Influence of wind on kittiwake Rissa tridactyla flight and offshore wind turbine collision risk

Offshore windfarms are a potential threat to seabirds, partly due to collision risk with turbine blades. Wind influences the mode, height and speed of seabird flight, and therefore the risk of collision with turbines. We investigated how wind influences the flight of black-legged kittiwakes Rissa tridactyla, a gull of conservation concern, in order to incorporate these findings into collision risk estimates and identify mitigation measures. We used GPS telemetry data (23rd June to 10th August 2021) from 20 kittiwakes breeding in Aberdeenshire, UK (57.385°N, 1.868°W) to estimate the effect of wind on behavioural state, proportion of flight at collision risk height, probability of collision when within the rotor-swept zone, and overall collision risk. We found that as windspeed increased, kittiwakes commuted less and rested more. With increasing windspeed, kittiwakes spent a considerably smaller proportion of their flight time in the rotor-swept zone, but had a slightly higher probability of collision while in it. Uncertainty was high for most relationships between windspeed and kittiwake flight metrics. The overall effect of increasing windspeed on collision risk was negative, although we did not model avoidance rate. Effects of windspeed on collision risk were largely mediated through effects on commuting flight, and contingent on wind direction. Collision risk estimates incorporating the effects of windspeed may have greater precision and accuracy, but considerable uncertainty in windspeed-flight parameter relationships remains. Therefore although kittiwake collision risk may be mitigated by raising the ‘cut-in’ windspeed above which wind turbines generate power, the magnitude of this effect is uncertain.