Avoidance of offshore wind farms by Sandwich Terns in the North Sea increases with turbine density

Sandwich Tern, by Philip Croft / BTO

Author(s): van Bemmelen, R.A., Leemans, J.J., Collier, M.P., Green, R.M.W., Middelveld, R.P., Thaxter, C.B. & Fijn, R.C.

Published: October 2023  

Journal: Ornithological Applications

Digital Identifier No. (DOI): 10.1093/ornithapp/duad055

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Offshore wind energy is considered an essential part of humanity’s transition away from fossil fuels, but it is important to understand the consequences that wind farms can have for wildlife. In this study, GPS data revealed how breeding Sandwich Terns avoid offshore wind farms in the North Sea.

The study, led by Waardenburg Ecology in the Netherlands, used data from GPS tracking of breeding Sandwich Terns carried out at Scolt Head, Norfolk, and De Putten in the Netherlands between 2016 and 2021. Scolt Head had four operational offshore wind farms nearby (within the distance that Sandwich Terns are known to fly when searching for food), and De Putten had three.

The authors examined the terns’ so-called ‘macro-avoidance rate’, which is the rate at which birds avoid entering an offshore wind farm altogether. This avoidance amounts to habitat loss, since the birds will no longer use this area of the sea, and perhaps incur additional energetic costs by flying around wind farms or having to forage in less optimal alternative areas.

The results showed that Sandwich Terns reduced their use of the Dutch offshore wind farms areas by 41%, and British offshore wind farms by 54%. Birds were more likely to avoid wind farms the closer together the turbines were.

This study’s findings could inform not only the positioning of future offshore wind farm developments, but also their design, as taller, more widely spaced turbines could be preferable to shorter, most densely packed ones in terms of minimising any detrimental effects on Sandwich Terns and related species.


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 2 breeding colonies in western Europe: Scolt Head (United Kingdom) and De Putten (the Netherlands). The foraging ranges of birds from each colony overlapped with multiple OWFs. 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 min, in which Sandwich Terns traveled ~2 km on average. Besides the effects of OWFs and the direct surroundings of OWFs, iSSFs considered distance from the colony and habitat characteristics (water depth and sediment grain size) as well as movement characteristics. Macro-avoidance rates, where 1 means complete avoidance, were estimated at 0.54 (95% CI: 0.35, 0.7) for birds originating from Scolt Head and 0.41 (95% CI: 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.


Tracking Sandwich Terns at De Putten was funded by Rijkswaterstaat WVL as part of the Wozep programme. Tracking Sandwich Terns at Scolt Head was funded by Equinor as part of the strategic monitoring programme for Dudgeon.
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