Avoidance of offshore wind farms by Sandwich Terns increases with turbine density

The expanding use of wind farms as a source of renewable energy can impact
bird populations due to collisions and other factors. Globally, seabirds
are one of the avian taxonomic groups most threatened by anthropogenic
disturbance; adequately assessing the potential impact of offshore wind
farms (OWFs) is important for developing strategies to avoid or minimize
harm to their populations. We estimated avoidance rates of OWFs — the
degree to which birds show reduced utilization of OWF areas — by Sandwich
Terns Thalasseus sandvicensis at two breeding colonies in western Europe:
Scolt Head (United Kingdom) and De Putten (the Netherlands). We modeled
GPS tracking data using integrated Step Selection Functions (iSSFs) to
estimate the relative selection of habitats at the scale of time between
successive GPS relocations – in our case 10 minutes, in which terns
traveled ca. 2 km on average. The foraging ranges of birds from each
colony overlapped with multiple OWFs. iSSFs considered distance from the
colony and habitat characteristics (water depth and sediment grain size)
and movement characteristics. Macro-avoidance rates, where 1 means
complete avoidance, were estimated at 0.54 (95% CrI = 0.35, 0.7) for birds
originating from Scolt Head and 0.41 (95% CrI = 0.21, 0.56) for those from
De Putten. Estimates for individual OWFs also indicated avoidance but were
associated with considerable uncertainty. Our results were inconclusive
with regard to the behavioral response to the areas directly surrounding
OWFs (within 1.5 km); estimates suggested indifference and avoidance and
were associated with large uncertainty. Avoidance rate of OWFs
significantly increased with turbine density, suggesting OWF design may
help to reduce the impact of OWFs on Sandwich Terns. The partial avoidance
of OWFs by Sandwich Terns implies that the species will experience risks
of collision and habitat loss due to OWFs constructed within their
foraging ranges.