Some of the emerging investments at different stages of their life cycle may cause negative impacts on protected environmental elements, including bats. This may involve destruction of roosts, occupation of feeding areas, creation of a barrier along the flyway, or causing direct mortality.

One of the cases where pre-investment surveys of bat occurrence and activity are necessary is the planning of a wind farm. However, they are very secretive animals – careful observation and trained hearing are not enough, as is the case with birds. Their nocturnal lifestyle and use of hiding places located in hard-to-reach places mean that conducting chiropterofauna research requires unusual means. It is necessary to reach for the help of technology.

What research looks like
Each of the 27 species of bats found in Poland uses echolocation. Using appropriate equipment – an ultrasound detector – it is possible to make recordings at the study site and analyze them later with dedicated computer programs, presenting the obtained data in graphic form.
Most of the species show differences in the ultrasounds issued in terms of parameters such as minimum and maximum frequency, the length of individual pulses and the intervals between them. The analyst’s task is to identify the recorded species and estimate the level of activity in the area of the planned project.

Fig. 1 Sonogram of the Nyctalus noctula
Fig. 2 Sonogram of the Myotis brandtii

While this sounds relatively simple in theory, there are several factors that can make analysis very challenging and time-consuming. Although you can find programs that allow automatic identification using artificial intelligence, they are unreliable, the probability of pinpointing the correct species is insufficient. The sonogram may differ for the same species depending on the conditions and environment in which the animal was present – the ultrasound sequence issued during flight in the open air will look different, different during hunting (feeding buzz), and still different are the social voices issued during mating or used to convey information to other individuals in the area. Therefore, human input is necessary each time during analysis.

Fig. 3 Sonogram showing echolocation of Nyctalus noctula
Fig. 4 Sonogram showing feeding buzz of Nyctalus noctula
Fig. 5 Sonogram showing the social voice of Nyctalus noctula

Impact of the results on the fate of the investment
Bats, unlike many bird species, do not usually avoid wind turbines. Some studies indicate the opposite effect. If turbines are sited in areas with high activity of these mammals, the mortality caused could have a significantly negative impact on population status, leading to the need for mitigation measures, such as the introduction of periodic shutdowns or even the dismantling of existing turbines.
In order to avoid the above situation, it is necessary to carry out at least annual monitoring of the entire area under consideration for planning the project and its surroundings. It makes it possible to determine the level of bat activity in each phenological period and to study the use of the space, allowing the location of turbines to be planned outside the flight paths – both seasonal and diurnal, between roosts and feeding and watering grounds. A thorough study of the site at the layout planning stage thus protects both the bats and the future of the project itself.