Birds in southern Öresund in relation to the wind farm at

Transcription

Birds in southern Öresund in relation
to the wind farm at Lillgrund
Final report of the monitoring program 2001-2011
Leif Nilsson & Martin Green
Biologiska institutionen, Lunds Universitet
Department of Biology, University of Lund, Lund, Sweden
Lund 2011
Commissioned by Vattenfall Vindkraft AB
Data
Title:
Birds in southern Öresund in relation to the windfarm at
Lillgrund. Final report of the monitoring program 2001-2011.
.
Authors:
Leif Nilsson & Martin Green
Institut
Biologiska Institutionen, Lunds Universitet
Publisher
Biologiska Institutionen, Lunds Universitet
Published
November 2011
Download from
http://www.vattenfall.se/sv/lillgrund-vindkraftpark.htm
Number of pages
85 + Appendix 43
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Contents
Summary
Svensk sammanfattning
Introduction
Study area
Methods
Survey methods
Boat surveys
Aerial surveys
Analysis of survey data
Radar studies of bird migration
Results
Staging and wintering birds
Cormorant Phalacrocorax carbo
Long-tailed Duck Clangula hyemalis
Common Eider Somateria mollissima
Red-breasted Merganser Mergus serrator
Herring Gull Larus argentatus
Spring- north-easterly directed migration
Spring- southerly directed migration
Autumn
Discussion
Migrating birds
Literature
Appendix
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Summary
This report presents the results of the monitoring programme for Lillgrund offshore wind
farm. Base-line studies were undertaken during 2001-2006 (Green & Nilsson 2006, see also
Nilsson 2001 for background information). According to the original plans the studies should
be continued for three seasons after the wind farm was set in operation but due to problems
with the data collection during cold periods this was extended to four seasons, i.e. 2007/092010/11.
Staging and wintering birds in the area were surveyed both from boat and from the air. Boat
counts covered the area from the Öresund Bridge over Lillgrund to Bredgrund south of the
wind farm. Aerial surveys covered a larger area from the bridge to the shallow areas south of
the Falsterbo peninsula. The aim of the aerial surveys was to cover a larger area than the wind
farm and its neighbourhood, and the areas south of Falsterbo were included as a reference
area. In all 19 boat counts were made during 2001-2005, and 8 in 2007-2011, whereas five
aerial surveys were undertaken in 2004 and 2006 and 15 in 2008-2011.
The numbers of staging and wintering waterbirds showed a large variation between seasons
and years both during the base-line studies and during the surveys after the establishment of
the wind farm. This kind of variation is well-known from other surveys of seabirds in offshore
waters. Three species of diving ducks dominated the bird fauna of the wider Lillgrund area:
the Eider Somateria mollissima, the Red-breasted Merganser Mergus serrator and to a
smaller extent the Long-tailed Duck Clangula hyemalis. Two other species occurred in larger
numbers in the same area: Herring Gull Larus argentatus and Cormorant Phalacrocorax
carbo. Other seabirds were only found in smaller numbers and the analysis was focused on
the possible effects of the wind farm on the five mentioned species.
The population of Red-breasted Merganser in the area is the largest concentration known
from the country and the area is an internationally important wintering area with a large
proportion of the entire Baltic (and Northwest European) population. Eiders winter in
relatively large numbers in the southern Öresund and around Falsterbo (reference area). The
species also has a large colony on Saltholm and the area is also much used as stopover area
during spring migration. The third seaduck species, the Long-tailed Duck, occurs regularly in
much smaller numbers, the main wintering area for this species is in the Baltic proper.
The surveys did not show any larger changes in numbers of staging and wintering water birds
in southern Öresund that could be related to the establishment of the wind farm. Locally,
Long-tailed Ducks and Eiders were found to avoid the actual wind farm area at least initially.
For Eiders there were signs of habituation, especially during the last study season. During the
first three years with the farm in operation only single birds or small groups were seen in the
wind farm area, but during the last surveys in 2011 larger flocks were recorded on the water
within the wind farm. The patterns for Red-breasted Mergansers were less clear and numbers
using the whole area were lower during the post- compared to the pre-construction period.
Cormorants and Herring Gulls were seemingly not affected at all by the presence of the wind
farm. For Herring Gulls an avoidance of the wind farm is implied by some of the results, but
this is most likely not an effect of the wind farm as such but instead of the absence of fishing
vessels within the wind farm in the post-construction period.
The bird migration over the area was studied with surveillance radar. The radars used in this
study cover birds migrating in flocks, but not birds migrating singly. Furthermore, the larger
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the birds and/or the flocks, the better they are covered by these radars. This means that the
migration patterns studied here mainly concern birds such as waterbirds and pigeons. Dense
passerine migration is also covered during some days, but it is more uncertain to what extent
the passage of for example raptors over the area is covered. In all, radar data were analysed
for five spring seasons (2001 and 2005 pre-, 2008, 2009 and 2010 post-construction) and
three autumn seasons (2001 pre- and 2008 and 2009 post-construction). No larger changes in
the migration patterns were found, neither during spring and autumn nor during day and night,
that could be related to the construction of the wind farm at Lillgrund. On the other hand the
fraction passing over Lillgrund since the wind farm was established was only about 20 % of
the proportion passing before the wind farm was built. We interpret this as that most birds
avoid flying through the wind farm area. This avoidance reduces the risk for the birds to come
into conflict with the wind farm. The collision risks are probably small, at least for the birds
that can be followed by surveillance radar. We estimate that somewhere in the order of
between 100 and a few hundred individual birds may collide with (and get killed by) the wind
farm at Lillgrund. This is about a tenth of the numbers probably colliding with (and getting
killed by) the nearby Öresund Bridge.
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Svensk sammanfattning
Södra Öresund är ett viktigt rastnings- och övervintringsområde för ett betydande antal
vattenfåglar. Både Saltholm på den danska sidan och Falsterbo- Foteviken har utpekats som
speciella fågelskyddsområden enligt EUs fågeldirektiv. Även andra delar av södra Öresund
såsom Lommabukten och Lundåkrabukten är viktiga fågelområden med internationellt
betydelsefulla koncentrationer av flera sjöfågelarter. Södra Öresund är också ett område där
stora mängder med aktivt flyttande fåglar passerar både vår och höst (Alerstam 1978, 1990).
Mot denna bakgrund var det naturligt att fåglar kom att inta en viktig del av
miljökonsekvensstudierna när Lillgrunds vindkraftpark (Fig.1) planerades Nilsson 2001). I
samband med parkens projektering igångsattes ett kontrollprogram för att utvärdera ev.
påverkan från vindkraftparken på fågelfaunan i området. Kontrollprogrammet omfattade både
rastande/övervintrande och flyttande fåglar i området. När det gällde rastande och
övervintrande fåglar avsåg programmet att belysa om de olika fåglarnas utnyttjande av
området, speciellt för födosök, skulle påverkas av vindkraftparken. När det gällde flyttande
fåglar studerades de övergripande mönstren, speciellt mot bakgrunden att vindkraftverk i
flyttningsstråk skulle kunna medföra risker för ökad mortalitet och/eller fungera som barriärer
för de flyttande fåglarna.
Kontrollprogrammet omfattade inventeringar av det möjliga påverkansområdet, här definierat
som vattnen mellan Öresundsbron och Skanör samt ett referensområde söder om Falsterbo
både före och efter uppförandet av vindkraftverken. I påverkansområdet genomfördes
inventeringar både med flyg och med båt (se metoder). Båtinventeringarna var begränsade till
offshore-områdena, medan flyglinjerna sträckte sig från stranden och utåt. I våra analyser har
vi emellertid koncentrerat oss på de arter som förekommer i offshore-områdena.
Flyttningen genom området studerades med hjälp av övervakningsradar. Under
baslinjeundersökningarna genomfördes också visuella observationer över flyttfågelsträcket i
området från närbelägna observationspunkter (Green & Nilsson 2006). Bakgrundsinformation
över flyttfågelrörelserna i området återfinns också i rapporter från undersökningar kring
Öresundsbron, strax norr om vindkraftparken (Nilsson et al. 2009, 2010).
Baslinjestudierna (före uppförandet av vindkraftparken) genomfördes under 2001-2006
(rapporterade av Green & Nilsson 2006). Den andra fasen (efter uppförandet) påbörjades i
december 2007 och var avsedd att genomföras under tre år, men perioden utsträcktes
ytterligare ett år då vinterförhållandena under 2009/10 medförde att inventeringsprogrammet
detta år inte kunde genomföras fullt ut enligt planerna.
Denna rapport ger en analys av undersökningarna före och efter vindkraftparkens uppförande.
För en omfattande dokumentation av fågelförhållandena före parkens uppförande hänvisas till
Green & Nilsson (2006), se också Nilsson (2001) samt Nilsson et al. (2009, 2010).
Undersökningsområde
Undersökningsområdets läge i södra Öresund framgår av Fig.1, medan en mer detaljerad bild
över vindkraftparken och dess närmaste omgivningar visas i Fig. 2. För en detaljerad
information om undersökningsområdet hänvisas till Green & Nilsson (2006), medan tekniska
data rörande vindkraftparken återfinns i boken Vattenfall Vindkraft (2009).
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Metoder
Inventeringarna av rastande/övervintrande sjöfåglar genomfördes både med båt och med flyg.
Båda metoderna har för och nackdelar. Båtinventeringar är bättre på att täcka in vissa mindre
arter, medan flyginventeringarna ger möjlighet att täcka in större områden på samma dag. De
senare var också nödvändiga för att under samma dag kunna täcka in både Lillgrundsområdet
och referensområdet.
Båtinventeringarna genomfördes som linjetaxeringar efter en standardiserad rutt (Fig. 3) med
linjer med 2 km mellanrum över Lillgrund och Bredgrund, med undantag för att två linjer
hade en lucka på 4 km då djupförhållandena inte medgav passage. Normalt täckte två
observatörer var sin sida av båten och rapporterade observerade fåglar i olika zoner. Båtens
position noterades löpande varje minut med GPS. Observationer med lägesangivning lades in
i en databas. 19 båtinventeringar genomfördes under baslinjestudierna, medan åtta
inventeringar genomfördes efter parkens uppförande. Det mindre antalet båtinventeringar
under den senare perioden berodde huvudsakligen på isproblem under två vintrar.
Flyginventeringarna genomfördes med en tvåmotorig Cessna 337 Skymaster (Fig. 4).
Inventeringarna genomfördes som linjetaxeringar (Fig. 5) med två km mellanrum mellan
linjerna. Flyghöjden var ca 70 m och hastigheten 180 km/tim och två observatörer
registrerade fåglar på var sin sida av flygplanet i en zon ut till 200 m från flyglinjen. Flockar
som observerades utanför 200 m-gränsen registrerades som tilläggsinformation. Sedan
vindkraftparken uppförts modifierades linjerna så att vi kunde flyga i de öppna gator som
finns mellan vindmöllorna. Totalt genomfördes sju inventeringar före och 15 efter
vindkraftverkens uppförande.
Om fåglarna undviker vindkraftparken eller ej analyserades med hjälp av Jacobs selektivitets
index D (härefter Jacobs index, Jacobs 1974). Detta index användes för att analysera om de
fem talrikaste arterna på båt- och flyginventeringarna föredrog eller undvek området där
vindkraftparken står idag, både före byggnation och efter att parken tagits i drift. Preferens
eller undvikande av området utanför men intill parken, upp till 2 km avstånd från turbinerna,
analyserades också (för geografisk avgränsning av de olika delområdena i analysen se Fig. 6).
Jacobs index beskriver i vilken grad som fåglarna använder ett visst område i förhållande till
områdets förväntade användande.
För att få en mera storskalig överblick av fågelflyttningen i området, och även för att kunna
studera nattsträckets förlopp, utnyttjades data från två spaningsradaranläggningar.
Anläggningarna, som är belägna centralt i sydvästra Skåne ca 30 km från Öresundsbron, är
avsedda att bevaka sjö- och lufttrafik runt Skånes väst- och sydkust. De borde därmed ge en
acceptabel täckning även av fågelrörelser i de flesta höjdintervall (se vidare nedan). Radardata
lagrades digitalt för att sedan föras över till VHS eller DVD i form av filmer. I dessa filmer
framträder allt som återkastar radarns radiovågor såsom prickar, sk. radarekon, som rör sig
över landskapet. I allmänhet finns en filterfunktion i systemet för att plocka bort stillastående
ekon. Alla föremål av metall (exempelvis flygplan och båtar), men även föremål som
innehåller vatten (exempelvis levande varelser som fåglar) skapar radarekon, dvs. deras
rörelser är möjliga att följa med radartekniken. Baserat på den hastighet som ekona rör sig
över landskapet kan fågelekon väljas ut och sedan kan materialet analyseras med avseende på
antal fågelekon (dvs. flyttningsintensitet), flygriktningar, flyghastigheter mm. Även enskilda
flygbeteenden, exempelvis vid mötet av en vindkraftpark är möjliga att studera.
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Eftersom majoriteten av alla flyttfågelrörelser över området under våren har en östlig och på
hösten en västlig riktningskomponent, räknades antalet fågelekon längs en 50 km lång
transekt i nord-sydlig utsträckning. (Fig. 7). Transekten baserades på Rikets nät och tangerar
Lillgrundsområdets östra sida, mitt i Öresund (1310 E, enligt Rikets nät). För att få en mer
detaljerad upplösning av flyttfågelrörelsernas geografiska fördelning delades sedan transekten
i 10 km långa segment efter Rikets nät (A-E, Fig. 7). Som tillägg till detta användes även
ytterligare en transekt tvärs över sundet (från väst till öst) för att beskriva det nord-sydliga
ejder- (och sjöorre) vårsträckets fördelning i sundet (6160 N, enligt Rikets nät (Fig. 7). Även
denna transekt delades upp i tio km långa avsnitt för att få en mer detaljerad upplösning av
sträckets fördelning (1-4, Fig.7). Antalet passerande fågelekon (flockar) per segment och
timme räknades sedan för att få mått på sträckintensiteten.
Resultat
Rastande och övervintrande fåglar
I detta avsnitt analyserar vi de rastande och övervintrande sjöfåglarnas uppträdande i
Lillgrund området före och efter vindkraftparkens uppförande samt jämför med förhållandena
i referensområdet söder om Falsterbo. Summan av samtliga inräknade vattenfåglar per båt
resp. flyginventering framgår av tabeller i appendix (Tabell A1-A9). Totalt observerades 26
olika arter vid båtinventeringarna, medan 35 arter registrerades vid flyginventeringarna. De
sistnämnda sträckte sig från land ut till öppet vatten och kom därför att också innefatta arter
som endast finns i de strandnära områdena och som inte förekommer vid Lillgrund. Tillfälligt
observerade fåglar under lokala rörelser eller flyttande är inte medräknade.
Flertalet arter har endast setts i mindre antal och ger inte underlag för analyser. I princip har
fem arter observerats i tillräckligt stort antal för att ge underlag för närmare analyser: alfågel,
ejder, småskrake, storskarv samt gråtrut. För de fem huvudarterna redovisas diagram över
medel, maximum och minimiantal från inventeringarna, summakartor för olika säsonger före
och efter vindkraftparkens uppförande (kartor uppdelade på år finns i appendix), analys av
preferens/undvikandeförhållanden med Jacobs index samt för de tre andfåglarna jämförelser
mellan tätheter i olika zoner runt vindkraftparken före och efter dess uppförande. I samtliga
fall är figurtexterna försedda med svensk och engelsk text. Fördelningen av de inräknade
fåglarna av huvudarterna på Lillgrundområdet och referensområdet söder Falsterbo vid
flyginventeringarna framgår av Tabell 3, medan översiktliga Jacob’s index redovisas i Tabell
4.
Storskarv (Fig. 8-13)
Antalet inräknade storskarvar vid flyg och båtinventeringarna har visat betydande variationer.
Stora flockar av storskarv fiskar i södra Öresund och utnyttjar Pepparholm och Saltholm för
att vila. Endast vid något tillfälle har dessa stora flockar observerats vid våra inventeringar
och de tycks inte utnyttja själva Lillgrundområdet. Storskarvar har observerats i
vindkraftparken, men antalet i detta område tycks vara något lägre än före kraftverkens
uppförande. Trots detta finns inget som tyder på någon mer omfattande påverkan på de
storskarvar som nyttjar Öresund.
8
Alfågel (Fig. 14-19)
Alfågeln övervintrar i huvudsak i egentliga Östersjön och beståndet i södra Öresund är ganska
ringa även om arten är en regelbunden vintergäst också här. Maximiantalet inräknade alfåglar
mellan Falsterbohalvön och Öresundsbron har varit något hundratal individer, medan mer än
1000 alfåglar regelbundet setts i farvatten söder om Falsterbo. Före vindkraftparkens
uppförande sågs regelbundet mindre grupper av alfåglar på Lillgrund, men efter parkens
uppförande sågs få alfåglar i densamma och tätheten på Lillgrund var lägre än före parkens
uppförande. Trots det undvikande av vindkraftparken som våra analyser antyder ska man
komma ihåg att detta har väldigt liten biologisk betydelse. Lillgrund är av mycket marginell
betydelse för alfågeln i stort.
Ejder (Fig. 20-26)
Ejdern är regelbundet förekommande i området runt Falsterbohalvön och i södra Öresund
under vinterhalvåret och upp till 7000-8000 har regelbundet observerats vid inventeringarna.
Totalt beräknas det övervintrande beståndet i området till mellan 10 000 och 15 000 med
merparten söder om Falsterbo även om större flockar också finns norr om Falsterbo. Under
våren utnyttjas Lillgrund och Bredgrund och kringliggande vatten i betydande utsträckning av
ejdrar från den stora kolonin på Saltholm, där 4000-5000 ejdrar häckade 2000 (Desholm et al.
2002). Södra Öresund är också en viktig rastlokal under vårflyttningen. Vid inventeringar i
maj fanns merparten av ejdrarna i det norra delområdet.
Ejdrarna undvek tydligt att vistas i vindparken under de närmaste åren efter att parken tagits i
drift. Samtidigt ökade tätheten i de intilliggande delarna. En viss tillvänjning antyds av de
sista inventeringarna 2011 då större flockar av ejder sågs inne i själva parken.
Småskrake (Fig. 27-33)
Småskraken var den vanligaste arten vid de flesta inventeringar i området norr om Falsterbo,
dvs. runt Lillgrund, med undantag för vår- och tidiga höstinventeringarna när ejdern var den
vanligaste arten. Vinterbeståndet i det undersökta området har beräknats till ca 10 000-12 000
individer, vilket är den största koncentrationen av småskrake i svenska vatten och i
Östersjöområdet som helhet. Merparten av småskrakarna i det norra området observerades
mellan Bredgrund och Öresundsbron.
Färre småskrakar registrerades i hela undersökningsområdet efter parkens tillkomst jämfört
med perioden före. Resultaten från våra analyser ger dock inget enhetligt svar på om arten
undviker vindkraftparken eller inte. Få fåglar sågs dock inne i parken under de första åren
med denna i drift, medan antalen därefter varierat ordentligt mellan olika tillfällen. Sannolikt
har sådana variationer mer att göra med variationer i födans fördelning (småfisk) än med
vindkraftparken som sådan.
Gråtrut (Fig. 34-39)
Gråtruten var den dominerande måsfågeln i undersökningsområdet både runt Lillgrund och
Bredgrund samt söder om Falsterbo. Normalt var gråtrutarna spridda ensamma eller i små
grupper och större koncentrationer sågs endast i anslutning till fiskebåtar, rastande på
Måkläppen eller vid hamnarna.
9
Någon påverkan på gråtrutarnas uppträdande i relation till vindkraftparkens uppförande har
inte kunnat konstateras. Större ansamlingar är näst intill alltid knutna till aktiva fiskebåtar och
eftersom sådant fiske ej förekommer i vindkraftparken så förekommer heller inga större
ansamlingar av gråtrutar i denna.
Flyttande fåglar
Radardata från två vårar (2002 & 2005) före byggnation av vindkraftparken kunde jämföras
med data från tre vårar med parken i drift (2008-2010). För huvuddelen av
flyttfågelrörelserna, dvs. de som passerar med grovt sett nordostliga riktningar (Fig. 40)
noterades inga storskaliga förändringar av det geografiska mönstret som kunde härledas till
tillkomsten av vindkraftparken. Andelen flockar som passerade över den centrala delen av
södra Öresund, där Lillgrund ligger, minskade förvisso med drygt 20 % men samtidigt fanns
även andra förändringar i hur sträcket fördelade sig längs den nord-sydliga transekten (se Fig.
7) på ett sätt som knappast kan ha med vindkraftparken att göra (Fig. 41). Mönstret var
detsamma oavsett tid på dygnet (Fig. 42). Vissa skillnader fanns mellan olika tider av våren
där sena flyttare (exempelvis prutgås) uppvisade en större minskning av andelen passerande
flockar över de centrala delarna av sundet (-36 %, Fig. 45) jämfört med tidiga flyttare
(exempelvis ejder, Fig. 43, -15 %) och de som passerar mitt på våren (exempelvis vitkindad
gås, Fig. 44, - 23 %).
Däremot minskade andelen flockar som passerade själva Lillgrund, vindkraftparken, kraftigt
från åren före vindparkens tillkomst (82 % minskning, Fig. 46). Minskningen var lika kraftig
på natten som på dagen (Fig. 47).
För sjöfåglar som passerar Öresund med sydliga flygriktningar på våren, såsom många ejdrar
och sjöorrar (Fig. 48) noterades redan innan Lillgrundsparkens tillkomst att en väldigt liten
andel passerar så långt ut i sundet som vid Lillgrund (Fig. 49). Andelen flockar som passerade
själva Lillgrund tenderade trots detta att minska. Innan vindkraftparken byggdes passerade 09 % av den totala sträckvolymen med sydliga riktningar över Lillgrund, åren med parken i
drift var motsvarande andelar 0-3 % (Fig. 50).
Från hösten (Fig. 51) analyserades radardata från en höst (2001) innan vindkraftparken
byggdes och jämfördes med två höstar (2008 & 2009) med vindkraftparken i drift. Här fanns
inga skillnader i hur stor andel av det totala fågelsträcket som passerade över centrala
Öresund, med Lillgrund, mellan före och efter parken byggdes (Fig. 52). Mönstret var
detsamma både dag och natt (Fig. 53).
Återigen var det dock så att andelen flockar som passerade själva Lillgrund (vindkraftparken)
minskade kraftigt (78 % minskning, Fig. 54). Minskningen var lika stor både dag och natt
(Fig. 55).
Diskussion
Rastande och övervintrande fåglar
Inventeringarna i samband med kontrollprogrammet bekräftade södra Öresunds stora
betydelse för de övervintrande och rastande sjöfåglarna med viktiga koncentrationer av
speciellt småskrake och ejder i det undersökta området.
10
Liksom vid andra inventeringar av rastande och övervintrande sjöfåglar konstaterades en
betydande variation i antalet individer mellan olika inventeringstillfällen både för
Lillgrundområdet och i referensområdet söder om Falsterbo, samt för både flyg och
båtinventeringarna. Inventeringarna ger därför inte tillräckligt underlag för en formell
statistisk analys av skillnaderna i fåglarnas täthet i olika delområden före och efter parkens
uppförande. För att sådana analyser skulle kunna genomföras hade ett betydligt större antal
inventeringar än vad som ingått i planerna för kontrollprogrammet krävts.
För den vanligaste sjöfågeln, småskrake, noterades ett viss undvikande av vindkraftparken
särskilt under de första åren efter parkens uppförande. Totalt sett noterades dock inte någon
större negativ påverkan på småskrakarnas utnyttjande av området. Ejdern visade också ett
undvikande av själva vindkraftparken, men här syns ett visst tillvänjande ha skett. Den tredje
andarten i området, alfågel, visade en klar undvikandeeffekt, men alfågeln är sparsamt
förekommande i området och dess reaktion på Lillgrundparken saknar betydelse för arten i
området, som är perifert för arten.
Sammanfattningsvis kan man inte konstatera några större effekter på de rastande och
övervintrande sjöfåglarnas utnyttjande av södra Öresund även om det initialt fanns ett
undvikande av själva vindkraftparken av vissa arter. Även om de viktigaste andarterna till en
del undvek själva vindkraftparken eller förekom där i mindre tätheter så var det aktuella
området så litet i relation till den samlade arealen av lämpliga födosöksområden för aktuella
arter.
Även om det finns relativt få andra resultat från vindkraftparker till havs som vi kan jämföra
resultaten från Lillgrund med så är antalet studier i ständigt ökande efterhand som fler
anläggningar byggs i denna miljö. I Sverige har inga liknande studier som de vid Lillgrund
gjorts någon annanstans. De två små parkerna i Kalmarsund studerades exempelvis aldrig
med ett före-efter upplägg och utgörs dessutom av en annan typ av anläggningar (en enkel rad
av kraftverk)(Pettersson 2005).
Storskaliga undersökningar har genomförts i Danmark (Dong Energy 2006, Petersen et al.
2006, Petersen & Fox 2007 och ytterligare referenser i dessa rapporter) och generellt visar
dessa på liknande resultat som hittades vid Lillgrund. Nyare studier har också gjorts i
Nordsjöområdet, med till stor del andra arter inblandade (Percival 2010, Leopold et al. 2010).
Generellt börjar en mer komplicerad bild framträda där det inte verkar som om havsbaserade
vindkraftparker har så entydigt negativa effekter på sjöfåglars utbredning som man kanske
först trodde. Vissa arter, främst havslevande dykänder, lommar och havssulor uppvisar i regel
någon form av undvikande under de inledande åren efter det att en vindkraftpark har byggts.
Undvikandet är dock sällan totalt och för vissa arter (främst havslevande änder) finns tecken
på att någon form av tillvänjning successivt sker.
Flyttfåglar
Det finns inga tecken på någon storskalig påverkan av flyttfågelrörelserna i sundet som kan
härledas till vindkraftparken på Lillgrund. Den översiktliga analys som gjorts visar att andelen
flockar som väljer att passera genom den 10 km sektor där Lillgrund ligger har minskat med
ca 20 % sedan vindparken kom på plats. Den mest markanta förändringen i vårsträcket är
annars att en mycket högre andel av alla passerande flockar under perioden med
vindkraftparken i bruk passerade över norra delen av undersökningsområdet (Saltholm).
11
Samtidigt med en ökad andel flockar som passerat i norr 2008-2010 så finns även en minskad
andel som passerat längst i söder, varför den troligaste förklaringen till det funna mönstret
kanske är eventuella skillnader i vindförhållanden på väg till Öresundsområdet. Flyttande
fåglar driver till viss del med vinden, antingen för att det är gynnsamt för dem eller för att de
inte kan kompensera fullt ut. Detta leder till viss variation i var exakt som en viss
flyttningskorridor går under en given dag eller under en viss säsong. Små skillnader i
vindförhållanden kan därför ge upphov till skillnader av den typ som vi ser i det storskaliga
mönstret mellan åren innan vindparken var byggd och åren efter.
Ett otvetydigt resultat är dock att andelen flockar som passerar över själva Lillgrund har
minskat kraftigt efter det att vindparken kom på plats. Blott ca en femtedel så stor andel av
alla flockar passerar över Lillgrund idag som innan vindparken fanns där. Vi tolkar detta som
att flyttande fåglar i stor utsträckning undviker vindkraftparken på Lillgrund, men att
undvikandet sker i Lillgrunds närområde, dvs. inom någon km från parken. Dessa resultat
ligger helt i linje med vad man hittat på andra håll vid studier av flyttande (sjö)fåglar vid både
små och stora vindkraftparker (Pettersson 2005, Petersen et al. 2006, Krijgsveld et al. 2010).
Resultaten innebär att befarade kollisionsrisker för de fåglar som täcks av radaranalysen är
relativt små. Endast en liten andel av de totala fågelrörelserna över Öresund passerar så nära
Lillgrundsparken att de löper risk för att kollidera med kraftverken. Större delen av de flockar
som flyger i anslutning till Lillgrund viker av och undviker att komma i omedelbar kontakt
med parken. Samtidigt bör det nämnas att de radaranläggningar som använts vid dessa studier
ej kan mäta flyghöjder. Detta innebär att vi i vårt material inte kan särskilja mellan lågt
flygande flockar, som potentiellt kan komma i kontakt med turbinerna, och de som flyger på
högre höjd, en bra bit över vindkraftparken utan någon som helst kollisionsrisk. Sannolikt
utgör en stor del av de flockar som noterats passera igenom eller nära vindkraftparken av
sådana som färdas på betydligt högre höjd (upp till flera 1000 m höjd) och därmed är andelen
fåglar som är utsätts för reell kollisionsrisk troligen betydligt lägre än vad vi kan visa här.
Om vi använder oss av kollisionsfrekvenser som registrerats vid eller beräknats från andra
havsbaserade vindkraftparker i Östersjöområdet bör det vara i storleksordningen 100- några
100 fåglar som årligen kolliderar med och förolyckas vid Lillgrundsparken. Detta kan
jämföras med att det vid den närbelägna Öresundsbron sannolikt är ungefär tio gånger fler
fåglar som kolliderar och förolyckas varje höst (Nilsson & Green 2002).
12
Introduction
Southern Öresund is an important staging and wintering area for a large number of waterfowl
species. Therefore Saltholm (on the Danish side) and Foteviken-Falsterbo (in Sweden) have
been appointed as ”Special Bird Protection Areas” (SPA) under the bird’s directive of the
European Union (79/409/EEG). Both these areas are also appointed as areas of international
importance under the Ramsar convention (www.ramsar.org). Other parts of the southern
Öresund, e.g. Lommabukten and Lundåkrabukten are also important for different wetland
species and show bird numbers higher than the criteria for international importance.
The southern part of Öresund is also an area where large numbers of migrating birds of
different species are passing both during spring and autumn. These parts probably hold the
largest concentrations of migrants in Scandinavia (Alerstam 1978, 1990) as this is where the
over-water passage over the Baltic between Scandinavia and the Danish islands (and in the
longer perspective the European continent) is shortest. This means that large numbers of
migrants arrive to Scandinavia from southerly and southwesterly winter quarters here in
spring, and that even higher numbers depart from Scandinavia over this area in autumn. The
migratory bird movements over the area have been studied for many years at Falsterbo Bird
Observatory (http://www.falsterbofagelstation.se/ ).
Based on this background, avian studies formed an important part of the Environmental
Impact Assessment when the Lillgrund Wind farm was planned in southern Öresund (Fig. 1).
A desktop study of the possible effects on the bird fauna of the planned wind farm was
published by Nilsson (2001). As a part of the conditions for the wind farm a monitoring
program was established to study the possible impact of the wind farm on the bird fauna.
The monitoring program included studies both on staging/wintering birds in the area and the
bird migration through the area. For staging/wintering water birds the study aimed to establish
whether the wind farm had any effects on their possibilities to utilize their feeding areas. For
actively migrating birds the program aimed at looking at if the wind farm affected the
migratory movements over the area, if there was any avoidance behavior that could lead to
increased costs for the birds or if there were any large risks for collisions with the turbines.
These questions were analyzed through studies performed before the construction and during
the first years of operation of the wind farm. Staging/wintering birds were counted from both
boat and aircraft both in the possible impact area, here defined as the area between the
Öresund Bridge between Sweden and Denmark and the Falsterbo peninsula and a reference
area south of Falsterbo (aerial surveys only), where we did not expect any risks for effects.
This latter part of the study was important to get background information on fluctuations in
numbers of staging/wintering water birds in the area.
Bird migration over the area was studied using data from two surveillance radar stations.
During the base-line studies visual observations of bird migration was conducted from a
neighboring vantage point (Green & Nilsson 2006). Background information of the general
bird migration over the area was also obtained from studies in connection with the Öresund
Bridge, just north of the wind farm area (Nilsson et al. 2009, 2010).
The first phase of the monitoring program (before the building of the wind farm) was
undertaken during 2001 – 2006 (Green & Nilsson 2006). There was no field work during the
construction period as it is clear that this work would lead to large disturbances on the birds
13
and that these most probably are temporary. The second phase started in December 2007 and
was originally planned for a period of three years, i.e. until 2010. Due to the unusually hard
winter weather it was not possible to do all of the planned work in the winter 2009/2010 so
the second phase of the study was extended to include also the 2010/11 winter and the spring
in 2011.
This report analyze the results of the monitoring program with the aim to establish whether
the establishment of the wind farm had any effects on the bird fauna in the area or not.
Preliminary results from the second phase of the program have been published in reports of
Nilsson & Green (2009, 2011). For a general background description of the staging/wintering
bird fauna of the area and the migration through the area see the report from the first phase
(Green & Nilsson 2006) and the first preliminary description (Nilsson 2001).
Study area
Fig. 1. The southern part of Öresund showing the important bird areas at Foteviken, Falsterbo
peninsula and Saltholm. Water depths are shown with different grades of blue: 0-3m
(darkest), 3-6 m, 6-10 m and 10-20 m (lightest). Deeper areas in the south are shown in white.
Turbines at Lillgrund are shown with black dots.
Södra Öresund med Lillgrund och de viktiga fågelområdena vid Foteviken, Falsterbohalvön
och Saltholm markerade. De olika djupnivåerna i södra Öresund visas med olika mörka blå
nyanser: 0-3 m (mörkast), 3-6 m, 6-10 m samt 10-20 m (ljusast blått). Djupare områden
saknar färg på kartan. Vindkraftverken vid Lillgrund visas med svarta punkter.
14
Lillgrund is situated in the southern part of Öresund, about six km west of Klagshamn south
of Malmö (Fig. 1). Most parts have a depth of four-five meter but some areas are as shallow
as about two meter. Some parts of the wind farm are on the shallowest areas, whereas other
turbines stand in somewhat deeper water. South of Lillgrund there is another shallow area,
Bredgrund, also with water depths of about two-three m in parts. Large shallow areas are also
found around the Falsterbo peninsula and in the Foteviken area, these areas forming important
feeding areas for different water birds.
The bottom substrate of the area as well as the submerged vegetation and benthic fauna of the
area is well documented in studies made in connection with the establishment of the Öresund
Bridge north of Lillgrund. Lillgrund is situated in what in that case was called the “outer
impact zone” and was therefore included in the studies. Large areas of Zostera vegetation was
found in the area (Semac 1997), these areas being important for many benthic organisms and
thus important as feeding areas for several water birds (Nilsson 1972). The benthic fauna
showed high biomasses and the coverage by Blue Mussels (Mytilus edulis) was around 40%
(Semac 1998, 1999). The area has apparently large capacities as feeding areas for Eiders and
other diving ducks.
Fig. 2. Detailed map of Lillgrund with the turbines showed as black dots. Bredgrund to the
south is also shown. Water depths are shown with different grades of blue: 0-3m (darkest), 36 m, 6-10 m and 10-20 m (lightest).
Detaljkarta över Lillgrund med vindkraftparken. Bredgrund i söder visas också. De olika
djupnivåerna i södra Öresund visas med olika mörka blå nyanser: 0-3 m (mörkast), 3-6 m, 610 m samt 10-20 m (ljusast blått).
15
The wind farm at Lillgrund consists of 48 turbines placed in eight rows of three to eight
turbines in the direction NE – SW, with 300 m between the turbines in one direction and 400
m in the other (Fig. 2). The wind farm is situated about 7 km from the Swedish coast (Fig.1).
The total height of the turbines is 115 m up to the top of the wings. The hub height is at 68.5
m above sea level and the rotor diameter is 93 m. For further general information on the wind
farm see Vattenfall Vindkraft (2009).
Methods
Survey methods
Censuses of birds in offshore waters can be performed from different platforms, either from
boats or from airplanes. Both have advantages and disadvantages. In Danish studies in
relation to offshore wind farms (Petersen et al. 2006) and also in other studies, aerial surveys
have been used, but boat counts have also been performed in some areas.
In the original plans for the monitoring program a combination of local boat counts and aerial
surveys covering larger areas were envisioned. In practice the surveys in the first years had to
be made by boat only as there were no suitable airplanes available in the region (offshore low
level flying must be done by twin-engined aircrafts for security reasons). However, we
managed to make aerial surveys in 2006 (plus at two occasions in 2004 to develop methods)
before the construction of the wind farm. In this way we also managed to cover the reference
area.
Aerial surveys were continued after the construction of the wind farm but due to the
sometimes difficult flying conditions in winter it was not possible to fly in some periods. The
surveys are especially sensitive to wind and turbulence as they implied flying in between the
turbines. There were also problems with the boat surveys in 2010 and 2011 due to the ice
conditions in Öresund. In these situations it was however possible to fly.
According to our experience both survey methods work well in the Lillgrund area but the
aerial surveys have the advantage that they cover a much larger area in shorter time. It is
however important to use both methods as some species can be difficult to detect and count
properly from an aircraft (Nilsson 1975) whereas it for other species is important that large
areas can be covered to avoid double-counting.
Boat surveys
The boat surveys at Lillgrund have followed the standardized methods used in the ESASproject (European Seabird at Sea Team) documented by Komdeur et al. (1992). The method
was originally established for larger ships in offshore areas but we have made the surveys
from a small boat and adapted the method accordingly.
The boat surveys were performed as line transects following a standardized route (Fig. 3)
from north of Lillgrund and over Lillgrund and Bredgrund with 2 km between the survey
lines except for Bredgrund where this was not possible due to the shallow water. The surveys
were normally conducted by two observers, each covering one side of the boat. Some counts
16
had to be made with only one observer (covering just one side). The observation height was
about 3 m above the water surface.
All birds seen were counted and the position of each observation (bird or flock of birds) was
estimated into five distance bands. The following bands were used: A= 0-50 m, B = 50-100
m, C= 100-200 M, D = 200-300 m and E >300 m. Observations were registered on tape or
digital recorder with time of observation, species, number, behavior and estimated position.
The position of the boat was recorded with a GPS every minute, meaning that a position was
recorded about every 170 m with the normal travelling speed (10 km/h).
Fig. 3. Map of the southern part of Öresund with the boat survey lines shown in red. Water
depths are shown with different grades of blue: 0-3m (darkest), 3-6 m, 6-10 m and 10-20 m
(lightest). The turbines at Lillgrund are shown with black dots.
Karta över södra Öresund med den standardiserade rutten för båtinventeringarna inritad i
rött. Vindkraftverken visas med svarta punkter. De olika blå nyanserna visar områden med
olika djup med de fyra djupintervallen 0-3 m (mörkast blått), 3-6 m, 6-10 m och 10-20 m och
djupare (ljusast).
Bird data were transcribed from tapes or data files after each survey and combined with the
position data recorded and stored in the GPS, hence giving all observations a position. The
observations were then stored in a data-base.
The number of boat surveys undertaken in different months and years is found in Table 1. The
low number of boat surveys undertaken during 2007 – 2011 was due to technical problems
with the boat and difficult ice conditions during the winter periods.
17
Table 1. Number of boat surveys (Fig. 3) and aerial surveys (Fig. 5) undertaken in the study
area during the different months and years.
Antal båt (Fig. 3)- och flyginventeringar (Fig. 5) inom undersökningsområdet under olika år.
Sept
BOAT
2001/02
2002/03
2003/04
2004/05
2005/06
Oct
Nov
Dec
Jan
Feb
March April
May
1
-
-
1
1
1
1
1
1
1
1
-
1
1
-
1
1
1
1
-
1
1
1
1
-
-
2007/08
2008/09
2009/10
2010/11
AERIAL
2005/06
1
1
-
1
-
1
-
-
1
-
-
1
1
1
-
-
-
-
1
1
1
1
1
2007/08
2008/09
2009/10
2010/11
-
-
-
1
-
1
1
1
1
2
1
1
2
1
1
-
1
1
1
Aerial surveys
Fig. 4. A CESSNA 337 Skymaster was used for the aerial surveys.
CESSNA 337 Skymaster användes för flyginventeringarna.
18
Fig. 5. Map of the southern part of Öresund and waters south of Falsterbo with the aerial
survey lines. N = the possible impact area (North) and S = reference area (South). For depth
intervals see Fig.1
Karta över södra Öresund och farvattnen runt Falsterbo med de standardiserade flyginventeringslinjerna markerade. Djupnivåer se Fig. 1. N = möjligt påverkansområde (norr), S=
kontroll område (söder).
The aerial surveys were undertaken from a CESSNA 337 Skymaster (Fig. 4), a high-winged
twin-engined aircraft with good visibility for the observers. The same aircraft and survey
methods have been used as a standard for monitoring of offshore seabirds (mostly sea ducks)
in Sweden over a number of years.
During the surveys two observers were always employed covering each side of the aircraft.
The survey speed was about 180 km/h and we flew the surveys at an altitude of 50-70 m
above sea level. Observations were registered on tape or digital recorder and the position of
the plane is continuously stored by GPS. We used separate GPS equipments for navigation
and registration.
The survey lines were separated by two km. The observers covered a sector of 200 m on each
side of the aircraft. There is a “dead zone” just under the aircraft implying that the sector
covered is a total of 320 m. Observations outside the survey belt were noted as “extra”
observations in the data base.
After the construction of the wind farm the survey lines 3 and 4 were modified so that they
passed from SE to NW through the wind-farm (see example in the species maps).
19
The number of aerial surveys undertaken in different months and years are to be seen in
Table 1. Gaps in the coverage was due to difficult flying conditions, the aerial surveys also
being dependent on the availability of suitable aircraft in the region.
Analysis of survey data
For the five most common species (Cormorant, Long-tailed Duck, Eider, Red-breasted
Merganser and Herring Gull) comparisons of the utilization of the Lillgrund area before and
after the construction of the wind farm was analyzed using two methods: with Jacob’s index
and by comparing densities. For these analyses we used three different zones: the wind farm
area, a buffer zone of 2 km around the outer limits of the wind farm and the outer area, i.e. the
northern area in general excluding the windfarm and buffer zone. In the aerial surveys we
considered lines 1 – 9 to constitute the northern area. In the density calculations we restricted
the analysis to the parts of the survey lines that covered water deeper than three meter (see
Fig. 6). The same area divisions were used below in the calculations of Jacob’s index. The
total areas of the three different zones were: windfarm area 5 km2 , buffer zone 29 km2 and for
the outer area 224 km2, of which 20%, 15% and 15 % were actually covered by the aerial
surveys.
The Jacob’s indices show the relative use of the different zones in relation to expected use.
Densities are just a measure of the number of birds per area unit. Hence the two measures in
part describe different things and results from the two may differ. Jacob’s indices do not give
any information at all about the absolute numbers or densities of birds using a specific zone,
but instead show the proportion of birds using the zone in relation to a) the total number of
birds using the whole study area (all zones) and b) the proportion of the zone out of the
whole study area. This means that it may very well be so that densities in a specific zone can
increase at the same time as the Jacob’s index for that zone can decrease, since the latter
depends on the total number of birds registered in the whole study area.
The density calculations were based on the aerial surveys as the boat surveys cover too small
parts of the areas outside the wind farm area and the buffer zone. The total area within the
survey belt of the aerial surveys were 1.0 km2 within the wind farm area, 4.2 km2 for the
buffer zone and 33.9 km2 for the areas outside these zones. The mean counts within the
survey belts within each zone were calculated for each year and season separately and the
densities were calculated from these means and the surveyed area within each zone (see
above). The means are found in Table A10 in the appendix.
If birds avoid the wind farm area or not was analyzed by calculating Jacob’s selectivity index
D (hereafter Jacob’s index, Jacobs 1974). This index was calculated for the five most
commonly recorded species during boat and air surveys, and was used for describing if the
birds avoided or were attracted to the wind farm area. Indices were calculated both for the
period before the construction of the wind farm and for the period with the farm in operation.
Separate indices were also calculated for each survey year (centered around mid-winter) in
order to look at annual variation in avoidance or preference. Avoidance or preference for the
area outside but close to the wind farm, up to 2 km away from the turbines, was also analyzed
(see Fig. 6 for delimitation of the areas used). The birds recorded in the remaining parts of the
study area covered by boat transects or the northern part of the aerial survey area were used in
the calculations of the total number of birds in the whole study area and for calculating
proportions of birds using the areas closest to the wind farm, but no indices were calculated
for these parts.
20
Fig. 6 . Map over the wind farm at Lillgrund, turbines showed by black dots, the wind farm
area (line connecting black dots), as well as the area within 2 km from the turbines used in the
calculations of Jacob’s index (see text).
Detaljkarta over vindkraftparken på Lillgrund samt omfattningen på buffertzonen inom ett
avstånd på 2 km från de yttersta kraftverken, vilka utnyttjas för beräkningar och analyser med
Jacobs index (se närmare i texten!).
The Jacob’s index describes to what extent the birds use a specific area in relation to the
expected use of that area. In the case with marine birds at sea the expected use is usually that
the birds should distribute themselves in relation to size of the area. The larger area, the more
birds in absolute numbers is expected to use the area. This is of course a simplification of
reality and many other factors such as water depth, food availability are also deciding how the
birds will be distributed. As a simple rule of thumb and as a reasonable starting point for
further discussions, the Jacob’s index works perfectly well and hence has been used in several
similar studies before (see for example Petersen et al. 2006, Petersen & Fox 2007).
An index value (D) of +1 show that all birds occur in the area of interest and will be
interpreted as that the birds prefer this area. An index value (D) of -1 show that no birds occur
in the area of interest and will be interpreted as that the birds avoid the area. The
interpretation of negative index values is that there is some sort of avoidance involved. The
lower (more negative) the index, the stronger is the avoidance. Positive index values are
interpreted as some sort of preference. The higher (more positive) index the stronger is the
preference. Index values close to zero shows that the area is used roughly as expected.
The Jacob’s index is calculated as follows:
D = (r - p) / (r + p - 2rp)
21
Where r = the proportion of birds within the area of interest in relation to the total number of
birds in the whole study area. P = the proportion of the area of interest in relation to the whole
study area. In our calculations of Jacob’s index we proportions of area for the boat survey
data. The boat surveys were in reality very close to total surveys of the area, i.e. all or most of
the birds present were actually seen. For the calculations based on aerial survey data we used
proportions of transect length within respective area as these surveys are done as samplings.
Even if the Jacob’s index gives an indication of if birds avoid or prefer certain areas, the
results should be interpreted with caution. The index only shows if the birds use an area in
relation to the expected use. It says nothing about the mechanisms behind why the birds
distribute themselves as they do.
To get a large-scale overview of the bird migration patterns in the area, as well as for also
being able to look at patterns during night time, we used data from two surveillance radar
stations in south central Scania, situated at about 30 km from Lillgrund. These radar stations
are used for monitoring air- and ship traffic along the Scanian west and south coasts and
should hence cover also bird migration in an acceptable way in these areas. Film from the
radars PPI was stored on VHS or DVD:s. In these films, anything that reflect the radio waves
from the radar shows up as distinct dots, radar echoes, moving over the landscape. Usually,
there is an activated function for removing stationary echoes. Objects containing metal, as
ships or airplanes as well as anything containing water, such as living creatures results in
radar echoes and are hence possible to follow by the radar technique.
Radar has been used successfully with bird migration research during the last 50 years (see
Eastwood 1967 and Alerstam 1990 for details about the technique). As it foremost is the three
above mentioned objects (airplanes, ships and birds) that gives rise to radar echoes in the
Sound area a routine for separating the three is needed. This is relatively simple as the three
types move with different typical speeds. Airplanes are fast and travel by 150-1000 km/h,
ships are slow and moves with speeds up to 30 km/h and birds, finally, are intermediate.
Typical ground speeds (the resulting flight speed over the ground, i.e. the birds own flight
speed + the effect of the wind) varies between 30 and 130 km/h.
Based on the speed of the echoes travelling over the area, bird echoes can be separated where
after the data set can be analyzed for migration intensity (number of bird echoes), flight
directions etc. Also behavior as when birds are facing a wind farm can be analyzed, although
the surveillance radars used here do not permit any more detailed analysis of bird behavior
close to, or within, the Lillgrund wind farm.
Since the most of all bird movements over the Sound in spring are directed towards between
north and east, bird echoes were counted along 50 km long north-south oriented transect (Fig.
7). The transect was based on the Swedish Grid (RT-90) and passes along the east side of the
Lillgrund area in the middle of the Sound (1310 E, according the Swedish Grid). To get a
more detailed resolution of the bird movements the transect was divided into 10 km long
segments, also based on the Swedish Grid (A-E, Fig. 7). In addition to the north-south
directed transect another one, perpendicular to the first one going from west to east was used
for describing the southerly oriented spring migration of waterfowl (mainly eiders and
common scoters) in the Sound (6160 N, according to the Swedish Grid (Fig. 7). Also this
22
transect was divided into 10 km long segments in order to get a more detailed resolution of
the geographical pattern of bird migration. (1-4, Fig. 7). The number of passing echoes
(flocks) per segment and hour was counted as a measure of bird migration intensity.
The same north-south directed transect in the middle of the Sound was used also for
describing the patterns of autumn migration over the area (Fig. 7). This since most of the
autumn migration over the area follows directions towards between south and west. The
perpendicular transect used for analyzing the spring migration patterns (see above) was not
used in autumn. Radar data from one autumn season before the construction of the wind farm
(2001) was analyzed in comparison with two seasons with the wind farm in operation (2008
and 2009).
In addition to analyzing the number of bird echoes (flocks) passing each 10 km segment we
also analyzed the number of echoes passing a 3x3 km large square covering the Lillgrund area
including the wind farm (Fig. 7), in order to decide how large proportion of the overall
migration volume that passed the wind farm area before and after the construction of the wind
farm.
The used surveillance radar does not cover all migratory movements of birds. Small birds
flying singly, such as night migrating passerines, do usually not give rise to any radar echoes
simply because they are too small. Flocks of small birds do however show up as radar echoes.
This means that the bird movements that are possible to follow with these radars primarily are
the ones of larger birds and those migrating in flocks. In general, large birds migrating in
flocks are the ones giving rise to the most obvious and easily recognizable echoes. This means
migrating water birds (ducks, geese, waders) and pigeon probably are over-represented in our
data set. The radar do also not cover the very lowest altitudes (<5 m) as the seas surface
creates interference problems (clutter) with the relatively speaking small bird bodies. On the
other hand the radar cover the altitudes mostly used by migrating birds well. Flight altitudes
are not possible to measure with these surveillance radars.
Table 2. Periods during which radar data was analysed together with data on number of days
analysed and the total number of hours covered during those days.
Perioder från vilka radar data analyserades för att beskriva fågelflyttningsmönster över
området. Antal analyserade dagar samt det totala antalet timmar som analyserades redovisas
också.
spring
spring
spring
spring
spring
13 Mar
31 Mar
20 Mar
21 Mar
28 Mar
26 May
29 May
29 May
27 May
5 Jun
17
24
23
26
20
382
573
539
624
467
% of total time
during selected days
94
>99
98
100
97
2001 autumn
2008 autumn
2009 autumn
20 Sep
11 Sep
8 Sep
19 Oct
6 Nov
30 Oct
11
13
17
240
288
408
91
92
100
Year Season From date To date No. of days No. of hours
2002
2005
2008
2009
2010
23
Periods during which radar data was analysed together with data on number of days analysed
and the total number of hours covered during those days are shown in Table 2. Days were
selected based on own field observations of migratory movements over the Sound (spring
2002, autumn 2001, see Green & Nilsson 2006), on recorded larger migratory movements of
waterfowl were selected (data on observed migratory movements were collected from the
web-based bird reporting system Svalan (spring 2005, 2008-2010, www.artportalen.se/birds)
or on heavy migration movements observed during the standardized migration counts made
at Falsterbo Bird Observatory, south of Lillgrund (autumn 2001, 2008-2009, see
http://www.falsterbofagelstation.se/).
.
A
B
1
3
2
4
C
D
E
Fig. 7. Map over the southern Sound showing the Lillgrund area (red square) and the transects
used in the radar analysis (yellow lines) as well as the different zones used for echo counting
along the transects (A-E, resp. 1-4). The background picture is from Google Earth.
Karta över södra Öresundsområdet visande Lillgrundsområdet (röd kvadrat) och
transekterna över vilka radaranalysen genomfördes (gula linjer) samt zonindelning av dessa
(A-E, resp. 1-4). Bakgrundsbild från Google Earth.
24
Results
In this chapter we analyze the occurrence and distribution of staging/wintering water birds in
relation to the wind farm at Lillgrund by comparing the patterns recorded before and after the
construction of the wind farm. We base the comparisons both on the boat and aerial surveys.
The total numbers of birds of all species counted at the surveys are shown in Tables A1 and
A2 in the appendix. Here we focus on the species occurring regularly at Lillgrund and which
could possibly be affected by the wind farm. Five species, (Cormorant Phalacrocorax carbo,
Long-tailed Duck Clangula hyemalis, Eider Somateria mollissima, Red-breasted merganser
Mergus serrator and Herring Gull Larus argentatus) were found regularly in the Lillgrund
area before the construction of the wind farm and will hence be in focus for this analysis.
During the boat surveys, which only cover offshore areas (Fig. 3), a total of 26 species were
recorded during the surveys (Table A1-A3 in the appendix). During the aerial surveys the
transects go from the shore to the outer limit of the study area (Fig. 5) and they will therefore
cover a number of inshore water bird species that never are found in the offshore areas (these
species will not be discussed any further here). In all 35 species were seen during the aerial
surveys (Table A4 - A9 in the appendix).
In addition to the offshore species occurring regularly at Lillgrund, two sea ducks were found
in larger numbers in the reference area south of Falsterbo: Velvet Scoter Melanitta fusca and
Common Scoter Melanitta nigra. These species were also found around Lillgrund in very
small numbers but not on a regular basis.
The Goldeneye Bucephala clangula is a diving duck that is normally found in shallow water
close to the coast and it is a very common species in the Foteviken area east of Lillgrund. In
cold ice winters larger flocks can sometimes occur far out in Öresund and it may be that
Lillgrund could be included in its offshore distribution in such situation. We did not find any
larger numbers at sea during the pre-construction years, but during the two hard, ice-winters
in 2010 and 2011 we found some larger flocks on Bredgrund, south of Lillgrund but none in
the Lillgrund area itself. Lacking a very hard winter before construction we cannot evaluate
whether the distribution of this species might be affected by the wind farm in cold winters.
Another diving duck species which could not be studied in relation to the wind farm is the
Tufted Duck Aythya fuligula. Large flocks roost over the day in the ponds at Klagshamn or in
the inner part of Höllviken (Falsterbo Canal) from where they make nocturnal feeding flights
out to offshore foraging areas. From previous analyses of radar data we know that the
foraging areas are mainly situated around the northern tip of Falsterbo peninsula and at
Bredgrund, but it cannot be excluded that Lillgrund may be used in some occasions. So far we
have not seen any movements towards Lillgrund.
For the main study species we analyze the distribution and numbers for each species
separately with the main emphasis to compare the situation pre- and post-construction of the
wind farm at Lillgrund. We show total numbers counted for each main species during the boat
surveys, Fig. 3) and for the aerial surveys, (Fig. 5). For the aerial surveys we separate
between the Northern area (including Lillgrund) and the Southern area (reference area). For
25
each species we also show summary maps of the distribution before and after the
establishment of the wind farm, whereas maps for the different years separately and divided
upon season (the different winters, springs and autumns) are shown in the appendix.
As is shown in Table 3 different species occur in different proportions in the northern and
southern part of the aerial survey area. Thus the majority of the Red-breasted Mergansers
were found in the Northern area of the study area, whereas the Long-tailed Ducks were
mostly found south of Falsterbo in the Southern area with smaller numbers in the Northern
area. The proportion of Eiders seen in the two parts varied between spring and winter surveys.
In winter most Eiders were seen in the Southern area, whereas more Eiders were found in the
Northern area during spring surveys, related to the large breeding colony on Saltholm and
temporary staging flocks during the migration.
Overall Jacob’s indices for the wind farm area and the adjacent buffer zone (up to 2 km from
the wind farm) are shown in Table 4. In this table we show the indices for the whole preconstruction period (2001-2005 for the boat surveys, 2006 only for the aerial surveys) in
comparison with the indices for the whole post-construction period (2007-2011 for the boat
surveys, 2008-2011 for the aerial surveys). The indices are commented upon in the species
texts below for respective species. In the species accounts we also show figures of the
variation of indices between years (centered on midwinter).
26
Table.3 Percentage of the total number of counted individuals of the more important species seen in the northern part of the area (Fig. 5) during
aerial surveys in January-May 2006 (pre-construction) and 2008-2011 (post-construction) based on the totals for all surveys in the different years.
Number of surveys is shown in brackets.
Andel (%) av det totala antalet inräknade individer vid samtliga flyginventeringar i jan- maj 2006 (före byggnation) och 2008- 2011(med
vindkraftparken i drift) som räknats i det norra delområdet (områdesindelning se Fig. 5). Antalet inventeringar anges inom parentes.
Eider Somateria mollissima
Red-breasted Merganser Mergus serrator
2006 (5)
%
Total
94
934
9
1051
74
4894
72
984
59
605
2008(4)
%
Total
36
416
12
1021
52
6416
78
1002
77
804
%
70
29
11
84
37
2009(5)
Total
521
509
6037
801
459
%
98
13
56
90
44
2010(2)
Total
157
513
3455
850
264
%
93
22
30
92
55
2011(4)
Total
120
1176
10956
2348
757
Table. 4. Overall Jacob’s indices for the wind farm area and the adjacent buffer zone (up to 2
km from the wind farm, excluding the wind farm area (see Fig. 7) for the five regularly
occurring species for aerial and boat surveys respectively. Negative indices indicate
avoidance of the area in question, positive ones preference. Indices close to zero shows that
the area is used roughly in proportion to the size of the area (see methods for more details
about the Jacob’s index).
Genomsnittliga Jacobs index (D) för själva Lillgrund och intilliggande områden (en zon på 2
km från de yttre turbinerna, se Fig. 7) för de fem talrikaste arterna baserat på flyg- och
båtinventeringar före och efter etablering av vindkraftparken på Lillgrund. Negativa
indexvärden visar på undvikande av området i fråga. Positiva indexvärden på preferens för
området i fråga. Värden nära noll visar på att området utnyttjas i proportion till hur stort det
är (se metoder för mer detaljer om Jacobs index).
Species
Sub-area
Cormorant
Wind farm
2 km Buffer zone
Wind farm
2 km Buffer zone
Wind farm
2 km Buffer zone
Wind farm
2 km Buffer zone
Wind farm
2 km Buffer zone
Long-tailed
Duck
Eider
Red-breasted
Merganser
Herring Gull
Aerial surveys
PrePostconstruction construction
- 0.49
-0.84
-0.52
0.82
-0.23
-0.85
0.06
-0.41
0.06
0.08
0.79
0.62
-0.26
-0.42
0.22
0.07
-0.36
0.03
0.06
-0.27
Boat surveys
PrePostconstruction construction
-0.79
-0.69
- 0.71
0.14
0.48
-0.14
0.78
0.77
0.80
-0.09
0.68
0.11
0.41
-0.27
0.47
0.03
-0.11
-0.71
-0.20
0.46
As is apparent from Fig. 8, the number of Cormorants counted during the aerial surveys
varies markedly between different surveys. Large flocks fish in the southern part of Öresund,
using Pepparholm and Saltholm for roosting, the total number of birds amounting to several
thousand at occasions (Bengtsson 1999, 2000). We have not seen these large flocks at the
aerial surveys in southern Öresund but large flocks have been seen (in a distance and outside
survey lines) during earlier boat counts (Green & Nilsson 2006, Nilsson & Green 2009).
Before the construction of the wind farm Cormorants in smaller groups were regularly found
on Lillgrund. Cormorants were still observed there in the post-construction period but
numbers in the wind farm were smaller than before (Fig. 11).
Densities of Cormorants in the three different zones around the windfarm are shown in Fig.
12. During the three surveys pre-construction, the mean densities were very similar in all
three zones, whereas Cormorants were hardly observed during the aerial surveys postconstruction. Two values in Fig.12 deviate markedly from the others, both in the buffer zones,
being related to observations of flocks. In general density calculations for the Cormorant are
much dependent on the occurrence of larger flocks. The occurrence of fish shoals will lead to
large concentrations of Cormorants on some occasions ( see above) but this did not occur at
the aerial surveys. The number of birds counted during the surveys in the different zones is
seen in Table A10 in the appendix.
During the surveys in 2006 (before) a mean total of three cormorants was found at the surveys
within the coming windfarm area, whereas the only Cormorants noted within the windfarm
after establishment were found in 2009, when a total of four individuals were counted during
the four surveys undertaken that winter. Mean totals for the buffer zone varied between 0 and
62, whereas the mean counts for the outer zone varied between 8 and 108 (Table A10). Too
few observations were obtained during spring for a meaningful calculation of densities.
29
800
700
Phalacrocorax carbo
600
500
MIN
400
MEAN
MAX
300
200
100
0
BEFORE
AFTER
BEFORE
SOUTH
AFTER
NORTH
Fig. 8. Mean, Maximum and Minimum counts of Cormorant Phalacrocorax carbo during
aerial surveys in the northern and southern area (Fig. 5) pre- (7 counts) and post- (15 counts)
construction of the wind farm at Lillgrund.
Medel, maximum och minimum antal av storskarv Phalacrocorax carbo i det norra och södra
området (Fig. 5) före (7 räkningar) och efter (15 räkningar) uppförandet av vindkraftparken
på Lillgrund.
6000
5000
Phalacrocorax carbo
4000
3000
MIN
MEAN
2000
MAX
1000
0
BEFORE
AFTER
Fig. 9. Mean, Maximum and Minimum counts of Cormorant Phalacrocorax carbo during the
boat surveys Fig. 3) pre- (19 counts) and post- (8 counts) construction of the wind farm at
Lillgrund.
Medel, maximum och minimum antal av storskarv Phalacrocorax carbo vid båtinventeringar
(Fig. 3) före (19) räkningar) och efter (8 räkningar) uppförandet av vindkraftparken på
Lillgrund.
30
Fig. 10. Summary distribution maps for winter and spring for the Cormorant Phalacrocorax
carbo from aerial surveys pre- (left) and post- (right) construction of the wind farm. For
annual maps see appendix.
Sammanfattande utbredningskartor vinter och vår för storskarv Phalacrocorax carbo från
flyginventeringar före (vänster) och efter (höger) uppförandet av vindkraftparken. För
årsvissa kartor se appendix
31
Fig. 11. Summary distribution maps for the Cormorant Phalacrocorax carbo from boat
surveys pre- (left) and post- (right) construction of the wind farm. For annual maps see
appendix.
Sammanfattande utbredningskartor för storskarv Phalacrocorax carbo från båtinventeringar
före (vänster) och efter(höger) uppförandet av vindkraftparken. För årsvisa kartor se
appendix.
4
3,5
3
Phalacrocorax carbo
Winter
2,5
Outer
2
Buffer
Windfarm
1,5
1
0,5
0
2006(3)
2008(1)
2009(4)
2010(1)
2011(3)
Fig. 12. Mean densities (individuals / km2) of Cormorants Phalacrocorax carbo based on
aerial surveys during winter in different zones around the wind farm at Lillgrund in different
years. Number of surveys shown in brackets.
Täthet (individer km2) av storskarv Phalacrocorax carbo baserade på flyginventeringar under
vintern inom olika zoner runt Lillgrunds vindkraftpark under olika år. Antalet inventeringar
anges inom parentes.
32
Overall Jacob’s index (D) for the wind farm area based on the aerial surveys was -0.49 for the
pre-construction period and -0.84 with the wind farm in operation. Corresponding indices
based on the boat surveys were -0.79 for pre-construction period and -0.69 for the postconstruction period. Both aerial and boat surveys show that Lillgrund is not an area that is
important for Cormorants, at least during the study years, irrespective of the presence of the
wind farm. The negative indices instead indicate that Lillgrund is used less than would be
expected from the size of the area.
The indices based on aerial surveys indicate a stronger avoidance with the wind farm in
operation, an indication not shown by the boat data. At the same time, both data sets indicate
that the area just outside of the wind farm (the buffer zone, up to 2 km from the wind farm)
was also used less than expected during the pre-construction period but (D-values of -0.52
and -0.71), while these parts were used more than, or almost as, expected during the postconstruction phase (D-values of 0.82 and 0.14). Fig. 12 shows the variation in Jacob’s index
for the different study years. In both cases we can see that the indices for the wind farm area
in general are lower during the post-construction period. This is somewhat surprising since
Cormorants, in small numbers though, often use the fundaments of the turbines for roosting
(own observations). Still, the distribution of Cormorants in Öresund is not in any major way
connected to the more shallow areas such as Lillgrund, but instead to the movements of the
Herring Clupea harengus shoals appearing there on a seasonal basis. Hence the biological
significance of an analysis like this is not especially large for this species. Our conclusion is
hence that the wind farm at Lillgrund has not affected the Cormorants using southern Öresund
and Lillgrund in any major way.
33
Aerial
1
Jacobs Index
0,5
0
-0,5
-1
2006
2008
2009
2010
2011
-1,5
Boat
Jacobs Index
1
0,5
0
-0,5
-1
20012002
20022003
20032004
2005a
2005b
20072008
20092010
20102011
Fig. 13. Variation in Jacob’s index (see text for explanation) between years (centered around
mid-winter for boat data) for Cormorants Phalacrocorax carbo based on aerial (top) and boat
survey (bottom) data. Indices from the pre-construction period are shown with open symbols
and broken lines, indices from the post-construction period with filled symbols and full lines.
Red = the wind farm area, Blue = the buffer zone, up to 2 km from the wind farm. 2005a =
winter-spring 2005, 2005b = autumn-winter 2005.
Variation i Jacobs index (se text för förklaring) mellan år (centrerade runt midvinter för
index från båtdata) för storskarv Phalacrocorax carbo vid flyg (överst) och båtinventeringar
(underst). Index från före vindkraftparken byggdes visas med ofyllda symboler och streckade
linjer, index från perioden med parken i drift med fyllda symboler och heldragna linjer. Röd
= vindkraftparken, blå = buffertzonen upp till 2 km från parken. 2005a = första halvåret
2005, 2005b = andra halvåret.
34
.
The Long-tailed Duck was regularly seen during the surveys in the study area but the numbers
counted were generally relatively low (Fig. 14 & 15). The majority of the Long-tailed Ducks
were counted in the reference area south of Falsterbo, whereas only smaller numbers occurred
in Öresund. In the southern area more than 1000 individuals were sometimes counted in the
survey belt, whereas maximum counts from the northern parts were around 100, up to 200
and a little more being maximum counts from the boat surveys.
Long-tailed Ducks were regularly seen at Lillgrund before the construction of the wind farm,
larger numbers being seen at the boat counts than during aerial surveys (Fig. 16 & 17). In the
post-construction years only few Long-tailed Ducks were counted in the wind farm area and
the density was much lower in both the wind farm area and in the 2 km buffer zone (Fig. 18).
Numbers counted in the different zones (used for the density calculations) was generally low.
In the windfarm area a mean count of two individuals was obtained for the three surveys in
2006, whereas only one Long-tailed Duck was seen during nine censuses post-construction.
Total number of Long-tailed Ducks counted within the buffer zone varied between four and
seven, whereas between 32 and 77 were counted at aerial surveys in the outer area. For further
details see Table A10 in the appendix. Spring numbers were too low to calculated densities
for this species.
The same pattern emerges when we look at the Jacob’s indices in Table 4. During the boat
surveys a certain amount of preference was recorded for the wind farm area during the preconstruction period (D = 0.48), which changed to a weak avoidance for the post-construction
years (D = -0.14). The direction of the change was similar based on data from the aerial
surveys although Jacob’s index indicated a weak avoidance already before the construction of
the wind farm (D = -0.23). Post construction a much stronger avoidance was indicated (D =
-0.85). Based on data from the buffer zone, up to 2 km from the wind farm, the two survey
methods yielded different overall results. While the boat surveys showed preference for these
parts both before after construction of the wind farm (D = 0.78 and 0.77 respectively), the
aerial surveys showed that the buffer zone was used as expected during the pre-construction
period but less than expected (avoided) with the wind farm in operation (D = 0.06 and -0.41
respectively).
35
1200
Clangula hyemalis
1000
800
MIN
MEAN
MAX
600
400
200
0
BEFORE
AFTER
BEFORE
SOUTH
AFTER
NORTH
Fig. 14. Mean, Maximum and Minimum counts of Alfågel Clangula hyemalis during aerial
surveys in the northern and southern area (Fig. 5) pre- (7 counts) and post- (15 counts)
Medel, maximum och minimum antal av alfågel Clangula hyemalis i det norra och södra
på Lillgrund.
300
250
Clangula hyemalis
200
150
MIN
MEAN
100
MAX
50
0
BEFORE
AFTER
Fig. 15. Mean, Maximum and Minimum counts of Long-tailed Duck Clangula hyemalis
during boat surveys (Fig. 3) pre- (19 counts) and post- (8 counts) construction of the wind
farm at Lillgrund.
Medel, maximum och minimum antal av alfågel Clangula hyemalis vid båtinventeringar i
Lillgrund området (Fig. 3) före (19) räkningar) och efter (8 räkningar) uppförandet av
vindkraftparken på Lillgrund
Looking at the variation in Jacob’s indices between years we note that this is large, especially
for the post-construction period, irrespective of survey method (Fig. 19). The main reasons
36
behind the large variation is that few Long-tailed Ducks were encountered in the area in these
years (see above), meaning that a few occasional observations will create rather dramatic
changes in the indices. Note also that no Long-tailed Ducks at all were seen during boat
surveys in 2009-2010, making it impossible to calculate a Jacob’s index for that year. The
pattern that emerges is at least that there was an initial, and complete, avoidance in the first
years of the operational phase (2008-2009). Later years show an ambiguous pattern with
expected use according to the 2010 aerial surveys, complete avoidance during the 2011 aerial
surveys and preference during the 2010-2011 boat surveys. One possible interpretation is that
there is some sort of habituation involved, where birds are more prone to use the wind farm
area when the turbines have been there for a couple of years. The low overall numbers
encountered in the post-construction years do however obscure any form of robust conclusion
The indices from the buffer zone are more straight-forward and these parts seem to be used as
expected (aerial survey data) or preferred (boat survey data) in most years irrespective of the
presence of the wind farm.
We conclude that there was complete initial avoidance of the actual wind farm, but that the
avoidance was of no biological significance as the area in question is of very low value for
Long-tailed Ducks in Öresund and in general.
37
Fig. 16. Summary distribution maps for the Long-tailed Duck Clangula hyemalis from aerial
surveys pre- (left) and post- (right) construction of the wind farm for the winter and spring
seasons. For annual maps see appendix.
Sammanfattande utbredningskartor vinter och vår för alfågel Clangula hyemalis från
flyginventeringar före (vänster) och efter(höger) uppförandet av vindkraftparken. För årsvisa
kartor se appendix.
38
Fig. 17. Summary distribution maps for the Long-tailed Duck Clangula hyemalis from boat
surveys pre- (left) and post- (right) construction of the wind farm. For annual maps see
appendix.
Sammanfattande utbredningskartor för Long-tailed Duck Clangula hyemalis från
båtinventeringar före (vänster) och efter (höger) uppförandet av vindkraftparken. För årsvisa
kartor se appendix.
2,5
Birds/km2
Clangula hyemalis
Winter
2
1,5
Outer
Buffer
Windfarm
1
0,5
0
2006(3)
2008(1)
2009(4)
2010(1)
2011(3)
Fig. 18. Mean densities (individuals / km2) of Long-tailed Duck Clangula hyemalis based on
years. Number of surveys shown in brackets.
Täthet (individer km2) av alfågel Clangula hyemalis baserade på flyginventeringar under
vintern inom olika zoner runt Lillgrunds vindkraftpark under olika år. Antalet inventeringar
anges inom parentes.
39
Aerial
Jacobs Index
0,5
0
-0,5
-1
2006
2008
2009
2010
2011
Boat
Jacobs Index
1
0,5
0
-0,5
-1
20012002
20022003
20032004
2005a
2005b
20072008
20092010
20102011
mid-winter for boat data) for Long-tailed Ducks Clangula hyemalis based on aerial (top) and
boat survey (bottom) data. Indices from the pre-construction period are shown with open
symbols and broken lines, indices from the post-construction period with filled symbols and
full lines. Red = the wind farm area, Blue = the buffer zone, up to 2 km from the wind farm.
2005a = winter-spring 2005, 2005b = autumn-winter 2005. Note that no Long-tailed Ducks
were seen at all during boat surveys in 2009-2010. Hence, no Jacob’s index can be calculated
for this year.
index från båtdata) för alfågel Clangula hyemalis vid flyg (överst) och båtinventeringar
2005, 2005b = andra halvåret. Notera att inga alfåglar alls sågs under båtinventering 20092010 varför inga Jacobs index kan beräknas.
40
Common Eider Somateria mollissima
The aerial surveys and the boat counts show marked variations in the number of Eiders in the
area (Fig. 20 & 21). Maximum counts were between 7000 and 8000 both for the parts
covered by the boat counts and the southern area covered by aerial surveys. Eiders are
regularly wintering in southern Öresund with the largest concentrations in the waters south of
Falsterbo, where estimated numbers regularly are between 10 000 and 15 000 individuals
(Nilsson unpubl.). Wintering flocks are also found north of Falsterbo, but there the numbers
present are usually lower.
In spring, during the migration period, the distribution of Eiders is markedly different from
the winter distribution with large flocks both in the waters north of Falsterbo and in the
reference area south of Falsterbo (Fig. 22). Large flocks of migrating Eiders are regularly
found resting both in the Öresund proper and in the waters south of Falsterbo during this time
of the year. Moreover, the breeding colony at Saltholm with between 4000 and 5000 pairs in
2000 (Desholm et al. 2002) is situated a short distance to the north of Lillgrund and probably
these birds use the shallow areas also on the Swedish side of Öresund for foraging. Regular
movements of pairs and small groups of Eider between Saltholm and the waters around
Bredgrund and Lillgrund were observed during studies of in the area around the bridge
(Nilsson et al. 2009, 2010).
In May, three flights in 2006, 2008 and 2009 showed that the majority of the Eiders were at
this time in the northern area. In May most of the migration has passed and the majority of the
Eiders counted were probably local birds, mainly from the Saltholm colony. The majority of
those late Eiders were males, as the most of the females were incubating at this time.
There were marked differences in the local distribution of the Eiders in the Lillgrund area
when comparing the pre- and post-construction years (Figs 22, 23, 24). The density of Eiders
was markedly higher in the wind farm area before the construction of the wind farm than
anywhere else in the northern study area, both in spring and in winter (Fig. 25). Postconstruction the densities in the wind farm area were much lower, while densities in the 2 km
buffer zone instead were higher than during the pre-construction period. The maps (Fig. 21,
22, 23) and the densities (Fig. 24) hence indicate a shift in the local distribution from the wind
farm area to adjacent parts of Lillgrund and its surroundings. Number of Eiders counted in the
aerial surveys showed much variation between years in all zones (Table A10, appendix). In
winter mean numbers varied between 1 and 22 Eiders within the windfarm area. In spring
high counts were obtained in 2006 (before) and 2011 (last year of study) with 296 and 280
Eiders counted, respectively. In the buffer zone mean numbers counted in the survey lines
varied between 26 and 327 in winter and between 391 and 1118 in spring.
41
8000
7000
6000
Somateria mollissima
MIN
5000
MEAN
MAX
4000
3000
2000
1000
0
BEFORE
AFTER
BEFORE
SOUTH
AFTER
NORTH
Fig. 20. Mean, Maximum and Minimum counts of Eider Somateria mollissima during aerial
surveys in the northern and southern area (Fig. 5) pre- (7 counts) and post- (15 counts)
Medel, maximum och minimi antal av ejder Somateria mollissima i det norra och södra
på Lillgrund.
9000
8000
7000
6000
5000
MIN
4000
MEAN
3000
MAX
2000
1000
0
BEFORE
AFTER
Fig. 21. Mean, Maximum and Minimum counts of Eider Somateria mollissima during boat
surveys (Fig. 3) pre- (19 counts) and post- (8 counts) construction of the wind farm at
Lillgrund.
Medel, maximum och minimi antal av ejder Somateria mollissima vid båtinventeringar i
Lillgrund området (Fig. 3) före (19) räkningar) och efter (8 räkningar) uppförandet av
vindkraftparken på Lillgrund
42
Fig. 22. Summary distribution maps for the Eider Somateria mollissima from aerial surveys
pre- (left) and post- (right) construction of the wind farm for the winter and spring seasons.
For annual maps see appendix.
Sammanfattande utbredningskartor vinter och vår för ejder Somateria mollissima från
årsvisa kartor se appendix.
43
Fig. 23. Details of Fig. 22 to show the distribution of Eiders Somateria mollissia in the wind
farm area and the close surroundings from aerial surveys in winter and spring pre- (left) and
post- (right) construction of the wind farm.
Detaljer från Fig. 22 för att visa ejderns Somateria mollissima utbredning i vindkraftparken
och dess närområde från flyginventeringar vinter och vår före (vänster) och efter (höger)
uppförandet av vindkraftparken.
44
Fig. 24. Summary distribution maps for the Eider Somateria mollissima from boat surveys
pre- (left) and post- (right) construction of the wind farm. For annual maps see appendix.
Sammanfattande utbredningskartor för ejder Somateria mollissima från båtinventeringar före
(vänster) och efter (höger) uppförandet av vindkraftparken. För årsvisa kartor se appendix.
Overall Jacob’s indices for the wind farm area and the 2 km buffer zone show somewhat
different results compared to the density analysis above (Table 3). The aerial survey data
show more or less unchanged D-values from the pre- and post construction period in total
(0.06 and 0.08 for the wind farm area, 0.79 and 0.69 for the buffer zone respectively)
indicating that irrespective of the presence of the wind farm, the Eiders used the wind farm
area as expected and preferred the buffer zone. The boat survey data however indicated a
similar pattern as the density analysis with preference for the wind farm area during the preconstruction period changing to expected use with the wind farm in operation (D = 0.80 pre,
-0.09 post). The overall change was in the same direction for the buffer zone where preference
changes to more or less expected use (D = 0.68 pre, 0.11 post).
Explanations for these unclear, and in relation to the density analysis above conflicting,
results can be found in a more detailed look at Jacob’s indices from the different years
separately (Fig. 26). Apparently there was a clear avoidance of the wind farm area during the
first years with the wind farm in operation (low indices 2007-2009) while the area was
preferred (aerial survey data) or used as expected (boat survey data) in 2011. This could be a
sign of habituation to the presence of the wind farm although others factors, such as changes
in food availability, can be involved as well.
Further indications of habituation of Eiders to the wind farm was that during the spring aerial
survey in 2011 flocks of a few hundred Eiders were found in the wind farm but outside the
survey belt and hence not included in any of the figures above. This was the first observation
of larger flocks inside the wind farm during operation.
45
90
Birds/km2
80
70
Winter
60
50
Outer
Buffer
40
Windfarm
30
20
10
0
2006(3)
2008(1)
2009(4)
2010(1)
2011(3)
350
Birds/km2
300
Spring
250
200
Outer
B uffer
150
Windfarm
100
50
0
2006(2)
2008(2)
2009(0)
2010(1)
2011(1)
Fig. 25. Mean densities (individuals / km2) of Eider Somateria mollissima uring winter and
spring in different zones around the wind farm at Lillgrund in different years. Number of
surveys in brackets.
Täthet (individer/km2) av ejder Somateria mollissima vinter och vår inom olika zoner runt
Lillgrunds vindkraftpark under olika år. Antalet inventeringar inom parentes.
46
Aerial
Jacobs Index
1
0,5
0
-0,5
-1
2006
2008
2009
2010
2011
Boat
Jacobs Index
1
0,5
0
-0,5
-1
20012002
20022003
20032004
2005a
2005b
20072008
20092010
20102011
mid-winter for boat data) for Eiders Somateria mollissima based on aerial (top) and boat
index från båtdata) för ejder Somateria mollissima vid flyg (överst) och båtinventeringar
(underst). Index från innan vindkraftparken byggdes visas med ofyllda symboler och
streckade linjer, index från perioden med parken i drift med fyllda symboler och heldragna
linjer. Röd = vindkraftparken, blå = buffertzonen upp till 2 km från parken. 2005a = första
halvåret 2005, 2005b = andra halvåret.
47
Red-breasted Merganser Mergus merganser
The Red-breasted Merganser was the most numerous species during most surveys in the study
area north of Falsterbo, with the exception of some surveys in spring, when the Eider was
more numerous. The majority of the Red-breasted Mergansers seen during the aerial surveys
were found in the areas north of Falsterbo (Table 3, Fig. 26). Within this area Mergansers
were concentrated to the parts between Bredgrund and the Öresund Bridge, i.e. the five
northernmost aerial transects.
The study area covered by the aerial surveys is the most important wintering area in Sweden
and the Baltic for the species. The total numbers occurring here has been estimated to be in
the order of 10-12 000 individuals which should be compared with that the total Baltic
wintering population is estimated to consist of around 26 000 individuals and that the entire
northwest European wintering population is estimated to 170 000 individuals (SOWBAS).
This means that 38-46 % of the total Baltic wintering population use this area in winter (6-7
% of the overall northwest European population). Hence, southern Öresund is of large
international importance for the species.
The majority of the Red-breasted Mergansers arrive in the area during late autumn and leave
relatively early in spring. At most surveys in early autumn and in April-May, only small
numbers are found in the area.
The distribution maps show fewer Red-breasted Mergansers within the wind farm area with
the farm in operation than during the pre-construction period, especially during the first years
after the construction of the farm (see maps in appendix).
Calculated densities decreased in all sub-areas from the pre- to the post construction period
(Fig. 32). With the wind farm in operation densities were rather similar in all sub-areas while
densities were distinctly higher in the buffer zone and the parts of the northern study area
being farthest from the wind farm in the pre-construction years (Fig. 32). Within the wind
farm area the density was only slightly lower in the post-construction period than before this.
The mean number counted within the windfarm area during the three surveys in the winter
2006 (preconstruction) was eleven as was also the case for the three surveys in 2011, with
smaller numbers in the intervening years. Mean numbers counted within the survey lines in
the buffer zone varied between 31 and 171, whereas means for the outer reference area varied
between 165 and 873. For annual means see Table A10 in the appendix. Numbers counted
during the spring surveys were too low for the calculation of densities.
48
2500
2000
Mergus serrator
1500
MIN
1000
MEAN
MAX
500
0
BEFORE
AFTER
BEFORE
SOUTH
AFTER
NORTH
Fig. 27. Mean, Maximum and Minimum counts of Red-breasted Merganser Mergus serrator
during aerial surveys in the northern and southern area (Fig. 5) pre- (7 counts) and post- (15
counts) construction of the wind farm at Lillgrund.
Medel, maximum och minimum antal av småskrake Mergus serrator i det norra och södra
på Lillgrund.
3000
2500
Mergus serrator
2000
1500
MIN
1000
MEAN
MAX
500
0
BEFORE
AFTER
Fig. 28. Mean, Maximum and Minimum counts of Red-breasted merganser Mergus serrator
at boat surveys (Fig. 3) pre- (19 counts) and post- (8 counts) construction of the wind farm at
Lillgrund.
Medel, maximum och minimum antal av småskrake Mergus serrator vid båtinventeringar
(Fig. 3) före (19) räkningar) och efter (8 räkningar) uppförandet av vindkraftparken på
Lillgrund
49
Fig. 29. Summary distribution maps for winter and spring for the Red-breasted merganser
Mergus serrator from aerial surveys pre- (left) and post- (right) construction of the wind
farm. For annual maps see appendix.
Sammanfattande utbredningskartor vinter och vår för småskrake Mergus serrator från
50
Fig. 30. Details of Fig. 29 to show the distribution of Red-breasted Merganser Mergus
serrator in the wind farm area and the close surroundings from aerial surveys in winter pre(left) and post- (right) construction of the wind farm.
Detaljer från Fig. 29 för att visa småskrakens Mergus serrator utbredning i vindkraftparken
och dess närområde från flyginventeringar under vintern före (vänster) och efter (höger)
uppförandet av vindkraftparken.
Fig. 31. Summary distribution maps for the Red-breasted merganser Mergus serrator from
boat surveys pre- (left) and post- (right) construction of the wind farm. For annual maps see
appendix.
Sammanfattande utbredningskartor för småskrake Mergus serrator från båtinventeringar före
(vänster) och efter (höger) uppförandet av vindkraftparken. För årsvisa kartor se appendix.
51
45
Birds/km2
40
Mergus serrator
Winter
35
30
25
Outer
Buffer
20
Windfarm
15
10
5
0
2006(3)
2008(1)
2009(4)
2010(1)
2011(3)
Fig. 32. Densities (individuals / km2) of Red-breasted Merganser Mergus serrator based on
years. Number of surveys in brackets.
Täthet (individer/km2) av småskrake Mergus serrator under vintern inom olika zoner runt
Lillgrunds vindkraftpark under olika år baserade på flyginventeringarna. Antalet
inventeringar inom parentes.
Overall Jacob’s indices showed qualitatively a general decrease in preference for both the
wind farm area and the buffer zone between pre- and post-construction periods (Table 4).
Data from the aerial surveys showed a weak avoidance already before the wind farm was
constructed (D = -0.26) and a somewhat stronger avoidance with the farm in operation (D =
-0.42). Boat survey data showed a change from preference (D = 0.41) to weak avoidance (D =
-0.27). For the buffer zone the changes were in the same direction, from preference (D = 0.22
and 0.47) to expected use (D = 0.07 and 0.03).
A separation of the indices for different years gives a less clear picture as the two survey
methods yield at least partly different results (Fig. 32). The boat survey data clearly indicates
change from preference for both the wind farm area and the buffer zone during the preconstruction period to, mainly, avoidance for both parts with the wind farm in operation. The
aerial survey data show elements of the same story for the wind farm area in some postconstruction years but not in all. According to this data set the buffer zone is used as expected
or weakly preferred in most years. No direct indications of habituation is given by the indices,
instead variation between years in the distribution of birds seem to be large.
We conclude that we can not see any major impact from the wind farm on the occurrence of
Red-breasted Mergansers in the area. Instead of just avoiding the wind farm, numbers have
been lower in the whole study area in the post- compared to the pre-construction years. Such
52
large-scale changes in abundance are more likely to be governed by for example food
availability than by a point source of disturbance, such as a wind farm.
Aerial
Jacobs Index
1
0,5
0
-0,5
-1
2006
2008
2009
2010
2011
Boat
Jacobs Index
1
0,5
0
-0,5
-1
20012002
20022003
20032004
2005a
2005b
20072008
20092010
20102011
mid-winter for boat data) for Red-breasted Merganser Mergus serrator based on aerial (top)
and boat survey (bottom) data. Indices from the pre-construction period are shown with open
symbols and broken lines, indices from the post-construction period with filled symbols and
full lines. Red = the wind farm area, Blue = the buffer zone, up to 2 km from the wind farm.
2005a = winter-spring 2005, 2005b = autumn-winter 2005.
index från båtdata) för småskrake Mergus serrator vid flyg (överst) och båtinventeringar
2005, 2005b = andra halvåret.
53
The Herring Gull was the most numerous gull species in the southern part of Öresund during
the winter season, other species were only found in smaller numbers. Normally, the Herring
gulls appear in small groups and singly well spread over the entire study area. Sometimes
larger concentrations occur, mostly in connection with fishing boats. Larger flocks of Herring
Gulls was also found at the roosting site on Måkläppen south of Falsterbo at several aerial
surveys. Maximum counts from the aerial surveys was about 500 in the northern area, but
close to 1300 were counted here during one early boat survey Fig. 34, 35).
No clear pattern in the distribution of the Herring Gulls related to the construction of the wind
farm was found in the aerial survey data (Fig. 36). The boat survey data on the other hand
clearly show a decreased use of the wind farm area during the operational phase (Fig. 37).
The densities of Herring Gulls in the three different zones at the Lillgrund windfarm showed
much variation between years without any clear pattern (Fig. 38). Some high densities found
were related to fishing activities in the area leading to a concentration of gulls. Number of
Herring Gulls actually counted at the aerial surveys varied between 0 and 3 for the windfarm
area, 2 and 35 for the buffer zone and 1 to 430 for the outer reference area.
The overall Jacob’s indices did not show any clear results connected to the wind farm for the
Herring Gull (Table 4). The aerial survey data showed a change from avoidance (D = -0.36)
pre-construction to expected use (D = 0.03) for the operational phase for the wind farm area.
The boat survey data showed a weak avoidance for the pre-construction period (D = -0.11)
and a stronger avoidance with the farm in operation (D = -0.71) for the wind farm area. The
buffer zone was used according to expectation or avoided during pre-construction (D = 0.06
and -0.20 based on aerial and boat survey data respectively). With the farm in operation this
area was avoided (D = -0.27) according to the aerial survey data, but preferred (D = 0.46)
based on boat survey data.
A closer look at the Jacob’s indices from separate year do not add much more to the story,
although the boat survey data clearly indicate that the wind farm area has been avoided after
the farm came into operation (Fig. 39). The main explanation for this is probably that fishing
vessels no longer can use the area where the wind farm is today.
54
600
Larus argentatus
500
400
MIN
MEAN
300
MAX
200
100
0
BEFORE
AFTER
BEFORE
SOUTH
AFTER
NORTH
Fig. 34. Mean, Maximum and Minimum counts of Herring Gull Larus argentatus during
aerial surveys in the northern and southern area (Fig. 5) pre- (7 counts) and post- (15 counts)
Medel, maximum och minimum antal av gråtrut Larus argentatus i det norra och södra
på Lillgrund.
1400
1200
Larus argentatus
1000
800
MIN
600
MEDEL
MAX
400
200
0
BEFORE
AFTER
Fig. 35. Mean, Maximum and Minimum counts of Herring Gull Larus argentatus during boat
surveys (Fig. 3) pre- (19 counts) and post- (8 counts) construction of the wind farm at
Lillgrund.
Medel, maximum och minimum antal av gråtrut Larus argentatus vid båtinventeringar (Fig.
3) före (19) räkningar) och efter (8 räkningar) uppförandet av vindkraftparken på Lillgrund
.
55
Fig. 36. Summary distribution maps for winter and spring for the Herring Gull Larus
argentatus from aerial surveys pre- (left) and post- (right) construction of the. For annual
maps see appendix.
Sammanfattande utbredningskartor vinter och vår för gråtrut Larus argentatus från
56
Fig. 37. Summary distribution maps for the Herring Gull Larus argentatus from boat surveys
pre- (left) and post- (right) construction of the wind farm. For annual maps see appendix.
Sammanfattande utbredningskartor för gråtrut Larus argentatus från båtinventeringar före
(vänster) och efter(höger) uppförandet av vindkraftparken. För årsvisa kartor se appendix.
57
14
12
Larus argentatus
Winter
10
8
Outer
Buffer
6
Windfarm
4
2
0
2006(3)
2008(1)
2009(4)
2010(1)
2011(3)
9
8
Larus argentatus
Spring
7
6
5
Outer
B uffer
4
Windfarm
3
2
1
0
2006(2)
2008(2)
2009(0)
2010(1)
2011(1)
Fig. 38. Mean densities (individuals / km2) of Herring Gull Larus argentatus during winter
and spring based on aerial surveys in different zones around the wind farm at Lillgrund in
different years. Number of surveys in brackets.
Täthet (individer/km2) av gråtrut Larus argentatus vinter och vår baserade på
flyginventeringar inom olika zoner runt Lillgrunds vindkraftpark under olika år. Antalet
inventeringar anges inom parentes.
58
Aerial
Jacobs Index
1
0,5
0
-0,5
-1
2006
2008
2009
2010
2011
Boat
Jacobs Index
1
0,5
0
-0,5
-1
20012002
20022003
20032004
2005a
2005b
20072008
20092010
20102011
mid-winter for boat data) for Herring Gull Larus argentatus based on aerial (top) and boat
index från båtdata) för gråtrut Larus argentatus vid flyg (överst) och båtinventeringar
(underst). Index från innan vindkraftparken byggdes visas med ofyllda symboler och
streckade linjer, index från perioden med parken i drift med fyllda symboler och heldragna
linjer. Röd = vindkraftparken, blå = buffertzonen upp till 2 km från parken. 2005a = första
halvåret 2005, 2005b = andra halvåret.
59
Spring - north-easterly directed migration
General
Most birds migrating over southern Öresund in spring approach from southwest and pass the
area in directions towards northeast. (Fig. 40). Several million of migratory birds are passing
each season and the movements include most groups of birds. Birds normally migrating at
lower altitude through the area and hence risking to get into contact with the wind farm
include Barnacle Geese, Brent Geese and other waterfowl species. Most migratory
movements of other species and groups probably pass at altitudes well above the turbines in
most cases, but can of course also pass at lower altitudes, especially in head wind conditions.
The annual total number of radar echoes (flocks) registered passing the 50 km transect A-E
during analysed days in spring 2002, 2005, 2008, 2009 and 2010 varied between 9000 and
18 000 (Table A11 in the appendix) probably corresponding to in the order of between 0.5
and 1 million individual birds if we assume an average flock size of 50 individuals per flock.
A
B
C
D
E
Fig. 40. General migration patterns over the southern Öresund in spring according to radar
data from 2002, 2005, 2008, 2009 and 2010 (yellow arrows show generalised migration
directions). Lillgrund with the wind farm is shown by the red square. The transect (A-E)
along which radar echoes (bird flocks) were counted is also shown.
Generellt flyttningsmönster hos majoriteten av alla fåglar över södra Öresund enligt
radarstudier vårarna 2002, 2005, 2008, 2009 och 2010 (gula pilar anger generella
flygriktningar). Lillgrund är markerat med en röd kvadrat. Transekten (A-E) som användes
vid eko (fågelflock) räkning visas också.
60
Lillgrund and the wind farm are situated in sector C, in the middle of the bird migration
corridor. Before the construction of the wind farm a large proportion of the recorded bird
migration in spring was recorded passing this sector (23-26 % of the total migration volume
in spring 2002 and 2005 (Fig. 41). When the wind farm was in operation this proportion
decreased to between 18 and 20 % of the total migration volume in 2008 -2010 (Fig. 41). This
means that on average 22 % less of the overall migration volume passed the sector containing
Lillgrund with the wind farm in operation compared to the pre-construction period. There are
differences between years, but the decrease seen in sector C do indicate that a lower
proportion of the overall migration volume over the region was passing through C during the
post construction period. More dramatic changes in the proportion of flocks passing were seen
over the southern (sector A) and northern (sector E) parts of the transect at a much longer
distance from the wind farm.
35
Lillgrund
% of all echoes (flocks)
30
25
2002
2005
20
2008
15
2009
2010
10
5
0
A
B
C
D
E
Sector
Fig. 41. Distribution of bird echoes (bird flocks) with north-easterly flight directions recorded
by radar over southern Öresund during spring 2002 and 2005 pre- (filled bars) and 2009,
2009, 2010 post-construction (open bars) of the wind farm at Lillgrund for the different 10 km
sectors A-E (see Fig. 7 and 40)
Fördelningen av fågelekon (flockar) med nordostliga flygriktningar registrerade med radar
över södra Öresundsområdet under vårarna 2002 och 2005 (före etablering av
vindkraftparken på Lillgrund, grå staplar) samt 2008 och 2009 (efter att parken tagits i drift,
vita staplar), fördelat på 10 km-sektorerna A-E (se Fig. 7 and 40).
The pattern was the same irrespective of time of the day. Day migration (during the light
hours of the day) made up 56 % of all passing bird echoes (flocks) in total. Night migration
(during the dark hours of the day) constituted 44 % of the overall migration volume during the
analysed spring seasons. In both cases did the proportion passing sector C with the wind farm
decrease from pre- to post construction years (Fig. 42). Just as for the whole data set the
differences were relatively small (-19 % during day time and -22 % at night), but at the same
time large enough to conclude that a lower proportion of the overall migration volume is
passing sector C both at day and night post construction of the wind farm.
61
Day-time
40
Lillgrund
35
30
2002
25
2005
2008
20
2009
15
2010
10
5
0
A
B
C
D
E
Sector
Night-time
40
Lillgrund
35
30
2002
25
2005
20
2008
15
2009
2010
10
5
0
A
B
C
D
E
Sector
Fig. 42. Distribution of bird echoes (bird flocks) with north-easterly flight directions recorded
by radar over southern Öresund during spring 2002 and 2005 pre- (filled bars) and 2009,
2009, 2010 post-construction (open bars) of the wind farm at Lillgrund for the different 10 km
sectors A-E (see Fig. 7 and 40) for day (top) and night (bottom) migration separately.
över södra Öresundsområdet under vårarna 2002 och 2005 (före etablering av
vindkraftparken på Lillgrund, grå staplar) samt 2008, 2009 och 2010 (efter att parken tagits i
drift, vita staplar), fördelat på 10 km-sektorerna A-E (se Fig. 7 och 40) och för dagsträck
(ovan) och nattsträck (under) separat.
62
The spring migration season, and hence the spring radar data set, can be divided in three
periods roughly covering different main groups of migrants. The early period (March-April
10) is the peak migration period of Eiders, Common Scoters and some other early migrants;
the middle period (April 11-May 15) cover the migration of Barnacle Geese, most ducks and
other migrants; the late spring period (last half of May) is the main migration period of Brent
Gees and waders breeding in arctic Russia. Analysing these three periods separately yielded
the same overall pattern as described above. A lower proportion of the overall migration
volume passed over sector C with the wind farm in operation compared to the preconstruction period (Fig. 43, 44, 45). The largest difference was found for the late spring
period where the proportion passing over sector C was 36 % lower post- compared to preconstruction (Fig. 45). For the other periods the corresponding decreases in the proportion of
the overall migration volume were 23 % (mid-spring) and 15 % (early spring) (Fig. 43, 44).
Early migrants
45
40
Lillgrund
35
2002
30
2005
25
2008
20
2009
15
2010
10
5
0
A
B
C
D
E
Sector
Fig. 43. Distribution of bird echoes (flocks) with north-easterly flight directions registered by
radar over southern Öresund in early spring (March-April 10) during spring 2002 and 2005
pre- (filled bars) and 2008, 2009 and 2010 post-construction (open bars) of the wind farm at
Lillgrund for the different 10 km sectors (A-E, see Fig 7 & 40)
över södra Öresundsområdet under den tidiga delen (mars-10 april) av vårarna 2002 och
2005 (före etablering av vindkraftparken på Lillgrund, grå staplar) samt 2008, 2009 och
2010 (efter att parken tagits i drift, vita staplar), fördelat på 10 km-sektorerna A-E (se Fig. 7
& 40)
63
Mid-spring migrants
45
40
35
Lillgrund
30
2002
2005
25
2008
20
2009
15
2010
10
5
0
A
B
C
D
E
Sector
radar over southern Öresund in mid-spring (April 11-May 15) during spring 2002 and 2005
pre- (filled bars) and 2008, 2009 and 2010 post-construction (open bars) of the wind farm at
över södra Öresundsområdet under den centrala delen (11 april-15 maj) av vårarna 2002
och 2005 (före etablering av vindkraftparken på Lillgrund, grå staplar) samt 2008, 2009 och
2010 (efter att parken tagits i drift, vita staplar), fördelat på 10 km-sektorerna A-E (se Fig. 7
& 40).
64
Late spring migrants
45
Lillgrund
40
35
2002
30
2005
25
2008
20
2009
15
2010
10
5
0
A
B
C
D
E
Sector
radar over southern Öresund in late spring (May 16-31) during spring 2002 and 2005 pre(filled bars) and 2008, 2009 and 2010 post-construction (open bars) of the wind farm at
över södra Öresundsområdet under den senare delen (15-31 maj) av vårarna 2002 och 2005
(före etablering av vindkraftparken på Lillgrund, grå staplar) samt 2008, 2009 och 2010
(efter att parken tagits i drift, vita staplar), fördelat på 10 km-sektorerna A-E (se Fig. 7 &
40).
Lillgrund
The proportion of echoes (flocks) that passed over Lillgrund, in this case defined as 3x3 km
covering the wind farm area and its close surroundings, with north-easterly flight directions
was lower with the wind farm in operation compared to the pre-construction period. Before
the wind farm was built between 12 and 14 % of the total migration volume passed over
Lillgrund, but post construction the proportion passing Lillgrund decreased to between 1 and
3 % (Fig. 46). The decrease in the wind farm area was hence much more marked (on average
-82 %) compared to the larger sector C (on average - 22 %).
The pattern was the same irrespective of time of the day. A lower proportion of the flocks
passed Lillgrund both during day time and at night with the wind farm in operation (Fig. 47).
The decrease was marginally larger during night (- 83 %) than during the day (- 80 %).
65
20
15
10
5
0
2002
2005
2008
2009
2010
Year
Fig. 46. The proportion of all bird echoes (bird flocks) with north-easterly flight directions
recorded by radar over southern Öresund during spring 2002 and 2005 pre- (filled bars) and
2008, 2009, 2010 post-construction (open bars) passing Lillgrund, 3x3 km including the wind
farm and its close surroundings (see Fig. 7 and 40)
Andelen fågelekon (flockar) med nordostliga flygriktningar registrerade med radar som
passerade över själva Lillgrundsområdet under vårarna 2002 och 2005 (före etablering av
vindkraftparken på Lillgrund, grå staplar) samt 2008, 2009 och 2010 (efter att parken tagits i
drift, vit stapel), (se Fig. 7 och 40).
66
20
15
Day-time
Night-time
10
5
0
2002
2005
2008
2009
2010
Year
Fig. 47. The proportion of all bird echoes (bird flocks) with north-easterly flight directions
recorded by radar over southern Öresund during spring 2002 and 2005 pre- and 2008, 2009,
2010 post-construction passing Lillgrund, 3x3 km including the wind farm and its close
surroundings (see Fig. 7 and 40) during day time (open bars) and at night (filled bars)
separately.
Andelen fågelekon (flockar) med nordostliga flygriktningar registrerade med radar som
passerade över själva Lillgrundsområdet under vårarna 2002 och 2005 (före etablering av
vindkraftparken på Lillgrund) samt 2008, 2009 och 2010 (efter att parken tagits i drift) på
dagen (vita staplar) och natten (grå staplar, se Fig. 7 and 40).
Spring- southerly directed migration
General
In addition to the main migratory movements towards northeast in spring there is also a rather
numerous passage of birds towards south (Fig. 48). These movements are mainly made up of
Eiders, wintering in Kattegat and following the Swedish west coast towards south before
entering the Baltic and then turning east and northeast. Other waterfowl such as Common
Scoters are also included in this passage. During analysed days in spring 2002, 2005, 2008
and 2009 annual totals passing the transect 1-4 varied between 200 and 1800 bird echoes
(flocks, Table A12 in appendix). Somewhere in the order of 100 000 birds probably pass with
south oriented flight directions each spring, although Eider numbers have decreased quite
heavily in later years. With same reasoning as above for the main migration route towards
northeast this probably corresponds to between 10 000 and 90 000 individual birds, if average
flock size was around 50 individuals.
The proportion of flocks passing sector 2 with the wind farm area was low both pre- (0-9 % of
the total migration volume) and post (1-7 % of the total migration volume) construction of the
wind farm. There was just a marginal difference between the periods in the proportion of all
67
flocks that pass sector 2, on average 5 % pre- and 4 % post-construction. The majority of the
flocks pass over land or very close to the Swedish coast in sectors 3 and 4 (85-100 % of the
total migration volume, Fig. 47). This means that a very low proportion of the overall passage
of Eiders and other waterfowl with southerly flight directions in spring are coming in contact
with the wind farm area.
1
2
3
4
Fig. 48. General migration patterns over the southern Sound in spring for the south directed
migratory movements according to radar data from 2002, 2005, 2008, 2009 and 2010 (yellow
arrows show generalised migration directions and the main migration corridor). Lillgrund
with the wind farm is shown by the red square. The transect along which radar echoes (bird
flocks) were counted (1-4) is also shown.
Generellt flyttningsmönster det sydriktade fågelsträcket över södra Öresund enligt
radarstudier vårarna 2002, 2005, 2008, 2009 och 2010 (gula pilar anger generella
flygriktningar). Lillgrund är markerat med en röd kvadrat.
68
70
60
50
2002
2005
40
2008
30
2009
Lillgrund
2010
20
10
0
1
2
3
4
Sector
Fig. 49. Distribution of bird echoes (flocks) with southerly flight directions in spring along
the transect 1-4 (see Fig 48). Pre-construction years are shown with filled bars (2002, 2005);
post construction years are shown with open bars (2008, 2009, 2010).
Fördelning av antal fågelekon (flockar) under det sydriktade vårsträcket genom Öresund
åren 2002 och 2005 (före etableringen av vindkraftparken på Lillgrund, grå staplar) och
2008, 2009, 2010 (efter att parken tagits i drift, vita staplar) på zonerna 1-4 (se Fig. 48)
Lillgrund
The proportion of echoes (flocks) that passed over Lillgrund, defined as 3x3 km covering the
wind farm area and its close surroundings, with southerly flight directions varied between 0
and 9 % during the pre-construction years, and between 0 and 3 % with the wind farm in
operation (Fig. 50). The differences were hence large between years, but average proportions
for the two periods, 5 % pre- and > 1 % post construction (a 87 % decrease) may indicate that
there was a similar pattern as for the major migratory movements towards north-east.
69
20
15
10
5
0
2002
2005
2008
2009
2010
Year
Fig. 50. The proportion of bird echoes (flocks) passing Lillgrund, 3x3 km covering the wind
farm area and its close surroundings, with southerly flight directions in spring during preconstruction (2002 and 2005, filled bars) and post construction (2008, 2009 and 2010, open
bars).
Andelen fågelekon (flockar) som passerade Lillgrund, 3x3 km innehållande vindkraftparken
och dess närmaste omgivningar, under det sydriktade vårsträcket av sjöfåglar åren 2002 och
2005 (före Lillgrundsparken byggdes, grå staplar) och 2008, 2009 och 2010 (efter att parken
tagits i bruk, vita staplar).
Autumn
General
The autumn bird migration over southern Öresund passes along a main axis from Northeast
towards southwest (Fig. 51). All sorts of birds are involved in the migratory movements in
autumn and it is harder to pin-point groups that are more likely to travel at low altitude
through the area, than it is in spring. Generally speaking, low-altitude migration is more
prevalent in head wind conditions. Depending on general weather conditions and especially
wind direction and strength, there are marked differences between different days in where the
corridor passes during that specific day. A general concentration effect to the Falsterbo
peninsula in the far southwest is usually apparent, as many land birds hesitate to the passage
of open water and tries to fly over land for as long as possible. The concentration to Falsterbo
is stronger in winds from the western sector and less pronounced in winds from north and
east.
The overall migration volume in autumn is of course higher than in spring, as all the offspring
of the breeding season are migrating at this time of the year in addition to all the adult birds.
This means that many millions of individual birds are passing over the southern Öresund area
in autumn. Annual totals of registered radar echoes (bird flocks) during analysed days in
autumn 2001, 2008 and 2009 varied between just under 9000 to 15 000 (Table A13 in
appendix). This probably corresponds to somewhere between 450 000 and 750 000 individual
70
birds given the assumptions used above. Since the number of analysed days in autumn was
lower than in spring, the overall migration rate (flocks passing per hour) was about twice as
high in autumn compared to spring.
A
B
C
D
E
Fig. 51. General migration patterns over the southern Öresund in autumn according to radar
data from 2001, 2008 and 2009 (yellow arrows show generalised migration directions).
Lillgrund with the wind farm is shown by the red square. The transect along which radar
echoes (bird flocks) were counted (A-E) is also shown.
Generellt flyttningsmönster hos majoriteten av alla fåglar över södra Öresund enligt
radarstudier höstarna 2001, 2008 och 2009 (gula pilar anger generella flygriktningar).
Lillgrund är markerat med en röd kvadrat. Transekten som användes vid eko (fågelflock)
räkning (A-E) visas också.
The distribution of autumn migration over southern Öresund during pre- (2001) and post(2008, 2009) construction of the wind farm at Lillgrund is shown in Fig. 52. As in spring
there is variation between years but the concentration to the southern part of the transect
(sectors D and E, in contact with the Falsterbo peninsula) is obvious in all years. Sector C
with Lillgrund and the wind farm area is passed by a rather modest proportion of the overall
migration volume in autumn (13-16 %). A small decrease in the proportion of passing flocks
from pre- to post construction years (- 9 %) should be regarded as within the normal variation
(Fig. 52).
71
40
35
30
Lillgrund
25
2001
2008
20
2010
15
10
5
0
A
B
C
D
E
Sector
Fig. 52. Distribution of bird echoes (bird flocks) with south-westerly flight directions
recorded by radar over southern Öresund during autumn 2001 pre- (filled bars) and 2008 and
2009 post-construction (open bars) of the wind farm at Lillgrund for the different 10 km
sectors A-E (see Fig. 7 and 51)
Fördelningen av fågelekon (flockar) med sydvästliga flygriktningar registrerade med radar
över södra Öresundsområdet under hösten 2001 (före etablering av vindkraftparken på
Lillgrund, grå staplar) samt 2008 och 2009 (efter att parken tagits i drift, vita staplar),
fördelat på 10 km-sektorerna A-E (se Fig. 7 and 51).
A much higher proportion of the overall migration volume in autumn passed during day time
(the light hours of the day, 76 %) compared to in spring (56 %, see above). Night migration
made up 24 % of the total migration volume in autumn. A somewhat lower proportion of all
flocks passed over sector C during day-time with wind farm in operation compared to the preconstruction year 2001 (- 15 %). At night there was almost no difference in the proportion of
flocks passing sector C between the pre- and post construction years (- 2 % on average, Fig.
53).
72
Day-time
40
35
30
Lillgrund
25
2001
2008
20
2009
15
10
5
0
A
B
C
D
E
Sector
Night-time
40
35
Lillgrund
30
25
2001
20
2008
2009
15
10
5
0
A
B
C
D
E
Sector
Fig. 53. Distribution of bird echoes (flocks) with south-westerly flight directions in autumn
2001 pre- (filled bars) and 2008, 2009 post- (open bars) construction of the wind farm at
Lillgrund on along the transect A-E (se Fig. 7 and 51) for day (top) and night (bottom)
migration separately.
Fördelningen av fågelekon (flockar) med sydvästliga flygriktningar registrerade med radar
över södra Öresundsområdet under höstarna 2001 (före etablering av vindkraftparken på
Lillgrund, grå staplar) och 2008, 2009 (efter att parken tagits i drift, vita staplar), fördelat på
10 km-sektorerna A-E (se Fig. 7 och 51) och för dagsträck (ovan) och nattsträck (under)
separat.
73
Lillgrund
Despite the marginal differences in large-scale distribution of the geographical pattern of
migrating flocks between pre- and post-construction years showed above, there were more
marked differences for Lillgrund at the local scale. In 2001, pre-construction of the wind
farm, 11 % of the overall migration volume passed the 3x3 km area covering the wind farm
area to be and the very close surroundings of this. In the two years with the wind farm in
operation, 2008 and 2009, the corresponding proportion was 2-3 % (Fig. 52). In other words
the proportion of flocks passing through the wind farm area decreased with 78 %.
20
15
10
5
0
År 2001
År 2008
år 2009
Year
Fig. 54. The proportion of bird echoes (flocks) passing Lillgrund (3x3 km covering the wind
farm area and its closest surroundings) in autumn 2001 pre- (filled bar) and 2008, 2009 post(open bars) construction of the wind farm at Lillgrund (see Fig. 7 and 51).
Andelen fågelekon (flockar) med sydvästliga flygriktningar registrerade med radar som
passerade över själva Lillgrundsområdet under höstarna 2001 (före etablering av
vindkraftparken på Lillgrund, grå staplar) och 2008, 2009 (efter att parken tagits i drift, vita
staplar), (se Fig. 7 och 51).
As in spring the decrease in the proportion of flocks passing Lillgrund in autumn was almost
the same during day and at night (Fig. 55).
74
% av alla ekon (flockar)
20
15
Day-time
10
Night-time
5
0
2001
2008
2009
År
Fig. 55. The proportion of bird echoes (flocks) passing Lillgrund (3x3 km covering the wind
farm area and its closest surroundings) in autumn 2001 pre- (filled bar) and 2008, 2009 post(open bars) construction of the wind farm at Lillgrund during day time (filled bars) and at
night (open bars).
Andelen fågelekon (flockar) med sydvästliga flygriktningar registrerade med radar som
passerade över själva Lillgrundsområdet under höstarna 2001 (före etablering av
vindkraftparken på Lillgrund) och 2008, 2009 (efter att parken tagits i drift) på dagen (vita
staplar) och natten (grå staplar).
75
Discussion
As stated already in the introduction, in earlier reports from the project (Green & Nilsson
2006, Nilsson 2001) and in reports from the Öresund Bridge project (Nilsson 1996a, 1996b,
1998), the southern part of Öresund is an important area for a number of water bird species,
several of them occurring in internationally important numbers. Even if the water birds of
southern Öresund had been studied for a long time, the offshore parts had only been surveyed
on a few occasions in connection with studies of wintering diving ducks around the coasts of
Scania (Nilsson 1972, unpubl.). During the base-line studies for the Lillgrund wind farm it
was established that the areas around Lillgrund together with neighboring shallow areas at
Bredgrund was an important staging and wintering area, especially for Red-breasted
Mergansers but also for Eiders (Green & Nilsson 2006). Smaller numbers of wintering Longtailed Ducks were also found in the area, whereas other species were only found in small
numbers, note however the nocturnal feeding flights for the Tufted Ducks to the Bredgrund
area (and maybe also to Lillgrund) discussed above (see also Nilsson 1972).
Among the wintering waterfowl species the large concentration of Red-breasted Mergansers
occurring in the area was not known before the base-line studies. This concentration is
actually the largest for the species in the entire Baltic (Durinck et al. 1994, SOWBAS
unpubl.). The wintering Red-breasted Mergansers, estimated to be up to 12 000 individuals,
form an important part of the northwestern European population.
For the other two sea ducks, the Eider and the Long-tailed Duck, the area is not of the same
importance as a staging area and wintering area as it is for the Red-breasted Merganser. The
Long-tailed Duck has its main winter distribution in the Baltic and numbers around the coasts
of Scania has decreased markedly during the last few decades. The main concentrations occur
in the central parts of the Baltic proper, the southern parts of Öresund is just a marginal
wintering area for the species. The Eider is a common wintering bird in the area, mainly in the
reference parts south of Falsterbo but wintering birds do also occurs in the Lillgrund area and
all the way northwards along the Öresund and the Swedish west coast. The spring situation is
different as Lillgrund is close to the important breeding colony on Saltholm with between
4000 and 5000 breeding pairs in 2000 (Desholm et al. 2002). The area is also used as a
stopover area during spring migration.
Besides the three duck species mentioned above Herring Gulls were regular and fairly
common in the southern part of the Öresund during our surveys. Moreover, the southern part
of the Öresund is also used by larger numbers of Cormorants during winter (Bengtsson 1999,
2000). Flocks of several thousand individuals have regularly been seen fishing in Öresund
using Saltholm and Pepparholm for roosting. Other seabirds were only found in small
numbers during the base-line studies.
In this report from the monitoring program we have focused on the five main species
mentioned above, these species being the only ones where it was likely to find any possible
impact from the wind farm.
The staging and wintering water birds in the Lillgrund area were surveyed both from a boat
and from the air. It was clear from the start of the program that both methods should be used
considering both the logistics of offshore surveys and differences in detectability of different
76
species, some species being better covered from boat, while aerial surveys makes it possible
to cover larger areas within short time (see Komdeur et al. 1992, Nilsson 1975). Moreover,
aerial surveys were the only way to cover both the Lillgrund area and a reference area in one
day
Both during the base-line studies and the post construction surveys a very marked variation in
the number of staging and wintering water birds were found both during the boat counts and
aerial surveys. The same variation was found during the aerial surveys both for the Lillgrund
area and for the reference area south of Falsterbo, applying to all species of interest here. This
kind of variation is typical for staging and wintering water birds and especially for offshore
sea ducks, which shows a very dynamic occurrence even if some areas hold regular
concentrations (Nilsson 1972, 1975, 2008, in prep.).
Due to the very marked variation in the counts and the relatively low numbers of surveys it
was not meaningful to make any formal statistical analysis of the pre- and post-construction
situation of the utilization for different zones around the windfarm. For this a much more
intensive study with a larger number of surveys would be necessary, but this was not possible
within the monitoring program. For practical reasons it would also have been difficult to
obtain enough surveys due to logistical problems, e.g. suitable aircrafts were only available
for one full season before the establishment of the windfarm and boat surveys in the last two
(most interesting) post-construction years could not be performed during the important winter
period due to the ice conditions.
Before the windfarm was built small groups of Long-tailed Ducks were regular on Lillgrund.
During the first post-construction year the Long-tailed Ducks clearly avoided the wind farm
area but later years show a less clear pattern. Some birds were seen within the wind farm
showing that avoidance is at least not 100 %. It may also be that some sort of habituation is
involved, but the low numbers encountered makes it hard to do any robust interpretation of
the results. It should also be remembered that the Long-tailed Duck is a relatively sparse bird
in southern Öresund, this region being a marginal winter area for the species.
For the Eider, the Lillgrund area clearly had a large attraction, especially for feeding birds in
spring, flying to the area from the colony on Saltholm a short distance to the north. This
attraction to the Lillgrund area was still there in the first post-construction years, but now the
Eiders were concentrated to the parts of Lillgrund just outside the wind farm, seemingly
avoiding the wind farm. In the last survey year, some larger flocks were seen in the wind farm
and this may be a sign of habituation.
Also for the third sea duck species found in the area, the Red-breasted Merganser, there were
some signs of initial avoidance of the wind farm area. Results are however less clear
compared to the other two duck species and numbers using the whole Öresund area has been
lower during the post-construction years compared to before. Hence, the actual effect of the
wind farm is hard to evaluate and the found changes in abundance may very well be related to
other factors.
For the other two common species in the area we could not find any clear effects of the
establishment of the wind farm. Cormorants could actually be attracted to the fundaments and
use them as roosting places, although this could not be shown by our analysis. When it comes
to the Herring Gull fewer flocks were seen in the windfarm area post-construction but most of
the concentrations seen in this species were related to fishing vessels. Fishing is allowed in
77
the windfarm area but fishing activity was low after the establishment of the windfarm as it
was before.
Taken together our studies of staging and wintering waterbirds in the Lillgrund area do not
show any larger changes in the distribution or their utilization of the area that could be related
to the construction of the windfarm. Some local effects were found for the sea ducks which
showed lower densities and some avoidance of the windfarm area, but the total area affected
is very small compared to the extent of the feeding areas for these species in southern
Öresund. Moreover, some signs of habituation to the wind farm was seen at least for the
Eider, and maybe also for the two other species (Long-tailed Duck and Red-breasted
Merganser). If this should be a general pattern, it means that local effects may arise in the first
years after construction of a wind farm but that after some time the birds will start using the
area again.
Even if there are few other studies of the impact of offshore wind farms on marine birds (cf.
reviews by Drewitt & Langston 2006, Fox et al. 2006) the number of such are increasing as
more farm are constructed in this habitat.
In Sweden, there are two small offshore wind farms in the Kalmarsund region (Pettersson
2005), but the studies here were concentrated to the effect of the wind farms on migrating
birds, especially the Eider and did not address staging and wintering waterbirds with pre- and
post-construction studies.
In Denmark, large scale impact assessment studies have been published for the two large
offshore wind farms, Nysted and Horns Rev (Dong Energy 2006, Petersen et al. 2006,
Petersen & Fox 2007 and further references in these reports) and also for the smaller farm at
Tunö Knob (Guillemette et al. 1997, 1999, Guillemette & Larsen 2002). In general the Danish
studies showed avoidance of the offshore wind farms when comparing pre - and postconstruction aerial surveys. However, the responses in the Danish wind farms as in the case of
Lillgrund were rather species specific. The species occurring at the two larger Danish sites
were also, at large, different from that at Lillgrund.
At both Lillgrund and Nysted, Long-tailed Ducks occur in smaller numbers, both sites being
situated at the margin of winter distribution of the species. A clear avoidance behavior of
Long-tailed Ducks was recorded at both sites. Numbers affected were however small in both
cases and the effect is of no importance for the general distribution and abundance in the area.
At Horns Rev, Common Scoters first seemed to avoid the wind farm but Petersen & Fox
(2007) discussed the possibility of a habituation effect. It was however not possible to rule out
possible effects of the food situation for the Scoters, meaning that also the initial apparent
avoidance may in fact have been caused by other factors than the wind farm itself. Avoidance
of Common Scoters and Eiders was also indicated in the studies at Tunö Knob, but here an
increase in Eiders was noticed later during post-construction, this increase possibly being due
to changes in the food resources (Guillemette et al. 1997, 1999).
The seabird community in the North Sea area where Horns Rev is situated is markedly
different from the Öresund and also the Baltic proper. In the Horns Rev area divers was an
important component, these birds showing a more or less total avoidance of the windfarm
area. Avoidance behavior was also noted for Guillemots and Razorbills at Horns Rev
(Petersen et al 2006). Other recent studies in the North sea show a rather strong avoidance
effect for Red-throated Divers at a wind farm at Kentish Flats, UK but results both from that
78
area and from a Dutch farm show that the avoidance is not 100 % (Percival 2010, Leopold et
al. 2010). The latter study show possible avoidance for Common Scoters and Gannets, but no
effects for gulls, terns and auks. Cormorants were on the other hand attracted to the Dutch
wind farm (Leopold et al. 2010)
In general it seems less clear, than initial results showed, that offshore wind farms have a
negative effect on the distribution of sea birds, although there are marked differences in the
reactions of different species to the wind farms. Some species show some sort of initial
avoidance in the first years after construction of a wind farm, but patterns in following years
are less clear. In some cases there is an effect also outside the windfarm but generally the area
affected seems to be quite small. Habituation may be involved for some species, but it is
always more or less impossible to rule out that the underlying factor for found patterns is
instead food availability.
Seen in relation to the total area of good feeding grounds available for sea ducks in southern
Öresund, the (initial) avoidance of the windfarm area at Lillgrund is of little importance. The
situation could however be different if there were many large wind farms covering most of
the shallow offshore areas, which are preferred feeding grounds for the sea ducks. In case of a
large-scale exploitation of offshore shallow areas for wind farms it is urgent that possible
cumulative effects are taken into consideration.
Migrating Birds
That southern Öresund is passed by large numbers of migrating birds has been known for a
long time (Rudebeck 1950, Alerstam 1972, Alerstam & Ulfstrand 1972, 1974, 1975, Zehnder
et al. 2001, Kjellén 2010). At the south westernmost tip of the Falsterbo peninsula between
1.5 and 3 million low-altitude migrating birds are counted during standardised counts between
August and November every year (Kjellén 2010). The total number of birds passing the area
every autumn is probably in the order of 100 million individuals. Large numbers also pass
during spring but the number of detailed studies are much lower during this time of the year
(but see Alerstam et al. 1974, Green 1998, 2004).
For the Lillgrund area (3x3 km including the wind farm area and its surrounds), we estimated,
based on visual counts, radar and literature data that somewhere in the order of five million
birds in autumn and 2 million birds in spring may pass every year (Green & Nilsson 2006).
These total numbers refer to the total volume of passing birds and the majority of these are
probably migrating at altitudes far above any wind turbines and do not run the risk of getting
into contact with these. The total volume of low altitude migration is not known in detail but
probably much lower than the figures above. What we do know is that southern Öresund are
passed by at least a few 100 000 geese and ducks at low altitude every spring. For these birds
the autumn migration over Öresund is of much smaller magnitude. Of these a low proportion
(14 %) was passing the Lillgrund area during the pre-construction period (Green & Nilsson
2006).
Our radar analysis here was focused on the general patterns of migration over the area and
looking in detail at if there were any differences between the pre- and post-construction
periods in this respect. The results do not show any large scale differences between the two
periods that can be related to the construction of the wind farm. There were differences
between the periods during spring when it comes to how large proportions of the overall
79
migration volume that passed over the northern (more in the latter period) and southern part
(less in the latter period) of the 50 km long analysed transect, but with distances to the wind
farm of more than 10 and 15 km respectively, it is hard to see that the wind farm should have
played any important role for these changes. More likely, these changes are governed by
prevailing weather and wind during the analysed migration days. The flight paths of migrating
birds are to some extent decided by winds, through so called wind drift (Alerstam 1990).
Within the migration corridor, the exact paths may vary between days and seasons due to that
the birds are affected by drift. This may be because the birds use adaptive drift strategies,
taking advantage of the extra speed they can get from the wind (without letting themselves
drift too far away from the desired migration path) or simply because they lack the capacity to
compensate fully for the drift effect of the wind (Alerstam 1990). Small differences in wind
directions and speed can hence create differences like the ones we see in our data set. In
autumn we see variation in the proportions passing different parts of Öresund between years
but not between the pre- and post-construction periods as such.
In contrast to the general picture given above, the proportion of the overall migration volume
that passed Lillgrund decreased both in spring and in autumn, and the decrease was of similar
magnitude in both seasons (70-80 % decrease). There was no difference between day and
night migration in this respect, the proportion passing Lillgrund decreased from pre-to postconstruction years irrespective of time of the day. Even though we do not have any data on
flight altitudes of the passing flocks (not possible to record with the used radars), and hence
cannot give an exact estimate on the proportion of flocks avoiding to fly into the wind farm.
The only reasonable interpretation of the results is that a large majority of the recorded flocks
approaching the wind farm along flight paths that would lead them through the park actually
avoid doing this. The avoidance behaviour is most likely performed at relatively close
distance to the farm, within one or a few km, since we do not find any large differences in the
large-scale patterns (see above).
These results are very much in line with findings from other offshore wind farms where
primarily waterfowl, but also other birds have been found to change flight directions before
reaching the resp. farms and flying around rather than through these. Here we have not made
any detailed analysis of detailed flight paths as there was not room for this within the
monitoring programme. Doing such analyses based on the collected data is of course possible,
but will take a lot of time to perform.
That migrating waterfowl and other birds to a large extent avoid flying into wind farms has
been recorded both at small farms (Pettersson 2005, 2011) and at larger ones, more similar to
the one at Lillgrund (Desholm & Kahlert 2005, Petersen et al. 2006, Krijgsveld et al. 2010).
Detailed studies performed with both radar and visual observations show that migrating
waterfowl (mainly Eiders) changed flight directions at distances between 1 and 2 km from
two small wind farms in Kalmarsund during daytime and at 0,5-1 km distance during night
(Pettersson 2005, 2011). The same behaviour was recorded during nights with low visibility,
although much fewer birds continued their flight in such circumstances (Pettersson 2011). At
this site only 3 % of all recorded flocks passed within 500 m of the wind farms (Pettersson
2005).
At the Danish farms at Nysted (72 turbines) and Horns rev (80 turbines) 78 % and 71-86 % of
all birds (mostly Eiders and other waterfowl), approaching the wind farms avoided to fly into
them (Petersen et al. 2006). The proportion of all flocks passing the wind farm area of Nysted
decreased from 40 % pre-construction to 9 % post-construction, a reduction very similar to
one recorded at Lillgrund. Here, changes in flight directions were sometimes recorded at 5 km
80
distance from the farm, although most changes occurred within 1-2 km from the farm. The
behaviour was the same during night time with the only difference that the deflections then
took place closer to the turbines. Birds and flocks recorded to enter the wind farm mainly
passed through the corridors created by the lines of the turbines, hence maximizing distance
to these (Desholm & Kahlert 2005, Petersen et al. 2006).
Recent Dutch studies from a farm consisting of 36 turbines confirm the above mentioned
results for sea ducks, divers, gannets and auks (Krijgsveld et al. 2010). For some other birds
no such clear patterns were recorded. No large-scale avoidance or deflection at all was for
example recorded for skuas, gulls, terns and raptors although many bird groups showed
hesitation before entering the wind farm (Krijgsveld et al. 2010).
Taken together these results show that collision risks, at least for waterfowl, are low. In our
particular area only a small fraction of the overall migration movements do actually pass so
close to the turbines so that the birds run the risk of collision. This is however not the same as
to say that no collisions will occur. There will be, and have probably already been, collisions
taking place at the Lillgrund farm. We cannot however see that these will be of any
importance for any of the populations being involved.
At the same time we must also admit that the radars used in our study do not allow any more
detailed description of how all birds behave around the wind farm. Birds not migrating in
flocks and especially small birds cannot be tracked in any detailed way. Hence we do not
know how these groups behave when encountering the wind farm. Furthermore the used
radars do not give any data on flight altitudes. This means that we in our data can not
discriminate between flocks flying at low altitude and actually running the risk of getting into
contact with the farm and those flying higher, well above any turbines. This also means that
there is a high probability that that many of the flocks recorded passing the wind farm area
actually did so at much higher altitude (up to several 1000 m). The proportion of all passing
birds that may be at risk for collision is therefore lower than shown here.
Our studies at Lillgrund do not provide us with any data on collsion rates at this wind farm
and getting data on such is hard for offshore areas as carcasses can not be retrieved as they
can on land. Instead one have to resort to other techniques for getting ideas about possible
collision rates. So far visual observations, detailed radar and thermal cameras (Pettersson
2005, Petersen et al. 2006) have been used for this purpose. Collision rates recorded or
calculated from areas similar to Lillgrund (the Baltic area, relatively large numbers of
migrating birds passing) are 1 waterfowl bird (Eider) /turbine and year in Kalmarsund
(Pettersson 2005), 0,7 waterfowl bird (Eider)/turbine and year at Nysted (Petersen et al. 2006)
and 0,5 passerine/turbine and year at Nysted (Petersen et al. 2006). Based on these data it
seems as if collisions at offshore wind farms in the Baltic area are very few and if we assume
comparable passage rates of birds att Lillgrund as at Nysted, which seems reasonable, similar
collision rates could be expected at Lillgrund as well. If so we would expect that the wind
farm at Lillgrund would kill in the order of 100 or a few hundred individual birds annually.
This can be compared to that in the order of 1000-5000 birds are expected to collide with (and
get killed by) the nearby Öresund Bridge every autumn (Nilsson & Green 2002). In none of
these cases we expect these collision rates to affect the populations of the involved bird
species in any way.
The extra flight distances that are incurred by the detours around wind farms are small. This
means that the extra energy costs for avoiding a wind farm also are small. Calculations based
on the Nysted data set show that the extra cost for the total migratory journey of an Eider
81
(1400 km) will increase with 0,5-0,7 % because of the detour around this farm (Petersen et al.
2006, Masden et al. 2009). For species migrating longer distances, as some of the geese
passing Lillgrund, the increase will be even lower. The extra flight distance and energy cost
for passing a single wind farm is in other words insignificant, but cumulative effects from
several wind farms along a migratory journey will of course increase the total cost and hence
the risk of negative effects in the long run (Masden et al. 2009). Still, the decreased collison
risk that the avoidance behaviour leads to are probably of overriding importance.
82
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Birds in southern Öresund in relation to the wind farm at

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