Impacts on biodiversity of exploitation of renewable energy sources: the example of birds and bats
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Hermann Hötker, Kai-Michael Thomsen, Heike Jeromin Impacts on biodiversity of exploitation of renewable energy sources: the example of birds and bats Facts, gaps in knowledge, demands for further research, and onithological guidelines for the development of renewabe energy exploitation
Impacts on biodiversity of exploitation of
renewable energy sources: the example of
birds and bats - facts, gaps in knowledge,
demands for further research, and
ornithological guidelines for the development
of renewable energy exploitation
Hermann Hötker, Kai-Michael Thomsen, Heike Jeromin
Translated by: Solveigh Lass-Evans
Supported by:
Michael-Otto-InstitutImprint Unchanged traslation of: Hötker, H.; Thomsen, K.-M. & H. Köster (2005): Auswirkungen regenerativer Energiegewinnung auf die biologische Vielfalt am Beispiel der Vögel und der Fledermäuse - Fakten, Wissenslücken, Anforderungen an die Forschung, ornitologische Kriterion zum Ausbau von regnerativen Energiegewinnungsformen. BFN-Skripten 142, Bonn. Recommended citation: Hötker, H., Thomsen, K.-M. & H. Jeromin (2006): Impacts on biodiversity of exploitation of renewable energy sources: the example of birds and bats - facts, gaps in knowledge, demands for further research, and ornithological guidelines for the development of renewable energy exploitation. Michael-Otto-Institut im NABU, Bergenhusen. Translation: Solveigh Lass-Evans Layout: Kai-Michael Thomsen Photographs: Dr. Hermann Hötker, Kai-Michael Thomsen Supported by: Bundesamt für Naturschutz (Support No. Z1.3-684 11-5/03) and Bundesministerium für Umwelt, Naturschutz und Reaktorsicherheit (Translation) Editor: Michael-Otto-Institut im NABU, Goosstroot 1, D-24861 Bergenhusen Published by: Books on Demand GmbH, Gutenbergring 53, D-22848 Norderstedt ISBN
Table
Table
Preface .................................................................................................... 5
Summary ................................................................................................ 6
1 Introduction .......................................................................................... 8
2 Material and Methods ........................................................................ 10
3 Impacts of wind farms on vertebrates .......................................... 14
3.1 Non-lethal impacts (disturbance, displacement, habitat loss) on birds .... 1 4
3.1.1 Change in distributions due to wind farms ......................................................... 1 4
3.1.2 Minimum avoidance distance of birds to windfarms ....................................... 1 4
3.1.3 Barrier effects of wind farms on birds ................................................................... 2 4
3.3 Collision of birds and bats with wind farms ....................................................... 2 7
3.3.1 Collisions of birds with wind farms ....................................................................... 2 7
3.3.2 Collisions of bats with wind farms ......................................................................... 3 3
4 Collison effects on population dynamics ...................................... 36
4.1 Application of the population simulation model ............................................... 3 6
4.2 Results of the population simulations .................................................................. 3 9
4.3 Discusion of the simulations calculations ........................................................... 4 0
5 Measures to reduce the impacts of wind farms .......................... 42
5.1 Coice of site ..................................................................................................................... 4 2
5.2 Design of the environment around wind farms .................................................. 4 2
5.3 Configuration of wind turbines within a wind farm ......................................... 4 3
5.4 The operation of wind farms ..................................................................................... 4 3
5.5 Design of individual wind farms .............................................................................. 4 3
5.6 Measures transferred on the conditions/circumstances in Germany ........ 4 4
6 Estimation of the impacts of ‘repowering’ ................................... 45
6.1 Repowering and disturbance of birds ................................................................... 4 5
6.2 Repowering and collisions of birds and bats ..................................................... 4 7
6.3 Summary of the assessment of repowering ........................................................ 4 7
7 Impacts of other types of renewable energy ............................... 49
8 Research requirements ..................................................................... 51
9 Acknoledgements ............................................................................... 54
10 Literature ............................................................................................. 55
4Impacts on biodiversity of exploitation of renewable energy sources: the example of birds
Preface
The Federal Government of Germany aims The publications used in this study allow
to increase the proportion of energy generated conclusions to be drawn on the impacts wind
by renewable sources to at least 12.5% by 2010. farms have on breeding, roosting, foraging and
The regulations of the „renewable-energy-bill“ migrating birds and bats. Furthermore, some
(EEG) offer incentives to do this. For the first conclusions can be reached about the impacts
time, in the first half of 2004, 10% of the power of wind farms on these taxa throughout the year.
supply in Germany was generated from re- Simulation models assess the additional morta-
newable sources and a substantial proportion lity rate caused by wind farms and the effects
(5.8% of total) is provided by wind energy. At of repowering on the bird and bat populations.
the same time, the associated impacts on eco-
logical balance and landscape caused by wind However, note that the data are limited and
farms construction is a controversial topic. open to a wide range of interpretation and there-
fore only tentative conclusions can be reached
The aim of this study „Impacts on biodiversi- on the impacts of wind farms on birds and bats.
ty of exploitation of renewable energy sources:
the example of birds and bats - facts, gaps in The results presented here should objecti-
knowledge, demands for further research, and vise the nation-wide discussions about the ex-
ornithological guidelines for the development of tent to which nature conservation is compatible
renewable energy exploitation“ compiled by the with renewable energy development (in particu-
Michael-Otto-Institute in NABU, is to analyse lar with wind farms). While the report was in pro-
national and international studies of the impacts gress, the results have been already discus-
of wind farms on birds and bats and to access sed with administrative bodies, with represen-
their statistical significance. The results give an tatives of nature conservation associations as
overview of the available data, as well as gaps well as the operating companies.
in knowledge and future research needs.
Prof. Dr. Hartmut Vogtmann
President of the Federal Nature Conservation
Office
5Summary & Introduction
Summary
Impacts on biodiversity of exploitation of significant evidence of negative impacts on po-
renewable energy sources: the example of pulations of breeding birds could be found. The-
birds and bats – facts, gaps in knowledge, re was a tendency waders nesting on open
demands for further research, and ornitho- grounds to be displaced by wind farms. Some
logical guidelines for the development of passerines obviously profited from wind farms.
renewable energy exploitation They were probably affected by secondary im-
pacts, e.g. changes in land management or aban-
The purpose of this report is to compile and donment from agricultural use next to the wind
to evaluate the available information on the im- plants.
pacts of exploitation of renewable energy sour-
ces on birds and bats. The focus is on wind The impact of wind farms on non-breeding
energy as there is only little information on the birds was stronger. Wind farms had significant-
impact on birds and bats of other sources of ly negative effects on local populations of gee-
renewable energy. The report aims at better un- se, Wigeons, Golden Plovers and Lapwings.
derstanding the size of the impact, the potential
effects of re-powering (exchanging small old wind With the exceptions of Lapwings, Black-tailed
turbines by new big turbines), and possible Godwits and Redshanks most bird species used
measures to reduce the negative impact on bir- the space close to wind turbines during the
ds by wind turbines. In addition the need for breeding season. The minimal distances obser-
further research is highlighted. ved between birds and pylons rarely exceeded
100 m during the breeding season. Some pas-
The evaluation is based on 127 separate stu- serines showed a tendency to settle closer to
dies (wind farms) in ten countries, most of them bigger than to smaller wind turbines.
in Germany. Most studies were brief (not more
than two years) and did not include the pre- During the non-breeding season many bird
construction period. Before-After Control Impact species of open landscapes avoided approa-
studies that combine data collection before and ching wind parks closer than a few hundred
after, in this case construction of a wind farm, metres. This particularly held true for geese and
on both the proposed development site and at waders. In accordance with published informa-
least one reference site were rare. In only a few tion disturbance of geese may occur at least up
cases, would the design of the study and the to 500 m from wind turbines. For most species
length of the study period theoretically allow sta- during the non-breeding season, the distances
tistically significant effects of wind farms on bir- at which disturbance could be noted increased
ds and bats to be found at all. Assessments of with the size of the wind turbines. For Lapwings
impacts, therefore, are usually based on few this relationship was statistically significant.
studies only. This report includes all studies rea-
dily available to the authors, irrespective of the There was no evidence that birds generally
length of the study period and the quality of the became „habituated“ to wind farms in the years
study design. In order to base the assessments after their construction. The results of the few
on as many independent samples as possible studies lasting longer than one season revealed
even rather unsystematic observations were in- about as many cases of birds occurring closer
cluded. The information of the data was redu- to wind farms (indications for the existence of
ced to a level that justified the application of habituation) over the years as those of birds
sign tests. The compilation of many different in- occurring further away from wind farms (indica-
dividual studies gave the following results: tions for the lack of habituation).
The main potential hazards to birds and bats The question whether wind farms act as bar-
from wind farms are disturbance leading to dis- riers to movement of birds has so far received
placement or exclusion and collision mortality. relatively little systematic scientific attention.
Although there is a high degree of agreement Wind farms are thought to be barriers if birds
among experts that wind farms may have nega- approaching them change their flight direction,
tive impacts on bird populations no statistically both on migration or during other regular flights.
6Summary & Introduction
There is evidence for the occurrence of a barri- capacity) on birds and bats is assessed by the
er effect in 81 bird species. Geese, Common available data and by simple models. There is
Cranes, waders and small passerines were af- no information, however, on the effects of the
fected in particular. However, the extent to which newest generation of very large wind turbines.
the disturbances due to wind farms of migrating According to current knowledge, repowering will
or flying birds influences energy budgets or the reduce negative impacts on birds and bats (dis-
timing of migration of birds remains unknown. turbance and mortality) if the total capacity of a
wind farm is not changed (many small turbines
Collision rates (annual number of killed indi- are replaced by few big turbines). In a scenario
viduals per turbine) have only rarely been stu- in which the capacity of a wind farm is increa-
died with appropriate methods (e. g. with cont- sed 1.5 fold, negative impacts start to domina-
rols of scarvenger activities). In particular, such te. In case of a doubling of wind farm capacity,
studies are missing for Germany. Collision rates repowering increases the negative impacts of
varied between 0 and more than 50 collisions the wind farm. Repowering offers the chance to
per turbine per year for both birds and bats. remove wind farms from sites that are associa-
Obviously the habitat influenced the number of ted with high impacts or risks for birds and bats.
collisions. Birds were at high risks at wind farms New turbines could be constructed on sites that
close to wetlands where gulls were the most are likely to be less problematic with respect to
common victims and at wind farms on mountain birds and bats.
ridges (USA, Spain), where many raptors were
killed. Wind farms in or close to forests posed Effective methods of reducing the negative
high collision risks for bats. For both birds and impacts of wind energy use on birds and bats
bats, the collision risk increased with increasing include:
size of the wind turbine. The relationship, howe-
ver, was not statistically significant. · choice of the right site for wind farms (avo-
idance of wetands, woodlands, important
Gulls and raptors accounted for most of the sites for sensitive non-breeding birds and
victims. In Germany the relatively high numbers mountain ridges with high numbers of rap-
of White-tailed Eagles (13) and Red Kites (41) tors and vultures),
killed give cause for concern. Germany hosts · measures to reduce the attractivness of wind
about half of the world population of breeding farm sites for potential collision victims,
Red Kites and has a particular responsibility for · configuration of turbines within wind farms
this species. Bird species that were easily dis- (placement of turbines parallel to and not
turbed by wind farms (geese, waders) were only accross the main migration or flight direc-
rarely found among the victims. Bats were struck tions of birds),
by wind turbines mostly in late summer or au- · construction of wind turbines: replacement
tumn during the period of migration and disper- of lattice towers, wire-cables and overhead
sal. power lines.
Population models created by the software Measures to increase the visibility of wind
VORTEX revealed that significant decreases in turbines and to reduce the effects of illuminati-
size of bird and bat populations may be caused on remain to be studied.
by relatively small (0,1 %) additive increases in
annual mortality rates, provided they are not In spite of many publications on windfarms
counter acted by density dependent increases and birds there still is a great demand for furt-
in reproduction rates. Short-lived species with her research. First of all there is an urgent need
high reproductive rates are more affected than for reliable data on collision rates at wind turbi-
long-lived species with low reproductive rates. nes of birds and bats in Germany. This holds
The latter, however, are less able to substitute true particularly for the new and big turbines
additional mortality by increasing reproductive which will replace the present generation of wind
rates. turbines.
The effects of „repowering“ (substitution of It is still unclear whether these big and ne-
old, small turbines by new turbines with higher cessarily illuminated turbines pose a high colli-
7Summary & Introduction
sion risk to nocturnal migrants which have not anwhile, losses of raptors were also recorded
yet been greatly affected by smaller turbines. at wind farms in Germany (Dürr, 2003a; Dürr,
The high collision rates of Red Kites in Germany 2004). New studies in America and Europe show
also merit urgently study. The aim of the research that bats as well as birds are be killed by wind
has to be a quick reduction of the collision ra- farms (Ahlén, 2002; Bach, 2001; Dürr & Bach,
tes. The sensitivity to wind farms of many other 2004; Johnson et al., 2000; Keeley, Ugoretz &
bird species that are of particular nature con- Strickland, 2001).
servation interest (storks, raptors, Cranes) has
not yet been sufficiently studied. Despite numerous studies the extent of eco-
logical impacts of wind farms is controversial.
There is hardly any information on the im- One possible reason might be the heterogeneity
pacts of arrays of solar panels on birds and of the available studies. They differ in recorded
bats. Studies should be initiated as soon as parameters (number of killed and injured birds,
possible. disturbance), in their analytical design (collec-
tion of data before or after construction, use of
control areas), in their extent, duration and in
their applied analytical methods. Many studies
1 Introduction are either published in barely assessable
places, or not published at all („grey“ literatu-
The Federal Government of Germany intends re). In only a few cases have studies been vali-
to set targets to develop further renewable en- dated by independent experts (as is common
ergy generation (BWU, 2004) in order to minimi- in peer-reviewed journals). Therefore, in these
se emissions of gases with damaging effects on circumstances, many specific questions could
climate. Germany generates more electricity not be answered concretely or scientifically. It
from wind than any country, followed by the USA has not been possible to forecast what sort of
(BIOCENOSE & LPO Aveyron- Grands Causses, impacts a wind farm in specific location might
2002; BMU, 2004). Even during the early phase have on birds or bats. The same applies to other
of wind energy development, worries were ex- forms of renewable energy sources, particular-
pressed mainly in the USA, but also in Europe, ly as considerably fewer research results exist.
that wind farms could have a harmful impact on
the animal world, particularly on birds. In the Popular discussions in wind farm energy are
USA, these apprehensions were confirmed by not based on objective facts but rather on as-
experiences from the first large-scale wind farm, sumptions. However, informed debate is re-
where at the Altamont Pass in California, roughly quired for a popular consensus about the usa-
5000 wind turbines have been responsible for ge of wind energy. Along with the database de-
the death of hundreds of raptors per year since veloped at the same time, this study should help
their construction. Protected species such as to objectivise these discussions.
golden eagles are among the species affected
(Orloff & Flannery, 1992). Due to high mortality This report attempts to summarise clearly
of raptors, there has been no further extension the contemporaneous datasets that might be
of this wind farm and overall the development of classified as „effects of renewable energy de-
wind energy in the USA has slowed down (Hunt, velopment on birds and bats“. The main em-
2000). In contrast to the USA, discussions in phasis was on wind energy, as other forms of
Europe focused on more indirect impacts, such renewable energy (with the exception of hydro-
as disturbance, habitat loss during the bree- electric) are not so well established and there-
ding season and on migration, as well as barrier fore relatively few observations have been made
effects for migrating birds (AG Eingriffsregelung, (see chapter 7).
1996; Crockford, 1992; Langston & Pullan, 2003;
Percival, 2000; Reichenbach, 2003; Schreiber, The statements made in this report are
2000; Winkelman, 1992b). Collisions of birds with based on bibliographic references and inter-
wind turbines were also significant in Spain, views with experts. The documented results of
where griffon vultures were particularly affected many studies were not only summarised, but
(Acha, 1998; Lekuona, 2001; SEO, 1995). Me- also analysed. In this way, a wide range of ob-
8Summary & Introduction
servations and data on this topic were available The following questions have been considered
to answer questions, which individual analyses in detail:
would not be capable of solving. The numerous
studies on the impact of wind energy enabled a · do wind farms cause changes in the distri-
search for connections, which identify, explain bution of animal populations?
and maybe even help to diminish the negative · how big is the distance animals keep to wind
impacts. The analysis of the data presented here farms?
from reports and publications about wind po- · do wind farms have a barrier effect on mi-
wer should contribute grating birds?
· to what extent are wind farms responsible
· to assess better the extent of impacts (if for mortality and what are the implications of
possible at the level of populations of spe- the losses for population dynamics?
cies) · how can the negative impacts of wind farms
· to estimate the potential impact of repowe- be mitigated?
ring (replacement of the old, small wind tur-
bines by bigger, more powerful (but possib- The questions have been as far as possible
ly fewer) turbines) treated for both birds and bats. In order to con-
· to identify possible measures to reduce ne- sider the consequences of mortality on wind
gative impacts of wind farms on birds and farms, populations have been modelled with help
bats. of a computer simulation program. Because ex-
tensive studies about possible impacts of off-
shore-wind energy usage on the marine envi-
ronment are at present still in progress (Kut-
scher, 2002), this report is restricted mainly to
land and coastal areas The literature study was
focused on central Europe, while from other
areas, only comprehensive published studies
were included.
9Material and Methods
2 Materials and Methods ning, 1999; Sinning & Gerjets, 1999; Smallwood
& Thelander, 2004; Sommerhage, 1997; Steiof,
The database and the presented results are Becker & Rathgeber, 2002; Still, Little & Law-
both based exclusively either on published or rence, 1996; Strickland et al., 2001b; Stübing &
„grey literature“ reports. No new data were col- Bohle, 2001; Thelander & Rugge, 2000; Thelan-
lected for this project. Within the project more der, Smallwood & Rugge, 2003; Trapp et al.,
than 450 literature references have been ana- 2002; van der Winden, Spaans & Dirksen, 1999;
lysed, i.e. checked and if necessary added to Vierhaus, 2000; Walter & Brux, 1999; Winkel-
the tables. Cross-checking showed that these man, 1989; Winkelman, 1992a; Winkelman,
references are derived from 127 different stu- 1992b; Young et al., 2003a; Young et al., 2003b
dies. Data from each wind farm was treated as
a single study, even if the data was gathered in Because the intention was to produce a re-
different years and from different observers. port primarily relevant to Germany, the main em-
This was done in order to ensure the indepen- phasis was on research from Germany. Howe-
dence of the data and to avoid using the same ver, the number of studies included from other
study more than once. The following sources countries also reflects the scale of the research
were used to derive the baseline data for this carried out in each country (Tab.1).
study:
Ahlén, 2002; Albouy et al., 1997; Albouy,
Dubois & Picq, 2001; Anderson et al., 2000b; Table 1. Countries of the 127 studies
Bach, in Druck ; Bach, 2001; Bach, 2002; Bach, evaluated in this report.
Handke & Sinning, 1999; Barrios & Rodriguez,
2004; Bergen, 2001a; Bergen, 2001b; Bergen,
2002a; Bergen, 2002b; Bergh, Spaans & Swelm, Country Number of studies
2002; Boone, 2003; Böttger et al., 1990; Braun- Belgium 4
Germany 75
eis, 1999; Brauneis, 2000; Clemens & Lammen,
Denmark 2
1995; De Lucas, Janss & Ferrer, 2004; Dulas
France 2
Engineering Ltd, 1995; EAS, 1997; Erickson, Great Britain 6
Kronner & Gritski, 2003; Everaert, 2003; Evera- Netherlands 5
ert, Devos & Kuijken, 2002; Förster, 2003; Ger- Austria 2
jets, 1999; Gharadjedaghi & Ehrlinger, 2001; Spain 10
Guillemette & Larsen, 2002; Guillemette, Larsen
& Clausanger, 1999; Hall & Richards, 1962; Hor- USA 27
mann, 2000; Hydro Tasmania, ; Isselbächer & Australia 2
Isselbächer, 2001; Janss, 2000; Johnson, 2002;
Johnson et al., 2003; Johnson et al., 2000; Kaatz,
2000; Kaatz, 2002; Kerlinger, 2000; Ketzenberg
et al., 2002; Koop, 1997; Koop, 1999; Korn &
Scherner, 2000; Kowallik & Borbach-Jaene,
2001; Kruckenberg & Borbach-Jaene, 2001;
More than 2/3 of the analysed data was col-
Kruckenberg & Jaene, 1999; Leddy, Higgins &
lected only during the operation of the wind farm,
Naugle, 1999; Lekuona, 2001; Meek et al., 1993;
therefore no information about the situation be-
Menzel, 2002; Menzel & Pohlmeier, 1999; Müller
fore the installation of thewind farm is provided
& Illner, 2002; Musters, Noordervliet & Keurs,
and consequently also no information about
1996; Orloff & Flannery, 1996; Osborn et al., 1996;
changes due to the construction. Results from
Pedersen & Poulsen, 1991a; Percival, 2000;
separate control areas, which are used to dis-
Phillips, 1994; Reichenbach, 2002; Reichen-
tinguish influences of wind farms from more ge-
bach, 2003; Reichenbach & Schadek, 2003;
neral factors (e.g. higher mortality caused by a
Reichenbach & Sinning, 2003; Sachslehner &
cold winter), were only available in a small num-
Kollar, 1997; Scherner, 1999a; Schmidt et al.,
ber of studies (Tab. 2). Nineteen of the 127 stu-
2003; Schreiber, 1992; Schreiber, 1993a;
dies included the construction period of the wind
Schreiber, 1993c; Schreiber, 1999; Schreiber,
farms.
2002; SEO, 1995; SGS Environment, 1994; Sin-
10Material and Methods
Number of Phase Table 2. Designs of studies
studies (study in pre-
8 pre-construction during operation and with separate construction period,
control site control sites) on the
23 pre-construction during operation impact of wind farms.
9 during operation and with separate
control site
87 only during operation
Nearly all studies refer to wind farms, only a As expected, most of the data relate to bir-
few to single wind turbines. There was not ds of the open habitats (Tab. 3); woodland bir-
enough material to distinguish between wind ds were rarely recorded. Even so, 39 species
farms and single wind turbines. appear at least 10 times in the data tables.
The average duration of the 127 studies was The 127 studies analysed differ considerably
2.8 years, where one year counts as one season both in their approach to and their extent of ob-
(breeding time, autumn migration etc.) and stu- servation. The survey intensity ranged from ca-
dies which continued into a new calendar year sual observations to very well-founded, long-
were counted for pragmatic reasons as two ye- running (several years) projects. Overall, only a
ars. The range was 1 to 17 years. 51 studies, few of the studies are scientifically robust enough
more than a third, only covered one season (Fig. in their own right to withstand statistical tests for
1). effects of wind farms on bird populations. The
minimum requirements for such studies are at
Most of the studies apply to several bird or least two years (or two seasons) of pre-
bat species. Often for each species several construction monitoring of the wind farm site and
parameters (for example, minimal distance to at least the same amount of monitoring once the
wind farms and change in the resting population wind farm is operating. In addition, contempor-
after the installation of a wind farm; for further aneous parallel studies on control areas with no
details see below) were analysed. A compari- wind farms are necessary, so that further fac-
son of species and parameters led to a data tors (for example land use) may be taken into
matrix with 1789 data sets. Only around a third account. These standards apply to the scienti-
are quantitative analyses, the remaining data fic evidence of impacts of a single wind turbine
sets are „single observations“. Many of these on bird populations. It should not be confused
„single observations“ had their source in syste- with investigations to prove whether a particular
matic surveys, but within the framework of which area might be suitable for wind energy develop-
certain bird species were only rarely observed. ment, as other criteria apply here.
References were only suitable for a formal
60 meta-analysis (Fernandez-Duque & Valeggia,
50
1994), if the observation lasted at least four ye-
Number of studies
ars, or if they use an appropriate number of
40
control areas. Because this was only the case
30 for a few studies, alternative methods needed
20 to be used: (1) restricting the analysis to the
10 studies with statistically significant results; or
0
(2) evaluating data from all studies, irrespective
1 2 3 4 5 6 7 8 9 10 17 of their quality and scope. For reasons given
Years above, only a few studies were suitable for sta-
tistical analysis (alternative (1)), therefore, for
further interpretation, alternative (2) has been
Figure 1. Number of study years of 127 wind chosen.
farm impact studies
11Material and Methods
In this procedure, all available results were large and therefore the results are less depen-
included in the analysis, whether or not they dent on single, well-researched, but possibly
were derived from systematic survey, or were atypical studies. The independence of the data
based on only a few casual observations. The is also guaranteed. With a large number of stu-
disadvantage of using all available studies is dies the chances are improved that confoun-
that both casual observations and extensive ding factors cancel each other out.
research are in statistical terms treated equal-
ly. It cannot be ruled out that „extreme“ obser- Unless stated otherwise, the statistical tests
vations have been recorded more frequently in this report use the „null-hypothesis“ that wind
than less spectacular events. Additional factors, farms have no influence on the parameter under
which could be important in individual cases, consideration (such as population size before
also may not have been fully considered. Ho- and after the wind farm installation). The alter-
wever, the advantage of this method is that the native hypothesis is that wind farms do have an
number of studies included in the analysis is influence. The tests determine how many stu-
Species Number of records Table 3. Bird species with at
Lapwing Vanellus vanellus 80 least 10 records in the
Skylark Alauda arvensis 55 database .
Black-headed gull Larus ridibundus 47
Starling Sturnus vulgaris 40
Golden plover Pluvialis apricaria 39
Mallard Anas platyrhynchos 37
Buzzard Buteo buteo 35
Carrion crow Corvus corone corone 35
Curlew Numenius arquata 33
Kestrel Falco tinnunculus 32
Meadow pipit Anthus pratensis 28
Herring gull Larus argentatus 26
Oystercatcher Haematopus ostralegus 25
Linnet Carduelis cannabina 25
Blackbird Turdus merula 22
Woodpigeon Columba palumbus 22
Reed bunting Emberiza schoeniclus 20
Common gull Larus canus 18
White wagtail Motacilla alba 15
Grey heron Ardea cinerea 15
Chaffinch Fringilla coelebs 14
Whitethroat Sylvia communis 14
Yellowhammer Emberiza citrinella 14
Red kite Milvus milvus 14
Redshank Tringa totanus 14
Yellow wagtail Motacilla flava 13
Griffon vulture Gyps fulvus 12
Cormorant Phalacrocorax carbo 12
Marsh warbler Acrocephalus palustris 12
Black-tailed godwit Limosa limosa 12
Jackdaw Corvus monedula 11
Wigeon Anas penelope 11
Grey partridge Perdix perdix 11
Tufted duck Aythya fuligula 11
Reed warbler Acrocephalus scirpaceus 11
Fieldfare Turdus pilaris 11
Blue tit Parus caeruleus 10
Whinchat Saxicola rubetra 10
Swallow Hirundo rustica 10
12Material and Methods
dies had negative or positive effects (e.g. de- It is assumed that animals which are compa-
crease or increase of the population). As menti- ratively bounded to their breeding areas react
oned above, neither the strength of effect, nor differently to wind turbines from the ones pas-
statistical significance have been considered. sing through areas outside the breeding season,
Neutral results (e.g. constant population) have when they are less dependent on the resources
been classified as positive, in order to avoid of a single area and lack local knowledge. There-
any false association of wind energy with nega- fore, it has been distinguished whether studies
tive impacts. At the same time, statistically sig- were carried out during or outside the breeding
nificant negative effects shall be made more season (definition varies, depending which spe-
convincing and safer, and are not „diluted“ by cies is looked at). Most studies did not indicate
the inclusion of neutral results. If wind farms which activities the animals were carrying out at
have no influence on bird populations, one would the time of the observation (e.g. foraging, res-
expect roughly equal proportions of positive and ting, roosting) and therefore, this factor could
negative effects. If the frequency of positive and not be considered in this report.
negative effects differs strongly, an impact of
wind energy can be assumed. In these cases, The results have been divided into the follo-
the statistical test used is the binomial test wing categories: „impact on bird population“;
(Sachs, 1978). Because not all of the available „disturbance effects“; „barrier effects on migra-
information is used in this procedure (for ex- ting and flying birds“; and „collision rates“, be-
ample the strength of the effects), it is very con- cause the studies analysed suggested such a
servative, meaning that differences and trends division and because other parameters have
are only classed as significant when they are been rarely studied.
very strong. The statistical tests were carried
out using SPSS 7.5 statistical software. The category „disturbance effects“ analy-
ses bird and bat activity on the ground and its
Because the individual bird and bats spe- minimum distance from wind farms; the catego-
cies differ greatly in their biology and their use ry „barrier effects“ refers both to migration and
of habitat, the evaluation was carried out whe- to regular flights of birds, for example between
never possible for separate species. In cases feeding and roosting places.
when such differentiation was not possible spe-
cies were grouped.
13Impacts of wind farms on vertebrates
3 Impacts of wind farms on
vertebrates
bird species. Only waders and gamebirds dis-
3.1 Non-lethal impacts (disturbance, played reduced numbers in connection with
displacement, habitat loss) on birds wind farms. Positive or neutral effects predomi-
3.1.1 Change in distributions due to wind nate for the remaining species. Two species,
farms which breed in reeds (marsh warbler and reed
bunting) even showed significantly more positi-
In order to test if wind farms have an impact ve or neutral reactions towards wind farms than
on bird populations, only activity taking place negative reactions.
on the ground or in the vegetation has been in-
cluded. Migrating birds or birds on regular mig- Studies carried out outside the breeding
ration movements will be considered in section season show a very different picture. The nega-
3.1.3. Because only relatively few studies inclu- tive impacts of wind farms predominate and
de a before-after-control impact comparison, geese (bean goose, white-fronted goose, greylag
studies comparing bird populations on the wind goose and barnacle goose), wigeons, lapwings
farm site with bird populations at similar sites in and golden plovers display significantly more
the surrounding area have also been used. The negative than positive effects. The main excep-
studies are not suitable each in their own right tion is starling, for which significantly more posi-
to prove effects of wind farms, because the ha- tive (or neutral) effects were recorded.
bitat composition of control areas is never the
same as the analysed areas. Even a before- Overall, this study confirms statistically the
after-comparison is not conclusive, because results of others (Langston, 2002; Reichenbach,
other factors, e.g. weather or supra-regional 2003), namely than wind farms have less impact
trends, could be responsible for changes in on breeding birds, but more impacts on non-
population size. As the analysed studies differ breeding birds.
greatly from each other, for the purposes of in-
terpreting the data only positive or negative ef-
fects of wind farms have been taken into ac-
count. Negative effects are (1) population decli- 3.1.2 Minimum avoidance distance of
ne after installation of the wind farm or (2) redu- birds to wind farms
ced numbers of birds within the wind farm or
the surrounding area in comparison to control Many studies report the avoidance of wind
areas. Positive effects are accordingly popula- farms by birds, as well as distances involved.
tion increase after the construction of the wind For 28 species, with at least five studies each,
farm, or increased bird numbers around the the median and mean values of the minimum dis-
wind farm. The strength of the effects has not tances were calculated (Tab. 5). Some of the
been considered. If no population differences studies are the same as those used in the pre-
were detected, the effects were classified as vious chapter („impacts of wind farms on popu-
positive in order to avoid falsely inflating the lations“).
impact of negative effects (see above).
The data show much variation, which may
If there are no impacts of wind energy, equal be seen by comparing results between species
ratios of positive and negative effects are ex- and „within“ species. Therefore, in some cases
pected. Statistical significance has been tested standard deviations are very high (Tab. 5). Fi-
using a binomial test (for which the null hypothe- gures 2 to 13 confirm high variances for some
sis is that data are randomly distributed) (Table results. This may be explained either by the use
4). of casual observations, which naturally show
higher dispersion, or by large differences
Data from 40 species which were included between individual wind farms (see below).
in at least six studies were good enough to be
included in statistical tests (Tab. 4). Negative Despite the high degree of variation, some
population impacts of wind farms during the trends are clearly noticeable. Avoidance dis-
breeding season could not be verified for any tances during the breeding season were smal-
14Impacts of wind farms on vertebrates
Table 4. Impacts of wind farms on bird populations as revealed from literature. The figures show
the numbers of studies with positive or negative effects. Positive effect: 1) Density of
birds higher or equal after construction of the wind farms or 2) density of birds close to
wind farm higher or equal to density of control sites. Grey shadings indicate predomina-
ting negative effects. The last column gives the result of sign tests.
Species No negative Negative Significance
effect effect
Breeding season
Mallard Anas platyrhynchos 6 5 ns
Common buzzard Buteo buteo 3 3 ns
Grey partridge Perdix perdix 4 5 ns
Quail Coturnix coturnix 1 5 ns
Black-tailed godwit Limosa limosa 5 6 ns
Redshank Tringa totanus 2 9 ns
Oystercatcher Haematopus ostralegus 6 7 ns
Lapwing Vanellus vanellus 11 18 ns
Skylark Alauda arvensis 15 15 ns
Meadow pipit Anthus pratensis 15 7 ns
Yellow wagtail Motacilla flava 7 3 ns
White wagtail Motacilla alba 4 4 ns
Whinchat Saxicola rubetra 2 6 ns
Stonechat Saxicola torquata 5 1 ns
Blackbird Turdus merula 5 4 ns
Wren Troglodytes troglodytes 5 1 ns
Willow warbler Phylloscopus trochilus 4 2 ns
Chiffchaff Phylloscopus collybita 4 2 ns
Sedge warbler Acrocephalus schoenobaenus 8 0 0.05
Reed warbler Acrocephalus scirpaceus 6 1 ns
Marsh warbler Acrocephalus palustris 6 4 ns
Whitethroat Sylvia communis 8 4 ns
Blue tit Parus caeruleus 4 3 ns
Yellowhammer Emberiza citrinella 4 5 ns
Reed bunting Emberiza schoeniclus 10 2 0.05
Linnet Carduelis cannabina 2 6 ns
Carrion crow Corvus corone 6 2 ns
Blackbird Turdus merula 5 4 ns
Non-breeding season
Grey heron Ardea cinerea 5 1 ns
Wigeon Anas penelope 0 9 0.01
Mallard Anas platyrhynchos 3 7 ns
Tufted duck Aythya fuligula 2 6 ns
Red kite Milvus milvus 3 4 ns
Common buzzard Buteo buteo 10 10 ns
Kestrel Falco tinnunculus 13 7 ns
Curlew Numenius arquata 11 19 ns
Oystercatcher Haematopus ostralegus 4 3 ns
Lapwing Vanellus vanellus 12 29 0.05
Golden plover Pluvialis apricaria 8 21 0.05
Common gull Larus canus 3 5 ns
Herring gull Larus argentatus 2 4 ns
Black-headed gull Larus ridibundus 14 5 ns
Woodpigeon Columba palumbus 1 6 ns
Skylark Alauda arvensis 4 2 ns
Fieldfare Turdus pilaris 1 5 ns
Starling Sturnus vulgaris 17 5 0.05
Jackdaw Corvus corone 12 7 ns
Goose spp. 1 12 0.01
15Impacts of wind farms on vertebrates
ler than outside the breeding season. Only a tercatcher, gulls, starling and crows, which were
few wader species avoided close contact with frequently observed close to or within wind
wind farms at all times of year. The unusually farms.
high breeding season avoidance distance for
black-tailed godwit may be due to chance, be- The sensitive species roosted at least 400-
cause this species is relatively rare. There is no 500m from wind farms (Tab. 5). Greater avo-
direct evidence so far that the population of idance distances are likely to cause negative
black-tailed godwit has been reduced by wind effects only in exceptional circumstances. To a
farms (Ketzenberg et al., 2002). The diagrams of large extent, the results correspond with the
the breeding skylark and reed bunting demons- conclusions of single studies on this topic (Kru-
trate that distances of more than 200m were ckenberg & Jaene, 1999; Reichenbach, 2003;
exceptional; the majority of birds were present Schreiber, 1993b; Schreiber, 1999).
in the immediate vicinity of wind farms.
When assessing the results, it should be re-
Higher avoidance distances from wind farms membered that it was only possible to analyse
were generally observed outside the breeding a large number of studies for a small number of
season. As expected, birds of open habitats, species. Many species were hardly ever or even
e.g. geese, ducks and waders, generally avoi- never examined. This is particularly so for the
ded turbines by several hundred meters. Gee- more controversial species (storks, birds of
se were particularly sensitive. Remarkable ex- prey, cranes). Therefore, the list of species sen-
ceptions were grey heron, birds of prey, oys- sitive to disturbance is not complete.
Geese, non-breeding season Common buzzard, non-breeding season
4 12
Anzahl der Studien
Number of studies
10
3
8
2 6
4
1
2
0 0
50 150 250 350 450 550 650 750 850 50 150 250 350 450 550 650 750 850
Distance (m) Distance (m)
Figure 2. Minimal distances to wind farms of Figure 3. Minimal distances to wind farms of
geese during the non-breeding season. Common Buzzards during the non-
The heights of the columns show the breeding season. The heights of the
numbers of studies. The minimum columns show the numbers of studies.
distances to wind farms (or the dis- The minimum distances to wind farms
tances up to which disturbances could (or the distances up to which distur-
be noticed) are shown on the x-axis. bances could be noticed) are shown
on the x-axis.
Figure 4. Minimal distances to wind farms of
Kestrel, non-breeding season
Kestrels during the non-breeding
14 season. The heights of the columns
show the numbers of studies. The
Number of studies
12
10 minimum distances to wind farms (or
8
6
the distances up to which disturbances
4 could be noticed) are shown on the x-
2 axis.
0
50 150 250 350 450 550 650 750 850
Distance (m)
16Impacts of wind farms on vertebrates
Lapwing, breeding season Lapwing, non-breeding season
7 12
Number of studies
Number of studies
6 10
5 8
4
6
3
4
2
1 2
0 0
50 150 250 350 450 550 650 750 850 50 150 250 350 450 550 650 750 850
Distance (m) Distance (m)
Figure 5. Minimal distances to wind farms of Figure 6. Minimal distances to wind farms of
Lapwings during the breeding season. Lapwings during the non-breeding
The heights of the columns show the season. The heights of the columns
numbers of studies. The minimum show the numbers of studies. The
distances to wind farms (or the dis- minimum distances to wind farms (or
tances up to which disturbances could the distances up to which disturbances
be noticed) are shown on the x-axis. could be noticed) are shown on the x-
axis.
Golden plover, non-breeding season Curlew, non-breeding season
10 10
Number of studies
Number of studies
8 8
6 6
4 4
2 2
0 0
50 150 250 350 450 550 650 750 850 50 150 250 350 450 550 650 750 850
Distance (m) Distance (m)
Figure 7. Minimal distances to wind farms of Figure 8. Minimal distances to wind farms of
Golden Plovers during the non-bree- Curlews during the non-breeding
ding season. The heights of the co- season. The heights of the columns
lumns show the numbers of studies. show the numbers of studies. The
The minimum distances to wind farms minimum distances to wind farms (or
(or the distances up to which distur- the distances up to which disturbances
bances could be noticed) are shown could be noticed) are shown on the x-
on the x-axis. axis.
Figure 9. Minimal distances to wind farms of
Black-headed gull, non-breeding season
Black-headed Gulls during the non-
14 breeding season. The heights of the
columns show the numbers of studies.
Number of studies
12
10 The minimum distances to wind farms
8
(or the distances up to which distur-
6
4 bances could be noticed) are shown
2 on the x-axis.
0
50 150 250 350 450 550 650 750 850
Distance (m)
17Impacts of wind farms on vertebrates
Skylark, breeding season Reed bunting, breeding season
12 10
Number of studies
Number of studies
10 8
8
6
6
4
4
2 2
0 0
50 150 250 350 450 550 650 750 850 50 150 250 350 450 550 650 750 850
Distance (m) Distance (m)
Figure 10. Minimal distances to wind farms Figure 11. Minimal distances to wind farms of
of Skylarks during the breeding Reed Buntings during the breeding
season. The heights of the columns season. The heights of the columns
show the numbers of studies. The show the numbers of studies. The
minimum distances to wind farms minimum distances to wind farms (or
(or the distances up to which the distances up to which disturbances
disturbances could be noticed) are could be noticed) are shown on the x-
shown on the x-axis. axis.
Starling, non-breeding season Carrion crow, non-breeding season
14 14
Number of studies
12
Number of studies
12
10 10
8 8
6 6
4 4
2 2
0 0
50 150 250 350 450 550 650 750 850 50 150 250 350 450 550 650 750 850
Distance (m) Distance (m)
Figure 12. Minimal distances to wind farms of Figure 13. Minimal distances to wind farms of
Starlings during the non-breeding Carrion Crows during the non-breeding
season. The heights of the columns season. The heights of the columns
show the numbers of studies. The show the numbers of studies. The
minimum distances to wind farms (or minimum distances to wind farms (or
the distances up to which disturbances the distances up to which disturbances
could be noticed) are shown on the x- could be noticed) are shown on the x-
axis. axis.
Habituation of birds to wind farms on“ is not used here in the strict behavioural
sense, but rather colloquially. In ethology, habi-
Animals can become accustomed to certain tuation means the capacity of an animal to be-
types of repeated disturbance. In the case of come accustomed to and no longer react to-
wind farms this could mean that distances by wards repeated disturbance, related neither to
which birds avoid turbines slowly reduce du- positive nor to negative consequences (Immel-
ring the years after installation. The negative ef- mann, 1976). The term is used here to describe
fects would get less and fewer birds would be a [hypothetical] phenomenon whereby the dis-
displaced from their area. The term „habituati- tribution of birds becomes closer to wind farms
18Impacts of wind farms on vertebrates
Table 5. Minimal distances to wind farms in studies of different bird species.
Species Number of Median Mean SD
studies
Breeding season
Mallard Anas platyrhynchos 8 113 103 56
Black-tailed godwit Limosa limosa 5 300 436 357
Oystercatcher Haematopus ostralegus 8 25 85 113
Lapwing Vanellus vanellus 13 100 108 110
Redshank Tringa totanus 6 188 183 111
Skylark Alauda arvensis 20 100 93 71
Meadow pipit Anthus pratensis 9 0 41 53
Yellow wagtail Motacilla flava 7 50 89 107
Blackbird Turdus merula 5 100 82 76
Willow warbler Phylloscopus trochilus 5 50 42 40
Chiffchaff Phylloscopus collybita 5 50 42 40
Sedge warbler Acrocephalus schoenobaenus 7 0 14 24
Reed warbler Acrocephalus scirpaceus 11 25 56 70
Marsh warbler Acrocephalus palustris 9 25 56 68
Whitethroat Sylvia communis 9 100 79 65
Reed bunting Emberiza schoeniclus 13 25 56 70
Linnet Carduelis cannabina 5 125 135 29
Non-breeding season
Grey heron Ardea cinerea 6 30 65 97
Wigeon Anas penelope 9 300 311 163
Swan spp. 8 125 150 139
Goose spp. 13 300 373 226
Mallard Anas platyrhynchos 9 200 161 139
Diving ducks 12 213 219 122
Common buzzard Buteo buteo 15 25 50 53
Kestrel Falco tinnunculus 14 0 26 45
Curlew Numenius arquata 24 190 212 176
Oystercatcher Haematopus ostralegus 6 15 55 81
Lapwing Vanellus vanellus 32 135 260 410
Common snipe Gallinago gallinago 5 300 403 221
Golden plover Pluvialis apricaria 22 135 175 167
Woodpigeon Columba palumbus 5 100 160 195
Common gull Larus canus 6 50 113 151
Black-headed gull Larus ridibundus 15 0 97 211
Skylark Alauda arvensis 6 0 38 59
Starling Sturnus vulgaris 16 0 30 54
Carrion crow Corvus corone 16 0 53 103
over time. There was no evidence to show if around wind farms some year after installation),
habituation is founded on an individual basis. it could not be completely ruled out that these
were due to other factors, e.g. changes in habi-
11 studies provided data with at least two tat. Because of the variable quality of the data,
years of observation after the installation of the the method, used elsewhere in this report has
wind farm. Each study analysed several spe- also been used here. The number of cases sug-
cies, which altogether resulted in 122 data sets. gesting habituation (see above), have been coun-
Only a few studies explicitly referred to „habitu- ted and compared with the number of cases,
ation“. Even if observations suggested habitua- which do not suggest habituation. If cases of
tion (closer distribution in relation to wind farms habituation strongly predominate, one could talk
after a few years; population increase in the area of a widespread phenomenon. If this is not the
19Impacts of wind farms on vertebrates
case, (e.g. the cases with or without habituation Only in a few cases were sufficient data avai-
are balanced or those without habituation pre- lable for individual species. During the breeding
dominate), then it is questionable whether birds season, results of six studies on lapwing indi-
can get used to wind farms on a large scale. cate no habituation while two cases assume
habituation. Outside the breeding season, three
For breeding birds, 38 out of 84 cases indi- out of five studies suggest habituation. There
cate habituation (45%, so less than half). For were six studies for both skylark and meadow
resting birds, the corresponding numbers are pipit; in each case, three studies indicated ha-
25 out of 38 cases. More than half of the resting bituation.
birds (66%) therefore seem to get used to wind
farms. None of the results differ significantly from The observed degree of habituation was in
random, effectively a balance between cases most cases very small. Even if it cannot ruled
with and without habituation. out that birds actually become habituated to
wind farms, the data clearly indicate that this is
neither a widespread nor a strong phenome-
non.
Table 6. Number of studies with or without indications of habituation of birds to wind farms. A
decreasing minimal distance between birds and wind farms in the course of study years
is considered as an indication of habituation, the reverse is considered as the lack of
habituation.
Species Number of Number of
cases without cases with
signs of signs of
habituation habituation
(increased (decreased
distance to distance to
wind farm) wind farm)
Non-breeding season
White-fronted goose Anser albifrons 1 0
Wigeon Anas penelope 0 1
Mallard Anas platyrhynchos 0 1
Eider Somateria mollissima 0 2
Common scoter Melanitta nigra 0 2
Red kite Milvus milvus 1 0
Common buzzard Buteo buteo 1 1
Kestrel Falco tinnunculus 1 1
Coot Fulica atra 0 1
Oystercatcher Haematopus ostralegus 0 1
Curlew Numenius arquata 4 0
Lapwing Vanellus vanellus 2 3
Golden plover Pluvialis apricaria 1 3
Common gull Larus canus 1 1
Herring gull Larus argentatus 1 0
Black-headed gull Larus ridibundus 1 1
Woodpigeon Columba palumbus 1 1
Starling Sturnus vulgaris 1 0
Carrion crow Corvus corone 1 2
20Impacts of wind farms on vertebrates
Species Number of Number of
cases without cases with
signs of signs of
habituation habituation
(increased (decreased
distance to distance to
wind farm) wind farm)
Breeding season
Mallard Anas platyrhynchos 0 2
Grey partridge Perdix perdix 0 4
Quail Coturnix coturnix 0 1
Pheasant Phasianus colchicus 0 1
Moorhen Gallinula chloropus 0 1
Oystercatcher Haematopus ostralegus 2 2
Common snipe Gallinago gallinago 0 1
Curlew Numenius arquata 1 0
Black-tailed godwit Limosa limosa 1 2
Redshank Tringa totanus 3 1
Lapwing Vanellus vanellus 6 2
Woodpigeon Columba palumbus 1 0
Skylark Alauda arvensis 3 3
Meadow pipit Anthus pratensis 3 3
White wagtail Motacilla alba 1 0
Yellow wagtail Motacilla flava 0 2
Red-backed shrike Lanius collurio 0 1
Dunnock Prunella modularis 0 1
Wheatear Oenanthe oenanthe 0 1
Whinchat Saxicola rubetra 1 2
Stonechat Saxicola torquata 1 1
Redstart Phoenicurus phoenicurus 1 0
Spotted flycatcher Muscicapa striata 1 0
Wren Troglodytes troglodytes 0 1
Mistle thrush Turdus viscivorus 1 0
Blackbird Turdus merula 1 0
Song thrush Turdus philomelos 1 0
Grasshopper warbler Locustella naevia 1 1
Sedge warbler Acrocephalus schoenobaenus 1 2
Reed warbler Acrocephalus scirpaceus 0 2
Marsh warbler Acrocephalus palustris 1 0
Icterine warbler Hippolais icterina 1 0
Blackcap Sylvia atricapilla 1 0
Garden warbler Sylvia borin 1 0
Whitethroat Sylvia communis 1 0
Chiffchaff Phylloscopus collybita 1 0
Willow warbler Phylloscopus trochilus 1 0
Great tit Parus major 1 0
Blue tit Parus caeruleus 1 0
Yellowhammer Emberiza citrinella 1 0
Reed bunting Emberiza schoeniclus 2 0
Greenfinch Carduelis chloris 0 1
Chaffinch Fringilla coelebs 1 0
Tree sparrow Passer montanus 0 1
Starling Sturnus vulgaris 1 0
Nutcracker Garrulus glandarius 1 0
21Impacts of wind farms on vertebrates
If the impacts of individual wind farms ap- oystercatcher and redshank, are less affected
pear to increase over the years, this could be by tall turbines than by small ones. Only lap-
explained by the reluctance of breeding birds wing and black-tailed godwit clearly avoid lar-
to give up their territory immediately after the ger turbines.
installation of the wind farm. As territories with
wind farms become less attractive to future ge- Resting birds show a different picture. With
nerations in this area, in time this results in a a few exceptions (grey heron, diving ducks,
thinning population density around the wind oystercatcher and common snipe), the higher
farms. It was not possible, on the basis of exis- the turbines, the greater the avoidance distance.
ting data, to determine if such a phenomenon It may be that differences between breeding and
actually occurs. non-breeding seasons are in fact the result of
observing different suites of species at these
different times of year. Breeding season obser-
Avoidance distance and height of turbine vations were mainly of songbirds, whereas non-
breeding observations tended to be of larger
As mentioned above, impacts on bird popu- species of open habitats.
lations differ between wind farms. The height of
wind turbines appears to be at least partly re-
sponsible for these differences. The question of 120
how the height of wind turbines relates to avo- 100
idance distances is also highly relevant to „re- Hub height (m) 80
powering“.
60
Turbine hub height is perhaps the most sig- 40
nificant factor influencing birds. Hub height is 20
closely correlated with the capacity (wattage) of
0
the wind turbine. The studies analysed in this 0,0 0,5 1,0 1,5 2,0
report show the following significant statistically Power capacity (MW)
relationship (regression function, Fig. 14):
Hub height (m) = 65.22 * power (MW) 0.457 Figure 14. Relationship between tower height
R 2 = 0.73 (n = 78; pYou can also read
