Offshore wind developments - collision and displacement in petrels and shearwaters: literature review

1 Executive summary

• Scottish Government published the Sectoral Marine Plan for Offshore Wind in 2020, setting out sustainable plan options for the continued development of commercial-scale offshore wind energy in Scotland, as a key contribution to achieving the target of net-zero greenhouse gas emissions by 2045. In January 2022, Crown Estate Scotland announced the lease option agreements for 17 new projects within 14 Plan Option Areas, principally on the eastern and northern coasts.
• Scotland's seas and coastlines are home to a rich diversity of marine life, including internationally important colonies of seabirds, many protected under Scottish, UK and international designations. The need to ensure that future offshore developments do not adversely impact on protected sites and species is embedded within the Scottish Government's National Marine Plan, and potential impacts to marine life and other users of the sea are required to be assessed as part of planning, consenting and licencing processes.
• Several frameworks, methods and tools have been developed in recent years to facilitate the assessment of the likely impacts of offshore wind farm developments on seabirds, and these require data inputs on a variety of parameters relating to species morphology, ecology, behaviour and distribution.
• This key information has not been collated for a group of seabird species for which Scotland holds some of the largest colonies in UK, Europe and globally; namely the Manx Shearwater Puffinus puffinus, Leach's Storm-petrel Hydrobates leucorhous, and the European Storm-petrel Hydrobates pelagicus. These species are active nocturnally, and there is evidence to suggest they are sensitive to light attraction ("phototaxis"), which could render them especially vulnerable to negative impacts from offshore windfarms, for example, if attracted to the rotor-swept area by lights on the turbines that are required for navigation purposes. We also consider, in less detail, two further species from the same taxonomic group, namely Northern Fulmar Fulmarus glacialis and Sooty Shearwater Ardenna grisea.
• Low fecundity rates and a relatively protracted time to reach maturity (3–6 years) for these species, means seemingly small impacts on survival rates can have large impacts on population viability, making them particularly vulnerable to lethal impacts of wind farm development.
• We reviewed the published peer-reviewed and grey literature for information on the 24 key parameters/data groups required to assess the vulnerability of these species to potential impacts of offshore wind farms and associated structures and activities.
• We compiled a library of more than 1000 scientific papers, reports and other publications, from which we extracted all relevant information to assist in the implementation of methods and tools to quantify the likely population-level impacts of sites leased in the Sectoral Marine Plan Option areas. We highlight critical data gaps that currently prevent a reliable assessment of population-level impacts on protected colonies of these three species.
• Good quality data from within Scotland exist for ten of the key parameters/data groups for all three main species (Manx Shearwater and the two storm-petrel species), and for just three parameters for the other two species. Data collected from elsewhere, or from closely related species, are available for 21 key parameters for all three main species. Less information is available for Leach's Storm-petrel in Scotland than for the Manx Shearwater or European Storm-petrel.
• The evidence needs that were highlighted as being most important for the three focal species were to improve understanding of: (i) biases in detectability of birds at sea; (ii) flight height and speed (and their variation); (iii) avoidance behaviour; (iv) light attraction and (v) foraging ranges from breeding colonies.
• There is a need for experimental validation of potential biases in aerial survey methods, including detectability, identification and diel variation. Detectability could be tested by carrying out targeted digital aerial surveys or vessel-based surveys with an experimental approach, using either tagged model "decoys" or tagged free-roaming birds, though achieving adequate sample sizes of the latter may be challenging.
• Estimates of flight parameters such as speed and height can be gained from tracking data, but acquiring accurate estimates is difficult, even with high resolution data. Where possible, "instantaneous" flight speeds from GPS tags, based on Doppler-shift information derived from the movement of the tag relative to the movement of the satellites, will be more accurate than that derived from distance covered between successive fixes. Constraints on device size/weight suitable for use on storm-petrels limit the range of tracking devices that can be deployed on these species.
• Assessment of macro-avoidance of windfarm development can be achieved by comparing marine distributions of seabird pre- and post-construction. In light of the limited tracking of the three focal species in Scotland to date, we recommend further tracking studies from key colonies to better understand the pre-construction movements and distribution of these species. Such tracking studies should continue as construction occurs and after it is completed, to inform understanding of avoidance behaviour. Such work will also increase understanding of drivers of marine distribution and foraging ranges.
• Crucially, we found that there is currently a lack of evidence on which to judge the existence and strength of light attraction in these species. It is clear from the evidence base that all three focal species may become disorientated by powerful light. This typically occurs in foggy conditions and particularly affects recently fledged young, who may still have under-developed visual capabilities. Under such circumstances, birds may circle a light source for many hours, until succumbing to dehydration or exhaustion. In the context of assessment of the likelihood of collision with turbine blades, the probability of collision is vastly increased, since a bird may pass through the rotor swept area many times. Attraction to or disorientation by light can also be considered a form of displacement, for example if birds are drawn away from foraging areas or behaviours.
• A further compounding factor is the extent to which birds are drawn from a distance to the lights on turbine towers, or whether such attraction is very local (i.e. "micro-scale attraction"). Whilst there are many documented cases in the literature of seabirds dazzled by lighthouses, ships' lights, gas flares from oil platforms, etc., the distances from which birds may be attracted are unknown. This is a critical distinction. If birds are attracted to bright light sources from considerable distance (i.e. hundreds of metres to kilometres) the potential for adverse impacts from collision is greatly increased, as the number of birds attracted scales as the square of the range from which they are drawn. Taken together, the effect of disorientation, causing birds to circle for many hours and increasing the number of passes through the rotor-swept area, and the potential for birds to be attracted from an area covering tens of square km, would render current methodologies of assessing impacts unreliable.
• We recommend urgent studies to quantify the distance over which flight paths of these species may be influenced by bright light sources, to examine the age class of individuals most likely to be affected, and to assess whether the wavelength and pattern of illumination (flashing vs constant) may affect the level of attraction or disorientation. Such studies will require the novel application of tracking technology (e.g. use of thermal video imaging, radar, VHF and/or GPS tags). The most appropriate approach for each species will depend on device size/weight constraints and logistic constraints of particular breeding locations. We make recommendations as to how such studies may be conducted, suggest suitable locations, and highlight potential challenges.
• We detail several options for mitigation of potential impacts, such as altering the wavelength or pattern of illumination of navigation lights on turbines and associated structures. We discuss the current technical and legislative constraints to such modifications.