Ecological impact of wind farms

Wind farms are a good bet for contributing to the UK's future energy demands but more needs to be done to evaluate their ecological impact, say Mark Gash and Jan Collins.

The UK has committed to deliver 15 per cent of its total energy demand from renewable sources by 2020. But because renewables account for just 1.5 per cent of that at the moment, growth in this sector needs to be rapid.

As tidal and wave power technologies are still being developed, they are unlikely to contribute significantly to total energy demand by 2020.

And although offshore wind capacity is huge, feasibility studies have only just started for the Round 3 areas, so onshore wind may well be our best renewable energy bet at the moment. But what are the likely ecological impacts?

Indeed, although a lot of research has been undertaken on the ecology of wind farms there is still much to learn: impacts on terrestrial habitats, vertebrates and invertebrates are relatively easy to predict owing to the limited land take; but things start to get difficult when dealing with birds and bats which are found in great numbers in upland and coastal areas - where the wind resource is greatest, and thus where the wind farms are located.

In the UK most of the research on the impacts of wind farms on birds has been completed in Scotland. Natural England, through the publication of a Technical Information Note (TIN069), is suggesting similar levels of survey effort and assessment methodology.

Minimum levels of survey effort are recommended for sites outside of designated areas such as Special Protected Areas (SPA), Special Areas of Conservation (SAC), Ramsar etc.

For example, each vantage point should be subject to a minimum of 36 hours' observation with the results of these surveys being used to inform the collision risk assessment. A greater level of survey effort may be needed for designated sites and this is also suggested for England.

But many wind farms in England are proposed for sites outside of designated areas and as such, it is probably questionable whether this level of survey is needed for such projects.

A Midlands breeding bird assemblage, for example, is far removed from Scottish upland moorland, while some sites of proposed wind farms may not even be suitable for important passage and/or winter bird assemblages.

Therefore each project in England should be considered on a case-by-case basis and closer working relationships between clients, consultants and consultees need to be established in England to allow this process, already well-established in Scotland, to develop.

Research

But pleasingly there have been projects in England where negotiation with consultees, specifically Natural England, has led to adaptation of survey guidelines. This included a reduction in seasonal survey effort based on a site's potential to support winter passage and breeding birds.

This approach was agreed on the understanding that if the site's actual bird assemblage was of greater interest then survey effort would be discussed with Natural England. The result was beneficial to the client while ensuring robust data collection.

TIN069 also suggests the need for further research into the effects of wind farms on birds in England through the establishment of control studies.

Post-construction monitoring is also standard for most projects, although few include before-after/control-impact (BACI) studies which are difficult to achieve, mainly because of the lack of available control sites and the trickier issue of whose responsibility it is to complete them.

Developers completing studies on their project sites are concerned with ensuring that data collected and assessment is sufficiently robust to gain planning permission. Post-construction studies aim to prove that the assessment for a particular project was correct and the real impacts are not greater than predicted.

BACI studies are designed to highlight greater understanding and insight into the effects on a wider scale but the issue remains: who organises and ultimately pays for these studies?

Other areas of further research include shadow flicker and possible disturbance effects, and more data is needed to inform the collision risk assessment model, specifically avoidance rates. Achieving this will be difficult but necessary to keep up with the required level of expansion in wind farm projects.

Bats

Another issue under debate is the impact of wind turbines on bat populations in the UK. Some pre-, during and post-construction impacts (such as harm to bats in roosts, destruction of roosts in structures or trees, disturbance at roost sites and loss of foraging or commuting habitat) may be similar to other landscape-scale developments.

However, operational wind turbines also have the potential to kill bats through collision or barotraumas (damage to the lungs caused by rapid excessive pressure changes around a wind turbine).

Research in the US and Europe has revealed that large numbers of bats are killed at some wind farms. Deaths are mostly associated with migrating species, although resident species may also be affected. Noctules and Common and Nathusius' Pipistrelles are the most frequently recorded casualties in Europe.

But the extent to which bats migrate in the UK is simply not known and we are severely lacking in research around the whole subject of wind turbines and bats. To mitigate this, the goalposts are likely to change with respect to surveys at proposed wind farm sites.

Interim guidance from Natural England published in February 2009 is not very specific about survey effort but it does identify which UK bat populations are likely to be at risk. It also offers recommendations to avoid impacts by siting turbines so that all parts are over 50 metres away from features that may be used by bats.

Indeed, a recent planning appeal was dismissed because extra transect and static surveys carried out for the purpose of the inquiry revealed the presence of more bat species than had been identified originally (including Barbastelle and Leisler's).

The original surveys had included six whole-night transect surveys spread between April and October. The inspector concluded that the favourable conservation status of Barbastelle might not have been maintainable locally or regionally, even though Natural England guidance states that this species is only under medium threat and does not appear on casualty lists from European wind farm sites.

In addition, the 50 metre buffer zone advised by Natural England was not considered sufficient and further measures were recommended, such as turning off turbines at certain times of the night. This appeal decision could perhaps act as a lesson regarding survey effort and proposed mitigation measures.

Various academic research projects are now underway and many ecological consultants are working with the wind farm industry in an attempt to find some answers. In other words, watch this space! More research into the impacts of wind farms in England is obviously needed as is the coordination of post-construction monitoring.