Base-Line Investigations of Birds in Relation to an Offshore Wind Farm at Rødsand: Results and Conclusions, 2002


Title: Base-Line Investigations of Birds in Relation to an Offshore Wind Farm at Rødsand: Results and Conclusions, 2002
Publication Date:
September 01, 2003
Pages: 53
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Desholm, M.; Kahlert, J.; Petersen, I.; Clausager, I. (2003). Base-Line Investigations of Birds in Relation to an Offshore Wind Farm at Rødsand: Results and Conclusions, 2002. Report by ENERGI E2 and National Environmental Research Institute (NERI). pp 53.

This report presents data from the base-line investigations of birds, which were carried out during 2002 in relation to the Nysted/ Rødsand offshore wind farm. Mapping of migration routes was carried out by use of radar day and night. The mapping of migration routes was combined with species identification during daytime by use of telescope. Waterfowl, which included staging migrants, wintering or wing moulting birds in the study area at the wind farm area, were monitored by aerial surveys.


The wind farm area is situated on a waterfowl migration route. Observations at Gedser Odde suggest that numbers of passing waterfowl may add up to 300,000 individuals during autumn. The baseline study has shown that between 26% (2002) and 49% (2000) of the waterfowl tracks registered by radar pass the eastern border of the wind farm area.


During spring, the percentage of waterfowl (mainly eiders), which passed the eastern edge of the wind farm area, was for the first time since the start of the base-line study in the same order of magnitude (25%) as in autumn (26%). Like in spring 2001, the 2002 main spring migration route of waterfowl was situated north of the wind farm area. In late May 2002, ca 9,000 dark-bellied brent geese followed the northern migration route.


Due to a temporary suspension of the study in autumn 2002, data on migrating landbirds from this period are absent in the present report. Spring migration of raptors, passerines and pigeons was almost absent both during 2000, 2001 and 2002.


All migration tracks were entered into a GIS – (Geographical Information System) database, subsets of data were selected for description of migration routes before the wind turbines are erected. These base-line data will be used for comparisons with similar data obtained during a monitoring programme carried out in a period after the wind farm has started to operate. Three key-variables are presented in this report:


  1. the orientation of autumn migration routes for waterfowl and terrestrial bird species; the variable is to be used to measure potential avoidance response to individual wind turbines;
  2. the probability that waterfowl will pass through the wind farm area during autumn and spring;
  3. the variable is to be used to measure the waterfowl response to the entire wind farm; the migration intensity measured as the number of bird flocks that pass the eastern and northern edge of the wind farm area; the variable is to be used to measure the effect of the avoidance responses to the volume of migration in the wind farm area.


Comparisons of key variables between individual base-line years were undertaken while controlling for various factors such as weather conditions, season and time of day, mainly by use of multi-factorial ANOVA or regression analyses. Measures of migration intensity tended to have least statistical power in between-year comparisons amongst the three key variables.


Count surveys of staging, wintering and moulting waterfowl have documented that cormorants (up to 5,200 individuals) and moulting mute swans (up to 9,700 individuals) occur in international important numbers (> 1% of total population in the entire study area) on an annual basis. Red-breasted merganser has not occurred in international important numbers since November 1999, when 1,600 individuals were counted.


On the basis of aerial count surveys waterfowl preferences of predefined areas were calculated by use of Jacobs’s selectivity index. Cormorant, mute swan, mallard, goldeneye, herring gull and little gull all showed significant avoidance of the wind farm area and the three distance bands around it. Long-tailed duck and common scoter showed significant preference for the wind farm and the adjacent distance bands, making these species susceptible to disturbance effects from the future wind farm. Red-breasted merganser showed avoidance of the wind farm site, but preference for the three distance bands, whereas eider showed index values very close to 0, which indicated neither preference nor avoidance.


Radar studies revealed that cormorants may undertake social foraging events during early mornings and late afternoons. Social foraging flocks may hold 5,000 individuals and may occur inside the wind farm area. This behaviour makes cormorant a potentially high-risk species with respect to collisions with the wind turbines, also because the species may be attracted by the turbine foundations for roosting.

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