SNH Guidance on Bats and Onshore Wind Turbines: implications for survey and monitoring?

SNH Guidance on Bats and Onshore Wind Turbines: implications for survey and monitoring?

On 8 January 2019 Scottish Natural Heritage (SNH) published “Bats and Onshore Wind Turbines: Survey, Assessment and Mitigation.” This is now the industry standard, and formally replaces Natural England’s TIN 051 and Chapter 10 of the Bat Conservation Trust (BCT) Guidance (Hundt, 2012). It is endorsed by all the statutory nature conservation stakeholders and by BCT.

This article provides an initial review of the changes in survey and monitoring the guidance brings, and comments on the implications of these for developers.

Baseline Survey

Static Acoustic Detectors

The SNH guidance puts more emphasis on the use of desk study and the seasonal deployment of static acoustic detectors to characterise sites than previous guidance documents. Many wind farm sites are located in relatively homogenous habitat, such as moorland, open pasture and coniferous plantation in upland areas of the UK. Habitat quality and weather on these sites often results in bat activity being relatively low and/or inconsistent in nature. It is therefore sensible to put greater emphasis on results from data loggers than on snapshots obtained through transects. Desk study, which includes study of aerial photographs and maps to determine landscape features, as well as the collation of existing biological data, is critical to understanding likely bat flight lines, and understanding whether data collection using static detectors should be complemented by other work.

The guidance provides a clear steer on the number of acoustic detectors that should be deployed, and emphasises the need to locate them at known or likely turbine locations. There is no mention of pairing detectors with habitat features (hedgerows or stream corridors), which assumedly reflects a lack of empirical data from across Europe to suggest that species that closely follow such features (such as horseshoe bats and Myotis species) change their behaviour in response to wind farm construction and are subsequently killed by turbines.

Notwithstanding this, in circumstances where features of potential importance to roosting or commuting bats occur close to wind turbines, or may be affected by associated infrastructure (such as access tracks) an appropriate level of survey data will need to be collected to assess impacts.

At height monitoring

At height data collection is not specifically recommended for wind farms in any habitat type, but is noted as being most relevant in woodland situations. To justify this, the guidance states “Monitoring at height can provide useful additional information on bat activity, but it is unlikely to detect the presence of any species not already recorded using detectors at ground level (except in woodland).” The guidance also indicates that at height data can only be collected where it is reasonably practicable to do so.

This clarification is welcome, as at height survey is often logistically complicated to complete and does not, in our experience, significantly alter the baseline for assessment.

Roost surveys

While retaining reference to investigating maternity roosts and significant hibernation sites within 200 m (plus rotor radius) of the proposed wind farm (as referred to in BCT (2012) guidance), it is noted that, “The search area may need to be extended if there is a high level of habitat connectivity in the surrounding area and this is considered likely to attract bats into the wind farm area from further afield.”

This seems a sensible, ecologically-led qualification of what previously appeared an unsupported recommendation. Post construction monitoring of any roosts located may also provide a means of putting any mortality data into wider context.

Transects and Vantage Points (VPs)

The guidance states: “Either/both of these survey methods can be used to complement the information gained from static detectors and other sources, but their applicability is discretionary and site-specific.”

This is also a positive change in our view.  It requires the consultant to consider the ecological questions the work needs to address, and how to go about doing this effectively. On many sites neither technique will necessarily be needed, significantly reducing costs without affecting data quality; on some, focussed work will be required to determine direction of movement, provide an insight into numbers of bats, and the ecological function of features and habitats.

Other Methods and Good Housekeeping

The guidance also encourages the novel use of alternative methods, such as thermal imaging, the deployment of weather stations, the use of on-site meteorological data, and the regular checking of hardware (particularly microphones) in order to obtain robust results / minimise data loss.

Viewpoint on Survey

In many cases, application of the guidance will results in the cost of baseline bat survey work at onshore wind farms work being reduced, as transect work in particular can be resource heavy. This may be partially offset by a need for more formal consultation to agree survey methods and, it follows, to de-risk planning applications. For subsidy-free schemes any sensible rationalisation of work to reduce cost that does not compromise planning consent is a welcome one.

There is also a clear indication that the guidance is more ecologically driven. Previous guidance had gradually morphed into a ‘requirement’ and the ecological rationale to completing work was being lost. The greater emphasis on a well thought out desk study in determining an approach indicates that outputs will be more robust and allow for more meaningful impact assessment.



The guidance recommends turbines at all wind farms are feathered while idling, and that additional consideration is given to curtailment, based on an assessment of risk to bats that the wind farm poses.

Risk can be determined through the use of the Ecobat database (which will essentially rank the site in relation to others) or through the consultant’s own analysis, on the assumption the process can be transparently presented. Any curtailment parameters that follow will be derived from a combination of site-specific baseline bat activity and weather data (if bat activity can be reliably predicted). Guidance recommends the effectiveness of curtailment is monitored for a minimum of three years.

Principles of Monitoring

Monitoring will involve the use of acoustic detectors to determine whether activity levels of bats change post construction, with the recommendation being that pre-planning survey effort is duplicated (so that results can be directly compared). Where noctule or Leisler’s bat is a key issue, it is noted that nacelle-level data collection is a useful addition to ground-based acoustic detector deployment. In this situation, the data would assumedly be compared to pre-construction at height data, albeit the relative lack of emphasis on at height survey in the guidance suggests that for many sites this will not necessarily be collected (so there will be no comparable baseline information)

In conjunction with acoustic detection, levels of fatality should be calculated using specially-trained search dogs. To be able to extrapolate the likely numbers of bats killed from dog search data, it will also be necessary to understand the natural rates of carcass removal by scavengers, and the efficiency of the dogs in detecting carcasses. Methods are presented in Appendix 4 of the guidance, but the proportion of turbines subject to dog searches is left to the consultant to determine. This seems eminently sensible, as habitat variability and topography should be considerations in this process, and the outcome will typically need to be robust enough to be agreed with nature conservation stakeholders.

Viewpoint on Monitoring

The starting point for monitoring is perhaps more contentious than the nature of the monitoring proposed.  The Defra-funded study by Exeter University found no direct link between pre-construction activity levels and operational levels of fatality. The SNH guidance, however, uses activity levels to rank sites and derive curtailment protocols. It might be legitimately contended that rather than moving directly to curtailment, there is some monitoring to look at whether fatality is, in fact, an issue, and there will be inevitable debate on this point.

The monitoring protocols are, in themselves, less contentious. For the past few years, in the absence of monitoring guidance wind farm developers have been required to commission work to address conditions relating to bats. For many schemes this has involved the type of post construction monitoring using dogs that is proposed in the guidance, and we (and a few other companies) are well practiced in completing it efficiently and effectively. The flexibility to develop an appropriate monitoring protocol on a site-by-site basis is welcome, is consistent with the survey guidance, and promotes a considered approach to the work.

Further Advice

If you have any questions with regard to the guidance, or would like assistance with survey, assessment or monitoring in relation to a wind farm, please contact:

Peter Shepherd – 01865 883833

Owain Gabb – 01792 363026

Rachel Taylor 



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