Ingemar Ahlén1 & Hans J. Baagøe2
1Department of Ecology, SLU, Box 7002 (Natur icum), SE-750 07
Uppsala, Sweden, ingemar.ahlen@slu.se
2Natura l History Museum of Denmark, Zoological Museum,
Universitetsparken 15, DK-2100 Copenhagen Ø, Denmark
Bats and wind power – investigations required for risk assessment in
Denmark and Sweden
We experienced an urgent need among authorities and consultancies to get
clear guidelines for planning and field investigations at suggested wind parks.
Certain minimum conditions must be fulfilled concerning evaluation of the
project area, timing of investigations etc. to provide data necessary for a
meaningful risk assessment.
We prepared “Guidelines for bat investigations prior to wind projects” for
distribution to authorities. Recommendations were based on our research on
bat ecology and behaviour at wind power installations and our many years of
experience of bat occurrence and behaviour in the landscape. To avoid misunderstandings
our guidelines are detailed and carefully argumented, but only
the headline contents can be given here:
Current knowledge justifies an introductory classification of project areas
into three categories: 1. high risk sites, 2. uncertain but possible, 3. low risk
already documented. Only category 2 needs field investigations, while 1 should
be stopped and 3 can go on. This will speed up the planning process and minimize
expensive field investigations to the areas in most need of risk assessments.
Field investigations require studies on activity and species composition
in a project area also including suitable colony habitats and hunting sites
within a radius of at least 2 km. Methods include automatic registration,
detector listening etc. to ensure data on species presence, number of observations
and facts on activity and status. Investigations are obligatory for the
following periods: A) At least two separate nights in the breeding season (late
June – early August), B) two nights in mid-August to mid-September when
bats migrate or disperse. C) If certain “key habitats” are suspected with mass
occurrence of insects in spring, two additional nights of investigation are
required in late April – May.
We warn that it is difficult to predict bat activity at wind turbines before
they are built. At certain weather conditions turbines may attract huge masses
of insects and bats are able to discover such new food resources even if they
occur far out in “non-bat areas”. This also occurs in the breeding season.
Investigations and risk assessments should be carried out by independent
bat specialists with high competence. All data and conclusions must be presented
with open access.
Post-construction surveys and stop regulation are suggested for cases with
remaining uncertainty about risks.