Operation and maintenance phase

  1. Operational wind turbines and associated infrastructure present a collision risk for seabirds flying within the array. This includes birds commuting between breeding and foraging sites, migrating birds, and those foraging for food within the array. Direct collision with infrastructure may result in injury or death, however, it is assumed that all collisions with operational wind turbines result in mortality.
  2. CRM for regularly occurring species was undertaken using the Stochastic Collision Risk Model (sCRM) developed by Marine Scotland (McGregor et al., 2018). The User Guide for the sCRM Shiny App provided by Marine Scotland (Donovan, 2017) has been followed for the modelling of collision impacts predicted for the Array. The full methodology is provided in volume 3, appendix 11.2 of the Array EIA Report.
  3. Input densities for CRM were based on MRSea modelling where available, with design-based estimates used for instances in which MRSea estimates were unavailable (volume 3, appendix 11.2 of the Array EIA Report).
  4. For all regularly occurring species, the assessment has been carried out on the basis of the input parameters recommended by NatureScot (2023g). However, it should be noted that there is considerable uncertainty around several of the key input parameters, including flight speed and avoidance rates. Therefore, in addition to the assessment value, a range of other input parameters has also been considered, as detailed in volume 3, appendix 11.2 of the Array EIA Report. The minimum and maximum collision estimates from this range are also presented. Further discussion of the range considered is provided in volume 3, appendix 11.2 and volume 2, chapter 11 of the Array EIA Report.
  5. It is acknowledged that migratory passage movements may not be adequately captured by traditional survey methods. Therefore, the British Trust for Ornithology (BTO) SOSSMAT was used to assess the population size of migratory bird species designated as features of the UK SPA network that may cross the Array; instructions are given in Wright et al. (2012). Further details are provided in volume 3, appendix 11.2, annex B of the Array EIA Report.
  6. The quantification of collision mortality provides an estimate of the total number of birds subject to mortality. For the purposes of this RIAA, it is necessary to estimate which of those birds may be associated with specific SPAs or Ramsar sites, in order to calculate the impact on the population for which each site is designated. This is done through the process of apportionment. Full details of the apportionment process and the resulting proportion of birds associated with each SPA or Ramsar are given in volume 3, appendix 11.4 of the Array EIA Report.
  7. Where the apportioned impact is estimated to increase baseline mortality to the population of a SPA or Ramsar by greater than 0.02 percentage points, PVA is subsequently carried out to further investigate the potential effect on the population. Details of the PVA methodology are presented in appendix 3B. For greater clarity, collision results (and PVAs, where relevant) are presented by species, rather than by SPA/Ramsar.
  8. The conclusions for each SPA/Ramsar are summarised in Table 5.46   Open ▸ , based on the results for each feature being assessed.
                        Kittiwake
  1. The impact of collision on kittiwake is summarised in Table 5.38   Open ▸ to Table 5.40   Open ▸ .

 

Table 5.38:
Kittiwake Seasonal Collision Mortality (Total)

Table 5.38: Kittiwake Seasonal Collision Mortality (Total)

 

Table 5.39:
Kittiwake Collision Mortality (Individuals) Apportioned to Each SPA or Ramsar – SNCB Approach (Range in Parenthesis)

Table 5.39: Kittiwake Collision Mortality (Individuals) Apportioned to Each SPA or Ramsar – SNCB Approach (Range in Parenthesis)

 

Table 5.40:
Kittiwake Increase in Annual Mortality (Individuals) at Each SPA or Ramsar

Table 5.40: Kittiwake Increase in Annual Mortality (Individuals) at Each SPA or Ramsar

 

  1. The increase in mortality rate does not exceed the 0.02 percentage point threshold advised by NatureScot (2023k) for any site and therefore it can be concluded, beyond reasonable scientific doubt, that there is no adverse effect to the integrity of the kittiwake feature of any site as a result of collision impacts from the Array alone. The impact of combined displacement and collision impacts is considered separately, below (section 5.4.5).
                        Gannet
  1. The impact of collision on gannet is summarised in Table 5.41   Open ▸ to Table 5.43   Open ▸ .

 

Table 5.41:
Gannet Seasonal Collision Mortality (Total)

Table 5.41: Gannet Seasonal Collision Mortality (Total)

 

Table 5.42:
Gannet Collision Mortality (Individuals) Apportioned to Each SPA or Ramsar – SNCB Approach (Range in Parenthesis)

Table 5.42: Gannet Collision Mortality (Individuals) Apportioned to Each SPA or Ramsar – SNCB Approach (Range in Parenthesis)

 

Table 5.43:
Gannet Increase in Annual Mortality (Individuals) at Each SPA or Ramsar

Table 5.43: Gannet Increase in Annual Mortality (Individuals) at Each SPA or Ramsar

 

  1. The increase in mortality rate does not exceed the 0.02 percentage point threshold advised by NatureScot (2023k) for any site and therefore it can be concluded, beyond reasonable scientific doubt, that there is no adverse effect to the integrity of the gannet feature of any site as a result of collision impacts from the Array alone. The impact of combined displacement and collision impacts is considered separately, below (section 5.4.5).
                        Migratory birds
  1. It is recognised that migratory birds may not be adequately characterised by the site-specific DAS carried out at the Array. Migratory birds may fly at night (when no DAS are carried out) or in pulse movements which could easily be missed by DAS, as they are conducted on a monthly basis. Therefore, the risk to migratory birds cannot be assessed using the same methodology as has been applied for regularly occurring seabirds (above). Instead, the potential impact on migratory birds has been assessed using a qualitative approach drawing on available resources (principally Woodward et al., 2023), as well as a quantitative approach, using the SOSSMAT (Wright et al., 2012).
  2. Woodward et al. (2023) provide a review of available information regarding to migratory birds in Scottish waters and the potential for collision risk. Key information compiled includes population estimates, migratory routes, timing of migration, migratory flight heights, migratory flight speeds, and migratory avoidance rates and behaviour. Woodward et al. (2023) compile this information for 69 species or sub-species, which are non-seabird features of relevant SPA including swans, geese, ducks, waders, raptors and other non-passerines. A summary of the key information for each species considered is given in Table 5.44   Open ▸ .

 

Table 5.44:
Assessment of Collision Risk to Migratory Species Based on Woodward et al. (2023)

Table 5.44: Assessment of Collision Risk to Migratory Species Based on Woodward et al. (2023)

  1. In addition, a quantitative assessment of collision risk to migratory birds has been carried out using SOSSMAT (Wright et al. 2012). The Applicant is aware that a new quantitative mCRM is under development, but this model is currently undergoing testing and seeking approval, and therefore not yet ready to be used for assessment (mCRM Authors, 2021) at the time of writing this chapter (April, 2024). The SOSSMAT therefore represents the best available tool currently available to provide quantitative estimates of the collision risk to migratory birds. Full details are presented in volume 3, appendix 11.2, annex B of the Array EIA Report. The results are presented in Table 5.45   Open ▸ .

 

Table 5.45:
Estimates of Collision Risk to Migratory Waterbirds

Table 5.45: Estimates of Collision Risk to Migratory Waterbirds

 

  1. The number of birds expected to be subject to collision mortality on migration is small, being zero or one bird annually for most species, and a maximum of three for pink-footed goose and eider, and well below a 0.02 percentage point increase in mortality rate. These numbers are the total number of collisions expected for the entire UK population. Therefore, the number of birds which are considered to be individuals associated with individual SPAs is expected to be negligible for all species, and not at a level that could be considered to have any potential of contributing materially to an AEOI for any of the species listed or the sites for which they are features.

                        Conclusion

  1. It is concluded, beyond reasonable scientific doubt, that no adverse effects on the qualifying interest features which could undermine the conservation objectives of the SPAs listed in Table 5.46   Open ▸ , will occur as a result of collision risk impacts during the operation and maintenance phase for the Array. An assessment of the impact of collision risk against each relevant conservation objective is presented in Table 5.46   Open ▸ . Where the justifications and supporting evidence are the same for more than one conservation objective, the assessments have been grouped.

Table 5.46:
Conclusions Against the Conservation Objectives of SPAs and their Qualifying Features from Collision during Operation and Maintenance

Table 5.46: Conclusions Against the Conservation Objectives of SPAs and their Qualifying Features from Collision during Operation and Maintenance

  1. As detailed in Table 5.46   Open ▸ ,  it can be concluded, beyond reasonable scientific doubt, that there is no risk of an adverse effect on the integrity of any of the SPAs listed in Table 5.46   Open ▸ or their qualifying features due to collision risk resulting from the operation and maintenance of the Array alone. There is no risk of undermining the Conservation Objectives of the sites considered due to the following:
  • given the Array and associated ZoI falls outside the SPA boundary, there is no potential for the Array to impact on the distribution and extent of supporting habitats and process within the SPA;
  • given the Array and associated ZoI falls outside the SPA boundary, there is no potential for the Array to influence the distribution of birds within the SPA;
  • given the Array and associated ZoI falls outside the SPA boundary, there is no potential for the Array to influence the structure, function and supporting processes of habitats supporting the species;
  • given the level of impact arising from collision from the Array area, there is no potential for the Array to influence the population of the species as a viable component of the site; and
  • given the level of impact arising from collision from the Array area, there is no potential for the Array to influence the disturbance of the species within the SPA.

5.4.5. Displacement and Collision Combined

  1. Certain seabird species may be impacted by both displacement and barrier effects (distributional responses) and collision risk and therefore an assessment of the impact of both pressures acting together is required. It is recognised that assessing these two potential impacts together could amount to double counting, as birds that are subject to distributional response could not be subject to potential collision risk as they are already assumed to have not entered the Array. Equally, birds estimated to be subject to collision risk mortality would not be subjected to mortality associated with displacement and barrier effects (distributional responses) as well. The results presented in this section are therefore considered highly precautionary, especially for species with high displacement and barrier effects (distributional response) rates (i.e. gannet). Specifically related to gannet, a recent Natural England report (Natural England, 2023) had the aim of delivering an evidence-based method to ensure macro-avoidance behaviour is appropriately accounted for in collision risk models of gannet at offshore wind farms. Macro-avoidance is defined as ‘the fraction of birds in flight that are unlikely to enter the wind turbine array following construction, where there is a risk of collision with rotating blades’. The report recommended a correction to be applied in project level CRM to account for this. The CRM undertaken for the Array has not applied macro avoidance following the current published NatureScot guidance (NatureScot, 2023g) (it is noted that updates to this guidance note is imminent. Updates to the note may recommend factoring in macro-avoidance. However as updates to the note are not yet known, collision risk modelling has been undertaken as set out in their current guidance) and therefore the results are viewed as precautionary (and likely to include some ‘double counting’).
  2. Of the seabird species considered in this RIAA, the species that have been identified as requiring assessment for both displacement and collision effects are kittiwake and gannet. As a potential LSE2 for collision risk was only identified in the Operation and Maintenance phase, only the Operation and Maintenance phase is considered within this combined assessment. The apportioned annual mortality rates for distributional responses and collision are extracted from the relevant supporting information within sections 5.4.1 and 5.4.4, respectively.
                        Kittiwake
  1. For kittiwake, the Applicant’s preferred displacement and mortality rates equal the lower end of the range suggested by NatureScot (2023h), i.e. 30% displacement and 1% mortality. Of the range of collision modelling parameters considered, the upper end is equal to the parameters advised by NatureScot (2023g). Therefore, for this combined assessment a “low” ( Table 5.47   Open ▸ ), “medium” ( Table 5.48   Open ▸ ) and “high” ( Table 5.49   Open ▸ ) value has been presented. The “low” value combines the lowest values for both displacement and collision; the “medium” consists of the Applicant’s preferred displacement and mortality rates and the NatureScot’s approach to CRM; the “high” approach is the upper end of NatureScot’s advised displacement and mortality rates and NatureScot’s preferred CRM parameters.

 

Table 5.47:
Kittiwake Combined Impact from Distributional Responses and Collision Risk (Low Approach)

Table 5.47: Kittiwake Combined Impact from Distributional Responses and Collision Risk (Low Approach)

 

Table 5.48:
Kittiwake Combined Impact from Distributional Responses and Collision Risk (Medium Approach)

Table 5.48: Kittiwake Combined Impact from Distributional Responses and Collision Risk (Medium Approach)

 

Table 5.49:
Kittiwake Combined Impact from Distributional Responses and Collision Risk (High Approach)

Table 5.49: Kittiwake Combined Impact from Distributional Responses and Collision Risk (High Approach)

 

  1. These results indicate that at the “high” approach, PVA is required to further assess the impacts on the kittiwake feature of Buchan Ness to Collieston Coast SPA, Farne Islands SPA, Forth Islands SPA, Fowlsheugh SPA and St Abb's Head to Fast Castle SPA. PVA is also required for Fowlsheugh SPA under the “medium” approach. Under all other approaches, the increase in mortality rate is below 0.02 percentage points and therefore there is no potential for an AEOI.
  2. The PVA results are summarised in Table 5.50   Open ▸ , with further details presented in appendix 3B.

 

Table 5.50:
Kittiwake PVA Results for Combined Displacement and Collision Impacts from the Array Alone

Table 5.50: Kittiwake PVA Results for Combined Displacement and Collision Impacts from the Array Alone

 

  1. The PVA results for all sites show that the population growth rate is less than 0.1% lower than the counterfactual, leading to a population size that, after 35 years, is 1.2% smaller than the counterfactual population size at Buchan Ness to Collieston Coast SPA, 0.9% smaller than the counterfactual population size at Farne Islands SPA, 0.9% smaller than the counterfactual population size at Forth Islands SPA, a maximum of 1.5% smaller than the counterfactual population size at Fowlsheugh SPA and 1.1% smaller than the counterfactual population size at St Abb’s Head to Fast Castle SPA. Overall, therefore, it is clear that the PVA results indicate that the impact levels modelled are indistinguishable from natural variation and would not adversely affect the kittiwake feature of Buchan Ness to Collieston Coast SPA, Farne Islands SPA, Forth Islands SPA, Fowlsheugh SPA or St Abb's Head to Fast Castle SPA. It should be further noted that this is the most precautionary approach to assessment – under the Applicant’s preferred approach or the lower end of the range of mortality rates recommended by NatureScot, the impact did not reach the threshold for running PVA.
  2. Therefore, it can be concluded, beyond reasonable scientific doubt, that there is no risk of an AEOI to the kittiwake feature of any SPA as a result of combined displacement and collision from the Array alone.
                        Gannet
  1. For gannet, the Applicant’s preferred displacement and mortality rates equal the lower end of the range suggested by NatureScot (2023h), i.e. 70% displacement and 1% mortality. Therefore, for this combined assessment a “low”, “medium” and “high” value has been presented. The “low” value combines the lowest values for both displacement and collision; the “medium” consists of the Applicant’s preferred displacement and mortality rates and the NatureScot’s approach to CRM; the “high” approach is the upper end of NatureScot’s advised displacement and mortality rates and the upper end of the range of CRM results. The combined impact of displacement and collision for gannet is presented in Table 5.51   Open ▸ to Table 5.53   Open ▸ .

 

Table 5.51:
Gannet Combined Impact from Distributional Responses and Collision Risk (Low approach)

Table 5.51: Gannet Combined Impact from Distributional Responses and Collision Risk (Low approach)

 

Table 5.52:
Gannet Combined Impact from Distributional Responses and Collision Risk (Medium Approach)

Table 5.52: Gannet Combined Impact from Distributional Responses and Collision Risk (Medium Approach)

 

Table 5.53:
Gannet Combined Impact from Distributional Responses and Collision Risk (High Approach)

Table 5.53: Gannet Combined Impact from Distributional Responses and Collision Risk (High Approach)

 

  1. These results indicate that at the “high” approach, PVA is required to further assess the impacts on the gannet feature of the Forth Islands SPA.
  2. The PVA results are summarised in Table 5.54   Open ▸ , with further details presented in appendix 3B.

 

Table 5.54:
Gannet PVA Results for Combined Displacement and Collision Impacts from the Array Alone

Table 5.54: Gannet PVA Results for Combined Displacement and Collision Impacts from the Array Alone

 

  1. The PVA for the Forth Islands SPA results show that, under the “high” approach, the population growth rate is less than 0.1% lower than the counterfactual, leading to a population size that, after 35 years, is 1.6% smaller than the counterfactual population size. Overall, therefore, it is clear that the PVA results indicate that the impact levels modelled are negligible and would not adversely affect the gannet feature of the Forth Islands SPA. It should be further noted that this is the most precautionary approach to assessment – under the Applicant’s preferred approach or the lower end of the range of mortality rates recommended by NatureScot, the impact did not reach the threshold for running PVA.
  2. Therefore, it can be concluded, beyond reasonable scientific doubt, that there is no risk of an AEOI to the gannet feature of any SPA as a result of displacement from the Array alone.

                        Conclusion

  1. It is concluded, beyond reasonable scientific doubt, that no adverse effects on the qualifying interest features which could undermine the conservation objectives of the SPAs listed in Table 5.55   Open ▸ , will occur as a result of combined collision and displacement impacts during the operation and maintenance phase for the Array. An assessment of the impact of combined collision and displacement against each relevant conservation objective is presented in Table 5.55   Open ▸ . Where the justifications and supporting evidence are the same for more than one conservation objective, the assessments have been grouped.

Table 5.55:
Conclusions Against the Conservation Objectives of the Qualifying Features from Distributional Responses and Collision during Operation and Maintenance

Table 5.55:  Conclusions Against the Conservation Objectives of the Qualifying Features from Distributional Responses and Collision during Operation and Maintenance

 

  1. As detailed in Table 5.55   Open ▸ , it can be concluded, beyond reasonable scientific doubt, that there is no risk of an adverse effect on the integrity of any of the SPAs listed in Table 5.55   Open ▸ or their qualifying features due to combined collision and disturbance and displacement resulting from the operation and maintenance of the Array alone. There is no risk of undermining the Conservation Objectives of the sites considered due to the following:
  • given the Array and associated ZoI falls outside the SPA boundary, there is no potential for the Array to impact on the distribution and extent of supporting habitats and process within the SPA;
  • given the Array and associated ZoI falls outside the SPA boundary, there is no potential for the Array to influence the distribution of birds within the SPA;
  • given the Array and associated ZoI falls outside the SPA boundary, there is no potential for the Array to influence the structure, function and supporting processes of habitats supporting the species;
  • given the level of impact arising from combined collision and disturbance and displacement from the Array area, there is no potential for the Array to influence the population of the species as a viable component of the site; and
  • given the level of impact arising from combined collision and disturbance and displacement from the Array area, there is no potential for the Array to influence the disturbance of the species within the SPA.

5.4.6. Barrier to Movement

  1. As previously stated within section 5.4.1, the current guidance from NatureScot (2023h) recommends treating both displacement and barrier effects together as “distributional responses” and, for breeding seabirds, recommends assessing these distributional responses together. For breeding seabirds, the approach to “disturbance and displacement” assessment covers both disturbance and barrier effects, whilst the assessment of “barrier to movement” only considers the barrier effect to migratory birds. Therefore, only migratory waterbirds are discussed and assessed separately within this section.
  2. The LSE2 assessment during the HRA screening process identified that during operation and maintenance phases, LSE2 could not be ruled out for barrier to movement. This relates to the following site(s) and relevant marine ornithological features:
  • Cameron Reservoir SPA and Ramsar site

-        pink-footed goose (non-breeding).

  • Din Moss – Hoselaw Loch SPA and Ramsar site

-        pink-footed goose (non-breeding); and

-        greylag goose (non-breeding).

  • Fala Flow SPA and Ramsar site

-        pink-footed goose (non-breeding).

  • Firth of Forth SPA and Ramsar site

-        bar-tailed godwit (non-breeding);

-        golden plover (non-breeding);

-        knot (non-breeding);

-        pink-footed goose (non-breeding);

-        red-throated diver (non-breeding);

-        redshank (non-breeding);

-        ringed plover (non-breeding);

-        sandwich tern (non-breeding);

-        1lavonian grebe (non-breeding)

-        turnstone (non-breeding); and

-        non-breeding waterbird assemblage (due to potential impact on above species (except Sandwich tern) and common scoter, cormorant, curlew, dunlin, eider, goldeneye, great crested grebe, grey plover, lapwing, long-tailed duck, mallard, oystercatcher, red-breasted merganser, ringed plover, scaup, shelduck, velvet scoter and wigeon).

  • Firth of Tay and Eden Estuary SPA and Ramsar site

-        bar-tailed godwit (non-breeding);

-        non-breeding greylag goose;

-        non-breeding pink-footed goose;

-        non-breeding redshank; and

-        non-breeding waterbird assemblage (due to potential impact on above species and common scoter, cormorant, dunlin, eider, goldeneye, goosander, grey plover, Icelandic black-tailed godwit, oystercatcher, long-tailed duck, red-breasted merganser, sanderling, shelduck and velvet scoter).

  • Gladhouse Reservoir SPA and Ramsar site

-        pink-footed goose (non-breeding).

  • Greenlaw Moor SPA and Ramsar site

-        pink-footed goose (non-breeding).

  • Holburn Lake and Moss SPA and Ramsar site

-        greylag goose (non-breeding).

  • Lindisfarne SPA and Ramsar site

-        bar-tailed godwit (non-breeding);

-        common scoter (non-breeding);

-        dunlin (non-breeding);

-        eider (non-breeding);

-        golden plover (non-breeding);

-        grey plover(non-breeding);

-        greylag goose (non-breeding);

-        light-bellied brent goose (non-breeding);

-        long-tailed duck (non-breeding);

-        red-breasted merganser (non-breeding);

-        redshank (non-breeding);

-        ringed plover (non-breeding);

-        sanderling (non-breeding);

-        shelduck (non-breeding);

-        whooper swan (non-breeding);

-        wigeon (non-breeding); and

-        waterbird assemblage (non-breeding).

  • Loch of Kinnordy SPA and Ramsar site

-        pink-footed goose (non-breeding); and

-        greylag goose (non-breeding).

  • Loch Leven SPA and Ramsar site

-        pink-footed goose (non-breeding);

-        shoveler (non-breeding);

-        whooper swan (non-breeding); and

-        non-breeding waterbird assemblage (due to potential impact on above species and cormorant, gadwall, goldeneye, pochard, teal and tufted duck).

  • Montrose Basin SPA and Ramsar site

-        greylag goose (non-breeding);

-        pink-footed goose (non-breeding);

-        redshank (non-breeding); and

-        non-breeding waterbird assemblage (due to potential impact on above species and oystercatcher, eider, wigeon, knot, dunlin and shelduck).

  • Northumbria Coast SPA and Ramsar site

-        purple sandpiper (non-breeding); and

-        turnstone (non-breeding).

  • Slamannan Platea SPA

-        taiga bean goose (non-breeding).

  • South Tayside Goose Roosts SPA and Ramsar site

-        pink-footed goose (non-breeding);

-        greylag goose (non-breeding);

-        wigeon (non-breeding); and

-        non-breeding waterbird assemblage (due to potential impact on above species).

  • Westwater SPA and Ramsar site

-        pink-footed goose (non-breeding); and

-        non-breeding waterbird assemblage (due to potential impact on above species).

  • Ythan Estuary, Sands of Forvie and Meikle Loch SPA / Ythan Estuary and Meikle Loch Ramsar site

-        pink-footed goose (non-breeding); and

-        non-breeding waterbird assemblage (due to potential impact on above species and eider, lapwing and redshank).

 

  1. The MDS considered within the assessment of barrier to movement is shown in Table 5.56   Open ▸ .

 

Table 5.56:
MDS Considered for the Assessment of Potential Impacts to Marine Ornithological Features due to Barrier to Movement during the Operation and Maintenance Phase

Table 5.56: MDS Considered for the Assessment of Potential Impacts to Marine Ornithological Features due to Barrier to Movement during the Operation and Maintenance Phase

 

                        Operation and maintenance phase

  1. JNCC et al. (2022) defines barrier effects as “A barrier is a physical factor that limits the migration, or free movement of individuals or populations, thus requiring them to divert from their intended path in order to reach their original destination. This effect is expected to increase the energy expenditure of birds if they have to fly around the area in question in order to reach their goal”. It is typically considered to affect birds in flight only, either whilst they are on migration between breeding and wintering areas (for example) or between a breeding colony and a foraging area. The latter of these scenarios may impose an additional energetic cost to movements at a key period in the annual cycle when seabirds are making daily commutes between foraging grounds at sea and breeding sites. Additional energetic costs could have long term implications for individuals, impacting bird fitness (breeding productivity and survival) and for populations. Barrier effects are considered to be less impactful when affecting migratory flights as avoidance of a single wind farm may be trivial relative to the total length and cost of the journey (Masden et al., 2010; 2012).
  2. For breeding seabirds, NatureScot (2023h) consider barrier effects alongside displacement as “distributional responses”. This is because it can be difficult to distinguish barrier effects from the effects of displacement, for breeding seabirds foraging in the region. NatureScot (2023h) advise that distributional responses are assessed using the matrix approach, and therefore for breeding seabirds, no separate assessment of barrier to movement is carried out, with impacts considered to be included in the assessments carried out under the impact Disturbance and Displacement.
  3. This section therefore only considers the impact of the barrier to movement on migratory receptors. In the absence of quantitative information available for individual species, the magnitude is considered qualitatively for all receptors.
  4. The diversion of flight lines as a result of a barrier effect created by the presence of the Array for migratory birds is considered less of an impact than for those barrier effects to daily foraging flights. Speakman et al. (2009) and Masden et al. (2010; 2012) calculated that the costs of one-off avoidances during migration were small, accounting for less than 2% of available fat reserves.
  5. A bird reaching the Array and following the perimeter around to resume the same flight path on the other side would fly a maximum of approximately 80 km to resume the flight path, compared to the approximately 20 km straight line across the middle of the array area, i.e. a 60 km increase in flight path. The shortest flight path from the east coast of Scotland to the west coast of Scandinavia that would pass through the Array is approximately 565 km. Therefore, the maximum impact would be an increase in migration route of 10.6%. In reality, this level of impact is unrealistic, as most birds will deviate by less, either by altering their flight path in a more efficient manner or by increasing their altitude to fly above the wind farm without any change in direction. It should also be noted that the shortest potential flightlines between the UK and Scandinavia would not pass through the Array at all, with the shortest mainland route being from south-west Norway to the north-east Aberdeenshire coast, or else “island hopping” through Shetland, Fair Isle and Orkney.
  6. This impact would have a negligible impact on the survival of any bird, and therefore there is no potential for an AEOI to any site.