assessing the impacts of wind farms on birds

Ibis (2006) 148 29ndash42

copy 2006 British Ornithologistsrsquo Union Ibis 148 29ndash42

Blackwell Publishing Ltd Assessing the impacts of wind farms on birdsALLAN L DREWITT1 amp ROWENA H W LANGSTON2

1Northminster House Peterborough PE1 1UA UK 2The Royal Society for the Protection of Birds Sandy Bedfordshire SG19 2DL UK

The potential effects of the proposed increase in wind energy developments on birds areexplored using information from studies of existing wind farms Evidence of the four maineffects collision displacement due to disturbance barrier effects and habitat loss is presentedand discussed The consequences of such effects may be direct mortality or more subtlechanges to condition and breeding success The requirements for assessing the impact offuture developments are summarized including relevant environmental legislation andappropriate methods for undertaking baseline surveys and post-construction monitoringwith particular emphasis on the rapidly developing area of offshore wind farm assessmentsMitigation measures which have the potential to minimize impacts are also summarizedFinally recent developments in the monitoring and research of wind energy impacts on birdsare outlined and some areas for future work are described

INTRODUCTION

The UK in common with many other EU memberstates is set to see a rapid increase in the number ofwind farms The UK governmentrsquos target is to derive10 of energy from renewables by 2010 of which7ndash8 would be from wind energy (8ndash10 GW intotal) It is estimated that using the latest turbinetechnology the installation of 2000 turbinesonshore and approximately 1500 offshore wouldbe sufficient to meet this target (wwwbweacom)Although it is widely accepted that greenhouse gasemission is the primary cause of anthropogenicallydriven global climate change (Huntley et al 2006)and that moving to renewable energy sources willplay a vital role in reducing emissions the unprece-dented rate and scale of development of wind farmsraises questions about impacts on wildlife Unfortu-nately understanding of the potential implications oflarge-scale wind energy developments especiallyoffshore has not kept pace with the recent rise in thenumber of development proposals

This paper explores the potential effects of theproposed increase in wind energy developments onbirds summarizing information collected from studiesof existing wind farms and identifying possible impactsresulting from the larger scale wind farms currentlyproposed and under development It outlines how

impact assessments for proposed developmentsshould be made and what mitigation measuresmight be available to minimize those impactsFinally it explores recent developments in the mon-itoring and research of wind energy impacts on birdsand describes some important areas for future work

WIND ENERGY IN THE UK

The UK has one of the largest wind resources inEurope with 40 of Europersquos total potentialresource for wind-generated power the equivalentto three times the UKrsquos current electricity usage(Troen amp Petersen 1989) There are currently 101wind farms in the UK consisting of 1234 turbineswhich produce 979 MW of generating capacity(wwwbweacom) No significant impacts on birdshave been recorded at any of these wind farms todate The majority of developments in the UK arerelatively small consisting of 1ndash20 turbines and lessthan 10 MW output This is in contrast to recent andproposed developments especially offshore whichare of a much larger scale in terms of number of tur-bines turbine size and wind farm extent For exam-ple the recently constructed wind farms at NorthHoyle in Liverpool Bay and Scroby Sands off theEast Anglian coast both comprise 30 turbines witheach having a 2 MW output These developmentsare dwarfed by the latest offshore proposals withthe proposed London Array in the Thames estuaryCorrespondence Allandrewittenglish-natureorguk

30 A L Drewitt amp R H W Langston


comprising up to 300 turbines each having an out-put of 3 MW or more and extending over 200 km2Onshore developments although generally notapproaching the scale of the latest offshore propos-als are also exploiting technological advances andnow tend to use larger turbines These developmentscould have different implications for birds than theearlier smaller wind farms and turbines

The potential vulnerability of wildlife to large-scale wind energy developments has been recog-nized in the latest round of offshore developmentproposals in the Greater Wash the Thames Estuaryand off north-west England Developments are cur-rently excluded from a coastal strip of a minimumwidth of 8 km from the shoreline and extending to13 km in areas of particular landscape sensitivityAdditionally in north-west England wind farmdevelopment is excluded from waters 10 m deep orless This is in recognition of the potentially high sen-sitivity of shallow coastal waters to wind farm devel-opments especially with regard to displacement ofseaducks that dive to feed on shallow subtidal habi-tats visual impacts from the shore and the possibleimpacts on inshore fishing and recreational activities

Wind farms comprise the wind turbines them-selves interconnecting cables transformer stationsmeteorological masts and ancillary infrastructureincluding onshore access roads and visitor centresThe components of the individual turbines comprisea tapering mast the nacelle or hub foundations androtor blades The proportions of the turbine aredetermined by the rotor blade length and towerheight The largest 2 MW machines onshore canhave a tower height of 80 m and a rotor diameter of90 m resulting in an overall height of 125 m (over400 feet) By comparison a normal electricity trans-mission pylon is 52 m tall In the case of these largeturbines the height of the rotor sweep above groundcan be as much as 35 m Turbine design for offshorewind farms is currently similar to that for terrestrialuse although the economics of offshore develop-ment will tend to result in turbines which are signif-icantly larger than those deployed onshore Offshoremachines with a generating capacity of at least5 MW are already anticipated

POTENTIAL EFFECTS ON BIRDS

To be effective wind farms must be sited in openexposed areas where there are high average windspeeds This means that they are often proposed inupland coastal and offshore areas thus potentially

affecting important habitats for breeding winteringand migrating birds The effects of a wind farm onbirds are highly variable and depend on a wide rangeof factors including the specification of the develop-ment the topography of the surrounding land thehabitats affected and the number and species ofbirds present With so many variables involved theimpacts of each wind farm must be assessed individ-ually The principal areas of concern with regard toeffects on birds are described below Each of thesepotential effects can interact either increasing theoverall impact on birds or in some cases reducing aparticular impact (for example where habitat losscauses a reduction in birds using an area which mightthen reduce the risk of collision)

COLLISION

Collision mortality

Direct mortality or lethal injury of birds can resultnot only from collisions with rotors but also withtowers nacelles and associated structures such asguy cables power lines and meteorological mastsThere is also evidence of birds being forced to theground as a result of being drawn into the vortexcreated by moving rotors (Winkelman 1992b) Themajority of studies of collisions caused by wind tur-bines have recorded relatively low levels of mortality(eg Winkelman 1992a 1992b Painter et al 1999Erickson et al 2001) This is perhaps largely a reflec-tion of the fact that many of the studied wind farmsare located away from large concentrations of birdsIt is also important to note that many records arebased only on finding corpses with no correction forcorpses that are overlooked or removed by scaven-gers (Langston amp Pullan 2003)

Accepting that many wind farms result in only lowlevels of mortality even these levels of additionalmortality may be significant for long-lived species withlow productivity and slow maturation rates espe-cially when rarer species of conservation concernare affected In such cases there could be significanteffects at the population level (locally regionally orin the case of rare and restricted species nationally)particularly in situations where cumulative mortal-ity takes place as a result of multiple installations

Collision risk

Collision risk depends on a range of factors relatedto bird species numbers and behaviour weather


Impacts of wind farms on birds 31

conditions and topography and the nature of thewind farm itself including the use of lightingClearly the risk is likely to be greater on or near areasregularly used by large numbers of feeding or roost-ing birds or on migratory flyways or local flightpaths especially where these are intercepted by theturbines Large birds with poor manoeuvrability(such as swans and geese) are generally at greater riskof collision with structures (Brown et al 1992) andspecies that habitually fly at dawn and dusk or atnight are perhaps less likely to detect and avoidturbines (Larsen amp Clausen 2002) Collision risk mayalso vary for a particular species depending on agebehaviour and stage of annual cycle For examplework on terns has shown that birds making regularforaging flights to provision chicks are more suscep-tible to collision with overhead wires because theytend to fly closer to the structures at this time(Henderson et al 1996)

Risk also changes with weather conditions withevidence from some studies showing that more birdscollide with structures when visibility is poor due tofog or rain (eg Karlsson 1983 Erickson et al 2001)although this effect may be to some extent offset bylower levels of flight activity in such conditionsBirds that are already on migration however cannotavoid poor weather conditions and will be more vul-nerable if forced by low cloud to descend to a loweraltitude or land Strong headwinds also affect colli-sion rates and migrating birds in particular tend to flylower when flying into the wind (Winkelman 1992bRichardson 2000) Collision risk in coastal and off-shore areas is also likely to vary as birds move aroundin response to the state of tide and offshore currents

The precise location of a wind farm site can becritical Particular topographic features may be usedfor lift by soaring species (eg Alerstam 1990) or canresult in large numbers of birds being funnelledthrough an area of turbines Birds also lower theirflight height in some locations for example whenfollowing the coastline or crossing a ridge (Alerstam1990 Richardson 2000) which might place them atgreater risk of collision with rotors

Features of wind turbines associated with collision riskThe size and alignment of turbines and rotor speedare likely to influence collision risk (Winkelman1992c Thelander et al 2003) as are aviation andshipping warning lights on turbines which mayincrease the risk of collision by attracting and dis-orientating birds The effects of lights in thesecircumstances are poorly known though collisions

of large numbers of migrants with illuminatedstructures especially during overcast nights withdrizzle or fog are well documented (Hill 1990Erickson et al 2001) The current advice is to use theminimum number of intermittent flashing whitelights of lowest effective intensity (Huumlppop et al2006) It is not known if the use of lights on theouter turbines alone which would perhaps result inmore diffuse lighting would be less likely to disori-entate birds than a single bright point source

Recorded collision ratesA review of the available literature indicates thatwhere collisions have been recorded the rates perturbine are very variable with averages ranging from001 to 23 bird collisions annually (the highest figureis the value following correction for scavengerremoval for a coastal site in Belgium and relates togulls terns and ducks amongst other species (Ever-aert et al 2001)) Although providing a helpful andstandardized indication of collision rates averagerates per turbine must be viewed with some cautionas they are often cited without variance and canmask significantly higher rates for individual tur-bines or groups of turbines (as Everaert et al (2001)demonstrate)

Some of the highest levels of mortality have beenfor raptors at Altamont Pass in California (Howellamp DiDonato 1991 Orloff amp Flannery 1992) and atTarifa and Navarre in Spain (Barrios amp Rodriguezunpublished data) These cases are of particularconcern because they affect relatively rare and long-lived species such as Griffon Vulture Gyps fulvus andGolden Eagle Aquila chrysaetos which have lowreproductive rates and are vulnerable to additivemortality At Altamont Golden Eagles congregate tofeed on super-abundant prey which supports veryhigh densities of breeding birds In the Spanish casesextensive wind farms were built in topographicalbottlenecks where large numbers of migrating andlocal birds fly through a relatively confined area dueto the nature of the surrounding landscape forexample through mountain passes or use risingwinds to gain lift over ridges (Barrios amp Rodriguez2004) Although the average numbers of fatalitiesannually per turbine were generally low at AltamontPass and Tarifa ranging from 002 to 015 collisionsturbine overall collision rates were high because ofthe large numbers of turbines involved (over 7000 atAltamont) At Navarre corrected annual estimatesranging from 36 to 643 mortalitiesturbine wereobtained for birds and bats (unpublished data)



Thus a minimum of 75 Golden Eagles are killedannually at Altamont and over 400 Griffon Vulturesare estimated (following the application of correc-tion factors) to have collided with turbines at Nav-arre Work on Golden Eagles at Altamont Passindicated that the population was declining in thisarea thought to be at least in part due to collisionmortality (Hunt et al 1999 Hunt 2001)

Examples from coastal sites in north-west Europeprovide corrected yearly average collision ratesranging from 001 to 12 birdsturbine (winteringwaterfowl gulls passerines) in the Netherlands(Winkelman 1989 1992a1992b1992c 1995) 6birdsturbine (Common Eider Somateria mollissimaand gulls) at Blyth in Northumberland (Painter et al1999) and 4ndash23 birdsturbine (ducks gulls terns ndashobserved range 0ndash125) at three study sites in Flan-ders Belgium (Everaert et al 2001) Nearly all thesecases involve small turbines of 300ndash600 kW capac-ity in relatively small clusters At Blyth there was aninitial additional mortality of 05ndash15 for CommonEider but collision rates dropped substantially insubsequent years None of these examples have beenassociated with significant population declinesOften the highest levels of mortality occurred atspecific times of the year and in some cases werecaused by particular turbines or groups of turbines(eg Everaert et al 2001)

Information relating to collision mortality attrib-utable to offshore wind farms is currently very lim-ited largely as a consequence of the difficulties ofdetecting collisions at sea Improved methods tomeasure collisions and flight avoidance at offshorewind farms are urgently needed and techniquescurrently under development include radar thermalimagery and acoustic detection (Desholm 20032005 Desholm et al 2005 2006) Radar studiesat Nysted offshore wind farm Denmark show thatmost birds start to divert their flight paths up to3 km away in daytime and within 1 km at nightshowing marked flight deviations to fly around theturbine cluster (Kahlert et al 2004a 2004b Desh-olm 2005) In addition thermal imagery indicatesthat Common Eiders are probably subject to onlyrelatively low levels of collision mortality (M Desh-olm NERI Denmark pers comm) Similarly visualobservations of Common Eider movements inresponse to two small relatively near-shore windfarms (seven 15 MW and five 2 MW turbines) in theKalmar Sound Sweden recorded only one collisionevent during observations of 15 million migratingwaterfowl (Pettersson 2005) However it is not

known what impact larger wind farms or multipleinstallations may have in the longer term or on dif-ferent species

Displacement due to disturbance

The displacement of birds from areas within andsurrounding wind farms due to visual intrusion anddisturbance can amount effectively to habitat lossDisplacement may occur during both the construc-tion and operational phases of wind farms and maybe caused by the presence of the turbines themselvesthrough visual noise and vibration impacts or as aresult of vehiclevessel and personnel movementsrelated to site maintenance The scale and degree ofdisturbance will vary according to site- and species-specific factors and must be assessed on a site-by-sitebasis

Unfortunately few studies of displacement dueto disturbance are conclusive often because of thelack of before-and-after and control-impact (BACI)assessments Onshore disturbance distances (inother words the distance from wind farms up towhich birds are absent or less abundant thanexpected) up to 800 m (including zero) have beenrecorded for wintering waterfowl (Pedersen ampPoulsen 1991) though 600 m is widely acceptedas the maximum reliably recorded distance Thevariability of displacement distances is illustratedby one study which found lower post-constructiondensities of feeding European White-fronted GeeseAnser albifrons within 600 m of the turbines at awind farm in Rheiderland Germany (Kruckenbergamp Jaene 1999) while another showed displacementof Pink-footed Geese Anser brachyrhynchus up toonly 100ndash200 m from turbines at a wind farm inDenmark (Larsen amp Madsen 2000)

Studies of breeding birds are also largely inconclu-sive or suggest lower disturbance distances (Winkel-man 1992d Ketzenberg et al 2002) though thisapparent lack of effect may be due to the high sitefidelity and long life-span of the breeding speciesstudied This might mean that the true impacts ofdisturbance on breeding birds will only be evident inthe longer term when new recruits replace existingbreeding birds Few studies have considered the pos-sibility of displacement for short-lived passerinesalthough Leddy et al (1999) found increased densi-ties of breeding grassland passerines with increaseddistance from wind turbines and higher densities inthe reference area than within 80 m of the turbinesindicating that displacement did occur at least in this



case The consequences of displacement for breedingproductivity and survival are crucial to whetheror not there is likely to be a significant impact onpopulation size In the absence of any reliableinformation on the effects of displacement onbirds it is precautionary to assume that significantdisplacement will lead to a population reduction

Looking at effects offshore studies of two Danishwind farms at Tunoslash Knob and Horns Rev are helpful(Guillemette et al 1998 1999 Petersen et al 2004)At the former site a decrease in the number ofCommon Eiders and Common Scoters Melanittanigra was observed in the development site in the 2years following construction Although CommonEider numbers subsequently increased supportingthe view that the decline following constructionwas not due to the wind farm there was only apartial recovery for Common Scoter It is also possiblethat the increase in Common Eider numbers post-construction may have occurred as a result ofchanges in the abundance of Mussels Mytilus edulisor due to birds habituating to the wind farm Thiswork is subject to a number of caveats regarding itsapplication to other developments in particularrelating to the small size of the wind farm(ten 500 kW turbines) and the small size of theflocks studied

More recent studies at Horns Rev (80 2 MW tur-bines) found that divers Northern Gannets Morusbassanus Common Scoters and Common Guille-mots Uria aalgeRazorbills Alca torda occurred inlower numbers than expected in the wind farm areaand the zones within 2 and 4 km of it followingconstruction (Petersen et al 2004) Converselygulls and terns showed a preference for the windfarm area following construction However thecauses of changes in distribution are unknown andcould be due to any one or a combination of thepresence of wind turbines increased human andboat activity due to maintenance visits and changesin food distribution

These studies show that the scale of disturbancecaused by wind farms varies greatly This variation islikely to depend on a wide range of factors includingseasonal and diurnal patterns of use by birds loca-tion with respect to important habitats availabilityof alternative habitats and perhaps also turbine andwind farm specifications Behavioural responses varynot only between different species but betweenindividuals of the same species depending on suchfactors as stage of life cycle (wintering moultingbreeding) flock size and degree of habituation The

possibility that wintering birds in particular mighthabituate to the presence of turbines has been raised(Langston amp Pullan 2003) though it is acknowl-edged that there is little evidence and few studies oflong enough duration to show this A recent systematicreview of the effects of wind turbines on bird abun-dance has shown that increasing time since operationresulted in greater declines in bird abundance (Stewartet al 2004) This evidence that impacts are likely topersist or worsen with time suggests that habituationis unlikely at least in some cases

Barrier effect

The effect of birds altering their migration flyways orlocal flight paths to avoid a wind farm is also a formof displacement This effect is of concern because ofthe possibility of increased energy expenditure whenbirds have to fly further as a result of avoiding a largearray of turbines and the potential disruption oflinkages between distant feeding roosting moultingand breeding areas otherwise unaffected by the windfarm The effect depends on species type of birdmovement flight height distance to turbines thelayout and operational status of turbines time of dayand wind force and direction and can be highly var-iable ranging from a slight lsquocheckrsquo in flight directionheight or speed through to significant diversionswhich may reduce the numbers of birds using areasbeyond the wind farm

Studies of bird movements in response to offshoredevelopments have recorded wildfowl taking avoid-ing action between 100 and 3000 m from turbines(Winkelman 1992c Christensen et al 2004 Kahlertet al 2004b) There is limited evidence to show thatnocturnally migrating waterfowl are able to detectand avoid turbines at least in some circumstancesand that avoidance distances can be greater duringdarker nights (Winkelman 1992a Dirksen et al1998 2000) At Horns Rev and Nysted (72 23 MWturbines) there were strong indications that CommonScoters on migratory flights avoided the wind farmand its immediate vicinity though changes in theirdistribution were not solely influenced by the pres-ence of the wind farm (Christensen et al 2004Kahlert et al 2004a Petersen et al 2004) Depend-ing on the distance between turbines some birdswill fly between turbine rows for example in thecase of Common Eider at Nysted where the tur-bines are 480 m apart Although evidence of thistype of response is limited (Christensen et al 2004Kahlert et al 2004a) these observations clearly have



implications for wind farm design ndash see Mitigationmeasures below

A review of the literature suggests that none of thebarrier effects identified so far have significantimpacts on populations However there are circum-stances where the barrier effect might lead indirectlyto population level impacts for example where awind farm effectively blocks a regularly used flightline between nesting and foraging areas or whereseveral wind farms interact cumulatively to create anextensive barrier which could lead to diversions ofmany tens of kilometres thereby incurring increasedenergy costs

Habitat change and loss

The scale of direct habitat loss resulting from theconstruction of a wind farm and associated infra-structure depends on the size of the project but gen-erally speaking is likely to be small per turbine baseTypically actual habitat loss amounts to 2ndash5 of thetotal development area (Fox et al 2006) thougheffects could be more widespread where develop-ments interfere with hydrological patterns or flowson wetland or peatland sites (unpublished data) orwhere they disrupt geomorphological processesoffshore resulting in changes including increasederosion Habitat changes as a result of alterationsin land-use or use of the seabed might also occurThere is much uncertainty about the scale andnature of such changes and whether they could besignificant notably offshore and there is ongoingresearch on marine geomorphology in response toplacement of wind turbines (P Leonard DEFRApers comm) Some changes could also be beneficialFor example habitat changes following the develop-ment of the Altamont Pass wind farm in Californialed to increased mammal prey availability for somespecies of raptor (for example through greater avail-ability of burrows for Pocket Gophers Thomomysbottae around turbine bases) though this may alsohave increased collision risk (Thelander et al 2003)

Offshore developments could cause the loss ofhabitats in terrestrial areas (transformer stations) aswell as marine habitats due to the construction ofturbine foundations and the use of scour protectionmaterials The scale of offshore developments espe-cially in the context of relatively limited areas ofshallow sandbanks supporting large aggregations offeeding seabirds might be significant in this contextOther related effects include turbidity (as a result ofincreased scour of the seabed due to interactions

between the turbine bases and tidal currents) andvibration from the turbines both of which mightinfluence fish distribution and have effects on pisciv-orous birds More beneficially turbine structures canact as artificial reefs perhaps increasing structuraldiversity and creating a local abundance of preyspecies Of course this is only of net benefit to birdsif they are not displaced by the presence of theturbines themselves and if there is no significantmortality due to collisions

ASSESSING POTENTIAL IMPACTS

Legislation and consents

In the UK there is a range of national and interna-tional environmental legislation relevant to windfarm development In relation to environmentalassessment there are two key pieces of legislationthat apply in the EU the Environmental ImpactAssessment (EIA) Directive 85337EEC on Assess-ment of certain public and private projects on theenvironment (as amended by Directive 9711EC)and the Strategic Environmental Assessment (SEA)Directive 200142EC on the assessment of theeffects of certain plans and programmes on the envi-ronment The EIA Directive requires an impactassessment to be carried out in support of an appli-cation for development consent for certain types ofproject including lsquoinstallations for the harnessing ofwind power for energy production (wind farms)rsquoUnder UK legislation an EIA may be (and invariablyis) required if there are potentially significant envi-ronmental impacts as a result of the developmentand would normally be required where a Ramsarsite a potential or classified Special Protection Area(SPA) or a candidate agreed or designated SpecialArea of Conservation (SAC) could be affected

The SEA Directive aims to integrate environmen-tal considerations into the preparation of plans andprogrammes building on the project-level EIA byconsidering environmental issues much earlier in thedecision-making process To assist decision-makingon the design and terms of the competition for off-shore sites leases the UK government has commis-sioned a SEA in line with the requirements of theDirective Three strategic areas for competition forleases have been identified Liverpool Bay theThames Estuary and the Greater Wash Phase 1 ofthis SEA resulted in the preparation of an Environ-mental Report which suggests a strategic approach isadopted which will amongst other things avoid



development in shallow water where CommonScoter Red-throated Diver Gavia stellata and otherspecies are known to congregate and address theuncertainties of cumulative impacts (BMT CordahLtd 2003) It is intended that follow-on work to becarried out at the strategic area level will address cumu-lative impacts not only as a result of the interactionof wind farm developments but also in combinationwith other offshore developments and activities

Where proposals are likely to significantly affectRamsar sites potential or classified SPAs or candi-date or designated SACs (known collectively as Nat-ura 2000 sites) there are additional obligations forassessment under Article 6 of the Habitats Directive9243EEC on The conservation of natural habitatsand of wild fauna and flora and under the UK Habi-tats Regulations 1994 Under the Habitats Regula-tions and in accordance with the Directive a plan orproject can only be consented if it can be ascertainedthat there will be no adverse effect on the integrityof the site (the coherence of its ecological structureand function which supports the habitats andorspecies for which it has been designated) If it cannotbe ascertained that no adverse effect will result theplan or project can only be carried out if there areno alternative solutions and if there are imperativereasons of overriding public interest (which may beof a social or economic nature) Where such a planor project is consented the UK Secretary of Statemust secure any necessary compensatory measuresto ensure the overall coherence of Natura (2000)However especially offshore compensatory meas-ures will be particularly difficult to achieve

Wind farms onshore are consented by localplanning authorities or the relevant Governmentdepartment (Department of Trade amp Industry (DTI)Scottish Executive or the National Assembly forWales) A range of consents are relevant to offshorewind farms including a consent from the Depart-ment of Environment Food and Rural Affairs (DEFRA)(or the Scottish Executive Rural Affairs Department(SERAD) or the Welsh Assembly) under the CoastProtection Act 1949 for the construction of worksbelow mean high water springs if they are likely tocause an obstruction to navigation a licence fromDefra (or SERAD or the Welsh Assembly) under theFood amp Environment Protection Act 1985 for theplacing of structures below mean high water springsto ensure protection of the marine environment inEngland and Wales a consent from the DTI underthe Electricity Act 1989 for an offshore wind farmwhich will have an export capacity of more than 1

MW and planning permission for cables and gridconnections above mean low water

Method and scope of assessment

In the majority of cases nature conservation impactscould be minimized to the level where they areof no significant concern by careful siting At thepreliminary stages of a development proposal itis clearly important to use existing information todetermine the likelihood of impacts Ideally thiswould be undertaken in a pre-emptive strategic waycollating information to identify those areas wherethere are unlikely to be significant impacts on birds(or other nature conservation interests) and priori-tizing them for development Unfortunately manyonshore wind farms were already constructed or inthe planning process before the SEA Directivewhich would have provided the necessary lever totrigger this approach came into force in July 2004Consequently onshore wind farms in the UK have sofar been dealt with on a case-by-case basis

Where at all possible developers should avoidareas supporting the following(1) a high density of wintering or migratory water-fowl and waders where important habitats might beaffected by disturbance or where there is potentialfor significant collision mortality(2) areas with a high level of raptor activity espe-cially core areas of individual breeding ranges and incases where local topography focuses flight activitywhich would cause a large number of flights to passthrough the wind farm and(3) breeding wintering or migrating populations ofless abundant species particularly those of conserva-tion concern which may be sensitive to increasedmortality as a result of collision

Developments potentially affecting one or moreof these features are likely to require detailed assess-ments The nature of an assessment will depend onsite-specific factors such as the scale of the develop-ment and species vulnerability related to behaviourhabitat requirements and productivity

Onshore Assessments

An assessment should include a minimum 12-monthfield survey to determine the baseline numbersof birds present during an annual cycle (ScottishNatural Heritage 2005) This survey should providedata on bird distribution and movements includingobservations of bird numbers intensity of movements



altitude and orientation of flight during differentweather conditions and tidal cycles Nocturnal sur-veys minimally using image-enhancing equipmentwith an infra-red spotlight for near observationsand perhaps radar should also be undertaken whenimportant numbers of nocturnally active speciessuch as the European Golden Plover Pluvialisapricaria are likely to be affected For species thatshow significant annual variation in numbers anddistribution it may be necessary to undertake atleast 2 yearsrsquo baseline survey In order to assess thepotential for collisions it is clearly important tocollect as much information as possible on thenumbers of birds using or moving through the areaand the proportion occurring at rotor heightStudies should include an area around the windfarm which might be subject to displacement andbarrier effects (up to at least 600 m from the outerturbines)

Many recent assessments have employed a colli-sion risk model (eg Band et al 2005) to predict therate of bird collisions following the construction of awind farm Such models are potentially useful butin order to be effective require sufficient data onbird movements (numbers intensity flight heightand angle of approach) both throughout the annualcycle and across a range of conditions including dif-ferent weather conditions state of the tide at coastalsites at day and night Collision risk models enablea standardized approach to be taken to the measure-ment of the likelihood of collisions where birds takeno avoiding action However a significant limitationof these models is that their accuracy in determiningactual collision risk depends greatly on the applica-tion of reliable flight avoidance rates obtained frommonitoring of existing wind farms (Chamberlainet al 2006 Madders Whitfield 2006 Band et al2005) Unfortunately very few studies of existingdevelopments allow the calculation of reliable avoid-ance rates and at present these only exist for alimited range of species under a restricted range ofcircumstances This has led to some environmentalassessments utilizing available estimates of collisionrisk even though they have been derived for differ-ent species in different habitats and without thenecessary testing of their relevance In future it isessential that avoidance rates applied to a particulardevelopment are derived from the same or similarspecies in response to similar structures in a similarsituation to that being assessed In the absence ofreliable collision avoidance rates for the relevantspecies and until such models have been adequately

validated by follow-up monitoring particular care isneeded in their application and the interpretation oftheir outputs

Any potentially significant harmful effect on wildbirds identified by an assessment must be addressedIf an impact can be avoided or mitigated by suitablemeasures then the assessment should identify them(see Mitigation measures below) In addition in theevent that the wind farm is consented the assess-ment should include measures to compensate forany residual damage not covered by the mitigationmeasures Often both onshore and offshore severalwind farms can be proposed in relatively close prox-imity to each other If there are any other projects(including non-wind energy developments) whichhave been developed or are being proposed in anarea where affects on an SPA or SAC are likely thenit is required that the assessment should take intoaccount any cumulative effects that may arise fromthe wind farm development in combination withthese other projects

For those developments which are consented it isessential that appropriate monitoring is made a con-dition of the consent Pre- and postdevelopmentmonitoring should be carried out using the BACIapproach and details of the monitoring programmemust be set out in the assessment This monitoring isneeded to indicate whether further remedial meas-ures are required in the event of additional unpre-dicted impacts occurring It is also needed to helpincrease the understanding of actual impacts whichcan then be used to improve future assessmentsPost-construction monitoring must continue longenough to identify both short- and long-term effectsand to enable these to be satisfactorily addressedIt is important that all monitoring work is carriedout to an adequate level using standardized andrepeatable methods appropriate for the key issuesand species enabling comparison across sites Post-construction monitoring and research are urgentlyneeded on all aspects of avian response to wind tur-bines particularly displacement as a result of boththe presence of turbines and related maintenanceactivities and collision avoidance rates across a rangeof different wind farm specifications locations andweather conditions In order to obtain results thatcan be applied more generally site-based monitoringshould where feasible be both compatible and inte-grated with targeted research on key species andissues It is also essential that the results of monitor-ing and research are communicated widely and asquickly as possible



Offshore assessments

In offshore areas the species groups of most concernare seabirds grebes seaducks and migrating water-fowl and passerines Unfortunately information onthe distribution of concentrations of these birdstheir variability in numbers between and withinyears and the underlying determinants of theiroccurrence in a given location is often unavailable orat too broad a scale to be useful Food supply isclearly an important factor influencing bird distribu-tion and more information is needed on food avail-ability and changes in its distribution offshore andhow it is exploited by birds As a consequence it iscurrently only possible to give broad indications ofthe locations of important areas for birds offshore Arecently developed programme of aerial surveys inthe Irish Sea and off the east coast of England jointlyfunded by government and the wind energy industryshould improve the level of information on the loca-tion of feeding birds in the strategic areas identifiedfor offshore wind farm development in the UK(wwwdtigovukrenewablesrenew_2137htm)

Collecting information on the movements of birdsat sea is more problematic Knowledge of localinshore movements as well as observations of longdistance migrants as they approach land (includingmovements and flight heights in different weatherconditions and at night) is essential for assessing thepotential impacts of collision and barriers to move-ments (Huumlppop et al 2006) Some broad informa-tion on the timing of bird movements is availablefrom bird observatories and recent work on the dis-tances travelled by breeding seabirds on foragingtrips is useful (Allcorn et al 2003 Perrow et al2006) However for the vast majority of the birdsthat fly in near shore and offshore areas very littleis known This lack of data is of particular concerngiven the large scale of proposed offshore windfarms and the probability of cumulative effects

The BACI principles outlined above are equallyapplicable to offshore developments although thescope for developers to share responsibility forcontrol or reference areas might be greater offshoreA recent review of ship-based and aerial surveysfor wind farm studies concluded that the use of thetwo platforms is complementary with each fulfillingdifferent objectives (Camphuysen et al 2004)Aerial survey provides simultaneous coverage ofextensive offshore areas and reliable lsquosnapshotrsquoinformation on distribution and numbers Ship-based survey is better for detailed observations of

behaviour (perhaps in relation to oceanographicdata collected at the same time) for determining ageand sex of birds and for discriminating betweensimilar species

This account gives a brief summary of the require-ments of wind farm impact assessments Althoughmethodologies are still to a large extent underdevelopment more detailed guidance on currentapproaches and recommendations is available inCamphuysen et al (2004) DEFRA (2005) Crans-wick (2002) Komdeur et al (1992) Scottish NaturalHeritage (2005) and Desholm et al (2005)

MITIGATION MEASURES

Mitigation measures fall into two broad categoriesbest-practice measures which could be adopted byany wind farm development and should be adoptedas an industry standard and additional measureswhich are aimed at reducing an impact specific to aparticular development

Examples of best practice measures are(1) ensuring that key areas of conservation impor-tance and sensitivity are avoided(2) implementing appropriate working practices toprotect sensitive habitats(3) providing adequate briefing for site personneland in particularly sensitive locations employing anon-site ecologist during construction(4) implementing an agreed postdevelopmentmonitoring programme through planning or licenceconditions(5) siting turbines close together to minimize thedevelopment footprint (subject to technical con-straints such as the need for greater separationbetween larger turbines)(6) grouping turbines to avoid alignment perpen-dicular to main flight paths and to provide corridorsbetween clusters aligned with main flight trajectorieswithin large wind farms(7) increasing the visibility of rotor blades ndash researchindicates that high contrast patterns might helpreduce collision risk (at least in conditions of goodvisibility (McIsaac 2001)) although this may notalways be acceptable on landscape grounds Anothersuggested but untested possibility is to paint bladeswith UV paint which may enhance their visibility tobirds(8) where possible installing transmission cablesunderground (subject to habitat sensitivities and inaccordance with existing best practice guidelines forunderground cable installation)



(9) marking overhead cables using deflectors andavoiding use over areas of high bird concentrationsespecially for species vulnerable to collision(10) timing construction to avoid sensitive periods(11) implementing habitat enhancement for speciesusing the site and(12) offshore carefully timing and routing main-tenance trips to reduce disturbance from boatshelicopters and personnel

Turning to more site-specific mitigation it maybe necessary to prepare a site management plan de-signed to reduce or prevent harmful habitat changesfollowing construction and to provide habitatenhancement as appropriate Other measures whichmay be suitable in some circumstances include therelocation of proposed or actual turbines responsiblefor particular problems halting operation duringpeak migration periods or reducing rotor speedAgain post-construction monitoring is essential inorder to test the effectiveness of such mitigationmeasures and research is needed to provide moreinformation on specific impacts and novel mitigationmeasures that might reduce impacts

RECENT DEVELOPMENTS AND PRIORITIES FOR FUTURE WORK

There have been a number of recent developmentsin the assessment and monitoring of the effects ofwind farms on birds In particular there has beenmuch work in Denmark using remote sensing tech-nologies to measure potential and actual collisionmortality (Desholm amp Kahlert 2005 Desholm et al2005 2006 Desholm 2005 Fox et al 2006)

Radar

The most important advantage of radar over visualobservations is that it allows continuous and simul-taneous sampling of bird movements over a largearea regardless of time of day and visibility condi-tions (although limited in high moisture radarextends the range of observations considerablybeyond that possible for visual observations)Clearly continuous sampling is desirable for moni-toring bird movements especially at sea as suchmovements are often complex and fluctuate greatlyA combination of horizontal and vertical radar canprovide information on flight direction and flightheights

The technology is not without limitations how-ever Marine radar the technology most often used

for tracking bird movements is impaired by rain andfog and has a relatively short effective range (up to11 km for radar equipment used for bird studies inthe UK) which can be reduced further by topogra-phy Large-scale surveillance radar has a longer rangeand tracking radar can be used to provide detailedinformation on the movements of individual flocksthough these systems are more expensive and diffi-cult to use than marine radar Although radar recordsa range of signal characteristics such as reflectivitysize and speed which have been used in somestudies to separate signals into species groups verifi-cation of species identification still requires comple-mentary visual andor acoustic survey effort whichmay be a severe limitation in practice Furthermorebecause of lsquoshadowrsquo caused by the turbines andmoving rotors radar cannot be used to detect colli-sions Another drawback is the need to place offshoreradar on a fixed platform or a boat Although not atechnical constraint keeping a boat at sea for severaldays or weeks or the construction of a platform (forexample met mast wind turbine or jack-up barge)is costly

Radar has been used to monitor bird movementsand flight responses to several offshore and near shorewind farms in Sweden and Denmark (Christensenet al 2004 Kahlert et al 2004a2004b Pettersson2005) Most recently radar observations have beenmade from offshore transformer stations at theHorns Rev and Nysted wind farms off the coast ofDenmark Although subject to various limitationsincluding effectiveness over only a relatively shortdistance and usage under a limited range of weatherconditions this work has provided some extremelyuseful insights to birdsrsquo responses to wind farms atsea (as described earlier under Barrier effects)

In the UK there has until recently been littledeployment of radar to assist wind farm environ-mental assessments partly because of the lack ofavailable equipment and expertise This situationshould be remedied with the recent development ofradar specifically for bird monitoring (Allan et al2004) This equipment detects bird movements inboth the horizontal and vertical planes and analysesand summarizes radar data using GIS tools andstatistical techniques

Thermal Animal Detection Systems (TADS)

Researchers in Denmark (NERI) have been develop-ing the use of remote Thermal Animal DetectionSystems (TADS) using an infra-red video camera in



an attempt to record birds flying in close proximityto wind turbines (Desholm 2003) TADS can be setto detect and film birds of a particular size and up toa given distance Provisional assessments indicatethat it is possible to distinguish species type fromsilhouette flight behaviour and approximate sizeThis system has been piloted most recently at theNysted offshore wind farm with a camera attachedto a turbine directed up at the rotors and controlledremotely using computer software (Desholm ampKahlert 2005 Desholm 2005 Desholm et al 2006)

TADS can provide valuable information on flightbehaviour avoidance and collisions especially inoffshore areas where visual observations and thecollection of corpses is not feasible thus providingessential data to populate collision avoidancemodels TADS can also function in conditions ofpoor visibility and at night However the work atNysted has shown that there is under normal cir-cumstances a very low probability of an individualcamera recording a collision event (Desholm 2003)This is in part due to the narrow field of view pro-vided by the camera with only a third of the rotor-swept area observed and because of the very limitednumber of birds passing the visible area Althoughthe system clearly has potential and at Nysted hasgiven an indication of the magnitude of collisionsexperienced by Common Eider in order for it toprovide more precise data on collision rates it wouldbe necessary to install many cameras on turbinesthroughout a wind farm The camera at Nysted hasalso helped verify radar data which indicate that Com-mon Eiders fly between turbine rows at that devel-opment (M Desholm NERI Denmark pers comm)

Other remote techniques are being investigatedincluding the use of pressurevibration sensors withinturbine blades to detect bird strikes (Desholm et al2005) and acoustic detection to monitor bird move-ments from their calls (Evans 2000) The COWRIE(Collaborative Offshore Wind Research into theEnvironment) Steering Group has commissioned aproject to develop best practice guidance for the useof remote techniques for observing bird behaviour inrelation to offshore wind farms (Desholm et al 2005)

Population modelling

As well as improving remote technology for observ-ing behavioural reactions of birds including collisionsand displacement the development of demographicand distributional (or spatial) models is also importantto predict and subsequently test predictions of

population-level impacts attributable to the windfarm as distinct from other factors Spatial modelsare especially valuable for studies of displacementof birds in the offshore environment where the dataon abundance and distribution are usually based onparticularly small samples and are themselves sub-ject to wide confidence limits As well as predictingthe impacts of a single wind farm spatial modellingis essential for predicting the possible cumulativedisplacement of bird populations on a wider scaleresulting from the combined impacts of severalwind farms

Demographic models were developed to evaluatethe effects of collision mortality on the populationdynamics of Golden Eagles at Altamont Pass (Huntet al 1999 Hunt 2001) Such research requires longtimescales to verify model predictions and is there-fore a costly and long-term process which will notbe appropriate for all species nor for all wind farmproposals Modelling is also needed to predictpopulation level impacts as a result of changes insurvival and breeding productivity following reducedintake rates and increased energy consumption dueto displacement and barrier effects An example ofthis approach is the development of a predictivemodel in the UK to determine the potential impactsof offshore wind farms including displacementfrom feeding areas on Common Scoter (COWRIEwwwoffshorewindfarmscouk Kaiser et al 2006West amp Caldow 2006)

CONCLUSIONS

The development of wind-energy is a vital com-ponent of the Europe-wide objective to increasethe proportion of energy derived from renewablesources thus helping to reduce the emission ofgreenhouse gases However wind energy develop-ments are themselves not without impacts on theenvironment and the current pace and scale ofdevelopment proposals combined with a poorunderstanding of their impacts is a cause for concern

One of the main areas of concern is the potentialimpact of wind farms on birds Although many of thestudies carried out on collision mortality displace-ment barrier effects and direct habitat loss causedby wind farms are either inconclusive due in part toinadequate study methods or indicate effects thatare not significant for a given species site and seasonthis should not be used as justification for poor orinadequate assessments of future developmentsIndeed the relatively few studies that do indicate



a significant impact are a clear warning that theinappropriate location of wind farms can adverselyaffect wild bird populations The potential implica-tions of wind farms for birds are of even greaterconcern when considering the scale of current pro-posals and the possibility of the effects of individualwind farms interacting to produce much largercumulative impacts on bird populations

Developers should avoid wherever possible con-centrations of vulnerable bird species In cases wherethis is not possible or where information on birdsis not available (as is often the case offshore) thendetailed and sometimes long-term environmentalassessments are likely to be necessary Althoughexisting information on birds may help to designthese assessments it will in almost every case benecessary to collect data on bird numbers distribu-tion and movements in order to predict impacts Themethods and technology available to carry out theseassessments are broadly speaking well developedonshore though further verification and refinementsare necessary for some techniques (for examplecollision risk models)

The current challenge is to develop suitable tech-niques for offshore assessments The application andfurther development of ship-based and aerial surveytechniques have been invaluable in carrying outassessments The next step is to develop and success-fully apply remote data-gathering equipment such asradar and infra-red cameras to provide informationon bird distribution and movements These tech-niques are needed now particularly in the UK whereenvironmental assessments of offshore wind farmsare underway and the collection of information onbird movements is a high priority

As this overview has shown there is a pressingneed for more information on the range of potentialimpacts of wind farms on birds both onshore andoffshore It is essential that detailed monitoring andresearch is carried out on avian responses to windfarms and that developers consenting authoritiesand their advisors gather and communicate suchinformation as a matter of the most urgent priorityFurther research is required in particular to developspatial and demographic models which can help pre-dict the effects of individual wind farms and groupsof developments which have cumulative effectsacross extensive areas Increasing understanding ofthe implications of wind farms for birds in commonwith other environmental impacts will depend onthe close collaboration of industry governments andresearchers A central element to this work is the design

and implementation of detailed post-construction mon-itoring of the actual effects of existing wind farms (ofthe type being undertaken at Horns Rev and Nystedfor example) which will not only help to assess theeffectiveness of mitigation of any harmful impactsresulting from these developments but will also pro-vide valuable information for future assessments

ACKNOWLEDGEMENTS

We would like to thank Jeremy Wilson and MikeMadders for improvements to the paper

REFERENCES

Alerstam T 1990 Bird Migration Cambridge UK CambridgeUniversity Press

Allan J Bell M Brown M Budgey R amp Walls R 2004Measurement of Bird Abundance and Movements Using BirdDetection Radar Central Science Laboratory (CSL)Research report York UK CSL

Allcorn R Eaton MA Cranswick PA Perrow M Hall CSmith L Reid JB Webb A Smith KW LangstonRHW amp Ratcliffe N 2003 A Pilot Study of Breeding TernForaging Ranges in NW England and East Anglia in Relationto Potential Development Areas for Offshore Wind FarmsSlimbridge UK Wildfowl amp Wetland Trust

Band W Madders M amp Whitfield DP 2005 Developing fieldand analytical methods to assess avian collision risk at windfarms In De Lucas M Janss G and Ferrer M eds Birdsand Wind Power wwwquercuspt

Barrios L amp Rodriguez A 2004 Behavioural and environ-mental correlates of soaring-bird mortality at on-shore windturbines J Appl Ecol 41 72ndash81

BMT Cordah Limited 2003 Offshore Wind Energy GenerationPhase 1 proposals and environmental report for considera-tion by the Department of Trade and Industry Report noCordahDTI0090401062003 Edinburgh BMT Cordah

Brown MJ Linton E amp Rees EC 1992 Causes of mortalityamong wild swans in Britain Wildfowl 43 70ndash79

Camphuysen CJ Fox AD Leopold MF amp Petersen IK2004 Towards Standardised Seabirds at Sea CensusTechniques in Connection with Environmental ImpactAssessments for Offshore Wind Farms in the UK aComparison of Ship and Aerial Sampling Methods forMarine Birds and their Applicability to Offshore Wind FarmAssessments Report commissioned by COWRIE Texel TheNetherlands Royal Netherland Institute for Sea Research

Chamberlain D Rehfisch MR Fox AD Desholm M ampAnthony SJ 2006 The effect of avoidance rates on birdmortality predictions made by wind turbine collision riskmodels In Wind Fire and Water Renewable Energy andBirds Ibis 148 (Suppl 1) 198ndash202

Christensen TK Hounisen JP Clausager I amp PetersenIK 2004 Visual and Radar Observations of Birds in Relationto Collision Risk at the Horns Rev Offshore Wind FarmAnnual status report 2003 Report commissioned by ElsamEngineering AS 2003 NERI Report Roslashnde DenmarkNational Environmental Research Institute



Cranswick PA 2002 Surveillance of seaducks in the UnitedKingdom a review of methods and proposals for future activ-ity Slimbridge UK Wildfowl and Wetland Trust

DEFRA 2005 Nature conservation Guidance on Offshore Windfarm Development a Guidance Note for Developers Under-taking Offshore Wind farm Developments Prepared byDepartment of Environment Food and Rural Affairswwwdefragovuk

Desholm M 2003 Thermal Animal Detection Systems (TADS)Development of a Method for Estimating Collision Frequencyof Migrating Birds at Offshore Wind Turbines NERI TechnicalReport no 440 Roslashnde Denmark National EnvironmentalResearch Institute

Desholm M 2005 Preliminary Investigations of Bird-TurbineCollisions at Nysted Offshore Wind Farm and Final QualityControl of Thermal Animal Detection System (TADS) RoslashndeDenmark National Environmental Research Institute

Desholm M Fox AD amp Beasley P 2005 Best practiceGuidance for the Use of Remote Techniques for ObservingBird Behaviour in Relation to Offshore Wind farms A Pre-liminary Discussion Document Produced for COWRIECollaborative Offshore Wind Research into the Environ-ment COWRIE ndash REMOTE-05ndash2004 London The CrownEstate

Desholm M Fox AD Beasley P amp Kahlert J 2006Remote techniques for counting and estimating the numberof bird-wind turbine collisions at sea a review In Wind Fire andWater Renewable Energy and Birds Ibis 148 (Suppl 1) 76ndash89

Desholm M amp Kahlert J 2005 Avian collision risk at anoffshore wind farm Royal Society Biol Lett 1 296ndash298

Dirksen S Spaans AL amp van der Winden J 2000 Studieson Nocturnal Flight Paths and Altitudes of Waterbirds in Rela-tion to Wind Turbines A Review of Current Research in theNetherlands In Proceedings of the National Avian-WindPower Planning Meeting III San Diego California May 2000Prepared for the National Wind Coordinating CommitteeOntario LGL Ltd

Dirksen S van der Winden J amp Spaans AL 1998 Noctur-nal collision risks of birds with wind turbines in tidal and semi-offshore areas In Ratto CF amp Solari G eds Wind Energyand Landscape Rotterdam Balkema

Erickson WP Johnson GD Strickland MD Young DPJr Sernja KJ amp Good RE 2001 Avian collisions withwind turbines a summary of existing studies and compar-isons to other sources of avian collision mortality in the UnitedStates Western EcoSystems Technology Inc NationalWind Coordinating Committee Resource Document httpwwwnationalwindorgpublicationsavianhtm

Evans WR 2000 Applications of Acoustic Bird Monitoring forthe Wind Power Industry In Proceedings of the NationalAvian-Wind Power Planning Meeting III San Diego CaliforniaMay 2000 Prepared for the National Wind CoordinatingCommittee Ontario LGL Ltd

Everaert J Devos K amp Kuijken E 2001 Windtrubinesen vogels in Vlaaneren Voorlopige OnderzoeksresultatenEn Buitenlandse Bevindingen [Wind Turbines and Birds inFlanders (Belgium) Preliminary Study Results in a EuropeanContext] Instituut Voor Natuurbehoud Report R200203Brussels B76pp Brussels Belgium Institut voor Natuurbehoud

Fox AD Desholm M Kahlert J Christensen TK amp KragPetersen IB 2006 Information needs to support environ-mental impact assessments of the effects of European

marine offshore wind farms on birds In Wind Fire and WaterRenewable Energy and Birds Ibis 148 (Suppl 1) 129ndash144

Guillemette M Larsen JK amp Clausager I 1998 ImpactAssessment of an Off-Shore Wind Park on Sea Ducks NERITechnical Report no 227

Guillemette M Larsen JK amp Clausager I 1999 Assessingthe Impact of the Tunoslash Knob Wind Park on Sea Ducks theInfluence of Food Resources NERI Technical Report no 263Roslashnde Denmark National Environmental Research Institute

Henderson IG Langston RHW amp Clark NA 1996 Theresponse of common terns Sterna hirundo to power lines anassessment of risk in relation to breeding commitment ageand wind speed Biol Conserv 77 185ndash192

Hill D 1990 The Impact of Noise and Artificial Light on Water-fowl Behaviour a Review and Synthesis of Available Litera-ture BTO Research Report 61 Thetford UK British Trust forOrnithology

Howell JA amp DiDonato JE 1991 Assessment of avian useand mortality related to wind turbine operations AltamontPass Alameda and Contra Costa Counties California Sep-tember 1988 Through August 1989 Final report prepared forKenentech Windpower

Hunt WG 2001 Continuing studies of golden eagles at AltamontPass Proceedings of the National Avian-Wind Power PlanningMeeting IV

Hunt WG Jackman RE Hunt TL Driscoll DE amp CulpL 1999 A Population Study of Golden Eagles in the AltamontPass Wind Resource Area Population Trend Analysis 1994ndash97 Report to National Renewable Energy LaboratorySubcontract XAT-6-16459ndash01 Santa Cruz University ofCalifornia

Huntley B Collingham YC Green RE Hilton GMRahbeck C amp Willis SG 2006 Potential impacts ofclimatic change upon geographical distribution of birds InWind Fire and Water Renewable Energy and Birds Ibis 148(Suppl 1) 8ndash28

Huumlppop O Dierschke J Exo K-M Fredrich E amp Hill R2006 Bird migration studies and potential collision risk withoffshore wind turbines In Wind Fire and Water RenewableEnergy and Birds Ibis 148 (Suppl 1) 90ndash109

Kahlert J Petersen IK Fox AD Desholm M amp Clau-sager I 2004a Investigations of Birds During Constructionand Operation of Nysted Offshore Wind Farm at RodsandAnnual status report 2003 Report Commissioned by EnergiE2 AS 2004 Roslashnde Denmark National EnvironmentalResearch Institute

Kahlert J Petersen IK Desholm M amp Clausager I 2004bInvestigations of migratory birds during operation of Nystedoffshore wind farm at Roslashdsand Preliminary Analysis of Datafrom Spring 2004 NERI Note commissioned by Energi E2Roslashnde Denmark National Environmental Research Institute

Kaiser MJ Galanidi M Showler DA Elliott AJ Cal-dow RWG Rees EIS Stillman RA amp SutherlandWJ 2006 Distribution and behaviour of common scoter rel-ative to prey resources and environmental parameters InWind Fire and Water Renewable Energy and Birds Ibis 148(Suppl 1) 110ndash128

Karlsson J 1983 Faglar och vindkraft Lund SwedenEkologihuset

Ketzenberg C Exo K-M Reichenbach M amp Castor M2002 Einfluss von Windkraftanlagen auf brutende Wiesen-vogel Natur Landsch 77 144ndash153



Komdeur J Bertelsen J amp Cracknell G 1992 Manual foraeroplane and ship surveys of waterfowl and seabirds Inter-national Waterfowl and Wetlands Bureau (IWRB) SpecialPublication no 19 Roslashnde Denmark National Environ-mental Research Institute

Kruckenberg H amp Jaene J 1999 Zum Einfluss eines Wind-parks auf die Verteilung weidender Blaumlszliggaumlnse im Rheider-land (Landkreis Leer Niedersachsen) Natur Landsch 74420ndash427

Langston RHW amp Pullan JD 2003 Wind farms and birds ananalysis of the effects of wind farms on birds and guidance onenvironmental assessment criteria and site selection issuesReport written by Birdlife International on behalf of the BernConvention Council Europe Report T-PVSInf

Larsen JK amp Clausen P 2002 Potential wind park impacts onwhooper swans in winter the risk of collision Waterbirds 25327ndash330

Larsen JK amp Madsen J 2000 Effects of wind turbines andother physical elements on field utilization by pink-footedgeese (Anser brachyrhynchus) A landscape perspectiveLandscape Ecol 15 755ndash764

Leddy KL Higgins KF amp Naugle DE 1999 Effects of WindTurbines on Upland Nesting Birds in Conservation ReserveProgram Grasslands Wilson Bull 111 100ndash104

Madders M amp Whitfield PD 2006 Upland raptors and theassessment of wind farm impacts In Wind Fire and WaterRenewable Energy and Birds Ibis 148 (Suppl 1) 43ndash56

McIsaac H 2001 Raptor acuity and wind turbine bladeconspicuity In Proceedings of the National Avian-WindPower Planning Meeting IV httpwwwnationalwindorgpublicationsavianhtm

Orloff S amp Flannery A 1992 Wind turbine effects on avianactivity habitat use and mortality in Altamont Pass andSolano County Wind Resource Areas 1989ndash91 CaliforniaEnergy Commission

Painter A Little B amp Lawrence S 1999 Continuation of BirdStudies at Blyth Harbour Wind Farm and the Implications forOffshore Wind Farms Report by Border Wind Limited DTIETSU W13004850000

Pedersen MB amp Poulsen E 1991 Impact of a 90 m2MWwind turbine on birds Avian responses to the implementationof the Tjaereborg wind turbine at the Danish Wadden SeaDanske Vildtunderogelser Haefte 47 Roslashnde DenmarkDanmarks Miljoslashundersoslashgelser

Perrow M Skeate ER Lines P amp Brown D 2006 Radiotelemetry as a tool for impact assessment of wind farms thecase of Little Terns Sterna albifrons at Scroby Sands NorfolkUK In Wind Fire and Water Renewable Energy and BirdsIbis 148 (Suppl 1) 57ndash75

Petersen IK Clausager I amp Christensen TJ 2004 BirdNumbers and Distribution on the Horns Rev Offshore Wind FarmArea Annual Status Report 2003 Report commissioned byElsam Engineering AS 2003 Roslashnde Denmark NationalEnvironmental Research Institute

Pettersson J 2005 The Impact of Offshore Wind Farms onBird Life in Southern Kalmar Sound Sweden A final reportbased on studies 1999ndash2003 Report for the SwedishEnergy Agency Lund Sweden Lund University

Richardson WJ 2000 Bird Migration and Wind TurbinesMigration Timing Flight Behaviour and Collision Risk Pro-ceedings of National Avian-Wind Power Planning Meeting II132ndash140 httpWwwNationalwindOrgPublicationsAvianHtm

Scottish Natural Heritage 2005 Methods to assess theimpacts of proposed onshore wind farms on bird com-munities SNH Edinburgh wwwsnhorgukpdfsstrategyrenewablebird_surveypdf

Stewart GB Coles CF amp Pullin AS 2004 Effects ofWind Turbines on Bird Abundance Sytematic Review no 4Birmingham UK Centre for Evidence-based Conservation

Thelander CG Smallwood KS amp Rugge L 2003 BirdRisk Behaviours and Fatalities at the Altamont Pass WindResource Area Report to the National Renewable EnergyLaboratory Colorado

Troen I amp Petersen EL 1989 European Wind Atlas RoskildeDenmark Risoslash National Laboratory

West AD amp Caldow RWG 2006 The development and use ofindividuals-based models to predict the effects of habitat lossand disturbance on waders and waterfowl In Wind Fire and WaterRenewable Energy and Birds Ibis 148 (Suppl 1) 158ndash168

Winkelman JE 1989 Birds and the wind park near Urk bird collisionvictims and disturbance of wintering ducks geese and swansRIN rapport 8915 Arnhem Rijksintituut voor Natuurbeheer

Winkelman JE 1992a The Impact of the Sep Wind Park NearOosterbierum the Netherlands on Birds 1 Collision VictimsRIN rapport 922 Arnhem Rijksintituut voor Natuurbeheer

Winkelman JE 1992b The impact of the Sep wind park nearOosterbierum the Netherlands on birds 2 nocturnal collisionrisks RIN rapport 923 Arnhem Rijksintituut voor Natuurbeheer

Winkelman JE 1992c The impact of the Sep wind park nearOosterbierum the Netherlands on birds 3 flight behaviourduring daylight RIN rapport 924 Arnhem Rijksintituut voorNatuurbeheer

Winkelman JE 1992d The Impact of the Sep Wind Park NearOosterbierum the Netherlands on Birds 4 Disturbance RINrapport 925 Arnhem Rijksintituut voor Natuurbeheer

Winkelman JE 1995 Birdwind turbine investigations inEurope In Proceedings of the National Avian-Wind PowerPlanning Meeting 1994



comprising up to 300 turbines each having an out-put of 3 MW or more and extending over 200 km2Onshore developments although generally notapproaching the scale of the latest offshore propos-als are also exploiting technological advances andnow tend to use larger turbines These developmentscould have different implications for birds than theearlier smaller wind farms and turbines

The potential vulnerability of wildlife to large-scale wind energy developments has been recog-nized in the latest round of offshore developmentproposals in the Greater Wash the Thames Estuaryand off north-west England Developments are cur-rently excluded from a coastal strip of a minimumwidth of 8 km from the shoreline and extending to13 km in areas of particular landscape sensitivityAdditionally in north-west England wind farmdevelopment is excluded from waters 10 m deep orless This is in recognition of the potentially high sen-sitivity of shallow coastal waters to wind farm devel-opments especially with regard to displacement ofseaducks that dive to feed on shallow subtidal habi-tats visual impacts from the shore and the possibleimpacts on inshore fishing and recreational activities

Wind farms comprise the wind turbines them-selves interconnecting cables transformer stationsmeteorological masts and ancillary infrastructureincluding onshore access roads and visitor centresThe components of the individual turbines comprisea tapering mast the nacelle or hub foundations androtor blades The proportions of the turbine aredetermined by the rotor blade length and towerheight The largest 2 MW machines onshore canhave a tower height of 80 m and a rotor diameter of90 m resulting in an overall height of 125 m (over400 feet) By comparison a normal electricity trans-mission pylon is 52 m tall In the case of these largeturbines the height of the rotor sweep above groundcan be as much as 35 m Turbine design for offshorewind farms is currently similar to that for terrestrialuse although the economics of offshore develop-ment will tend to result in turbines which are signif-icantly larger than those deployed onshore Offshoremachines with a generating capacity of at least5 MW are already anticipated

POTENTIAL EFFECTS ON BIRDS

To be effective wind farms must be sited in openexposed areas where there are high average windspeeds This means that they are often proposed inupland coastal and offshore areas thus potentially

affecting important habitats for breeding winteringand migrating birds The effects of a wind farm onbirds are highly variable and depend on a wide rangeof factors including the specification of the develop-ment the topography of the surrounding land thehabitats affected and the number and species ofbirds present With so many variables involved theimpacts of each wind farm must be assessed individ-ually The principal areas of concern with regard toeffects on birds are described below Each of thesepotential effects can interact either increasing theoverall impact on birds or in some cases reducing aparticular impact (for example where habitat losscauses a reduction in birds using an area which mightthen reduce the risk of collision)

COLLISION

Collision mortality

Direct mortality or lethal injury of birds can resultnot only from collisions with rotors but also withtowers nacelles and associated structures such asguy cables power lines and meteorological mastsThere is also evidence of birds being forced to theground as a result of being drawn into the vortexcreated by moving rotors (Winkelman 1992b) Themajority of studies of collisions caused by wind tur-bines have recorded relatively low levels of mortality(eg Winkelman 1992a 1992b Painter et al 1999Erickson et al 2001) This is perhaps largely a reflec-tion of the fact that many of the studied wind farmsare located away from large concentrations of birdsIt is also important to note that many records arebased only on finding corpses with no correction forcorpses that are overlooked or removed by scaven-gers (Langston amp Pullan 2003)

Accepting that many wind farms result in only lowlevels of mortality even these levels of additionalmortality may be significant for long-lived species withlow productivity and slow maturation rates espe-cially when rarer species of conservation concernare affected In such cases there could be significanteffects at the population level (locally regionally orin the case of rare and restricted species nationally)particularly in situations where cumulative mortal-ity takes place as a result of multiple installations

Collision risk

Collision risk depends on a range of factors relatedto bird species numbers and behaviour weather



























Barrier effect

























Onshore Assessments

















MITIGATION MEASURES









Radar

















CONCLUSIONS










ACKNOWLEDGEMENTS


REFERENCES































































































Barrier effect

























Onshore Assessments

















MITIGATION MEASURES









Radar

















CONCLUSIONS










ACKNOWLEDGEMENTS


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Onshore Assessments

















MITIGATION MEASURES









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CONCLUSIONS










ACKNOWLEDGEMENTS


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MITIGATION MEASURES









Radar

















CONCLUSIONS










ACKNOWLEDGEMENTS


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Radar

















CONCLUSIONS










ACKNOWLEDGEMENTS


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assessing the impacts of wind farms on birds

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