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Marine Ecology Progress Series

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MEPS 723:185-200 (2023)  -  DOI:

Thermal soaring over the North Sea and implications for wind farm interactions

Jens van Erp1,*,#, Elspeth Sage1,#, Willem Bouten1, Emiel van Loon1, Kees C. J. Camphuysen2, Judy Shamoun-Baranes1

1Department of Theoretical and Computational Ecology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, 1090 GE Amsterdam, The Netherlands
2Royal Netherlands Institute for Sea Research (NIOZ) Texel, 1790 AB Den Burg (Texel), The Netherlands
*Corresponding author:
#These authors contributed equally to this work

ABSTRACT: Seabirds use several flight modes at sea, including thermal soaring, in which thermal uplift is used to gain altitude and save energy. An increase in flight altitude may have consequences for wind farm interactions if it results in birds spending more time within the rotor-swept zone (RSZ). To understand conditions under which thermal soaring occurs and potential implications for wind farm interactions, we investigated thermal soaring in relation to atmospheric conditions in June and July at 2 study areas in the North Sea, west and north of the Dutch coast. We developed algorithms that identified thermal soaring in GPS tracks of lesser black-backed gulls Larus fuscus and radar tracks of seabirds. By combining species-specific 3-dimensional information on flight behaviour from bio-logging with the continuous spatiotemporal coverage of radar positioned at wind parks, we obtained a more comprehensive overview of thermal soaring at sea than either method would obtain alone. Our results showed that birds flew at higher altitudes during thermal soaring than non-soaring flight, increasing the proportion of flight time within the RSZ. Thermal soaring occurred inside offshore wind farms to a similar degree as outside. Thermal soaring was positively correlated with positive temperature differences (ΔT) between sea surface and air (at 2 m above sea level), and north and north-westerly winds. We show that the probability of thermal soaring over the North Sea, inside and outside wind farms, increases with larger temperature differences, resulting in increased time spent within the RSZ and an increased collision risk for seabirds.

KEY WORDS: Offshore wind farm · Thermal convection · Bird radar · GPS telemetry · Seabirds · Gulls · Human-wildlife interactions

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Cite this article as: van Erp J, Sage E, Bouten W, van Loon E, Camphuysen KCJ, Shamoun-Baranes J (2023) Thermal soaring over the North Sea and implications for wind farm interactions. Mar Ecol Prog Ser 723:185-200.

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