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

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
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