Human activities can negatively impact biodiversity, including bats, leading to excessive mortality, population declines and potentially species extinction. Amongst these threats, wind power and light pollution are both known to affect bats when foraging, commuting, or roosting. This can have consequences on species presence at a local scale, but when cumulative impacts from all wind turbines and artificial lighting sources, consequences are greater on species’
survival.

As the dominating boreal forest is of great importance for Finnish bats, especially during the summer and its permanent twilight, I investigated how wind turbines and artificial lighting could affect the presence and activity of bats in this habitat. This choice was motivated by the vast proportion of wind turbines being built there at the moment, and the general increase in the use of artificial lighting at night. The final reason is that there is no data on the impacts of artificial lighting and wind power on bats in the country.

I monitored bat acoustic activity at several wind farms located in forest and observed that the presence of bats increased when getting away from wind turbines, for both Eptesicus nilssonii and Myotis spp. The range of this repelling effect was estimated at 800 m for the former species, and more than 1,000 m for the latter. This avoidance of wind turbines and their surroundings could mean a loss of commuting and foraging habitats for bats. The reasons behind this phenomenon are not understood but could be explained by the changes in landscape consequent of the construction of turbines in the forest, or the consequences of these changes on insects. Regarding light pollution, I set up flood lights in the forest and recorded bat activity to assess the effect on E. nilssonii and Myotis spp. The response of the latter was negative towards flood lights, with significantly lower presence at lit sites than dark sites. The observed response of E. nilssonii was also negative, but not significantly, and could be explained by the absence of UV emission by the flood lights, that would fail to attract insects.

In this thesis, I showed that wind power and light pollution have negative impacts on the presence of bats in Finland. At a local scale, the existence of wind turbines or artificial lighting will shape the presence of E. nilssonii and Myotis spp. When looking at the cumulative impacts of all wind turbines and artificial lighting in Finland, but also other sources of disturbance such as roads or power lines, we could see a considerable part of the country’s total area being affected, i.e., being avoided by bats. Therefore, I recommend better consideration of bats in wind power projects and in the use of artificial lighting. More globally, I recommend that the actual impacts of wind power on bats – including fatalities - in the country to be assessed, and the use of artificial lighting to be reevaluated, as renewable energy and energy sobriety are both key components for our transition to sustainability.