Hiding behaviour of bats in sandstone mines of North-Eastern Ukraine

Abstract

Winter counting of bats in hibernacula is one of the main methods of estimating their population trends in Europe. However, it is not always possible for humans to identify and count all bats in the maze of big karstic caves or abandoned mines. Previously we notice a significant fluctuation in the numbers of bat species and individuals in sandstone mines located in the Kharkiv region (NE Ukraine), and hypothesized that a significant undercount happened due to the hiding of bats in deep crevices of sandstone. Here using a camera trap placed inside a mine (September 17-19, 2017) we tested this hypothesis. Firstly we identified significant levels of bat flight activity where no roosting bats had been observed through conventional visual survey methods. The proportion of identified bats (Myotis group and Plecotus auritus) on footage was similar to that obtained by usual winter counts. Finally, we filmed and documented cases of crawling bats inside the deep crevices in the wall depths. We ventured to make an extrapolation of bat numbers in a mine on the basis of autumn-spring mist-netting data, and our evidence that they do hide in crevices. Our observations clearly demonstrate that hiding bat behaviour in mines might result in an underestimation of the real number of hibernating bats in sand-stone mines.