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

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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 km 2 , buffer zone 29 km 2 and for the outer area 224 km 2 , 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 km 2 within the wind farm area, 4.2 km 2 for the buffer zone and 33.9 km 2 for the areas outside these zones. The mean counts within the survey belts within each zone were calculated for each year and season separately and the densities were calculated from these means and the surveyed area within each zone (see above). The means are found in Table A10 in the appendix. If birds avoid the wind farm area or not was analyzed by calculating Jacob’s selectivity index D (hereafter Jacob’s index, Jacobs 1974). This index was calculated for the five most commonly recorded species during boat and air surveys, and was used for describing if the birds avoided or were attracted to the wind farm area. Indices were calculated both for the period before the construction of the wind farm and for the period with the farm in operation. Separate indices were also calculated for each survey year (centered around mid-winter) in order to look at annual variation in avoidance or preference. Avoidance or preference for the area outside but close to the wind farm, up to 2 km away from the turbines, was also analyzed (see Fig. 6 for delimitation of the areas used). The birds recorded in the remaining parts of the study area covered by boat transects or the northern part of the aerial survey area were used in the calculations of the total number of birds in the whole study area and for calculating proportions of birds using the areas closest to the wind farm, but no indices were calculated for these parts. 20
Fig. 6 . Map over the wind farm at Lillgrund, turbines showed by black dots, the wind farm area (line connecting black dots), as well as the area within 2 km from the turbines used in the calculations of Jacob’s index (see text). Detaljkarta over vindkraftparken på Lillgrund samt omfattningen på buffertzonen inom ett avstånd på 2 km från de yttersta kraftverken, vilka utnyttjas för beräkningar och analyser med Jacobs index (se närmare i texten!). The Jacob’s index describes to what extent the birds use a specific area in relation to the expected use of that area. In the case with marine birds at sea the expected use is usually that the birds should distribute themselves in relation to size of the area. The larger area, the more birds in absolute numbers is expected to use the area. This is of course a simplification of reality and many other factors such as water depth, food availability are also deciding how the birds will be distributed. As a simple rule of thumb and as a reasonable starting point for further discussions, the Jacob’s index works perfectly well and hence has been used in several similar studies before (see for example Petersen et al. 2006, Petersen & Fox 2007). An index value (D) of +1 show that all birds occur in the area of interest and will be interpreted as that the birds prefer this area. An index value (D) of -1 show that no birds occur in the area of interest and will be interpreted as that the birds avoid the area. The interpretation of negative index values is that there is some sort of avoidance involved. The lower (more negative) the index, the stronger is the avoidance. Positive index values are interpreted as some sort of preference. The higher (more positive) index the stronger is the preference. Index values close to zero shows that the area is used roughly as expected. The Jacob’s index is calculated as follows: D = (r - p) / (r + p - 2rp) 21
Page 1 and 2: Birds in southern Öresund in relat
Page 3 and 4: Contents Summary 4 Svensk sammanfat
Page 5 and 6: the birds and/or the flocks, the be
Page 7 and 8: Metoder Inventeringarna av rastande
Page 9 and 10: Alfågel (Fig. 14-19) Alfågeln öv
Page 11 and 12: Liksom vid andra inventeringar av r
Page 13 and 14: Introduction Southern Öresund is a
Page 15 and 16: Lillgrund is situated in the southe
Page 17 and 18: had to be made with only one observ
Page 19: Fig. 5. Map of the southern part of
Page 23 and 24: transect was divided into 10 km lon
Page 25 and 26: Results Staging and wintering birds
Page 27 and 28: 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
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% of all echoes (flocks) % of all e
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% av alla ekon (flockar) 20 15 10 5
Page 77 and 78:
species, some species being better
Page 79 and 80:
area and from a Dutch farm show tha
Page 81 and 82:
distance from the farm, although mo
Page 83 and 84:
Literature Alerstam, T. 1972. Noctu
Page 85:
Petersen, I. K. & Fox A. D. 2007. C
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Birds in southern Öresund in relation to the wind farm at ... - Vattenfall

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