Birds in southern Öresund in relation to the wind farm at ... - Vattenfall

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migration volume that passed over the northern (more in the latter period) and southern part (less in the latter period) of the 50 km long analysed transect, but with distances to the wind farm of more than 10 and 15 km respectively, it is hard to see that the wind farm should have played any important role for these changes. More likely, these changes are governed by prevailing weather and wind during the analysed migration days. The flight paths of migrating birds are to some extent decided by winds, through so called wind drift (Alerstam 1990). Within the migration corridor, the exact paths may vary between days and seasons due to that the birds are affected by drift. This may be because the birds use adaptive drift strategies, taking advantage of the extra speed they can get from the wind (without letting themselves drift too far away from the desired migration path) or simply because they lack the capacity to compensate fully for the drift effect of the wind (Alerstam 1990). Small differences in wind directions and speed can hence create differences like the ones we see in our data set. In autumn we see variation in the proportions passing different parts of Öresund between years but not between the pre- and post-construction periods as such. In contrast to the general picture given above, the proportion of the overall migration volume that passed Lillgrund decreased both in spring and in autumn, and the decrease was of similar magnitude in both seasons (70-80 % decrease). There was no difference between day and night migration in this respect, the proportion passing Lillgrund decreased from pre-to postconstruction years irrespective of time of the day. Even though we do not have any data on flight altitudes of the passing flocks (not possible to record with the used radars), and hence cannot give an exact estimate on the proportion of flocks avoiding to fly into the wind farm. The only reasonable interpretation of the results is that a large majority of the recorded flocks approaching the wind farm along flight paths that would lead them through the park actually avoid doing this. The avoidance behaviour is most likely performed at relatively close distance to the farm, within one or a few km, since we do not find any large differences in the large-scale patterns (see above). These results are very much in line with findings from other offshore wind farms where primarily waterfowl, but also other birds have been found to change flight directions before reaching the resp. farms and flying around rather than through these. Here we have not made any detailed analysis of detailed flight paths as there was not room for this within the monitoring programme. Doing such analyses based on the collected data is of course possible, but will take a lot of time to perform. That migrating waterfowl and other birds to a large extent avoid flying into wind farms has been recorded both at small farms (Pettersson 2005, 2011) and at larger ones, more similar to the one at Lillgrund (Desholm & Kahlert 2005, Petersen et al. 2006, Krijgsveld et al. 2010). Detailed studies performed with both radar and visual observations show that migrating waterfowl (mainly Eiders) changed flight directions at distances between 1 and 2 km from two small wind farms in Kalmarsund during daytime and at 0,5-1 km distance during night (Pettersson 2005, 2011). The same behaviour was recorded during nights with low visibility, although much fewer birds continued their flight in such circumstances (Pettersson 2011). At this site only 3 % of all recorded flocks passed within 500 m of the wind farms (Pettersson 2005). At the Danish farms at Nysted (72 turbines) and Horns rev (80 turbines) 78 % and 71-86 % of all birds (mostly Eiders and other waterfowl), approaching the wind farms avoided to fly into them (Petersen et al. 2006). The proportion of all flocks passing the wind farm area of Nysted decreased from 40 % pre-construction to 9 % post-construction, a reduction very similar to one recorded at Lillgrund. Here, changes in flight directions were sometimes recorded at 5 km 80
distance from the farm, although most changes occurred within 1-2 km from the farm. The behaviour was the same during night time with the only difference that the deflections then took place closer to the turbines. Birds and flocks recorded to enter the wind farm mainly passed through the corridors created by the lines of the turbines, hence maximizing distance to these (Desholm & Kahlert 2005, Petersen et al. 2006). Recent Dutch studies from a farm consisting of 36 turbines confirm the above mentioned results for sea ducks, divers, gannets and auks (Krijgsveld et al. 2010). For some other birds no such clear patterns were recorded. No large-scale avoidance or deflection at all was for example recorded for skuas, gulls, terns and raptors although many bird groups showed hesitation before entering the wind farm (Krijgsveld et al. 2010). Taken together these results show that collision risks, at least for waterfowl, are low. In our particular area only a small fraction of the overall migration movements do actually pass so close to the turbines so that the birds run the risk of collision. This is however not the same as to say that no collisions will occur. There will be, and have probably already been, collisions taking place at the Lillgrund farm. We cannot however see that these will be of any importance for any of the populations being involved. At the same time we must also admit that the radars used in our study do not allow any more detailed description of how all birds behave around the wind farm. Birds not migrating in flocks and especially small birds cannot be tracked in any detailed way. Hence we do not know how these groups behave when encountering the wind farm. Furthermore the used radars do not give any data on flight altitudes. This means that we in our data can not discriminate between flocks flying at low altitude and actually running the risk of getting into contact with the farm and those flying higher, well above any turbines. This also means that there is a high probability that that many of the flocks recorded passing the wind farm area actually did so at much higher altitude (up to several 1000 m). The proportion of all passing birds that may be at risk for collision is therefore lower than shown here. Our studies at Lillgrund do not provide us with any data on collsion rates at this wind farm and getting data on such is hard for offshore areas as carcasses can not be retrieved as they can on land. Instead one have to resort to other techniques for getting ideas about possible collision rates. So far visual observations, detailed radar and thermal cameras (Pettersson 2005, Petersen et al. 2006) have been used for this purpose. Collision rates recorded or calculated from areas similar to Lillgrund (the Baltic area, relatively large numbers of migrating birds passing) are 1 waterfowl bird (Eider) /turbine and year in Kalmarsund (Pettersson 2005), 0,7 waterfowl bird (Eider)/turbine and year at Nysted (Petersen et al. 2006) and 0,5 passerine/turbine and year at Nysted (Petersen et al. 2006). Based on these data it seems as if collisions at offshore wind farms in the Baltic area are very few and if we assume comparable passage rates of birds att Lillgrund as at Nysted, which seems reasonable, similar collision rates could be expected at Lillgrund as well. If so we would expect that the wind farm at Lillgrund would kill in the order of 100 or a few hundred individual birds annually. This can be compared to that in the order of 1000-5000 birds are expected to collide with (and get killed by) the nearby Öresund Bridge every autumn (Nilsson & Green 2002). In none of these cases we expect these collision rates to affect the populations of the involved bird species in any way. The extra flight distances that are incurred by the detours around wind farms are small. This means that the extra energy costs for avoiding a wind farm also are small. Calculations based on the Nysted data set show that the extra cost for the total migratory journey of an Eider 81
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Birds in southern Öresund in relat
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Contents Summary 4 Svensk sammanfat
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the birds and/or the flocks, the be
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Metoder Inventeringarna av rastande
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Alfågel (Fig. 14-19) Alfågeln öv
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Liksom vid andra inventeringar av r
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Introduction Southern Öresund is a
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Lillgrund is situated in the southe
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had to be made with only one observ
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Fig. 5. Map of the southern part of
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Fig. 6 . Map over the wind farm at
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transect was divided into 10 km lon
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Results Staging and wintering birds
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Table.3 Percentage of the total num
Page 29 and 30: Cormorant Phalacrocorax carbo As is
Page 31 and 32: Fig. 10. Summary distribution maps
Page 33 and 34: Overall Jacob’s index (D) for the
Page 35 and 36: Long-tailed Duck Clangula hyemalis
Page 37 and 38: ehind the large variation is that f
Page 41 and 42: Common Eider Somateria mollissima T
Page 47 and 48: Jacobs Index Jacobs Index 1 0,5 0 -
Page 49 and 50: 2500 2000 1500 1000 500 0 MIN MEAN
Page 51 and 52: Fig. 30. Details of Fig. 29 to show
Page 53 and 54: large-scale changes in abundance ar
Page 55 and 56: 600 500 400 300 200 100 0 MIN MEAN
Page 59 and 60: Jacobs Index Jacobs Index 1 0,5 0 -
Page 61 and 62: Lillgrund and the wind farm are sit
Page 63 and 64: The spring migration season, and he
Page 65 and 66: % of all echoes (flocks) 45 40 35 3
Page 71 and 72: irds given the assumptions used abo
Page 73 and 74: % of all echoes (flocks) % of all e
Page 75 and 76: % av alla ekon (flockar) 20 15 10 5
Page 77 and 78: species, some species being better
Page 79: area and from a Dutch farm show tha
Page 83 and 84: Literature Alerstam, T. 1972. Noctu
Page 85: Petersen, I. K. & Fox A. D. 2007. C
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