Collision, Displacement and Barrier Effect Concept Note


Title: Collision, Displacement and Barrier Effect Concept Note
Publication Date:
January 01, 2015
Document Number: BTO Research Report No. 669
Pages: 37
Publisher: British Trust for Ornithology

Document Access

Website: External Link


Humphreys, E.; Cook, S.; Burton, N. (2015). Collision, Displacement and Barrier Effect Concept Note. Report by British Trust for Ornithology (BTO). pp 37.

1. Offshore wind farms (OWFs) may potentially affect birds in a number of ways, most notably through: i) collisions with turbines; ii) displacement of birds due to effective loss of habitat; and iii) barrier effects where the wind farm creates an obstacle to regular movements to and from breeding colonies or migration. These effects have usually been considered separately in Environmental Impact Assessments (EIAs). There is a need to consider whether the multiple impacts from these different effects in combination may be significant.


2. This summary concept note outlines the issues associated with and options for integrating the impacts associated with collision, displacement and barrier effects associated with OWFs in a statistically and ecologically appropriate way. The extent to which barrier effects have been differentiated from displacement effects is questionable, however, as both are manifested as a reduction in the number of birds in flight within the wind farm.


3. An initial overview is provided of key reviews which have assessed the sensitivities or vulnerabilities of species to the likely effects of OWFs. This information has then been used to derive a list of key species where two or more effects could operate together and therefore where multiple impacts need to be considered in combination. Displacement, barrier and collision effects have often not been considered in combination because the species considered at greatest risk from collision have generally been considered to be of low risk from displacement and vice versa. Based on the methodology outlined above, none of the species considered here required the effects of wind farms to be combined. Caution is urged, however, with using this approach as the basis for making the decision as to whether effects should be combined or not and a watching brief needs to be maintained on the evidence base.


4. A further review briefly summarises how collision, displacement and barrier effects have been assessed and treated by different OWF project applications for these species in the UK.


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