The underground cavities are used by bats from all families and the numbers found in the cavities can be very high. There is a little ecological difference between natural and man-made underground cavities; whether they are frequented by bats is governed by other attributes, such as size, situation and number of entrances, air currents, temperature and relative humidity. The specific microclimate conditions of both types of underground roost sites can play an important role in the life strategies of individual species of bats. There are a lot of caves in the territory of Spišsko-gemerský karst, Slovenský karst and Drienčanský karst (in Slovakia). Revúcka highland (a part of the project area) surrounded by these territories, and Štiavnické mountains are well-known for mineral richness, which inspired the development of mining. Today there are hundreds of sites hidden in the past mines. Abandoned shafts and galleries (the old mines) are mostly used by bats.
The occurrence of Miniopterus schreibersii was recorded in two old mines, one used during the summer season and the other whole year-round. Some 40 years ago the underground roost site degraded and the numerous colony (about thousand individuals) left these spaces. Another record of the species occurrence in the area was not noted for long time. In the years 1999 - 2000 a few individuals were found hibernating. The species might occupy also other underground roosts in this area.
About Rhinolophus euryale colonies in Revúcka highland and Veporské mountains we have also insufficient data. We know two undeground roost sites in the old mines of the species there, with about thousand of individuals in the colony. In Veporské mountains were found only 1-3 individuals. For providing its protection it is necessary to complete the data. To conserve the bat species colonies, it may be necessary to protect the whole network of roosts used throughout the annual cycle.
In the case of Miniopterus schreibersii, there is cca 1/3 of population bound to rely on the old mines as important roosting sites. For Rhinolophus euryale it is cca 1/5 of the population, but this information is only a guess. There is a question - what will happen with demolition of, for example four entrances to the old mine, that serves as a significant roost side for bats? In the old mines are reproduction colonies (Rhinolophus hopposideros), too. In Slovakia they use mostly the attic rooms.
In Revúcka highland we will collaborate with a team of experts from the Institute of Biology and Ecology of Pavol Jozef Šafárik University in Košice. In the area, they will continue with the research of Rhinolophus euryale by the telemetry method. The results of this activities can include the information on new territories of species occupation. From the Slovak Bat Conservation Society, the members of the Society will be helpful with the project activities implementation (field survey).