study Area using design-based analysis, accounting for availability bias. Data include “no-identification” birds apportioned to species
Figure 5.14: Distribution of razorbills across the Offshore Ornithology Study Area between March 2019 and March 2020
Figure 5.16: Distribution of razorbills across the Offshore Ornithology Study Area in April S02 2021
Figure 5.17: Summarised flight direction of razorbills across the Offshore Ornithology Study Area
Figure 5.18: Percentage of flying razorbills per survey across the Offshore Ornithology Study Area
5.4. Puffin
- A small auk species, puffins are most abundant in UK waters during the spring and summer, dispersing mainly westwards from early autumn into the winter. In the UK they nest in a few major colonies and are Red-listed on the UK Birds of Conservation Concern list (Stanbury et al., 2021), following a listing as a vulnerable species on the ICUN Red List. A large breeding colony is present on the Isle of May, with the most recent count of 39,200 Apparently Occupied Burrows in 2017 (AOB’s; SMP, 2021). Usually only present in coastal areas during the breeding season, puffins generally return to colonies between March and April, with egg laying occurring in April and May (Harris et al., 2010). Typically, adult birds return to the same burrow year-on-year, raising one chick which generally fledges between July and August (Anker-Nilssen and Røstad, 1993; Finney et al., 2003).
- After adjusting for availability bias, density and population estimates suggest the species utilise the Offshore Ornithology Study Area predominantly between March and September which is largely coincident with the breeding season ( Figure 5.19 Open ▸ ). When accounting for availability bias, design-based density estimates ranged from 0.00 birds/km2 to 3.84 birds/km2 (95%CI 2.93 – 4.92) in 2019/20 and 0.03 birds/km2 (95%CI 0.02 – 0.05) to 8.81 birds/km2 (95%CI 7.43 – 10.17) in 2020/21. Mean seasonal peak abundance was higher in the non-breeding season, with an estimated population 20,667 birds (95%CI 17,298 – 24,031) compared to 12,290 birds (95%CI 9,857 – 14,997) in the breeding season.
- Data collected during boat-based surveys of Berwick Bank reported that puffins accounted for 7.26% of all observations. The IMPRESS project (Camphuysen et al., 2004) suggested puffins were likely to be numerous within the outer Firth of Forth, with the species accounting for 21% of all observations. The total count of puffins at SPAs within the foraging range (mean max distance +1 sd from Woodward et al. 2019) of the Project approximates the regional population and is estimated at 233,550 breeding adults.
- High abundance during summer months suggests birds at nearby colonies use the Offshore Ornithology Study Area to forage during chick-rearing. Mapped observations indicate varied use of the Offshore Ornithology Study Area, but with a more westerly distribution in the Offshore Ornithology Study Area during the breeding season ( Figure 5.20 Open ▸ - Figure 5.22 Open ▸ ). High densities in the west of the Offshore Ornithology Study Area in months such as June and July 2019, July 2020 and April 2021, suggest many birds use areas closer to colonies and chicks during this time. More widespread dispersal towards the end of the chick-rearing period, such as in September 2020, suggests movement of birds offshore, with elevated densities also observed to the east of the Offshore Ornithology Study Area in September 2019. Offshore movement of birds following the breeding season is expected, since the species usually overwinters at sea; the North Sea hosts significant concentrations of the species during winter months (Harris, 1984; Jessop et al., 2013).
- Across all seasons, most birds were recorded as sitting on the water, with few birds recorded as flying during the 25 months of surveys ( Table 5.23 Open ▸ ). In Year 1, peaks in flying birds were observed in June, with about 6% of birds recorded as flying, however in Year 2 peaks occurred in March and June, with approximately 29% and 17% of birds recorded as flying respectively (Figure 5.25). High proportions of sitting birds are to be expected considering the feeding strategy adopted by the species as pursuit-divers diving from the water surface (Cramp and Simmons, 1983). Typical prey species are small to mid-sized schooling pelagic fish, including sandeels and sprats, supplemented by crustaceans, molluscs and polychaetes during the breeding season (del Hoyo et al., 1996). Considerable differences in diet between colonies and years has been identified, with sub-optimal prey species negatively affecting fledgling growth in some cases (Harris and Hislop, 1978).
- The paucity of flying birds during the programme presented difficulties when assessing trends in flight direction, although many birds were recorded flying west in June 2019 and June and July 2020. Some birds were also recorded flying north and southeast in July 2019 and July 2020 respectively ( Figure 5.23 Open ▸ ).
- Ages of birds are not presented for the species since adults can only be aged when in the presence of a juvenile for size comparison and they occur almost always as single adult-chick pairs.
Table 5.21: Puffin bio-seasons taken from NatureScot (2020a)
Table 5.23: Monthly density and population estimates of flying puffins only across the Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species
Figure 5.19: Estimated absolute densities (birds/km2) of all puffins across the Offshore Ornithology Study Area using design-based analysis, accounting for availability bias. Data include “no-identification” birds apportioned to species
Figure 5.20: Distribution of puffins across the Offshore Ornithology Study Area between March 2019 and March 2020
Figure 5.22: Distribution of puffins across the Offshore Ornithology Study Area in April S02 2021
Figure 5.23: Summarised flight direction of puffins across the Offshore Ornithology Study Area
Figure 5.24: Percentage of flying puffins per survey across the Offshore Ornithology Study Area
5.5. Gannet
- As the largest pelagic seabird in the North Atlantic, gannets have considerable influence on marine food chains, preying on various fish species and competing with other seabird species for discards from commercial fisheries (Hamer et al., 2000). It is likely that fisheries discards currently make up a much smaller percentage of the diet than previously, following the discard ban in 2015 which was fully implemented in 2019 (Ulhmann et al., 2019). Typical prey includes pelagic fish such as mackerel and sandeel, the latter species being abundant within the Firth of Forth and North Sea (Greenstreet et al., 2010). Gannet distribution and abundance is likely to be influenced by prey availability (Furness and Tasker, 1999) although its sensitivity to sandeel abundance is less than for other species such as kittiwake because of the greater variety of prey species it exploits (Daunt et al., 2008; B. Furness, pers. comms., 2021). The nearest gannetry is the Bass Rock in the Firth of Forth, which is the world’s largest colony with 75,259 Apparently Occupied Sites (AOS) recorded in 2014 (Murray et al., 2014; SMP, 2021). The species is currently Amber-listed on the UK Birds of Conservation Concern List (Stanbury et al., 2021).
- Gannets were most abundant in the Offshore Ornithology Study Area in the breeding season. Design-based analysis estimated gannet density to range between 0.00 birds/km2 (95%CI 0.00 – 0.01; February 2020) and 4.06 birds/km2 (95%CI 3.42 – 4.79; August 2019) in 2019/20 and 0.05 birds/km2 (95%CI 0.02 – 0.09; February 2021) and 3.27 birds/km2 (95%CI 2.88 – 3.68; July 2020) in 2020/21. Densities peaked in August and July in Year 1 and Year 2 respectively, coinciding with the breeding season ( Table 5.28 Open ▸ ).
- Gannets were frequently encountered within the Offshore Ornithology Study Area and wider area during other studies of the outer Firth of Forth (Camphuysen et al., 2004; Kober et al. 2010, 2012; Lane et al. 2020). WWT Waterbird surveys also indicated high gannet abundance, although the survey block was located approximately 20km from the Offshore Ornithology Study Area. Gannets were identified as a key species during boat-based surveys of Seagreen between 2009-2011 (accounting for 16.10% and 16.60% of all observations respectively) and Berwick Bank between 2019-2020 (accounting for 16.12% of all observations). The total count of gannets within the foraging range (mean max distance +1 sd from woodward et al. 2019) of the Project is estimated at 323,836 breeding adults.
- Mean seasonal peak density calculated for the breeding season was 3.66 birds/km2 (95%CI 3.15 – 4.24), equating to a population of 14,581 birds (95%CI 12,528 – 16,840) ( Table 5.31 Open ▸ ). High densities are to be expected within the Offshore Ornithology Study 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).
- Following peaks in abundance in the breeding season, gannet abundance in the Offshore Ornithology Study Area declined steadily until December 2019 in Year 1 and until October and November 2020 in Year 2 ( Table 5.28 Open ▸ ) Fluctuations in abundance later in the year may be attributed to fledgling birds leaving nests and spending time at sea (Nelson, 1966).
- Distribution of gannets varied between months, with a tendency for a north-westerly distribution within the Offshore Ornithology Study Area during the breeding season (e.g., between August and September in both years). Generally, in both Year 1 and Year 2, it appeared that higher densities of gannets were more widespread throughout the Offshore Ornithology Study Area during the breeding season compared to the non-breeding season, such as in December 2019 and November 2020 specifically.
- Of the birds that could be aged, most were recorded as adults ( Table 5.33 Open ▸ ). Few young birds were observed in the Offshore Ornithology Study Area with the highest proportions of immature birds (2% of aged birds) and juvenile birds (2% of aged birds) occurring in the non-breeding period.
- Within the breeding season, particularly between June and August, proportions of gannets recorded as flying and sitting on the water were broadly similar, suggesting the Offshore Ornithology Study Area is used during foraging and during passage to foraging grounds further afield. Peaks in the percentage of flying birds were observed in September in both survey years (). Flexibility in diet and foraging behaviour and duration is likely linked to the species success in the North Sea (Hamer et al., 2007). During the return migration period, proportions of sitting and flying birds were more variable.
- Flight direction was variable, with many birds flying in easterly and westerly directions, such as in August 2019 and July 2020 ( Figure 5.29 Open ▸ ). The presence of the Bass Rock to the southwest of the Offshore Ornithology Study Area may explain the abundance of eastwards and westwards flight, since many birds travel from this colony to foraging grounds further offshore in the North Sea.
Table 5.27: Gannet bio-seasons taken from NatureScot (2020a)
Table 5.28: Monthly density and population estimates of all gannets across the Offshore Ornithology Study Area using design-based analysis. Data include “no-identification” birds apportioned to species
Table 5.31: Mean seasonal peak (MSP) population and density (birds/km2) of all gannets 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 5.28: Distribution of gannets across the Offshore Ornithology Study Area in April S02 2021
Table 5.33: Mean count, SD and proportion of gannets in each age class averaged across bio-season
Figure 5.29: Summarised flight direction of gannets across the Offshore Ornithology Study Area
Figure 5.30: Percentage of flying gannets per survey across the Offshore Ornithology Study Area