Investigating avoidance and attraction responses in Lesser Black-backed Gulls Larus fuscus to offshore wind farms
Author(s): Johnston, D.T., Thaxter, C.B., Boersch-Supan, P.H., Humphreys, L., Bouten, W., Clewley, G.D., Scragg, E.S., Masden, E.A., Barber, L.J., Conway, G., Clark, N.A., Burton, N.H.K & Cook, A.S.C.P.
Published: March 2022
Journal: Marine Ecology Progress Series Volume: 686
Digital Identifier No. (DOI): 10.3354/meps13964
GPS tracking is a valuable tool for increasing our understanding of bird behaviour. In this study, researchers used tracking technology to investigate movements of Amber-listed Lesser Black-backed Gulls around offshore wind farms. Their results reveal a detailed picture of both avoidance of and attraction towards turbines in this species, which may be used to inform future collision risk assessments.
Movements through or use of offshore wind farms by seabirds while commuting or foraging may increase the potential for collision with turbine blades. Collision Risk Models (CRMs) provide a method for estimating potential impacts of wind farms on seabird populations, but are sensitive to input parameters, including avoidance rates. Refining understanding of avoidance through the use of high-resolution empirical movement data has the potential to inform assessments of the collision impacts of offshore wind farms on seabird populations. In this study we assessed the movements of Global Positioning System (GPS) tagged lesser black-backed gulls Larus fuscus from a breeding colony in northwest England to estimate the species’ Avoidance Rate (AR) and Avoidance/Attraction Index (AAI) to nearby offshore wind farms. To investigate both macro-(0-4 km) and meso-scale (0-200 m) responses to wind turbines we used calculations of AR and AAI based on simulated vs. observed tracks. We found that birds exhibited an AR of -0.15 (95% CI [-0.44, 0.06]), indicating a degree of attraction within 4 km of the wind farms. However, AAI values varied with distance from the wind farm boundaries, with a degree of avoidance displayed between 3-4 km, which weakened as distance bands approach wind farm boundaries. Meso-scale avoidance/attraction was assessed with regard to the nearest individual turbine, and flight height relative to the rotor height range (RHR) of the nearest turbine. We found attraction to increase below the RHR at distances <70 m, while avoidance increased within the RHR at distances approaching the turbine. We explore how high-resolution tracking data can be used to improve our knowledge of avoidance and attraction behaviour in lesser black-backed gulls to established wind farms, and so inform assessments of collision impacts.
The UK government’s pledge to reach net-zero by 2050 includes investments in offshore wind farms around the UK’s coast. Wind turbines can affect seabirds in several ways, from presenting barriers to their commuting or migratory flight paths and altering habitat to collisions with rotor blades. However, they can also attract foraging seabirds by creating reef-like structures for marine fauna, and pylons can provide attractive roosting sites.
The risk of seabird mortality around wind turbines can be calculated using Collision Risk Models, which inform environmental impact assessments for proposed developments. To provide robust outputs, models rely on accurate data relating to birds’ movements, but the impact of attraction to the foraging or roosting opportunities associated with wind farms on bird behaviour is poorly understood.
To increase our understanding, researchers tracked 25 tagged Lesser Black-backed Gulls from a breeding colony in northwest England from 2014 to 2019. They collected data on the gulls’ avoidance and attraction behaviours in response to nearby offshore wind farms on both large and small scales. By comparing the observed flight paths of the gulls with simulated paths, the scientists determined that the behaviour they observed was not only a consequence of chance. Significant avoidance behaviour occurred 3 to 4 km outside the wind farm, which weakened nearer the area. The majority of birds did not alter flight routes to avoid wind farms but avoided the turbines when flying within them, remaining outside the rotor area or altering their flight height to avoid the blades. This suggests that the energetic costs of safely navigating rotor blades may be outweighed by the foraging and roosting benefits of entering the wind farm.
The results indicate that avoidance behaviours vary across spatial scales, so the boundary of the area selected for investigation when considering the potential effects of an offshore development may influence the overall avoidance rate calculated. The study also notes that its results are indicative of Lesser Black-backed Gulls from only one colony, and only during the breeding season; interactions with wind farms are likely to vary temporally and between colonies and species too. It is vital that Collision Risk Models take this variation into account.
While there is more research needed to develop Collision Risk Models which accurately reflect bird behaviour in the marine environment, the results of this study are a step toward this. Increasing the accuracy of estimates for avoidance and attraction behaviours will increase the confidence we can have in the outputs of Collision Risk Models and the impact assessments they inform.
NotesThis project was supported by the Natural Environment Research Council, Ørsted and Natural England, and also drew from a previous tracking study funded by the Department for Business, Energy and Industrial Strategy Offshore Energy Strategic Environmental Assessment research programme, and the Marine Renewable Energy and the Environment project (funded by Highlands and Islands Enterprise, the European Regional Development Fund, and the Scottish Funding Council). Thanks to the Cumbria Wildlife Trust and Natural England for permissions and to all helping with fieldwork and discussion. Comments from anonymous reviewers improved this manuscript.
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