Behavioural responses of Sandwich terns following the construction of offshore wind farms

Author(s): Thaxter, C.B., Green, R.M.W., Collier, M.P., Taylor, R.C., Middelveld, R.P., Scragg, E.S., Wright, L.J., Cook, A.S.C.P. & Fijn, R.C.

Published: January 2024

Journal: Marine Biology

Digital Identifier No. (DOI): 10.1007/s00227-023-04353-7

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GPS tracking sheds light on the ‘barrier effects’ of offshore wind farms, where renewable energy developments may act as obstacles that impede the movements of seabirds to and from their colonies during the breeding season, or on migration.

Between 2016 and 2019, BTO scientists fitted Sandwich Terns breeding at Scolt Head Island in Norfolk with long-life GPS tags which tracked the birds’ movements over multiple years. When the research began, there were five operational offshore wind farms within the distance that Sandwich Terns are known to fly on foraging trips. Two more offshore wind farms were under construction, and became operational during the course of the study.

The results revealed that Sandwich Terns entered offshore wind farms, but the extent to which they used these areas varied over time and between sites. For the two wind farms that were completed during the study, there was a marked reduction in the amount of time birds spent at these sites between the first and second year of operation. Although birds sometimes entered offshore wind farms while foraging, they appeared to avoid them when commuting between foraging areas and their colony. This created an apparent ‘funnelling’ effect between important feeding locations. The changes found could be driven by changes to the birds’ sandeel prey distribution, avoidance of wind farms, or changes in airflow patterns following wind farm construction.

The study shows that the responses of seabirds to offshore wind farms are many and complex. Further research is needed to fully understand the nature of these interactions, at a time when ever more wind farms are being constructed to mitigate the impacts of climate change.

Abstract

Offshore wind farms (OWFs) are a key part of efforts to mitigate the impacts of climate change. However, they have the potential to negatively impact seabird species through collisions with turbine blades, displacement from preferred foraging habitat and the perception of wind farms as a barrier to migrating or foraging birds. Whilst the data available to model these impacts are increasing, many data gaps remain, particularly in relation to the impacts of barrier effects. We analyse the movements of Sandwich terns in relation to an offshore wind farm cluster using data collected as part of a multi-year GPS tracking study. Over the course of the study, two additional wind farms were built within the home range of the breeding colony. The construction of these wind farms coincided with a change in the foraging and commuting areas used by breeding terns. Whilst birds entered OWFs when foraging, they appeared to avoid them when commuting, driving an apparent ‘funnelling’ effect to important feeding locations. We discuss if this could be driven by changes to the prey base, subsequent displacement and potentially altered routes reflecting new favourable air flow patterns following OWF construction. Our results suggest that behavioural responses of birds to OWFs may be the result of a complex series of ecological and environmental interactions, as opposed to simplistic assumptions around the perception of the OWF as a barrier to movement.