Birds in Southern Öresund in Relation to the Wind Farm at Lillgrund

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

2 Contents

Summary 4 Svensk sammanfattning 6 Introduction 13 Study area 14 Methods 16 Survey methods 16 Boat surveys 16 Aerial surveys 18 Analysis of survey data 20 Radar studies of bird migration 22 Results 25 Staging and wintering birds 25 Cormorant Phalacrocorax carbo 29 Long-tailed Duck Clangula hyemalis 35 Common Eider Somateria mollissima 41 Red-breasted Merganser Mergus serrator 48 Herring Gull Larus argentatus 54 Radar studies of bird migration 60 Spring- north-easterly directed migration 60 Spring- southerly directed migration 67 Autumn 70 Discussion 76 Staging and wintering birds 76 Migrating birds 79 Literature 83 Appendix

3 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. 2007/09- 2010/11.

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

4 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.

5 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).

6 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.

7 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 0- 9 % 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), 3- 6 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, 6- 10 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 ESAS- project (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 Oct Nov Dec Jan Feb March April May BOAT 2001/02 - - - 1 - 1 1 1 - 2002/03 1 - 1 1 1 - 1 1 - 2003/04 - - 1 - 1 1 1 1 - 2004/05 ------1 1 - 2005/06 - - 1 1 - - - - -

2007/08 - - - 1 - 1 - 1 - 2008/09 1 ------2009/10 1 ------2010/11 - 1 - - - - - 1 1 AERIAL 2005/06 - - - - 1 1 1 1 1

2007/08 ------2 1 1 2008/09 - - - 1 1 1 1 - 1 2009/10 ------1 1 - 2010/11 - - - - 1 1 2 - 1

Aerial surveys

Fig. 4. A CESSNA 337 Skymaster was used for the aerial surveys. CESSNA 337 Skymaster användes för flyginventeringarna.

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 flyginvente- ringslinjerna 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.

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.

Radar studies of bird migration

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.

% of total time Year Season From date To date No. of days No. of hours during selected days 2002 spring 13 Mar 26 May 17 382 94 2005 spring 31 Mar 29 May 24 573 >99 2008 spring 20 Mar 29 May 23 539 98 2009 spring 21 Mar 27 May 26 624 100 2010 spring 28 Mar 5 Jun 20 467 97

2001 autumn 20 Sep 19 Oct 11 240 91 2008 autumn 11 Sep 6 Nov 13 288 92 2009 autumn 8 Sep 30 Oct 17 408 100

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/). .

1 2 3 4 C

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

Staging and wintering birds

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 pre- construction 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).

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. 2006 (5) 2008(4) 2009(5) 2010(2) 2011(4) % Total % Total % Total % Total % Total Cormorant Phalacrocorax carbo 94 934 36 416 70 521 98 157 93 120 Long-tailed Duck Clangula hyemalis 9 1051 12 1021 29 509 13 513 22 1176 Eider Somateria mollissima 74 4894 52 6416 11 6037 56 3455 30 10956 Red-breasted Merganser Mergus serrator 72 984 78 1002 84 801 90 850 92 2348 Herring Gull Larus argentatus 59 605 77 804 37 459 44 264 55 757

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 Aerial surveys Boat surveys Pre- Post- Pre- Post- construction construction construction construction Cormorant Wind farm - 0.49 -0.84 -0.79 -0.69 2 km Buffer zone -0.52 0.82 - 0.71 0.14 Long-tailed Wind farm -0.23 -0.85 0.48 -0.14 Duck 2 km Buffer zone 0.06 -0.41 0.78 0.77 Eider Wind farm 0.06 0.08 0.80 -0.09 2 km Buffer zone 0.79 0.62 0.68 0.11 Red-breasted Wind farm -0.26 -0.42 0.41 -0.27 Merganser 2 km Buffer zone 0.22 0.07 0.47 0.03 Herring Gull Wind farm -0.36 0.03 -0.11 -0.71 2 km Buffer zone 0.06 -0.27 -0.20 0.46 Cormorant Phalacrocorax carbo

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 post- construction. 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.

800

700 Phalacrocorax carbo

600

500 MIN

400 MEAN

MAX 300

200

100

0 BEFORE AFTER BEFORE AFTER

SOUTH 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.

3,5

Phalacrocorax carbo 3 Winter

2,5

Outer 2 Buffer Windfarm 1,5

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 post- construction 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 post- construction 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.

Aerial

0,5

-0,5 Jacobs Index -1 2006 2008 2009 2010 2011 -1,5

Boat

0,5

Jacobs Index -0,5

-1 2001- 2002- 2003- 2005a 2005b 2007- 2009- 2010- 2002 2003 2004 2008 2010 2011

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 Long-tailed Duck Clangula hyemalis . 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 pre- construction 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

1000 Clangula hyemalis

800

MIN 600 MEAN MAX

400

200

0 BEFORE AFTER BEFORE AFTER

SOUTH 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) construction of the wind farm at Lillgrund. Medel, maximum och minimum antal av alfågel Clangula hyemalis i det norra och södra området (Fig. 5) före (7 räkningar) och efter (15 räkningar) uppförandet av vindkraftparken på Lillgrund.

300

250 Clangula hyemalis

200

150 MIN

MEAN

100 MAX

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.

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.

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

2 Clangula hyemalis Winter

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 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 alfågel Clangula hyemalis baserade på flyginventeringar under vintern inom olika zoner runt Lillgrunds vindkraftpark under olika år. Antalet inventeringar anges inom parentes.

Aerial

0,5

-0,5 Jacobs Index Jacobs

-1 2006 2008 2009 2010 2011

Boat

0,5

-0,5 Jacobs Index Jacobs

-1 2001- 2002- 2003- 2005a 2005b 2007- 2009- 2010- 2002 2003 2004 2008 2010 2011

Fig. 19. Variation in Jacob’s index (see text for explanation) between years (centered around 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. Variation i Jacobs index (se text för förklaring) mellan år (centrerade runt midvinter för index från båtdata) för alfågel Clangula hyemalis 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. Notera att inga alfåglar alls sågs under båtinventering 2009- 2010 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). Post- construction 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.

8000

7000

6000 Somateria mollissima MIN

5000 MEAN

MAX 4000

3000

2000

1000

0 BEFORE AFTER BEFORE AFTER

SOUTH 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) construction of the wind farm at Lillgrund. Medel, maximum och minimi antal av ejder Somateria mollissima i det norra och södra området (Fig. 5) före (7 räkningar) och efter (15 räkningar) uppförandet av vindkraftparken på Lillgrund.

9000

8000 Somateria mollissima 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 flyginventeringar före (vänster) och efter (höger) uppförandet av vindkraftparken. För årsvisa kartor se appendix.

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.

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 pre- construction 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.

90 Birds/km2 80

70 Somateria mollissima Winter 60

50 Outer Buffer 40 Windfarm 30

0 2006(3) 2008(1) 2009(4) 2010(1) 2011(3)

350 Birds/km2

300 Somateria mollissima Spring 250

200 Outer B uffer 150 Windfarm

100

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.

Aerial

0,5

Jacobs Index Jacobs -0,5

-1 2006 2008 2009 2010 2011

Boat

0,5

-0,5 Jacobs Index Jacobs

-1 2001- 2002- 2003- 2005a 2005b 2007- 2009- 2010- 2002 2003 2004 2008 2010 2011

Fig. 26. Variation in Jacob’s index (see text for explanation) between years (centered around mid-winter for boat data) for Eiders Somateria mollissima 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 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 AFTER

SOUTH 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 området (Fig. 5) före (7 räkningar) och efter (15 räkningar) uppförandet av vindkraftparken 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 flyginventeringar före (vänster) och efter (höger) uppförandet av vindkraftparken. För årsvisa kartor se appendix.

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 35 Winter

25 Outer Buffer 20 Windfarm

0 2006(3) 2008(1) 2009(4) 2010(1) 2011(3)

Fig. 32. Densities (individuals / km2) of Red-breasted Merganser Mergus serrator based on aerial surveys during winter in different zones around the wind farm at Lillgrund in different 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 pre- construction 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 post- construction 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

0,5

Jacobs Index Jacobs -0,5

-1 2006 2008 2009 2010 2011

Boat

0,5

-0,5 Jacobs Index Jacobs

-1 2001- 2002- 2003- 2005a 2005b 2007- 2009- 2010- 2002 2003 2004 2008 2010 2011

Fig. 33. Variation in Jacob’s index (see text for explanation) between years (centered around 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. Variation i Jacobs index (se text för förklaring) mellan år (centrerade runt midvinter för index från båtdata) för småskrake Mergus serrator 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.

53 Herring Gull Larus argentatus

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

500 Larus argentatus

400 MIN MEAN 300 MAX

200

100

0 BEFORE AFTER BEFORE AFTER

SOUTH 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) construction of the wind farm at Lillgrund. Medel, maximum och minimum antal av gråtrut Larus argentatus i det norra och södra området (Fig. 5) före (7 räkningar) och efter (15 räkningar) uppförandet av vindkraftparken 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 .

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 flyginventeringar före (vänster) och efter (höger) uppförandet av vindkraftparken. För årsvisa kartor se appendix.

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

8 Outer Buffer 6 Windfarm

0 2006(3) 2008(1) 2009(4) 2010(1) 2011(3)

8 Larus argentatus Spring 7

5 Outer 4 B uffer Windfarm 3

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.

Aerial

0,5

Jacobs Index Jacobs -0,5

-1 2006 2008 2009 2010 2011

Boat

0,5

-0,5 Jacobs Index Jacobs

-1 2001- 2002- 2003- 2005a 2005b 2007- 2009- 2010- 2002 2003 2004 2008 2010 2011

Fig. 39. Variation in Jacob’s index (see text for explanation) between years (centered around mid-winter for boat data) for Herring Gull Larus argentatus 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 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.

Radar studies of bird migration

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.

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 30

25 2002 20 2005 2008 15 2009 2010 10 % of all echoes (flocks) echoes all % of

0 ABCDE 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

35 Lillgrund

30 2002 25 2005 20 2008 2009 15 2010

% of all echoes (flocks) 10

0 ABCDE Sector

Night-time

35 Lillgrund

30 2002 25 2005 20 2008

15 2009 2010

% of all echoes (flocks) 10

0 ABCDE 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. 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, 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 pre- construction 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 pre- construction (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 30 2002 2005 25 2008 20 2009 15 2010 10 % of all echoes (flocks) 5 0 ABCDE 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) Fördelningen av fågelekon (flockar) med nordostliga flygriktningar registrerade med radar 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 30 Lillgrund 2002 2005 25 2008 20 2009 15 2010 10 % of all echoes (flocks) 5 0 ABCDE Sector

Fig. 44. Distribution of bird echoes (flocks) with north-easterly flight directions registered by 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 Lillgrund for the different 10 km sectors (A-E, see Fig 7 & 40) Fördelningen av fågelekon (flockar) med nordostliga flygriktningar registrerade med radar 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).

Late spring migrants

45 40 Lillgrund 35

30 2002 2005 25 2008 20 2009 15 2010 10 % of all echoes (flocks) all% echoes of 5 0 ABCDE Sector

Fig. 45. Distribution of bird echoes (flocks) with north-easterly flight directions registered by 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 Lillgrund for the different 10 km sectors (A-E, see Fig 7 & 40) Fördelningen av fågelekon (flockar) med nordostliga flygriktningar registrerade med radar 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

% of all echoes (flocks) echoes all % of 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).

Day-time Night-time 10

% ofall echoes (flocks) 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

50 2002 40 2005 2008 30 Lillgrund 2009 2010 20 %of all echoes (flocks) 10

0 1234 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

5 % of all echoes (flocks)

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 pre- construction (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.

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

30 Lillgrund 25 2001 20 2008 2010 15

% of all echoes (flocks) echoes all % of 10

0 ABCDE 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 pre- construction 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

30 Lillgrund 25 2001 20 2008 2009 15

10 % of all echoes (flocks) echoes all % of 5

0 ABCDE Sector

Night-time

30 Lillgrund

25 2001 20 2008 2009 15

10 % ofall echoes (flocks) 5

0 ABCDE 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.

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 %.

% of all echoes (flocks) 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 20

Day-time 10 Night-time

% av alla ekon(flockar) 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

Staging and wintering birds

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 Long- tailed 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 post- construction 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 post- construction 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 Literature

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