Wildlife and Wind Farms: Conflicts and Solutions, Volume 2 provides a summary of current conflicts and solutions involving the rapid growth of wind farms and their impacts on wildlife. Chapters by leading experts cover topics from turbine siting and mortality monitoring to statistical evaluations and mitigation.
This is the second of two volumes, both edited by M.R. Perrow. They are thorough and authoritative, an important resource for professionals concerned with wind energy impacts on wildlife. Unfortunately, this is a complex subject, and industry has been slow to adopt many of the remedies reported. Issues for birds and bats differ significantly and typically require different solutions. This review emphasizes those involving bats.
Early investigations often failed to account for searcher detectability or scavenger removal rates when calculating wildlife fatalities at wind farms. Such problems were exacerbated by long intervals between searches, during which most corpses were removed by scavengers or arthropods. Small corpses can virtually disappear to human view in even a few inches of vegetation, and most of a night’s kill can be removed by scavengers within hours, depending on local circumstances. Trained dogs have performed far better than humans in searching for kills, but few are used. Fatality detection is complicated and often debated.
The impact of scavenger removal is difficult to accurately document. Depending on local scavenger faunas, removal rates can vary greatly. Scavengers may also take time to discover a new food source, causing removal rates to change from week to week or year to year.
Especially in the case of bats, no one knows how many may be permanently injured without detection. It is generally agreed that, early morning searches, are best for detecting bat fatalities prior to scavenger removal, but how often should these searches be conducted, and how can they avoid biases? Calculations of scavenger removal rates can be affected in many ways. What if scavengers learn to follow human scent trails to birds or bats intentionally placed as surrogates to measure scavenger removal? Also, how can we be sure that surrogate corpses are as attractive as fresh kills? Most surrogates are frozen prior to use. By becoming less attractive with age, scavenger removal could be significantly underestimated.
Statistical adjustments, predictive models, and invaluable insights to the most apparent biases are provided in this publication. However, some are extremely difficult to document. It is still impossible to accurately predict population-level impacts. Even if all other variables were accurately measured, knowledge of actual population size of impacted species rarely, if ever exists. As noted, estimates often fall short of reality, and losses may already be unsustainable in many cases.
Operational mitigation strategies that could significantly reduce bat mortality were reported as early as 2011. By slightly raising turbine cut-in speeds (the wind speeds at which turbines are permitted to spin for power production) above those set by manufacturers, bat mortality reductions of 50 to 93% are documented in this publication. By 2013, a German study of multiple sites, in different geographic regions, reported fatality reduction of 83% by including algorithms, such as season, time, and temperature.
Due to non-disclosure by power companies, few studies have reported amounts of power lost through such mitigation, but available evidence suggests less than 1%. Unfortunately, few companies, especially outside of Europe, have been willing to incorporate even these simple operational changes.
The possible use of acoustic deterrents has long been considered as a means of reducing bat mortality. However, the high frequency signals required for bats attenuate rapidly in air, making them ineffective in covering the large areas required to protect bats at wind turbines. By strategic placement of multiple transmitters on turbines, one study reduced mortality by 64%, but no ultrasonic deterrents are yet available for affordable commercial use. Changing turbine color to reduce attractiveness to insect prey, and use of electromagnetic signals have been proposed but appear unlikely to prove adequate.
Threshold numbers of bat fatalities, allowed prior to required mitigation, are frequently negotiated as part of the permitting process. However, in my experience in North America they are commonly exceeded with minimal or no remedial action taken.
Protection of key habitat, such as hibernation caves, may be useful for endangered species like Indiana myotis (Myotis sodalis), that seldom have been killed by turbines, but this is ineffective for migratory tree-dwelling species such as hoary (Lasiurus cinereus) and red (L. borealis) bats. Despite the absence of population estimates, trends can be regionally monitored at diverse locations not associated with wind farms. Mitigation planning should support systematic, standardized monitoring for such trends. These should be considered in future planning.
In reviewing current policies, I see a need for far more attention being paid to frequent fatalities of originally abundant species, rather than focusing almost exclusively on only occasionally killed endangered species. We cannot afford to ignore loss of still abundant bats like the Brazilian free-tailed bat (Tadarida brasiliensis), that play key ecological roles, not to mention their invaluable benefits to agriculture. This species already faces thousands of turbines, and is one of the most vulnerable. Yet, there is no reliable long-term monitoring, either of fatality or population trends.
Major advances in methodology for reducing threats to bats are reported in this publication. Yet, as one of the pioneers in the search for solutions, I’m deeply disappointed to see how little implementation has occurred thus far. Scientists have made important discoveries. Nevertheless, already proven methods for mortality reduction far too often have been ignored by regulators and industry. Standardized regulations are urgently needed at national and international levels.
The current North American goal of reducing bat fatalities by 50% is inadequate. Without limiting the number of turbines that can be permitted, such goals offer unrealistic solutions, even if attained.
Though some companies should be applauded for their special efforts, there are few incentives for investing in wildlife. Many of the largest companies still ruthlessly ignore wildlife. However, by providing token financial support for solution-finding research, they lull an environmentally concerned public into complacency.
In my opinion, far more progress could be made if a fair-minded rating system were organized collaboratively by concerned industry and environmental representatives. Companies could be ranked according to their wildlife policies (i.e. cooperation in solution finding and the extent to which existing mitigation knowledge is implemented). They needn’t be perfect to rate higher than unconcerned competitors. Such information could be shared with green energy investment advisors, providing potentially strong incentives.