Non-breeding Season

513. No lesser black-backed gull collisions were predicted for either the Developer Approach or the Scoping Approach in the non-breeding season ( Table 11.59   Open ▸ ), therefore no further assessment for the non-breeding season was undertaken.

Assessment of Collision Mortality throughout the Year

514. As there were no predicted lesser black-backed gull collisions for the non-breeding season, the totals for the breeding season therefore represent the annual collision totals for this species.
515. Using the Developer Approach, the predicted theoretical additional annual mortality due to collision was an estimated three adult lesser black-backed gulls. This corresponds to an increase in the baseline mortality rate of 0.25% ( Table 11.60   Open ▸ ).
516. Using the Scoping Approach, the predicted theoretical additional annual mortality due to collision was an estimated five adult lesser black-backed gulls. This corresponds to an increase in the baseline mortality rate of 0.41% ( Table 11.61   Open ▸ ).
517. Although these collision mortality estimates did not suggest a potential significant increase in the baseline mortality rate for lesser black-backed gull for the Developer or Scoping Approaches, PVA analysis was conducted on the lesser black-backed gull regional SPA population.

Summary of PVA Assessment

518. PVA was carried out on the lesser black-backed gull regional SPA population considering a range of collision scenarios. The results of the PVA for predicted collision impacts for the Project alone during the operation phase for the lesser black-backed gull regional SPA population for the 35-year projection is summarised in Table 11.63   Open ▸ . Further details of the PVA methodology, input parameters and an explanation of how to interpret the PVA results can be found in volume 3, appendix 11.6.

Table 11.63: Summary of PVA Collision Outputs for Lesser Black-backed Gull for the Proposed Development array area after 35 years

1 Starting population taken from volume 3, appendix 11.6.
Developer Approach = CRM based on mean monthly density.
Scoping Approach = CRM based on maximum monthly density.

519. For both the with and without Project scenarios, the lesser black-backed gull regional SPA population is predicted to increase over the 35-year period. For the Developer Approach, the end population size with Project scenario was very slightly lower than the without Project scenario. There was no predicted difference in the counterfactual of the population growth rate, and the counterfactual of the population size was also very close to 1.000, while the 50th Centile value was close to 50. These values indicate that the PVA did not predict a significant negative effect from the project alone effects of collision mortality from the Developer Approach on the lesser black-backed gull regional SPA population after 35 years.
520. For the Scoping Approach, the end population size with Project scenario was slightly lower than the without Project scenario. There was a very slight predicted difference in the counterfactual of the population growth rate, and the counterfactual of the population size was also close to 1.000, while the 50th Centile value was close to 50. These values indicate that the PVA did not predict a significant negative effect from the project alone effects of collision mortality from the Scoping Approach on the lesser black-backed gull regional SPA population after 35 years.
521. Based on the results from the collision assessment and the regional PVA assessment for both the Developer Approach and the Scoping Approach, the magnitude of collision impacts on the regional SPA lesser black-backed gull population is negligible.

Sensitivity of the Receptor

522. A review of post-construction studies of seabirds at offshore wind farms in European waters concluded that lesser black-backed gull was one of the species that showed a weak attraction to offshore wind farms (Dierschke et al., 2016). A review of vulnerability of Scottish seabirds to offshore wind turbines ranked lesser black-backed gull with the third highest score in the context of collision impacts, based on flight activity at blade height, manoeuvrability, time spent in flight, nocturnal flight activity and conservation importance (Furness and Wade, 2012). Similarly, Furness et al., (2013) scored lesser black-backed gull as the third-highest species of concern in the context of collision impacts, while Bradbury et al., (2014), classified the lesser black-backed gull population vulnerability to collision mortality as very high.
523. On this basis, lesser black-backed gull sensitivity to collision from operational offshore wind farms is considered to be very high ( Table 11.16   Open ▸ ).
524. In addition, estimated numbers of lesser black-backed gulls recorded within the Proposed Development would occasionally qualify as nationally important in the breeding season (See volume 3, appendix 11.1, annex G), with individuals likely originating from a number of SPAs and non-SPAs in the region. On this basis the conservation importance for lesser black-backed gull was considered to be medium.

Significance of the Effect

525. For collision effects on lesser black-backed gull from the Project alone, for the Developer Approach, the magnitude of the impact is deemed to be negligible, and the sensitivity of the receptor is considered to be very high. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.
526. For the Scoping Approach, the magnitude of the impact is deemed to be negligible, and the sensitivity of the receptor is considered to be very high. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.

Secondary and Tertiary Mitigation and Residual Effect

527. No offshore and intertidal ornithology mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond designed in measures outlined in section 11.10) is not significant in EIA terms. Therefore, the residual impact is considered to be of minor adverse significance, which is not significant in EIA terms.

Kittiwake

528. For the Developer Approach, annual estimated kittiwake mortality from collision impacts in the Proposed Development was based on mean densities of flying birds recorded on baseline digital aerial surveys. For the Scoping Approach, this was based on maximum densities of flying birds recorded on baseline digital aerial surveys.
529. The estimated number of collisions per bio-season for kittiwake based on the Developer Approach and the Scoping Approach are presented in Table 11.64   Open ▸ . Figures are presented for the breeding season and the autumn and spring migration periods of the non-breeding seasons, based on the worst-case design scenario (307x14 MW wind turbines). Highest numbers of collisions were predicted for the breeding season, for both approaches, with lower numbers of collisions predicted for the autumn and spring migration periods of the non-breeding season.
530. A complete range of collision numbers for the Proposed Development, and the different design scenarios for both the Developer Approach and the Scoping Approach are presented in volume 3, appendix 11.3.

Table 11.64:  Estimated number of collisions for kittiwake by bio-season in the Proposed Development for the Worst-Case Scenario (SNCBs avoidance rates, wind turbine 14 MW, Option 2) for the Developer Approach and the Scoping Approach. Estimates are rounded to nearest whole bird.

Magnitude of Impact

531. The overall baseline mortality rates were based on age-specific demographic rates and age class proportions from aerial surveys as presented in Table 11.21   Open ▸ . The potential magnitude of impact was estimated by calculating the increase in baseline mortality within each bio-season with respect to the regional populations.

Table 11.65: Estimated Numbers of Collisions for Kittiwake in the Proposed Development array area by bio-season in Relation to Baseline Mortality, for the Developer Approach

1 Breeding season assessment is for breeding adults only.

Table 11.66: Estimated Numbers of Collisions for Kittiwake in the Proposed Development array area by bio-season in Relation to Baseline Mortality, for the Scoping Approach

1 Breeding season assessment is for breeding adults only.

Breeding Season

532. For the Developer Approach in the breeding season, the total estimated number of kittiwake collisions was 426 birds ( Table 11.64   Open ▸ ). However, this includes non-breeding adults and immature birds, as well as breeding adults. Based on the proportion of immature kittiwakes recorded on digital aerial baseline surveys in the breeding season, 3% of the population present in the breeding season are immature birds ( Table 11.29   Open ▸ ). This would mean that 413 adult kittiwakes and 13 immatures bird are predicted to collide with wind turbines in the breeding season, based on the worst-case design scenario.
533. However, a proportion of adult birds present at colonies in the breeding season will opt not to breed in a particular breeding season. It has been estimated that 10% of adult kittiwakes may be “sabbatical” non-breeding birds in any particular breeding season (volume 3, appendix 11.6), and this has been applied for this assessment. On this basis, 41 adult kittiwakes were considered to be not breeding and so 372 breeding adult kittiwakes were taken forward for the breeding season assessment.
534. The total kittiwake regional baseline breeding population is estimated to be 319,126 individuals ( Table 11.9   Open ▸ ). The adult baseline survival rate is estimated to be 0.855 ( Table 11.21   Open ▸ ), which means that the corresponding rate for adult mortality is 0.145. Applying this mortality rate, the estimated baseline mortality of kittiwakes is 46,273 adult birds per breeding season. The additional predicted mortality of 372 breeding adult kittiwakes would increase the baseline mortality rate by 0.80% ( Table 11.65   Open ▸ ).
535. For the Scoping Approach in the breeding season, the total estimated number of kittiwake collisions was 617 birds ( Table 11.64   Open ▸ ). However, this includes non-breeding adults and immature birds, as well as breeding adults. Based on the proportion of immature kittiwakes recorded on digital aerial baseline surveys in the breeding season, 3% of the population present in the breeding season are immature birds ( Table 11.29   Open ▸ ). This would mean that 598 adult kittiwakes and 19 immature birds are predicted to collide with wind turbines in the breeding season, based on the worst-case design scenario.
536. As above, a sabbatical rate of 10% for non-breeding adult kittiwakes (volume 3, appendix 11.6) has been applied for this assessment. On this basis, 60 adult kittiwakes were considered to be not breeding and so 538 breeding adult kittiwakes were taken forward for the breeding season assessment.
537. Applying the adult baseline mortality rate of 0.145, the estimated baseline mortality of kittiwakes is 46,273 adult birds per breeding season. The additional predicted mortality of 538 breeding adult kittiwakes would increase the baseline mortality rate by 1.16% ( Table 11.66   Open ▸ ).

Non-breeding Season – Autumn Migration Period

538. For the Developer Approach in the autumn migration period, the total estimated number of kittiwake collisions was 155 birds ( Table 11.64   Open ▸ ), however, this includes adult and immature birds. Based on information presented in Furness (2015), in the non-breeding season 47% of the population present are immature birds and 53% of birds are adults. This would mean that 82 adult kittiwakes and 73 immature birds are predicted to collide with wind turbines, in the autumn migration period of the non-breeding season, based on the worst-case design scenario.
539. Based on Furness (2015), the total kittiwake BDMPS regional baseline population for the autumn migration period is estimated to be 829,937 individuals ( Table 11.9   Open ▸ ). Using the average baseline mortality rate of 0.160 ( Table 11.21   Open ▸ ), the estimated regional baseline mortality of kittiwakes is 132,790 birds in the autumn migration period. The additional predicted mortality of 155 kittiwakes would increase the baseline mortality rate by 0.12% ( Table 11.65   Open ▸ ).
540. For the Scoping Approach in the autumn migration period, the total estimated number of kittiwake collisions was 190 birds ( Table 11.64   Open ▸ ), however, this includes adult and immature birds. Based on Furness (2015), 47% of the population present in the non-breeding season are immature birds and 53% of birds are adults. This would mean that 101 adult and 89 immature kittiwakes are predicted to collide with wind turbines, based on the worst-case design scenario. The estimated regional baseline mortality of kittiwakes in the autumn migration period is 132,790 birds. The additional predicted mortality of 190 kittiwakes would increase the baseline mortality rate by 0.14% ( Table 11.66   Open ▸ ).

Non-breeding Season – Spring Migration Period

541. For the Developer Approach in the spring migration period, the total estimated number of kittiwake collisions was 104 birds ( Table 11.64   Open ▸ ), however, this includes adult and immature birds. Based on Furness (2015), 47% of the population present in the non-breeding season are immature birds and 53% of birds are adults. This would mean that 55 adult and 49 immature kittiwakes are predicted to collide with wind turbines in the spring migration period of the non-breeding season, based on the worst-case design scenario.
542. Based on Furness (2015), the total kittiwake BDMPS regional baseline population for the spring migration period is estimated to be 627,816 individuals ( Table 11.9   Open ▸ ). Using the average baseline mortality rate of 0.160 ( Table 11.21   Open ▸ ), the estimated baseline mortality of kittiwakes is 100,451 birds in the spring migration period. The additional predicted mortality of 104 kittiwakes would increase the baseline mortality rate by 0.10% ( Table 11.65   Open ▸ ).
543. For the Scoping Approach in the spring migration period, the total estimated number of kittiwake collisions was 179 birds ( Table 11.64   Open ▸ ), however, this includes adult and immature birds. Based on Furness (2015), 47% of the population present in the non-breeding season are immature birds and 53% of birds are adults. This would mean that 95 adult and 84 immature kittiwakes are predicted to collide with wind turbines in the spring period of the non-breeding season, based on the worst-case design scenario. The additional predicted mortality of 179 kittiwakes would increase the baseline mortality rate by 0.18% ( Table 11.66   Open ▸ ).

Assessment of Collision Mortality throughout the Year

544. Predicted kittiwake mortality as a result of collision in the Proposed Development array area for all bio-seasons as calculated above, was summed for the whole year.
545. Using the Developer Approach, the predicted theoretical additional annual mortality due to collision was an estimated 631 kittiwakes. This corresponds to an increase in the baseline mortality rate of 1.02% ( Table 11.65   Open ▸ ).
546. Using the Scoping Approach, the predicted theoretical additional annual mortality due to collision was an estimated 907 kittiwakes. This corresponds to an increase in the baseline mortality rate of 1.48% ( Table 11.66   Open ▸ ).
547. These collision mortality estimates suggest a potential significant increase in the baseline mortality rate for kittiwake for the Developer Approach and the Scoping Approach, therefore PVA analysis was conducted on the kittiwake regional SPA population. Conclusions on displacement and collision mortality are presented below.

Summary of PVA Assessment

548. PVA was carried out on the regional kittiwake SPA population for a range of collision scenarios as well as a range of displacement and mortality rates.
549. The results of the PVAs for predicted displacement and collision impacts for the Project alone during the operation phase for the kittiwake regional SPA population for the 35-year projection is summarised in Table 11.67   Open ▸ . Further details of the PVA methodology, input parameters and an explanation of how to interpret the PVA results can be found in volume 3, appendix 11.6.

Table 11.67: Summary of PVA Displacement and Collision Outputs for Kittiwake for the Proposed Development array area plus 2 km buffer after 35 years

1 Starting population taken from volume 3, appendix 11.6.
Developer Approach = 30% displacement and 1% mortality in breeding season and mean monthly density for CRM.
Scoping Approach A = 30% displacement and 1% displacement mortality throughout year and maximum monthly density for CRM.
Scoping Approach B = 30% displacement and 3% displacement mortality throughout year and maximum monthly density for CRM.

550. For kittiwake, the PVA predicted that the regional SPA end population would be lower than the start population for both the with and without Project scenarios over the 35-year period. For the Developer Approach, the end population size with Project scenario was lower than the without Project scenario. There was a very slight predicted decrease in the counterfactual of the population growth rate, and the counterfactual of the population size was also very close to 1.000, while the 50th Centile value was close to 50. These values indicate that the PVA did not predict a significant negative effect from the project alone effects of displacement and collision mortality from the Developer Approach on the kittiwake regional SPA population after 35 years.
551. For Scoping Approach A, the end population size with Project scenario was lower than the without Project scenario. There was a very slight predicted decrease in the counterfactual of the population growth rate, and the counterfactual of the population size was also close to 1.000, while the 50th Centile value was close to 50. These values indicate that the PVA did not predict a significant negative effect from the project alone effects of displacement and collision mortality from Scoping Approach A on the kittiwake regional SPA population after 35 years.
552. For Scoping Approach B, the end population size with Project scenario was lower than the without Project scenario. There was a very slight predicted decrease in the counterfactual of the population growth rate, and the counterfactual of the population size was also close to 1.000, while the 50th Centile value was also close to 50. These values indicate that the PVA did not predict a significant negative effect from the project alone effects of displacement and collision mortality from Scoping Approach B on the kittiwake regional SPA population after 35 years.
553. Based on the results from the displacement and collision assessments, and the combined PVA on displacement and collision effects on the regional SPA populations for the Developer Approach, the magnitude of impact on the regional kittiwake population is low.
554. Based on the results from the displacement and collision assessments, and the combined PVA on displacement and collision effects on the regional SPA populations for Scoping Approach A, the magnitude of impact on the regional kittiwake population is low.
555. Based on the results from the displacement and collision assessments, and the combined PVA on displacement and collision effects on the regional SPA populations for Scoping Approach B, the magnitude of impact on the regional kittiwake population is low.

Sensitivity of the Receptor

556. A review of post-construction studies of seabirds at offshore wind farms in European waters concluded that kittiwake was one of the species that was hardly affected by offshore wind farms or with attraction and avoidance approximately equal over all studies (Dierschke et al., 2016). A review of vulnerability of Scottish seabirds to offshore wind turbines ranked kittiwake with the seventh highest score in the context of collision impacts, based on flight activity at blade height, manoeuvrability, time spent in flight, nocturnal flight activity and conservation importance (Furness and Wade, 2012). Similarly, Furness et al., (2013) scored kittiwake as the seventh-highest species of concern in the context of collision impacts, while Bradbury et al., (2014), classified the kittiwake population vulnerability to collision mortality as high.
557. On this basis, kittiwake sensitivity to collision from operational offshore wind farms is considered to be high ( Table 11.16   Open ▸ ).
558. Kittiwake sensitivity to displacement effects are discussed in Paragraph 248 onwards. In conclusion, for kittiwake, there is evidence from other operating offshore wind farm projects that displacement is not likely to occur to any significant level. A review of post-construction studies of seabirds at offshore wind farms in European waters concluded that kittiwake was one of the species which were hardly affected by offshore wind farms or with attraction and avoidance approximately equal over all studies (Dierschke et al., 2016). Two reviews of vulnerability of Scottish seabirds to offshore wind turbines in the context of disturbance and displacement ranked kittiwake with a score of two, where five was the most vulnerable score and one was the least vulnerable (Furness and Wade, 2012, Furness et al., 2013). Similarly, Bradbury et al., (2014), classified the kittiwake population vulnerability to displacement as very low.
559. On this basis, kittiwake sensitivity to displacement effects from operational offshore wind farms is considered to be low ( Table 11.16   Open ▸ ). Therefore, kittiwake sensitivity to collision impacts has been used to determine the sensitivity of this species.
560. In addition, estimated numbers of kittiwakes recorded within the Proposed Development were considered as nationally important in the breeding season (See volume 3, appendix 11.1, annex G), with individuals likely originating from a number of SPAs and non-SPAs in the region. On this basis the conservation importance for kittiwake was considered to be medium.

Significance of the Effect

561. For combined displacement and collision effects on kittiwake from the Project alone, for the Developer Approach, the magnitude of the impact is deemed to be low, and the sensitivity of the receptor is considered to be high. The effect will, therefore, be of minor to moderate adverse significance, which is significant in EIA terms.
562. For Scoping Approach A, the magnitude of the impact is deemed to be low, and the sensitivity of the receptor is considered to be high. The effect will, therefore, be of minor to moderate adverse significance, which is significant in EIA terms.
563. For Scoping Approach B, the magnitude of the impact is deemed to be low, and the sensitivity of the receptor is considered to be high. The effect will, therefore, be of minor to moderate adverse significance, which is significant in EIA terms.
564. As outlined in Section 11.9.2, in cases where the range for the significance of effect spans the significance threshold (minor to moderate), the final significance is based upon the expert's professional judgement as to which outcome delineates the most likely effect, with an explanation as to why this is the case.
565. As highlighted by NS in the NnG Scoping Opinion (Marine Scotland, 2017a), collision risk and displacement are considered to be mutually exclusive impacts, and therefore combining mortality estimates for displacement and collision as has been done for this PVA should be considered extremely precautionary. On this basis, it is considered that for all three approaches, the effect will be of minor adverse significance, which is not significant in EIA terms. For further discussion on levels of precaution in the Scoping Approach, see volume 3, appendix 11.3 and appendix 11.4.

Secondary and Tertiary Mitigation and Residual Effect

566. No offshore and intertidal ornithology mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond designed in measures outlined in section 11.10) is not significant in EIA terms. Therefore, the residual impact is considered to be of minor adverse significance, which is not significant in EIA terms.

Little Gull

567. For the Developer Approach, annual estimated little gull mortality from collision impacts in the Proposed Development was based on mean densities of flying birds recorded on baseline digital aerial surveys. For the Scoping Approach, this was based on maximum densities of flying birds recorded on baseline digital aerial surveys. Figures are presented for the breeding and non-breeding seasons, based on the worst-case design scenario (307x14 MW wind turbines).

Table 11.68:  Estimated number of collisions for little gull by bio-season in the Proposed Development for the worst-case scenario (SNCBs avoidance rates, wind turbine 14 MW, Option 2). Estimates are rounded to nearest whole bird.

Magnitude of Impact

568. The estimated number of collisions per bio-season for little gull based on the Developer Approach and the Scoping Approach are presented in Table 11.68   Open ▸ . Estimated numbers of collisions for little gull were zero in the breeding season. For the Developer Approach, two birds were predicted to collide with wind turbines in the non-breeding season. For the Scoping Approach, four little gull collisions were predicted over this period.
569. A complete range of collision numbers for the Proposed Development, and the different design scenarios for both the Developer Approach and the Scoping Approach are presented in volume 3, appendix 11.3.

Breeding Season

570. As little gulls do not breed in the UK, it is considered that the birds recorded in July on the digital aerial baseline surveys were non-breeding birds.
571. When CRM estimates were rounded to the nearest whole bird, there were zero little gull collisions predicted for the breeding season for both the Developer Approach and the Scoping Approach ( Table 11.69   Open ▸ and Table 11.70   Open ▸ ). There were therefore no collision impacts predicted for the breeding season for little gull.

Table 11.69: Estimated Numbers of Collisions for Little Gull in the Proposed Development array area by bio-season in Relation to Baseline Mortality for the Developer Approach

Figures in brackets represent collision estimates based on Scoping Approach (see text for details).

Table 11.70: Estimated Numbers of Collisions for Little Gull in the Proposed Development array area by bio-season in Relation to Baseline Mortality, for the Scoping Approach

Figures in brackets represent collision estimates based on Scoping Approach (see text for details).

Non-breeding Season

572. For the Developer Approach in the non-breeding season, the total estimated number of little gull collisions was two birds, based on the worst-case design scenario ( Table 11.69   Open ▸ ).
573. Little gull is not considered in the BDMPS report (Furness, 2015), therefore there is no BDMPS regional population available for the non-breeding season. Analysis of ESAS data by Skov et al. (1995) identified a geographically discrete autumn passage concentration of little gulls in the outer Firth of Forth and Firth of Tay (referred to as Tay Bay by Skov et al.). There is uncertainty regarding the current size of this population as the number estimated by Skov et al. (450 birds) is far lower than the typical total of about 1,000 birds seen at coastal roost counts in Fife and Lothian in the non-breeding season (Forrester et al., 2007). Furthermore, survey work commissioned in recent years to inform the Forth and Tay offshore wind farm projects has shown that this species is more common than previously appreciated (or numbers have increased), with for example a peak estimated population for the NnG study area of up to 3,841 birds in September 2012 (NnG, 2018).
574. The upper limit of 3,000 birds from an estimate of 1,500 to 3,000 individuals present between June and November in the Forth and Tay area (Forrester et al., 2007) has been used in this assessment as the best available regional reference population estimate during the non-breeding season, although this is considered likely to be an under-estimate.
575. The baseline mortality rate for little gull was based on an estimate of adult little gull survival of 0.8 published by Garthe and Hüppop (2004). The corresponding average baseline mortality rate of 0.2 was applied to the best available regional reference population estimate during the non-breeding season (3,000 birds) to give a predicted baseline mortality of little gulls of 600 birds per non-breeding season. Based on the Developer Approach, the additional predicted mortality of two little gulls would increase the baseline mortality rate by 0.033%.
576. For the Scoping Approach in the non-breeding season, the total estimated number of little gull collisions was four birds, based on the worst-case design scenario ( Table 11.70   Open ▸ ). This additional predicted mortality would increase the baseline mortality rate by 0.67%.

Assessment of Collision Mortality throughout the Year

577. There were no collision impacts predicted for little gull in the breeding season, therefore annual collision mortality will be the same as for the non-breeding season.
578. The estimated increase in the annual baseline mortality rate for little gull as a result of collision is predicted to be 0.033% for the Developer Approach and 0.67% for the Scoping Approach ( Table 11.69   Open ▸ ). The magnitude of this impact is therefore considered to be negligible.

Sensitivity of the Receptor

579. A review of post-construction studies of seabirds at offshore wind farms in European waters concluded that little gull was one of the species that weakly avoided offshore wind farms (Dierschke et al., 2016). Little gull was not included in vulnerability reviews by Furness and Wade (2012) or Furness et al., (2013) but Bradbury et al., (2014), classified the little gull population vulnerability to collision mortality as moderate.
580. On this basis, little gull sensitivity to collision from operational offshore wind farms is considered to be medium ( Table 11.16   Open ▸ ).
581. In addition, estimated numbers of little gulls recorded within the Proposed Development were considered as regionally important in the non-breeding season (volume 3, appendix 11.1, annex G). On this basis the conservation importance for little gull was considered to be low.

Significance of the Effect

582. For collision effects on little gull from the Project alone, for the Developer Approach and the Scoping Approach, the magnitude of the impact is deemed to be negligible, and the sensitivity of the receptor is considered to be medium. The effect will, therefore, be of negligible to minor adverse significance, which is not significant in EIA terms.

Secondary and Tertiary Mitigation and Residual Effect

583. No offshore and intertidal ornithology mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond designed in measures outlined in section 11.10) is not significant in EIA terms. Therefore, the residual impact is considered to be of negligible to minor adverse significance, which is not significant in EIA terms.

Common Tern

584. For the Developer Approach, estimated common tern mortality from collision impacts in the Proposed Development array area was based on mean densities of flying birds recorded on baseline digital aerial surveys. For the Scoping Approach, this was based on maximum densities of flying birds recorded on baseline digital aerial surveys.
585. The estimated number of collisions per month for common tern based on the Developer Approach and the Scoping Approach are presented in Table 11.71   Open ▸ . Figures are presented for the breeding and non-breeding seasons, based on the worst-case design scenario (307x14 MW wind turbines). Numbers are presented by month rather than seasonally, in order to demonstrate the typically low estimated numbers of collisions per month. For both the Developer Approach and the Scoping Approach, collision numbers were less than one bird per month in all months except for August.
586. For assessment purposes, the breeding season for common tern has been defined as May to mid-September (NatureScot, 2020). There are two BDMPS periods in the non-breeding season as defined by Furness (2015). The autumn migration period covers late July to early September, and the spring migration period covers April and May. As a precautionary assessment, all estimated collisions were assessed as being from the breeding season, as well as being part of the autumn migration period. Estimated collision numbers for the spring migration period of the non-breeding season were considerably less than one whole bird, therefore no assessment was carried out for this period of the non-breeding season.
587. A complete range of collision numbers for the Proposed Development array area, and the different design scenarios for both the Developer Approach and the Scoping Approach are presented in volume 3, appendix 11.3.

Table 11.71:  Monthly Estimated Collisions for Common Tern in the Proposed Development array area for the Worst-Case Scenario (SNCBs avoidance rates, wind turbine 14 MW, Option 2), based on the Developer and Scoping Approaches. Estimates are presented using the mean avoidance rate (0.980)

Magnitude of Impact

588. The overall baseline mortality rates were based on age-specific demographic rates and age class proportions as presented in Table 11.21   Open ▸ . The potential magnitude of impact was estimated by calculating the increase in baseline mortality for the relevant bio-seasons with respect to the regional populations.

Table 11.72: Estimated Numbers of Collisions for Common Tern in the Proposed Development array area by bio-season in Relation to Baseline Mortality, for the Developer Approach

Figures in brackets represent collision estimates based on Scoping Approach (see text for details).
1 There is an overlap in the months across the three seasons as the breeding season follows the NatureScot (2020) approach, while the Autumn and Spring Migration periods follow BDMPS (Furness 2015).
2 These collision estimates have been assessed for both the breeding season and the autumn migration period, and therefore have not been summed.

Table 11.73: Estimated Numbers of Collisions for Common Tern in the Proposed Development array area by bio-season in Relation to Baseline Mortality, for the Scoping Approach

Figures in brackets represent collision estimates based on Scoping Approach (see text for details).
1 There is an overlap in the months across the three seasons as the breeding season follows the NatureScot (2020) approach, while the Autumn and Spring Migration periods follow BDMPS (Furness 2015).
2 These collision estimates have been assessed for both the breeding season and the autumn migration period, and therefore have not been summed.

Breeding Season

589. Common tern collisions were predicted to occur between April and September, based on densities recorded in the Proposed Development array area on baseline digital aerial surveys. For the Developer Approach in the breeding season, the total estimated number of common tern collisions was six birds ( Table 11.72   Open ▸ ). However, this includes non-breeding adults and immature birds, as well as breeding adults. The age breakdown of common terns recorded on baseline digital aerial surveys by bio-season is presented in Table 11.74   Open ▸ . Based on the proportion of immature common terns recorded on digital aerial baseline surveys in the breeding season, 12% of the population present in the breeding season are immature birds, then this would mean that five adult common terns and one immature bird are predicted to collide with wind turbines in the breeding season, based on the worst-case design scenario.

Table 11.74: Proportions of juvenile, immature and adult Common Tern recorded on Digital Aerial Surveys

590. There are no common tern breeding colonies within mean maximum foraging range (plus 1S.D.) of the Proposed Development, based on the published range of 18.0±8.9 km (Woodward et al., 2019). On this basis, it was concluded that none of the predicted common tern collisions for the Developer Approach or the Scoping Approach during the breeding season were from the regional breeding population. Therefore, there will be no impact from collision on the common tern regional breeding population in the breeding season.

Non-breeding Season – Autumn Migration Period

591. According to NatureScot (2020) the non-breeding season is defined as mid-September to April, consequently for both the Developer and Scoping Approach, less than one common tern collision is predicted over this period ( Table 11.71   Open ▸ ).
592. However, according to the BDMPS review, the autumn migration period of the non-breeding season in UK waters is defined as late July to early September (Furness, 2015). Therefore, the predicted common tern collisions between July and August could be considered to be from the regional BDMPS population for the autumn migration period. As a precautionary approach, collision impacts for the Developer Approach and the Scoping Approach have been assessed on this basis.
593. For the Developer Approach in the autumn migration period, the total estimated number of common tern collisions (rounded up) was six birds ( Table 11.72   Open ▸ ). Based on Furness (2015), the total common tern BDMPS regional baseline population for the autumn migration period is estimated to be 144,911 individuals ( Table 11.9   Open ▸ ). Using the average baseline mortality rate of 0.180 ( Table 11.21   Open ▸ ), the estimated baseline mortality of common tern is 26,084 birds in the autumn migration period. The additional predicted mortality of six common terns would increase the baseline mortality rate by 0.023% ( Table 11.72   Open ▸ ).
594. For the Scoping Approach in the autumn migration period, the total estimated number of common tern collisions (rounded up) was nine birds. The additional predicted mortality of nine common terns would increase the baseline mortality rate by 0.035% ( Table 11.73   Open ▸ ).

Assessment of Collision Mortality throughout the Year

595. As there are no common tern colonies within mean maximum foraging range (plus 1S.D.) of the Proposed Development array area, there will be no impact from collision on the common tern regional breeding population in the breeding season.
596. As there were very low numbers of predicted common tern collisions for the spring period of the non-breeding season, the totals for the autumn period of the non-breeding season therefore represent the annual collision totals for this species.
597. Using the Developer Approach, the predicted theoretical additional annual mortality due to collision was an estimated six common terns. This corresponds to an increase in the baseline mortality rate of 0.023% ( Table 11.72   Open ▸ ).
598. Using the Scoping Approach, the predicted theoretical additional annual mortality due to collision was an estimated nine common terns. This corresponds to an increase in the baseline mortality rate of 0.035% ( Table 11.73   Open ▸ ).
599. The estimated increase in the annual baseline mortality for common tern as a result of collision would result in a very slight decrease in the size of the regional BDMPS population of common tern in the autumn migration period of the non-breeding season, for both the Developer Approach and the Scoping Approach. The magnitude of this impact is therefore considered to be negligible.

Sensitivity of the Receptor

600. A review of post-construction studies of seabirds at offshore wind farms in European waters concluded that common tern was one of the species that was hardly affected by offshore wind farms or with attraction and avoidance approximately equal over all studies (Dierschke et al., 2016). A review of vulnerability of Scottish seabirds to offshore wind turbines ranked common tern with the 15th highest score in the context of collision impacts, based on flight activity at blade height, manoeuvrability, time spent in flight, nocturnal flight activity and conservation importance (Furness and Wade, 2012). Similarly, Furness et al., (2013) scored common tern as the 14th highest ranked species of concern in the context of collision impacts, while Bradbury et al., (2014), classified the common tern population vulnerability to collision mortality as moderate.
601. On this basis, common tern sensitivity to collision from operational offshore wind farms is considered to be medium ( Table 11.16   Open ▸ ).
602. In addition, estimated numbers of common terns recorded within the Proposed Development were considered as regionally important in the breeding season (see appendix 11.1, annex G), with individuals likely originating from a number of SPAs and non-SPAs within and outside the region. On this basis the conservation importance for common tern was considered to be low.

Significance of the Effect

603. For collision effects on common tern from the Project alone, for the Developer Approach and the Scoping Approach, the magnitude of the impact is deemed to be negligible, and the sensitivity of the receptor is considered to be medium. The effect will, therefore, be of negligible to minor adverse significance, which is not significant in EIA terms.

Secondary and Tertiary Mitigation and Residual Effect

604. No offshore and intertidal ornithology mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond designed in measures outlined in section 11.10) is not significant in EIA terms. Therefore, the residual impact is considered to be of negligible to minor adverse significance, which is not significant in EIA terms.

Arctic Tern

605. For the Developer Approach, estimated Arctic tern mortality from collision impacts in the Proposed Development array area was based on mean densities of flying birds recorded on baseline digital aerial surveys. For the Scoping Approach, this was based on maximum densities of flying birds recorded on baseline digital aerial surveys.
606. The estimated number of collisions per month for Arctic tern based on the Developer Approach and the Scoping Approach are presented in Table 11.75   Open ▸ . Figures are presented for the breeding and non-breeding seasons, based on the worst-case design scenario (307x14 MW wind turbines). Numbers are presented by month rather than seasonally, in order to demonstrate the typically low estimated numbers of collisions per month. For both the Developer Approach and the Scoping Approach, collision numbers were less than one bird per month in all months except for August.
607. For assessment purposes, the breeding season for Arctic tern has been defined as May to August, with the non-breeding season defined as September to April (NatureScot, 2020). However, there are two BDMPS periods in the non-breeding season as defined by Furness (2015). The autumn migration period covers July to early September, and the spring migration period covers late April and May. As a precautionary assessment, all estimated collisions were assessed as being from the breeding season, as well as being part of the autumn migration period. Estimated collision numbers for the spring migration period of the non-breeding season were considerably less than one whole bird, therefore no assessment was carried out for this period of the non-breeding season.

Table 11.75:  Monthly estimated collisions for Arctic tern in the Proposed Development array area for the worst-case scenario (SNCBs avoidance rates, wind turbine 14 MW, Option 2), based on the Developer and Scoping Approaches. Estimates are presented using the mean avoidance rate (0.980)

608. Arctic tern collisions were predicted to occur between April and September, based on densities recorded in the Proposed Development on baseline digital aerial surveys. For both the Developer Approach and the Scoping Approach, collision numbers were less than one bird per month in all months except for July and August.
609. A complete range of collision numbers for the Proposed Development, and the different design scenarios for both the Developer Approach and the Scoping Approach are presented in volume 3, appendix 11.3.

Magnitude of Impact

610. The overall baseline mortality rates were based on age-specific demographic rates and age class proportions as presented in Table 11.21   Open ▸ . The potential magnitude of impact was estimated by calculating the increase in baseline mortality for the relevant bio-seasons with respect to the regional populations.

Table 11.76: Estimated Numbers of Collisions for Arctic Tern in the Proposed Development array area by bio-season in Relation to Baseline Mortality, for the Developer Approach

Figures in brackets represent collision estimates based on Scoping Approach (see text for details).
1 There is an overlap in the months across the three seasons as the breeding season follows the NatureScot (2020) approach, while the Autumn and Spring Migration periods follow BDMPS (Furness 2015).
2 These collision estimates have been assessed for both the breeding season and the autumn migration period, and therefore have not been summed.

Table 11.77: Estimated Numbers of Collisions for Arctic Tern in the Proposed Development array area by bio-season in Relation to Baseline Mortality, for the Scoping Approach

Figures in brackets represent collision estimates based on Scoping Approach (see text for details).
1 There is an overlap in the months across the three seasons as the breeding season follows the NatureScot (2020) approach, while the Autumn and Spring Migration periods follow BDMPS (Furness 2015).
2 These collision estimates have been assessed for both the breeding season and the autumn migration period, and therefore have not been summed.

Breeding Season

611. For the Developer Approach in the breeding season, the total estimated number of Arctic tern collisions was eight birds ( Table 11.76   Open ▸ ). However, this includes non-breeding adults and immature birds, as well as breeding adults. The age breakdown of Arctic terns recorded on baseline digital aerial surveys by bio-season is presented in Table 11.78   Open ▸ . Based on the proportion of immature Arctic terns recorded on digital aerial baseline surveys in the breeding season, 8% of the population present in the breeding season are immature birds. This would mean that seven adult Arctic terns and one immature bird are predicted to collide with wind turbines in the breeding season, based on the worst-case design scenario.
612. For the Scoping Approach in the breeding season, the total estimated number of Arctic tern collisions was 14 birds ( Table 11.77   Open ▸ ), however, this includes non-breeding adults and immature birds, as well as breeding adults. Based on the proportion of immature Arctic terns recorded on digital aerial baseline surveys in the breeding season ( Table 11.78   Open ▸ ), 8% of the population present in the breeding season are immature birds. This would mean that 13 adult Arctic terns and one immature bird are predicted to collide with wind turbines in the breeding season, based on the worst-case design scenario.

Table 11.78: Proportions of juvenile, immature and adult Arctic Tern recorded on Digital Aerial Surveys

613. There are no Arctic tern breeding colonies within mean maximum foraging range (plus 1S.D.) of the Proposed Development array area, based on the published range of 25.7±14.8 km (Woodward et al., 2019). In addition, numbers of Arctic terns recorded in the Proposed Development array area were very low in the early part of the breeding season, between April and June ( Table 11.75   Open ▸ ). Numbers increased slightly in July and August, by which time failed breeding birds or early fledged juveniles will have left breeding colonies elsewhere. Large flocks of Arctic terns on passage are regularly recorded on the east coast of Scotland in July and August, for example 1,000 at Tenstsmuir (Fife) on 9th August 1986, 1,500 there 26th July 1991 and 1,600 at Goosepools (Fife) on 7th August 2000. These birds are known to remain in Scottish coastal waters such as the Forth of Forth to feed for one to two weeks before migrating south for the winter (Forrester et al., 2007). For these reasons, it was concluded that none of the predicted Arctic tern collisions for the Developer Approach or the Scoping Approach during the breeding season were from the regional breeding population. Therefore, there will be no impact from collision on the Arctic tern regional breeding population in the breeding season.

Non-breeding Season – Autumn Migration Period

614. According to the BDMPS review, the autumn migration period of the non-breeding season in UK waters for Arctic tern is defined as July to early September (Furness, 2015). Therefore the predicted Arctic tern collisions between July and August could be considered to be from the regional BDMPS population for the autumn migration period, rather than from the regional breeding population, as outlined above. Collision impacts for the Developer Approach and the Scoping Approach have therefore also been assessed on this basis.
615. For the Developer Approach in the autumn migration period, the total estimated number of Arctic tern collisions (rounded up) was eight birds ( Table 11.76   Open ▸ ). Based on Furness (2015), the total Arctic tern BDMPS regional baseline population for the autumn migration period is estimated to be 163,930 individuals ( Table 11.9   Open ▸ ). Using the average baseline mortality rate of 0.246 ( Table 11.21   Open ▸ ), the estimated baseline mortality of Arctic tern is 40,327 birds in the autumn migration period. The additional predicted mortality of eight Arctic terns would increase the baseline mortality rate by 0.02% ( Table 11.76   Open ▸ ).
616. For the Scoping Approach in the autumn migration period, the total estimated number of Arctic tern collisions (rounded up) was 14 birds. The additional predicted mortality of 14 Arctic terns would increase the baseline mortality rate by 0.035% ( Table 11.77   Open ▸ )).
617. For both approaches, this level of potential impact is considered to be of negligible magnitude during the autumn migration period of the non-breeding season, as it represents no discernible increase to baseline mortality levels as a result of collision.