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

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 ESASproject
(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
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