High‐resolution multi‐sensor technology reveals low collision risk to seabirds in offshore wind farms

Abstract Monitoring of flying seabirds at offshore wind farms (OWFs) has a short history and, unsurprisingly, most studies have focused on the potential for collisions. However, strong evidence of collision mortality in seabirds or other groups of birds has been lacking due to the absence of empirical data on meso‐ and micro‐avoidance behaviour inside OWFs. We studied the meso‐ and micro‐avoidance behaviour of seabirds in the 11‐turbine Aberdeen OWF in the North Sea over two breeding seasons using an advanced automated multi‐sensor detection system with integrated high‐resolution radar and powerful digital cameras which constituted a further development of integrated radar‐camera systems. The flight behaviour of northern gannet Morus bassanus , herring gull Larus argentatus , lesser black‐backed gull Larus fuscus, great black‐backed gull Larus marinus and black‐legged kittiwake Rissa tridactyla was assessed at different distances from the rotor blades with a spatial resolution of 6.5 m and a temporal resolution of 2.5 s. Avoidance behaviour was investigated in relation to local wind and turbulence conditions using random forest models. The large sample of tracking data indicates that within wind farm avoidance response of the studied species of seabirds towards turbines takes place within 100–150 m distance from rotors and that the response intensifies as the seabirds approach the rotor blades. Consequently, seabirds seem to be exposed to very low risks of collision in OWFs due to high levels of meso‐ and micro‐avoidance. This finding was also supported by the fact that no collisions or even narrow escapes were recorded in the 9998 seabird videos examined during daylight hours and good visibility conditions. Despite evidence of the low risk of collision by the studied species of seabirds, the flight models revealed that the mean avoidance response pattern may break down in situations of strong turbine‐induced turbulence and high wind speeds. Synthesis and applications . These results clearly highlight the need to revise collision risk assessments in environmental impact assessments by applying high meso‐avoidance rates and very high micro‐avoidance rates for the target species of seabirds.