Mervyn Mason (Dogwood Ecology) and Greg Ford (Balance Environmental)

The current state of affairs

Australia’s transitioning away from fossil fuels for electricity generation has seen the large-scale development of wind farms across the country.  From a global perspective, Australia’s pursuit of large-scale wind-power projects is a relatively recent development (cf. ~10 to 15 years), with a few exceptions in Victoria and Tasmania.  Globally, large-scale wind-power development has been occurring for many decades, with concomitant improvements in not only turbine technology and efficiency, but also impact and risk assessment approaches.  

Birds and bats are known to interact with wind turbines, frequently with detrimental consequences (for example, see Arnett et al. 2008, Kuvlesky et al. 2007, Moloney et al. 2019), which has resulted in a focus on minimising and mitigating these impacts.  Critical to this is the collection of bird and bat utilisation data to understand the potential risks posed to birds and bats using a wind farm area, and the associated impacts.  Importantly, the risks are typically a result of complex interactions among species distribution, relative abundance, behaviour, weather conditions, and site characteristics.

There is a wealth of best practice approaches to the assessment of impacts and risks posed to birds and bats from wind farm development on the global stage.  For example, see USFWS 2012, Rodrigues et al. (2015), Perrow (2017), Bennun et al. (2021), NatureScot (2021).

Regardless of this wealth of information and best practice approaches available from international experience, the consideration of that knowledge, and proven methods, has not been well translated into the guidance offered at the national and state levels within Australia to assess impacts to birds and bats.  Indeed, from a baseline bird and bat utilisation perspective, the Clean Energy Council’s (2018) Best practice guidelines for implementation of wind energy projects in Australia suggests the following: 

• “identify significant bird and bat habitats and habitat components”
• “undertake bird utilisation surveys and modelling to identify species at risk of collision and/or displacement (particularly listed threatened species)”
• “undertake bat surveys to identify any listed threatened species in the area.”

Regarding the bird utilisation survey requirements, these “national” guidelines simply state that the surveys should identify bird species on the site, their numbers, the height they fly, how they use the site, with a description of their behaviours.  Similarly, for bats, the guidelines state that surveys should be carried out to identify species using the site, including for breeding, roosting, and movement.  Trapping and acoustic detection approaches are suggested.  Importantly, the guidelines do state that “bat utilisation data cannot be obtained by using the above techniques (that is, trapping and acoustic methods), they are only useful for species identification and to gain an appreciation of populations.” The guidelines also mention the use of radar for “quantifying the density of bats on a site”, but appear to discourage the use of radar systems due to “their limitations”. 

At the State level, guidelines and regulations around ecological assessment for wind farm development vary significantly.  For example, Queensland’s State Code 23 wind farm development planning guidelines (DSDILGP 2022) repeat almost verbatim the Clean Energy Council guidelines, whereas Victoria’s Policy and Planning Guidelines – Development of Wind Energy Facilities (DELWP 2021) suggest that proponents should contact relevant staff in State and Commonwealth environment departments for advice on what flora and fauna might be impacted and how and when to survey to determine potential impacts and mitigation measures.  The New South Wales Wind Energy Framework:

Standard Secretary’s Environmental Assessment Requirements (DPE 2016) refers to EIS requirements for biodiversity stipulated in that State’s Biodiversity Offsets Policy for Major Projects (OEH, 2014) and Framework for Biodiversity Assessment (OEH, 2014) and specifies that a wind farm proponent should “…assess the impact of the development on birds and bats, including blade strike, low air pressure zones at the blade tips (barotrauma), alteration to movement patterns, and cumulative impacts of other wind farms in the vicinity…”

The problem

With the intentional, or unintentional, vagueness of approaches presented in the available guidance documents comes a consequential assortment of methods to undertake bird and bat utilisation surveys.  Typically, consultants and experts develop their own methods and proprietary approaches, with little to no collaboration or knowledge sharing.  The authors have been involved in numerous bird and bat utilisation surveys for wind farms across eastern Australia over recent years, designed by different consultants and experts.  As such, we have been exposed to the many different approaches, and have made the following observations:  

• A lack of understanding as to why the data are being collected, and the end use of those data.  

For birds and bats, the key purpose of the utilisation survey is to estimate the risk of collision with turbines.  As such, when undertaking a survey, it is the visibility of the airspace to be occupied by the turbine rotors (that is, the collision risk volume) that is of prime importance.  Depending on the windfarm design, that space can be from 40 to 60 m above ground level to a height of 300 m above ground level; this is often referred to as the rotor-swept height or area.  The ability to see all or most of the site to ground level can be helpful in gauging overall bird activity of the site, but it is not as important as being able to view the collision risk volume within the rotor-swept height.

Many bird and bat species will not venture into the rotor-swept area.  Those species of birds and bats typically active at the ground level, for example, are somewhat inconsequential to a collision risk assessment because they are unlikely to enter the rotor-swept area.  The crux of this is the likelihood that a particular species will interact with the rotors, either directly or indirectly through displacement.  Many species simply do not move at those heights, and therefore can be excluded from the outset.  

Surveys should not be limited to threatened or rare species.  Common species can be very long lived, with a low fecundity.  Hence, assessment of potential long-term impacts to these more common species should not be overlooked.  

•  A basic understanding of bird and bat behaviour, and what influences that behaviour.

An understanding of the likely movement of species and the resources they require is important.  Therefore, an assessment of broad spatial patterns in the landscape, and resource “hotspots” (for example, comparing open versus vegetated habitats) in the utilisation data is required to determine if there are site characteristics associated with collision risk and predicted impacts.  For example, the phenology of the trees within the site is important to understand the attractiveness of the site to birds and flying-foxes; or the presence of caves that are important roosting and maternity sites for bats.

Additionally, knowing the timing of breeding seasons and movements is important when planning surveys to maximise effectiveness.  The paucity of this knowledge for bats, particularly regarding large-scale movements to and from maternity sites, needs to be acknowledged and accounted for in the assessment.  Additionally, migratory and breeding behaviour can be strongly influenced by rainfall patterns, which are often erratic in Australia.  

• The different approaches used do not allow for comparison.

Depending on the consultant’s preferred method, time-constrained bird counts can vary, for example, 15, 20, 30, or 60 minutes for each survey site, over various times of the day (that is, dawn, morning, mid-day, afternoon, evening; every half-hour, every hour).  There is no consistency in period, area surveyed, or time-of-day surveyed.  

Similarly, spatial and temporal distribution of acoustic detection effort for echolocating bats varies substantially.  At a site scale, detector deployments range from one or two nights per season to 60 or more nights per site per season.  Spatial representation across the proposed development area often includes stratification according to habitat types available, but in many cases seems to ignore the potential impact zones around probable turbine locations.  There appear to have been only limited attempts to monitor bat activity within the rotor-swept area (where collision-related mortality is inevitable) and under different wind-speed conditions.  The latter aspect is a critical consideration in understanding the potentially important mitigation strategy of operational curtailment to reduce bat mortality (see Bennett et al. 2022).

Further, there is no standard for a minimum baseline data collection period.  These can be influenced by the development schedule of the wind farm, with periods varying from one to four years not uncommon.  Seasonality also varies, with surveys completed either twice a year, in spring and autumn, or four times a year, spring, summer, autumn, and winter.  Relative stochasticity of bird and bat utilisation and densities between two baseline survey years is arguably a significant issue for determining overall utilisation.  This is often exacerbated by the natural variations and unpredictability of rainfall across Australia, and the nomadic nature of many species.

Overall, this lack of consistency in survey methods does not to allow meaningful comparison and cumulative impact assessment.  

•  The detection probability of species.

Bird utilisation surveys are typically conducted during the day when individuals can be observed.  Night-time surveys are very rarely, if ever, completed for obvious reasons.  However, many of Australia’s migratory species typically move at night, this is also a time when flying-foxes are foraging.  Importantly, these species are the ones that should be assessed given the high proportion of these species that are threatened.  

For bats, acoustic data are typically collected at ground level using Anabat and Song Meter detectors, with many studies simultaneously deploying a mixed range of models, often with different settings and detection capabilities.  The limitations of this approach are frequently not acknowledged in study reports; and are often exacerbated by users’ lack of understanding of the equipment and factors that influence the detectability of calls (for example, foliage cover, temperature, humidity, bat behaviour, and call frequency and amplitude).  For example, the effective range of the microphones attached to these devices is typically less than 30 m, a height that is usually within the canopy, and well below the rotor-swept area.  While some species with loud, low frequency calls may be detected at more than 50 m from the microphone, many species with higher-frequency, lower amplitude calls may not be detected even within 10 m of the microphone.  Consequently, for most bat species, the ground-level deployment of ultrasonic detectors will yield no useful information on the potential risk of collision with turbine blades.

Conclusions and recommendations

The importance of robust and repeatable baseline data cannot be understated to inform a meaningful impact assessment and risk analysis.  Sufficient and defensible data that are practical and proportionate to the needs of the analysis, with the end-use in mind, are important.  Data are expensive to collect and analyse, and there is no need to collect data for data’s sake.  This is especially true for bird and bat utilisation studies for wind farms.  

It is the authors’ opinion that there is no need to reinvent the wheel, there is a lot of guidance already available globally.  Based on our experience and observations, we advocate that a standard and consistent approach to bird and bat utilisation surveys for wind farms is developed and implemented.  That approach should consider the following: 

1. A standard survey method for birds that gives due consideration to the rotor-swept area, the effort of which is comparable between studies.
2. A set time-constrained period that is proportionate to the detection probabilities of species.
3. A minimum of two years of baseline data collected at quarterly intervals, or otherwise, to reflect the seasonality in the system, considering the variability of rainfall and its influence on vegetation flowering, coupled with the nomadic nature of many Australian bird species.  
4. Appropriate consideration of bat movement patterns over short-term (nightly foraging) and long-term (seasonal migration) temporal scales.
5. The collection of bat utilisation data within the rotor-swept area via appropriate and proven methods.
6. The training of field staff in the limitations and appropriate use of ultrasonic detection systems, including a basic understanding of bioacoustics and environmental influences on bat-call detectability.
7. The more widespread use of radar detection of bird and bat movements during the baseline assessment stage.
8. Incorporation of appropriate control sites that are independent of the project’s potential impacts that is, sites at a sufficient distance from the development.

References 

Arnett, E.B., Brown, W.K., Erickson, W.P., Fiedler, J.K., Hamilton, B.L., Henry, T.H., Jain, A., Johnson, G.D., Kerns, J., Koford, R.R., Nicholson, C.P., O’Connell, T.J., Piorkowski, M.D. and Tankersley, R.D. Jr. (2008).  Patterns of Bat Fatalities at Wind Energy Facilities in North America.  Journal Of Wildlife Management 72, 61–78

Bennett, E.M., Florent, S.N., Venosta, M., Gibson, M., Jackson, A. and Stark, E. (2022).  Curtailment as a successful method for reducing bat mortality at a southern Australian wind farm. Austral Ecology 47(6), 1329-1339.

Bennun L, van Bochove J, Ng C, Fletcher C, Wilson D, Phair N, and Carbone G. (2021). Mitigating biodiversity impacts associated with solar and wind energy development. Guidelines for project developers. Gland, Switzerland: IUCN and Cambridge, UK: The Biodiversity Consultancy 

Clean Energy Council (2018). Best Practice Guidelines for Implementation of Wind Energy Projects in Australia. 

Department of State Development, Manufacturing, Infrastructure, and Planning (2018). State code 23: Wind Farm development Planning Guidelines. Brisbane. 

Department of the Environment, Water, Heritage, and the Arts (2017). Survey guidelines for Australia’s threatened birds – Guidelines for detecting birds listed as threatened under the Environment Protection and Biodiversity Conservation Act 1999. Canberra.

Kuvlesky W.P., Brennan L.A., Morrison M.L., Boydston K.K., Ballard B.M. and Bryant F.C. (2007). Wind energy development and wildlife conservation: Challenges and opportunities.  Journal of Wildlife Management. 71, 2487-2498.

Moloney, P.D., Lumsden, L.F. and Smales, I. (2019). Investigation of existing post-construction mortality monitoring at Victorian wind farms to assess its utility in estimating mortality rates. Arthur Rylah Institute for Environmental Research Technical Report Series No. 302. Department of Environment, Land, Water and Planning, Heidelberg, Victoria.

NatureScot (2021).  Bats and onshore wind turbines: Survey, assessment and mitigation.  Version August 2021.  https://www.nature.scot/doc/bats-and-onshore-wind-turbines-survey-assessment-and-mitigation

Perrow MR (ed) (2017).  Wildlife and Wind Farms-Conflicts and Solutions: Onshore: Potential Effects.  Pelagic Publishing, Exeter, UK.

Rodrigues, L., Bach, L., Dubourg-Savage, M.-J., Karapandža, B., Kovač, D., Kervyn, T., Dekker, J., Kepel, A., Bach, P., Collins, J., Harbusch, C., Park, K., Micevski, B. and Minderman, J. (2015).  Guidelines for consideration of bats in wind farm projects – Revision 2014.  EUROBATS Publication Series No. 6 (English Version).  UNEP/EUROBATS Secretariat, Bonn, Germany.

Sutherland WJ, Newton I, and Green RE (eds) (2004). Bird ecology and conservation: a handbook of techniques. Oxford University Press, New York, New York, USA. 

Strickland MD, Arnett EB, Erickson WP, Johnson DH, Johnson GD, Morrison ML, Shaffer JA, and Warren-Hicks W (2011). Comprehensive guide to studying wind energy/wildlife interactions. Prepared for the National Wind Coordinating Collaborative, Washington,D.C., USA. 

Scottish Natural Heritage (2014). Guidance: Recommended bird survey methods to inform impact assessment of onshore wind farms.

USWFS (2012).  U.S. Fish and Wildlife Service Land-Based Wind Energy Guidelines.

Images (top to bottom):

T: Placement of ultrasonic bat detectors should be within the rotor swept area, not at ground level

B: Vantage point surveys are frequently used to identify birds using an area