Barbastelles and wind power – a project to improve knowledge and provide guide lines.
The world is a dangerous place for bats. One serious threat in Europe and elsewhere is the wind turbine industry, which is growing fast.
The research was focused on the western barbastelle (Barbastella barbastellus), a rare and threatened insectivorous bat suspected to be vulnerable at wind farms. The barbastelle is a moth specialist and lives in old broadleaf woodlands.
Our study was carried out in July and August 2016 in and around a wind farm known to harbour a population of barbastelles, located in south-western Sweden. The main goal of the project was to investigate how the bats move and feed in relation to the wind turbines, and hopefully to find ways to avoid collisions between bats and moving rotors. The presence of barbastelles is a common reason why wind farm projects in southern Sweden are denied. However, the guidelines for this are poorly founded and decisions are often based on non-scientific grounds. In fact, the barbastelle has never been intensively studied in Sweden.
By catching and tagging a lactating female by mist nets inside the wind farm, we managed to find the maternity colony by back-tracking her to the roost, where we could catch the number of females we wanted. We also managed to catch two males in the forest. Altogether, ten bats were tagged with 0.32 g Holohil LB-2X transmitters. The bats were followed during 11 consecutive nights by use of three Australis 26k (Titley Scientific Australia) receivers and 3 element Yagi antennas. The wind farm area turned out to be quite tricky for radio tracking because of inaccessible marshes, dense forest, biting midges and, over all, a hilly landscape. We therefore located our radio tracking teams on hill tops (Fig. 1), from where we were able to establish the approach bearings of tracked bats. One early morning while standing on a highest nearby hill top, we recorded a fantastic performance of the Holohil transmitters. We were able to hear signals from the maternity roost located 8.07 km away! The observation was checked again the following morning. From 8 tagged bats roosting in the colony, four were easily hearable from the hill top on all of our three receivers. The maternity roost with the bat colony was located in a wooden barn situated on a hill slope facing turbine located on a highest point (Fig. 2). Clearly we had a situation described as “transmitter seeing receiver”. Transmitter range is strongly affected by the landscape topography and vegetation, and may be significantly reduced by dense forest. This is a well-known phenomenon, but while it is easy to complain about the range limitations of small tags, we would like to express a different point of view and appreciate the outstanding range of the tiny transmitters that we used. We have worked with Holohil equipment before and have always been satisfied with the performance, but we never thought that the signal could travel so far! Also worth mentioning is that signals picked up from the hill top were usually clear and loud, suggesting they could have been picked up from an even greater distance. Additionally, all of 10 tags, which we used, worked through the whole two-week project without any significant malfunctions. Especially taking into account some harsh weather, the overall reliability of LB-2X helped us to finish our project successfully.
We were really lucky having our already exciting radio tracking study enriched by such outstanding performance of the equipment. Thanks a million to the Holohil team for providing such excellent transmitters! We will continue our co-operation with your company, and indeed look forward to break new records next summer!