Abstract
The aim of this survey was to investigate the impact caused by installation and operation of wind turbines on birds in the interior of a country. Due to the different sensibilities of birds according to their status roosting and wintering, breeding as well as migrating birds were treated separately. Another aspect focused on the effects of wind turbines on birds of prey.
Roosting and Wintering Birds
The primary goal of this part of the study was to analyse the use of wind resource areas as roosting and/or feeding habitats for birds. Therefore bird counts (cf. BIBBY et al. 1995) were conducted from January to April of 1998, 1999 and 2000 in three existing wind resource areas (on average every sixth day). In addition, a prae/post-test on one impact and one control site was carried out from 1998 to 2000. Species composition and numbers were comparable in the three years of examination on all sites. The results show no indication of a wind turbine effect on the number and the spatial distribution of Common Buzzard (Buteo buteo), Kestrel (Falco tinnunculus), Hen Harrier (Circus cyaneus) and Carrion Crow (Corvus c. corone), neither on the existing wind resource areas nor in the prae/post-test. However, flocks of a greater number of Carrion Crows seemed to avoid the entire wind resource area. European Starling (Sturnus vulgaris) and Woodpigeon (Columba palumbus) avoided the vicinity of the turbines in a 100 m radius, whereas it is not clear if the behaviour was caused by the turbines. The prae/post-comparison of the spatial distribution of roosting Lapwings (Vanellus vanellus), on the other hand, gives strong evidence of an avoidance behaviour within 200 m to the turbines which leads to a loss of roosting habitat. As possible causes of this behaviour turbulences as well as acoustic stimuli are discussed. Consequently, it is recommended that wind turbines should not be placed in a distance of 200 m to important Lapwing roosting sites.
Breeding Birds
In order to investigate the possible effects of the installation and operation of wind turbines on breeding birds a BACI-study (cf. STEWART-OATEN et al. 1986) was conducted on two planned wind resource areas with one control site each. The points of interests were density and spatial distribution of breeding birds. Data collection took place between 1997 and 2000. In consideration of the control sites no remarkable changes in the breeding bird communities and numbers of breeding pairs were observed. Wind turbines did not influence the spatial distribution of Skylark (Alauda arvensis) territories. This statement seemed to be accurate for Chaffinch (Fringilla coelebs) and Yellowhammer (Emberiza citrinella), too, however with a smaller degree of certainty. Due to the decreased number of Common Quails (Coturnix coturnix) on one impact site there is a weak hint of a disturbance effect. Additional studies are needed to investigate if the observed decline is linked to the installation and/or operation of wind turbines.
Additionally the singing behaviour of Skylarks was examined in detail using the animal-focus-sampling method (cf. ALTMANN 1974). Neither song length, song output within a 15 minutes period nor pauses between two song displays differed before and after the installation of the wind power plants, even in comparison to the control site.
Birds of Prey
Habitat use and behaviour of birds of prey were investigated on one control and one impact site before and after the installation of wind turbines (BACI-study, cf. STEWART-OATEN et al. 1986). Using the scan-sampling method (cf. ALTMANN 1974) a standardized observation scheme was developed to describe and quantify frequency of occurrence as well as spatial and temporal patterns of raptors between 1998 and 2000. For Common Buzzard, Kestrel and Red Kite (Milvus milvus) none of the analysed variables did differ significantly from what could be expected of the BACI-comparison. However, Common Buzzard and Kestrel showed slight differences in their perching behaviour in the wind resource area. This was not due to the operation of wind turbines, but to a loss of perching facilities and to an increase of disturbance stimuli as a result of installation and maintenance of wind turbines. Since Montagu`s Harrier (Circus pygargus), Hen Harrier and Marsh Harrier (C. aeruginosus) were using the wind resource area as hunting sites, wind turbines seemed to have no effect in terms of habitat fragmentation.
Migrating Birds
Concern was expressed about the disturbance to migrating birds from wind turbines and also about the potential mortality via bird strikes. To assess the frequency of reactions of migrating birds in the vicinity of wind turbines observations of visible migration took place at four locations in different -mainly upland- landscapes in autumn 1998 and 1999. Bird flight characteristics were determined in separate pre-defined behavioural categories, in this way accuracy of data collection was increased. A comparison of the results of the four wind resource areas should give some information about the main factors affecting the intensity of disturbance. Since nearly all migrating individuals at the four sites were small songbirds (Passeres), results are restricted to this group of species. The amount of events (an individual bird or a flock of birds) with a clear reaction of birds which was linked to turbines ranged between 4% and 45%. The most occurring reaction was a shift in the flight path in the horizontal plane. In 3% to 19% of all recorded events flocks split up in two or more groups. As a result of the comparison of the four wind resource areas number and density of wind turbines seemed to be positively correlated with the frequency of reactions. Further more higher reaction rates occurred where wind turbines were arranged in a line perpendicular to the main flight direction of migrating birds and where distance between the rotor and the ground was low. To sum up, disturbance of wind turbines in the interior of a country seems not to be as remarkable as to cause a significant negative effect on migrating songbirds.
Another aim of the survey was to estimate the collision risk of birds on wind turbines in the interior of a country. Therefore fatality searches were conducted on five study plots with one turbine each during autumn 1998 and 1999. In order to reduce the rate at which scavengers remove dead birds from the sites an electric fence was build up. Bird mortality was very low at the five study plots: only one dead bird, a Goldcrest (Regulus regulus), was found during 82 fatality searches. As a consequence, collision risk at wind turbines in the interior of a country can be seen as low. However, it should be mentioned that disturbance of migrating birds as well as mortality rate is affected by several factors and could vary between different areas.
Installation and operation of wind turbines could lead to some negative impacts on particular bird species. These impacts can be reduced to a tolerable degree by a responsible planning of future wind resource areas considering nature conservational aspects. Therefore wind turbines should not be placed in areas with a great importance for birds as well as in areas with a high occurrence of migrating birds.