Guidance Note 8: Guidance to support Offshore Wind Applications: Marine Ornithology Advice for assessing the distributional responses, displacement and barrier effects of Marine birds

Published: 2023
Version 1: January 2023

This document is part of a series of guidance notes available on Advice on marine renewables development - marine ornithology.

This guidance note sets out our advice on assessing distributional responses (i.e. displacement and barrier effects). Please see Guidance Note 1: Guidance to support Offshore Wind Applications: Marine Ornithology - Overview  which provides the context within which this guidance note is provided. We expect each and every developer to adhere to this guidance, including the recommended parameters to provide consistent and comparable results for all Scottish projects to be assessed as an individual project and cumulatively.  This guidance note should be used in conjunction with the Cumulative Effects Framework (CEF).

Please note this guidance was written prior to the development of a NatureScot position on how to account for the ongoing Highly Pathogenic Avian Influenza (HPAI) mortality event within an impact assessment. We are currently developing this advice and will provide updates and guidance as they become available. In the interim please contact [email protected] should you have any specific queries.

1. Introduction 

Seabird species show varying avoidance behaviours in response to anthropogenic activities and structures. For some species these can lead to changes in their distributions around offshore developments such as offshore wind farms. The two key distributional responses we assess in relation to offshore wind farms are displacement and barrier effects. There are two approaches to assessing the displacement and barrier effects of offshore wind farms on marine bird populations that are currently used in Scotland.  In addition to the Statutory Nature Conservation Bodies (SNCB’s) joint guidance note on displacement and barrier effects (SNCB 2017 and 2022 update), this guidance note sets out NatureScot’s recommendations for good practice in the impact assessments for Scottish casework. The SNCB guidance note was updated in 2022 to include an annex with interim advice on treatment of displacement for red-throated diver. Both guidance notes and the annex should be used while undertaking the displacement and barrier effects assessment. 

We acknowledge that there is ongoing research on this topic and that this note will therefore be subject to updates. Check the log of updates on Guidance Note 1: Guidance to support Offshore Wind Applications: Marine Ornithology - Overview to ensure the current version is being followed. Associated works closer to land may need to be considered for the inshore qualifying features such as the diver, grebe and seaduck species many of which demonstrate high or very high behavioural sensitivity to anthropogenic disturbance (see e.g. Jarrett et al. 2018; Goodship and Furness 2019) – see Guidance Note 4: Guidance to Support Offshore Wind Applications: Ornithology - Determining Connectivity of Marine Birds with Marine Special Protection Areas and Breeding Seabirds from Colony SPAs in the Non-Breeding Season on impact pathways for further details on assessing this. 

2. Barrier effects and displacement 

Marine bird distributional responses to the construction, operation including maintenance and repair activities and decommissioning of offshore development (including offshore wind farms) vary between species. Several species groups are likely to show an avoidance reaction to operational offshore development. However, for all development types during operation, construction and decommissioning related activities of towing, pile driving or operation of maintenance/service vessels in the vicinity may cause disturbance (Fox & Petersen 2006, Krijgsveld et al. 2011, Vanermen et al. 2014).  

We acknowledge that it can be difficult to disentangle barrier effects and displacement. However, with tracking data it may be possible to explore proportions of bird that forage either within a development footprint or commute beyond the development footprint. Should developers wish to explore using or collecting tagging data for this purpose, we advise discussing with NatureScot as early as possible.

These responses (see definitions in the Joint SNCB Interim Advice On The Treatment Of Displacement For Red-Throated Diver (2022) equate to indirect habitat loss for marine bird species. The ecological consequences of partial or complete exclusion of birds from the footprints of development area (and possibly vessel routes) and any zone of influence around them require careful consideration within the EIA and HRA process. 

3. Species to be assessed 

The priority species for assessment of displacement effects will typically be diver and sea duck species, guillemot, razorbill, puffin and gannet. Section 5 in the joint SNCB guidance note sets out a general guide for considering whether a displacement or barrier effects assessment is required.  

For species where both collision risk and displacement are considered, e.g. gannet and kittiwake, we advise that these impacts should be considered as additive. However, we are aware of ongoing work to explore this and this note will be updated once this work has been reviewed and published. 

4. Approaches for assessment 

Displacement and barrier effects should be assessed using the Joint SNCB Interim Advice On The Treatment Of Displacement For Red-Throated Diver (2022) matrix methods and the SeabORD tool (Searle et al. 2018) as appropriate to species and season.  The SeabORD user guide sets out how to run the tool and we advise this should be followed to undertake the assessment. 

4.1 When to use SeabORD vs the matrix approach? 

1. SeabORD can currently be used for: 

• Atlantic Puffin 
• Common Guillemot 
• Razorbill 
• Black-Legged Kittiwake 

2. SeabORD can currently be applied in the chick rearing period only presently. Other periods of the year require the use of the matrix approach. 
3. SeabORD can be run both with and without site-specific tracking data. The two key parts of this are the forage site selection and prey availability. 

• The forage site selection method uses either distance decay (where tracking data are not available) or the tool can be used to create a map where these data are available. 
• The prey distribution can either be a uniform distribution or when the “map” option is selected data can be uploaded (as described in the user guide) to create a heterogeneous distribution. 

For species where seabORD may be used in the breeding season, the matrix approach will still be required during the non-breeding season.

The colonies which require seabORD assessment should be agreed as part of scoping with NatureScot. Further input options for seabORD may become available through the Cumulative Effects Framework (CEF) project due to be published by Marine Scotland this year and this guidance note will be updated accordingly.

4.2  Matrix Approach 

The Joint SNCB Interim Advice On The Treatment Of Displacement For Red-Throated Diver (2022) details how this approach should be undertaken.  We advise this should be followed to complete the displacement assessment, noting in particular the following key advice: 

4.2.1 Input data 

Data should be provided in a format that allows the calculation of mean seasonal peak population estimates based on the minimum two years of baseline data. For example, for a species with a breeding season from April to July, this requires the average of the peak population estimates between April and July in year one and two. This may require the counts to originate from different months in the two years (e.g. May in the first year and June in the second year). In practice, this requires comparable monthly abundance estimates for each year of survey. This allows for year-to-year variation in the precise time (and magnitude) of peak abundance estimates to be taken into account in arriving at a mean peak population estimate. To allow recalculation of values, good practice requires presentation of monthly values in summary and full data from all surveys in an appendix to any report. 

4.2.2 Zone of Influence 

For all species requiring assessment, the wider zone of influence, which include impacts outside of the development footprint, should be considered.  For most species the zone of influence will extend to 2km beyond the development footprint, however, there are some exceptions to this for more sensitive species (red-throated divers being 10km, and for other divers and seaducks 4km). For specific advice on red-throated diver see the Joint SNCB Advice On The Treatment Of Displacement For Red-Throated Diver (2022).  

4.2.3 Displacement and mortality rates

For displacement assessments using the matrix approach we advise that a range of displacement rates are presented in the tables, however, guide values to be used within the assessment are outlined in table 1. We will be reviewing ongoing post consent monitoring data and research, so these displacement rates may be updated when new evidence is available.

We advise the adoption of a range of mortality figures, including consideration of potential seasonal differences. As outlined in the Joint SNCB Interim Advice On The Treatment Of Displacement For Red-Throated Diver (2022) distributional responses, such as displacement and barrier effects, could increase the extent to which marine birds suffer fitness consequences, such as reduced survival and /or productivity, through increases in energy expenditure and /or reduced energy intake. There is an ongoing ORJIP project to quantify associated mortality rates (QUMR), however this has not yet reported. Modelled data from SeabORD suggests that mortality due to displacement may be higher than 1%. Our current advice is therefore to use higher displacement mortality rates for the matrix method in order to ensure that outputs more closely match the SeabORD outputs.

The values that should be used for auks (guillemots, razorbills and puffins), gannet and kittiwake are shown in Table 1 below: 

Should a quantitative displacement and mortality assessment be required for a previously unassessed species we want to see the rationale for the proposed displacement and mortality rates before agreeing values to be used, noting in particular that the displacement rates suggested here may be insufficiently precautionary for other species.

4.3 Presentation of Displacement and Barrier Effect Outputs 

4.3.1 Presentation of CRM – Breeding season 

Our seasonal definitions guidance note should be used for determining which months to include for each species’ breeding season. A summary of the predicted displacement and barrier effects results should be presented in the main Ornithology chapter of the EIA Report and HRA. 

We expect the full outputs (as per the seabORD tool) to be presented within a technical ornithology appendix in the EIA report/HRA. The input parameters and SeabORD tool options, including the calibration, should be clearly stated. We advise that the matrix tables should be presented as per the SNCB guidance, with a range of mortality rates presented within each species table. 

Where tables are used, column titles should be standardised as far as possible to allow comparisons to be made where this is appropriate.  

4.3.2 Presentation of CRM – non breeding season  

The matrices should be presented for the non-breeding season for all species vulnerable to displacement and/or barrier impacts. The non-breeding season should be defined using our seasonal definitions guidance note.  

The non-breeding season assessment should be presented, as per the breeding season guidance (above) – however, as described in our apportioning guidance note the predicted mortality impacts should be considered in the context of the regional populations as defined by the Biologically Defined Minimum Population Scale (BDMPS) (Furness, 2015). 

5. Future updates to this guidance note 

This guidance note will be reviewed and updated as new evidence becomes available, i.e. following publication of relevant research projects, including but not limited to: 

• Post Consent Monitoring of Scottish and UK operational windfarms 
• The Cumulative Effects Framework  
• Offshore Renewable Joint Industry Programme (ORJIP) for Offshore Wind projects: 
• Improving Quantification of mortality rates associated with displacement within the assessment process (QUMR) 
• Effects of displacement from Offshore Renewable Developments in the non-breeding season (DisNBS). 
• Other relevant research such as through ScotMer etc.

Contact: [email protected]

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