Seabird flight height data collection at an offshore wind farm: final report

1. Introduction

The Scottish Government have a responsibility to manage the marine environment, including to conserve protected seabird species and designated sites within Scottish territorial waters. To achieve this, risk should be identified, potential impacts investigated, and where necessary appropriate conservation and mitigation actions taken to protect seabird species. The Scottish Government, through The Crown Estate Scotland, released details in February 2022 of multiple potential development areas as part of their 2022 ScotWind leasing round (Scottish Government, 2020). For each of these sites there are likely environmental implications to be considered and investigated as part of individual comprehensive Environmental Impact Assessments (EIAs) and Habitats Regulations Appraisals (HRA ;Scarff, et al. 2013).

In order to address the potential impacts and effects that offshore wind farms (OWFs) may have on seabird species within the marine environment, collision risk should be assessed (Masden, et al. 2016). In most cases this is achieved through collision risk modelling (CRM). At present, there are a number of tools which are commonly used to model collision risk, these require bird flight heights as an input parameter (Band, 2012, Johnston et al. 2014; McGregor, et al. 2018). Previously, site specific seabird flight heights have been estimated from individual surveyors performing boat-based surveys or size-based calculations from aerial digital survey imagery (Johnston et al. 2014; McGovern et al. 2019). These methods can have limitations such as low sample size, boat-based observations having bias, lack of validation and quantification of error and size-based methods relying on published information that leads to large confidence limits (Johnston, et al. 2014). Where uncertainly remains within the assessment process, for instance as a result of the input parameters, then this may lead to further uncertainty in the CRM results (Johnston, et al. 2014).

To address this uncertainty, flight heights from multiple sources are combined, negating the issues around sample size and reducing random error in results. However, data are lacking in some areas including the northern North Sea (Johnston, et al. 2014). Furthermore, these flight heights are not site-specific and do not allow the influence of wind turbines to be investigated once a site is constructed.

An alternate solution is to use Light Detection and Ranging (LiDAR) technology to measure seabird flight heights (Cook, et al. 2018). LiDAR uses laser light pulses to measure where objects are in space and when combined with aerial digital still imagery can provide highly accurate site-specific and species-specific bird flight heights. As a new application of this technology, LiDAR's effectiveness is in need of testing and review in order to understand how best it may be utilised in the future to fulfil its potential for use in the marine environment, particularly for reducing uncertainties in seabird flight heights and for OWFs EIAs / HRAs (Cook, et al. 2018).

In order to undertake a review of the capabilities of LiDAR for determining seabird flight heights in the marine environment Marine Scotland commissioned APEM Ltd (APEM) to undertake a series of surveys using APEM's bespoke combined high-resolution aerial digital stills and LiDAR system.

1.1.1 Survey Aims

1. Collect measurements of seabird flight heights for individual species to allow production of flight height distributions for use in CRM.

2. Investigate whether LiDAR was suitable for collecting robust species-specific avian flight height data from an operational wind farm.

3. Identify and discuss any methodological issues or challenges which may come from collecting data across these sites.

4. Examine whether seabird flights heights differ between an area with WTGs and a control area without WTGs.