Abstract
1. Protected seabirds present a serious constraint to offshore renewable energy expansion due to potential effects of displacement from habitat, barrier effects to movements, and collisions with turbine blades. The process of delivering compensatory measures to offset offshore wind (OW) impacts on seabirds is underway as deployments increase in scale and pace, driving cumulative impacts to become more severe. A range of ornithological compensatory measures have been proposed to offset impacts. However, wide uncertainty remains around the appropriateness of measures for different species, and in the magnitude of potential demographic and population benefits. Available empirical data for quantifying demographic consequences for compensatory measures is often limited to a single population, or lacking completely for some species. 2. To address this evidence gap we undertook an expert elicitation to estimate potential effectiveness of different compensatory measures for a suite of seabird species representing a significant proportion of UK North Sea breeding populations. 3. Experts identified 14 compensatory measures with potential for positively affecting seabird population demography in seven species or groups in the UK context: black-legged kittiwake, common guillemot, Atlantic puffin, razorbill, northern gannet, large gulls (herring gull, lesser black-backed, great black-backed) and terns (arctic, common, sandwich). 4. Experts ranked the 14 measures for each species, extracted a set of highly ranked measures, and elicited potential changes to breeding success and adult survival. We captured experts’ uncertainty in potential demographic consequences via eliciting a distribution for each demographic parameter through the quantification of statistical parameters. 5. Despite recognising considerable uncertainty in their estimates, the experts identified a suite of measures with potential to improve seabird breeding success and adult survival. However, experts also raised important challenges with successful implementation of compensatory measures for seabirds, including both practical, ecological and ethical considerations. Solution: We provide species-specific summaries of expert-elicited demographic gains of alternative compensatory measures for seabirds. Our elicitation provides a defensible and transparent base that can be used and updated to inform comparative assessments of different measures. We provide recommendations for the development of statutory guidance for successful selection and implementation of measures for seabirds, highlighting specific challenges and knowledge gaps.