Developing Guidance on Ornithological Cumulative Impact Assessment for Offshore Wind Farm Developers


Title: Developing Guidance on Ornithological Cumulative Impact Assessment for Offshore Wind Farm Developers
Publication Date:
June 01, 2009
Document Number: CIBIRD
Pages: 128

Document Access

Website: External Link
Attachment: Access File
(1 MB)


King, S.; Maclean, I.; Norman, T.; Prior, A. (2009). Developing Guidance on Ornithological Cumulative Impact Assessment for Offshore Wind Farm Developers. Report by British Trust for Ornithology (BTO) and TÜV SÜD. pp 128.
  • This project has developed guidelines on the processes, methods and techniques to be utilised for cumulative impact assessment for birds and offshore wind farms. The guidelines build on recommendations made at an earlier COWRIE workshop held in 2007
  • The need for guidance arises from the limited advice currently available and the increasing number of operational offshore wind farms, together with those under construction, consented or in planning which means that the issue of cumulative impact is becoming more prominent. Offshore wind farm development is likely to become the largest single engineering intervention in the UK’s marine environment over the next decade
  • A review of current practice illustrates the wide range of approaches used by developers in which assessment has often been qualitative rather than quantitative leading to uncertain conclusions and often major delays in project determination. Key issues have included: inadequate scoping, lack of understanding of the species involved, difficulties in assigning the range of projects which should be included within the assessment and the methods by which CIA should be undertaken
  • The current guidelines were developed by review and discussion of two specially commissioned position papers at an expert workshop held in Peterborough in October 2008
  • The process of scoping was agreed to be essential to the provision of robust CIA and requires regular communication and iterative information exchange between developers, statutory bodies and stakeholders. The detailed guidance points which have been developed focus on the completion of ‘key features’ documents. These are checklists of key facts that will be used to inform cumulative impact assessment i.e. species, conservation designations, projects and proposed surveys and analyses, and include a record of communications. It is hoped that these documents or similar can be endorsed by SNCAs in order to standardise the scoping phase of CIA. It was also agreed that there was a need for increased guidance and more certainty in policy coming from regulators and their statutory advisors
  • The recommendations relating to the tools and techniques used for CIA are divided into two parts: data gathering and cumulative effects. Data gathering and analysis currently suffer from a lack of standardisation therefore guidelines are given for selection of species for consideration, projects to be included in the assessment and the spatial scale of the bird reference population to be used. An overarching recommendation is for the provision of quantitative data on raw numbers, densities and population estimates for all species and that, wherever possible, impacts are assessed in a quantitative rather than a qualitative way
  • The cumulative effects of collision risk and displacement should be assessed by summing the impacts from each component project
  • Where collision mortality is likely to be significant, more detailed population modelling studies may be required
  • Disturbance and barrier-effects may accrue in a non-linear manner. They should, therefore, firstly be considered in a qualitative manner and, if thought likely to be significant, then a more detailed quantitative study of bird bioenergetics in relation to the effect should be carried-out
  • In general, all analyses should interpret the significance of mortality in relation to the species’ background mortality rate to enable its life history parameters and ecology to be taken into account
  • The guidelines summarised below are the first stage of an iterative process. They will need to be refined on the basis of evidence gathered from the monitoring of wind farms both during and post-construction and as our understanding of the impacts of cumulative effects on birds improves. Their adoption will require engagement from all parties involved in the process of impact assessment
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