Ponds in acidic mountains are more important for bats in providing drinking water than insect prey

Ponds, streams and other water bodies are known to attract high numbers of bats of various species and all foraging guilds. The attractiveness of these riparian habitats for bats lies in their providing the required large amounts of drinking water for successful reproduction and a potentially high supply of both aquatic and terrestrial prey insects compared to the surrounding habitats, and in the lower ultrasound interference over water than in forest habitats, important for foraging of open‐habitat bat species. The actual abundance of prey depends strongly on the productivity of the aquatic ecosystem, and therefore eutrophic riparian habitats are highly attractive to bats, but little is known about the reasons for the attractiveness of oligotrophic habitats. Here, we compared the bat activity, bat foraging activity and insect abundance around oligotrophic and less‐prey‐rich ponds in acidic near‐natural environments to two structurally similar, simple habitats, that is, clear‐cuts and meadows, by simultaneously recording echolocation calls and light trapping of insects. Our generalized linear mixed models showed no differences in prey abundance but higher bat activity at ponds than at meadows and clear‐cuts, and all locally indigenous bat species visited the ponds. The foraging activity of bats evaluated as the proportion of feeding buzzes to commuting passes positively correlated with prey abundance at meadows and clear‐cuts but not at water bodies. We therefore conclude that ponds in acidic mountain areas are more important to bats as a source of drinking water than as a source of prey. Our results indicate that bat monitoring in such a landscape by bat‐call recording and probably by mist netting is highly promising around water bodies, and that bat conservation strategies should maintain a continuous network of water sources as an important habitat feature.