Offshore wind developments assessment - seabird collision risk, displacement and barrier effects: study

1 Executive summary

Collision and displacement/barrier impacts for seabirds interacting with offshore wind farms (OWFs) are currently assessed using separate modelling methods. This means collision mortality is estimated separately from displacement and barrier effects, and the effect sizes are subsequently combined. However, there is concern with this approach because the parameters used in both assessments are not equivalent, making integration subject to error. Secondly, there is concern about double counting of mortalities: an individual seabird is potentially vulnerable to displacement and collision, yet it cannot be vulnerable to both simultaneously.

Accordingly, the objective of this project was to develop a framework within which collision, displacement and barrier effects can be aggregated into a single overall assessment of combined impacts in a way that is internally consistent, scientifically defensible, and practically useful.

Collision impacts with wind turbines are assessed using collision risk models (CRM). These are relatively simple mechanical models that combine estimates of the number of flights through a wind farm with an estimate of the likelihood that a bird of a specified size and speed will collide with a rotating turbine of a specified size and speed (Band 2012; further developed in Masden 2015, McGregor et al. 2018).

Displacement impacts during the breeding season are currently assessed using two general methods; individual-based simulation models, and simple deterministic 'matrix' approaches involving expert elicitation of likely displacement and mortality rates combined with estimates for the density of birds within footprints. Individual-based models predict the time/energy budgets of individual animals and translate these into projections of demographic rates, such as adult annual survival and productivity (e.g. Searle et al. 2014, Warwick-Evans et al. 2017, Searle et al. 2018). Matrix approaches (JNCC, 2017) use a more simplistic method, multiplying the observed number of individuals within a proposed wind farm site by the percentage expected to be displaced and the percentage of those displaced then expected to suffer mortality as a consequence.

The first stage of this project involved a workshop that brought together experts from research, government and conservation bodies to discuss how best to implement combined modelling of displacement and collision risks from OWFs for breeding seabirds. Current methods for estimating collision and displacement risks separately in assessments were discussed, with a following session on the extent to which the inputs, parameters and assumptions used in the different methods are consistent with each other. Finally, there was a session on how to combine collision and displacement risks into a single assessment of risk from both displacement and collision.

Building upon outcomes from the expert workshop, we developed a methodological framework for simultaneously quantifying the impacts of displacement and collision by adapting an individual-based mechanistic model of seabird movement, behaviour, demographics and OWF interactions (SeabORD) to be able to simultaneously estimate mortalities related to collision, barrier and displacement effects. We implemented an initial version of this framework that used output from the stochastic CRM (sCRM) (McGregor et al. 2018) as an input to a modified version of SeabORD – we do this by translating the current population-level sCRM calculations into corresponding calculations at the individual level, and then embedding these within SeabORD.

We demonstrate the integration of sCRM output with the individual based simulation model, SeabORD, by running the models using data for black-legged kittiwakes (Rissa tridactyla) at Forth Islands SPA.

We conclude with recommendations for future research to advance the integration of collision and displacement/barrier assessments. Primarily, we recommend research aimed at developing a more powerful and flexible approach by merging the functionality of individual-based models such as SeabORD, and the sCRM into a single model and software product. We also recommend research to develop a year-round individual-based simulation model to extend current methodologies beyond the chick-rearing period; efforts to obtain empirical data for validation of key mechanisms with both displacement/barrier and collision risk models. Finally, we recommend research to improve quantification of uncertainty within the modelling approaches, to better inform the level of appropriate precaution in assessments.