Therkildsen, O.R., Elmeros, M., Kahlert, J. & Desholm, M. (eds.) 2012. Baseline investigations of bats and birds at Wind Turbine Test Centre Østerild. Aarhus University, DCE – Danish Centre for Environment and Energy, 128 pp. Scientific Report from DCE – Danish Centre for Environment and Energy No. 28 http://www.dmu.dk/Pub/SR28.pdf
Mortality of bats at wind turbines and their effects on the conservation status of bats have received much attention in the planning and operation of wind turbines in most European and North-American countries. Bat mortality rates are affected by the location of wind turbines, the height of the turbines and the wind speed. The mortality of bats is highest at wind turbines located in or near important habitats as forests and wetlands, and on migration routes over land and along the coast. Bat mortality increases with increasing height of wind turbines, and mortality rates are highest on nights with low wind speeds. Bats are killed by the rotating turbine wings. As the reproductive rate of bats is low, the status of bat populations is very sensitive to even small increases in mortality rates.
A national test centre for large wind turbines has been constructed in Østerild Plantation in Denmark. To assess potential effects of the wind turbines on bat occurrence and their use of the test centre area, bats were monitored during summer and autumn 2011 prior to construction work. Bats were monitored with automatic and handheld ultrasound detectors.
Seven species, pond bat (Myotis dasycneme), Daubenton’s bat (Myotis daubentonii), Nathusius’ pipistrelle (Pipistrellus nathusii), soprano pipistrelle (Pipistrellus pygmaeus), serotine bat (Eptesicus serotinus), particoloured bat (Vespertilio murinus) and brown long-eared bat (Plecotus auritus), were recorded at the proposed wind turbine sites, ponds and lakes in the test centre area and its vicinity. Bats occur throughout the area from early July to late October. Bats were recorded on 57-100% of surveyed nights at the individual sites. The number of bat passes was lower along forest roads than at lakes and ponds.
High occurrence and bat activity levels were recorded along forest roads at the southernmost wind turbine sites and at lakes and ponds within the plantation. Lakes, ponds and adjacent forest clearings in the test centre area and its vicinity were used as feeding sites by bats, especially by pond bats and Daubenton’s bats. Several individual bats were observed feeding at lakes and ponds. The activity level of pond bats and Daubenton’s bats increased at ponds and lakes during autumn.
Extensive feeding activities were recorded at wetland sites in the plantation, and bats are expected to exploit the new feeding habitats in forest clearings at the turbine sites as well as feeding on the insects that congregate at the wind turbines and in the clearings around the turbines. Thus, the highest mortality risk is to be expected at the southernmost wind turbine sites as they are situated in forest and close to wetlands. Future monitoring studies on bat behaviour near wind turbines will focus on these sites.