Freshwater systems have been profoundly changed by the construction of dams, and the influence of dams on bat activity is poorly understood. In this study, we analyzed the effects of small dams along mountain streams on local bat communities. This work was carried out in five small streams located in the NE of Portugal using bioacoustic surveys during the summer of 2011. The present study confirms that, in the northeast areas of Portugal, the majority of bat species use artificial bodies of water for either drinking or foraging, but species differed in terms of their activity levels over the reservoirs when compared with intact stream habitats. As predicted, small dams in the study area were important centers of overall bat activity relative to other sampling areas. At the same time, feeding activity was also higher in the flooded areas. We also found that Pipistrellus pipistrellus, Myotis daubentonii, Pipistrellus kuhlii, Pipistrellus pygmaeus/Miniopterus schreibersii, Tadarida teniotis and Nyctalus leisleri/Eptesicus serotinus benefited from the presence of dam reservoirs. Hypsugo savii activity was also mostly recorded at reservoir points. However, the highest number of endangered and rare species was recorded at an intact stream habitat. This result emphasizes the relevance of riparian habitats for bats, especially for the most endangered species. The relationship between dam availability, riparian quality and bat diversity suggested that the changes in the streams promoted by damming could affect both bat species richness and activity levels, leading to changes in the overall composition of the bat community. In conclusion, this study found that small reservoirs have a significant influence on bat activity. However, dams appear to primarily benefit the most common species, while the endangered species were associated with riparian habitats. Therefore, for conservation proposes of the local bat community, riparian areas appear to be more important than reservoirs. Thus, this study provides a better understanding of the impact of small dams on bats contributing to the future management and conservation of bat species.
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