1. Since the previous report on the impact from wind power on birds and bats was published in 2011, much new and important information have appeared both internationally and in Sweden. The present report is a summary of the international research in this area in recent years, and also of the Swedish post-construction surveys made until 2015. This report is hence an update of the previous (2011) report.
2. With respect to birds, the results of new research largely confirm the conclusions from the previous report. For bats, however, new results show that wind power is a larger problem than we realized five years ago, but, on the other hand, new mitigation methods have recently been developed and tested, so that the problem can now be handled more efficiently.
3. Wind power facilities are generally a larger problem for bats than for birds. This is because more bats are being killed, and also because the mortality is concentrated to a few species of bats, which therefore may be affected seriously. At the same time, wind power facilities can also be a problem for certain kinds of birds, some of which may be affected negatively at the population level. Common for birds and bats that risk being negatively affected at the population level is that they have low reproductive potential, and therefore may have difficulties compensating for increased mortality.
4. The fatality rate of birds at wind turbines remain at 5–10 birds per turbine and year on average, even after several and more detailed surveys that have been conducted recently. The location of the turbine is often an important determinant of the fatality rate. While most turbines kill few birds, others may kill up to 60 birds per year. So far there is only one study from Sweden that has been executed in sufficient detail to allow estimation of annual fatality rates. This study was conducted at Näsudden on the island of Gotland, a coastal site very rich in birds, and show, as expected, fatality rates much higher than average. Regarding fatality rates of birds and bats at marine wind farms, no new evidence-based knowledge have been presented since the previous report.
5. Bird mortality at wind turbines generally increases with the size of the turbines. However, in relation to installed effect and produced electricity the mortality declines with increased turbine size. As fewer new, large plants replace old, small ones, the total mortality per wind farm can be lowered at the same time as the electricity production increases. This was the case at Näsudden when the old turbines were replaced by new ones. If a similar effect also is achieved for bats has not been investigated.
6. All kinds of birds can be killed at wind turbines. Also, birds are probably killed at all sites where modern wind turbines are being used. Most fatalities are small songbirds. Raptors, gulls and game birds are killed at higher rates than expected based on their population sizes. Relatively few swan, geese and cranes are killed at wind turbines, probably because these birds show strong avoidance behaviours. Relatively few birds are killed while in flight during migration. Generally, mortality is higher for birds that stay in an area over longer periods such as during breeding, wintering or at stopovers during migration.
7. Estimates of fatality rates for bats at wind turbines presented in 2011 were much too low. New research from Europe and North America suggest that on average a wind turbine kills 10–15 bats per year, in some cases up to 100 or more. We still have no comparable estimates from Sweden, but an ongoing study from a site in Halland suggests that the fatality rate is about 5 bats per turbine and year at that site.
8. Mortality of bats at wind turbines is limited to a few species that move and feed in the open air above the tree-canopies. We call them high-risk species. The consideration of bats at wind turbines should focus on them. The noctule, the parti-colored bat and in the north also the northern bat are those that we believe are in most need of concern, but the soprano-, common and Nathusius’ pipistrelles as well as the rarer Leisler’s bat and serotine are also high-risk species and thus potentially affected. Remaining species are rarely or never killed at wind turbines.
9. There have been some recent attempts to investigate if the mortality caused by wind turbines has negative population effects on bird species. In USA it was found that present wind farms probably do not affect any national population of songbirds. Similar results were obtained for Canada, but in this case the results applied to all breeding birds. No such broad studies have been made in Europe, but estimates have been made for species considered as particularly vulnerable. In northern Germany, with particularly many wind farms in operation, it is believed that the populations of red kites and common buzzards are already being affected negatively and this may perhaps apply to the white-tailed eagle as well.
10. We still have no estimates of population sizes for bats in Sweden or internationally and therefore we cannot evaluate if and how the increased mortality from wind turbines affects bat populations. However, there are concerns from North America and Europe that serious negative effects on bat populations of certain species already have occurred.
11. Recent results from studies on the impact of wind turbines on habitats, avoidance and disturbance of birds confirm the pattern from the previous report. There is large variation among different species, areas and habitats and general conclusions are difficult to draw. Nevertheless, avoidance behaviour is usually less obvious during the breeding season compared to the rest of the year. During the breeding season avoidance is usually obvious only within a few 100 m, the greatest distances are found among waders. During other parts of the year, it is birds that live in flocks and certain marine birds that show the greatest avoidance distances. Nothing new has appeared regarding habituation of birds to wind turbines and there is still considerable variation between different studies. There are some recent studies suggesting that the distance and habitat between the turbines affect the degree of avoidance behaviour and disturbance. Marine wind farms are avoided by most marine birds, but some species (cormorants and gulls) are attracted to the turbines, probably because the towers provide resting sites or access to food. Long-term studies of avoidance and disturbance are still lacking.
12. Impact on the habitats, avoidance behaviour and disturbance has not been investigated with respect to bats so far and may generally be less of a problem for bats than for birds. It is nevertheless obvious that drastic physical changes of the habitat will have effects also on bats, one way or another. On the contrary, it is clear that bats are attracted to wind turbines and that they search for them actively, in contrast to birds, which means that the problem usually requires different solutions for the two groups of animals.
13. Measures to minimize negative impact on birds are still mostly focused on avoiding building wind turbines in places that are rich in birds, particularly sites with high numbers of birds during breeding, wintering and stopovers during migration. Areas around specific occurrences and breeding sites of birds belonging to species or groups of species that have turned out to be particularly vulnerable to negative impact from wind turbines should be avoided. One such example is the larger raptors. Maintaining buffer zones, areas within which wind turbines should not be built, is a way to reduce the risks in such cases. In this report we review the current use of protection zones for birds and provide new suggestions for their future application. We discuss how we can achieve new and more scientifically based protection zones, particularly for our eagles. We appreciate that protection zones is a useful way to reduce the risks for some birds, but at the same time we emphasize that that this method cannot eliminate the risks entirely.
14. Although we consider buffer zones as an effective and practically useful way to reduce negative impact on particular birds, we and many other scientists are realising that this method may not always be sufficient for the protection and formation of viable populations of the species in question. To achieve such goals, planning at a larger scale may be necessary, where areas with the lowest risks of negative environmental impacts are designated suitable for e.g. establishment of wind farms. We believe that this would increase the efficiency of the planning and handling processes during wind turbine establishment and also facilitate the protection of both birds and bats, in comparison with current practices. This would also ensure that sufficiently large areas with relatively low risks are maintained for long-term conservation of (bird and bat) populations.
15. Once the turbines are built the available mitigation options are few when it comes to protection of birds. To mitigate by temporary halting the turbines during periods of high risk, as employed for bats, is a less useful method for birds. For birds there is no clear and general relationship between prevailing conditions on one hand, and the mortality risk on the other, which is in sharp contrast to the situation for bats. Although there are some cases from other countries where wind turbines have been halted to protect birds, this method do not seem to be useful in Sweden, as far as we can see. However, there is a promising development of various technical monitoring solutions that aim to keep bird fatalities at a very low level. As far as we know, no such system is yet fully developed and operational, but this is probably only a matter of time. Finally we also have the option of using compensation measures at a different site, a method that may help minimize the total effect on a population. It has barely been used in Sweden so far, but is more common internationally.
16. The most important measure for protection of bats at wind farms is to adjust the operation of turbines according to the occurrence of certain high risk species. This should be done by halting the rotors during periods when bat activity at rotor height is most frequent. Halting the rotors is a feasible method where noctules, parti-colored bats and serotines, and, particularly in the north, northern bats occur. This measure is expected to inhibit 60–90% of the potential fatalities.
17. To evaluate if mitigation at a particular site is feasible and decide how it should be applied locally, activity of the high risk species at rotor height should be measured continuously over longer periods, preferably during three seasons. Alternatively, searches for dead bats can be made, but this is quite complicated and requires more work. In some cases it may be more efficient to use a general mitigation scheme based on general knowledge about potentially dangerous situations, without spending resources and time to investigate bat activity. This option can be worth considering particularly in cases where it is clear already from the start that mitigation will be necessary.
18. How often halting the rotors will be required at a site depends primarily on the weather, and is hard to predict. A rough estimate for southern Sweden suggests that turbines need to be stopped during about 10 nights on average per year. Most likely mitigation will be required less frequently in the north.
19. Post-construction surveys so far made in Sweden have not contributed much new and useful data on how birds and bats are affected by wind farming. Unfortunately, most of them have not been up to expected standards and have not been able to answer even the most basic and relevant questions. A common impression is that it has been more important to do something, no matter why and how, rather than focussing on what has actually been achieved. There are certainly exceptions. A few programs have been carefully planned and well executed and have contributed with significant and important results that will be well used. This applies to birds and bats alike. There is every reason to reconsider the system of post-construction surveys as used at present in Sweden, so that future programs can contribute with useful information about local conditions and also can be used together with results from other programs to investigate broader patterns. Particularly for bats but sometimes also for birds, well designed programs are needed for efficient mitigation so that the negative impact on the fauna can be minimized.
20. We present guidelines on how surveys should be made and standardized to provide the best possible foundation for decisions and at the same time be cost-effective. Standardization of the methodology is important if the results are to be useful also in a broader context, although this is usually not the primary objective of the surveys. A national standard consisting of common guidelines for how surveys and measures should be employed with respect to methods and equipment is needed.