Assessing impacts to pink-footed and greylag geese from small-scale wind farms in Scotland

Background & Purpose

The purpose of this guidance is to set out a common approach to assessing the effects of small-scale wind farms on migratory greylag and pink-footed geese in Scotland, where they are connected with Special Protection Areas (SPAs) for these species (i.e. within 20km). 

Potential effects include:

• collision mortality;
• displacement from preferred feeding areas; and
• in extreme cases, possible barrier-type effects.

This guidance should be used to assess proposals that:

• meet NatureScot’s definition of small-scale wind energy; this is groups of three or fewer wind turbines with an output greater than 50kW 

  and

• will install turbines with a maximum blade-tip height of 150m.

The guidance should be used in conjunction with other published NatureScot guidance:

• Bird Survey Guidance for Onshore Wind Farms
• Assessing the cumulative impact of onshore wind farm developments
• Guidance on assessing connectivity with Special Protection Areas (SPAs)
• Assessing the impact of small-scale wind energy proposals on the natural heritage
• Guidance on using an updated collision risk model to assess bird collision risk at onshore wind farms

This document replaces the previous February 2014 version with minor text revision.

Collision mortality

Both wintering greylag and pink-footed geese are normally listed as 'target species' during vantage point (VP) surveys which are carried out to quantify bird activity around wind farm proposals in eastern and southern Scotland. Our migratory wintering populations often result in large numbers of these birds being recorded in flight around proposed wind farm sites, raising concerns about the potential for high levels of collision mortality. However, a range of evidence from Europe and America suggests that the frequency of goose collisions at wind farms is low (review in Rees 2012), and NatureScot recommend an avoidance rate of 99.8% for all goose species (see Use of Avoidance Rates in the NatureScot Wind Farm Collision Risk Model). 

Analyses of VP surveys found a reduction in goose flight activity with increasing distance from roosts (Patterson 2013; 2015). This work also confirmed that there can be considerable between-year variability in levels of flight activity at the same site. Importantly, there can also be large differences in the frequency of flights in neighbouring sites within the same year. This document presents a simple and streamlined method, commissioned from Ian Patterson, of assessing the number of goose collisions per year. The method uses these previous studies as a basis to estimate the number of collisions expected on average over the 25-year life of a small-scale wind energy development (Appendix 1), without the need for bespoke VP surveys. Table 1 sets out several critical assumptions associated with this method.

The following information is used:

• The distribution of feeding areas for greylag and pink-footed geese in Scotland;
• Knowledge of the flight behaviour of these species near roosts and feeding areas;
• The relationship between flight density and roost distance, as derived from multiple data sets, to predict the average number of goose encounters with turbines per year. 

The only data required to calculate the encounter rate are:

• the distance from the proposed wind farm to the nearest SPA designated for greylag or pink-footed geese;
• the rotor radius of the proposed turbines; and
• the number of proposed turbines.

Small scale wind farm sites may therefore be placed into one of three categories regarding collision risk to geese:

• High risk: sites less than 1.5km from SPA boundaries. These sites are likely to be associated with particularly high densities of birds at collision risk height. A programme of dedicated VP watches will normally be required to estimate collision mortality.
• Moderate risk: sites more than 1.5km from SPA boundaries, but within 1.5km of feeding areas as defined by Mitchell (2012). The numbers of geese in flight are likely to be variable but may be substantial in some years. Most birds will be at collision risk height. A generic collision risk calculation should be carried out in line with Appendix 1 and its accompanying spreadsheet.
• Low risk: sites more than 1.5km from SPA roosts and away from regularly used foraging areas. Almost all geese will be above collision risk height, and goose collisions at these sites are expected to be very rare.

Displacement

Displacement occurs when birds avoid areas around wind farms, thereby losing access to foraging sites. Pink-footed geese are known to partially habituate to the presence of a wind farm over c.10 years but can continue to be displaced for longer; in the worst cases, this can include the entire turbine envelope plus a zone of 100m around it (Madsen & Boertmann 2008). This is an important consideration because habitat quality during the non-breeding season can affect the body condition of geese and their departure dates in spring, both of which can, in turn, affect breeding success (Ebbinge & Spaans 1995; Madsen 1995).

The total extent of foraging areas available to grey geese at SPAs in Scotland is only understood at a few sites. However, it is generally considered that 20km is the normal maximum foraging geese fly to and from roosts (Michell 2012), so typically the total potential foraging area is very large. This suggests that the loss of foraging area around an individual small-scale wind farm is likely to be extremely small, in comparison with the extent of the entire resource (Appendix 2).

A wind farm may be proposed for land where the habitat is completely unsuitable for foraging grey geese, and displacement effects may be confidently ruled out. Conversely, there are rare circumstances under which displacement may require more detailed consideration, for example:

• in known foraging areas near SPAs at which the total foraging resource is geographically localised or where geese are particularly constrained by disturbance or other factors; and/or
• in the case of applications where the land was previously managed to be attractive to geese, for example though a goose management scheme.

Barrier effects

Direct observations and radar studies at large marine wind farms indicate that geese in flight prefer to avoid the entire turbine envelope, either by gaining height to pass over the turbines or by altering course to fly around them (Plonczkier & Simms 2012). There is less evidence onshore, although a recent study in Denmark showed vertical and horizontal avoidance behaviour in large-bodied birds (including geese) to large turbines (Therkildsen et al. 2021). Therefore, the potential exists for badly-sited proposals to cause barrier effects, by increasing the energetic costs of geese forced to alter their preferred flight paths.

Within 1.5km of an SPA boundary, where birds are more likely to be flying at collision risk height, it is important to establish whether preferred flight lines are likely to be affected. Information on this may be available from local observations of goose feeding areas and flights. If such information is unavailable it will normally be necessary to commission dedicated VP work to inform the issue. However, any such decisions on fieldwork should be made on a case-by-case basis, using any existing information on flight lines, feeding areas and proximity to main roosting areas within an SPA. The size and layout of the proposed turbines should also be considered; for example, a line of three turbines perpendicular to a flight line is a more serious potential barrier than three turbines arranged parallel to the preferred direction of flight.

Summary of recommendations

A Habitat Regulations Appraisal (HRA) is required where a plan or project could affect an SPA. Table 2 considers those circumstances under which a small-scale wind farm proposal is considered to have a likely significant effect on an SPA designated for greylag or pink-footed geese.

References and Appendices