Long-term re-use of tree roosts by European forest bats

Abstract

The few studies that have assessed the long-term patterns of re-use of tree cavities by bats all concern North American bats. We studied long-term re-use of tree cavities by two species of European bat, Daubenton's bats ( Myotis daubentonii) and noctules ( Nyctalus noctula). Cavities were inspected during consecutive years via direct capture of bats (more than 340 positive capture events, ca 2950 captured bats), observations of emerging bats, or by listening for bats during the early evening when bats emit typical vocalization (over 160 positive checks, over 450 observed bats). Between 1968 and 2007, we found 80 tree cavities used by bats (mostly excavated by woodpeckers) in the Czech Republic. Although more than half of the cavities were occupied for ≤4 summers, 28 cavities (35%) were re-used for 5–10 years. The longest period a cavity was used was 11 and 16 years for Daubenton's and noctule bats, respectively. Sixteen tree cavities (20%) were occupied solely by Daubenton's bats and 33 cavities (41%) were occupied only by noctules. The other 31 cavities (39%) were used by both species, either at separate times or simultaneously. Our data suggest that the larger volume of a cavity, the longer duration of re-use and the greater the probability of being occupied by both species. Continuous excavation of cavities by woodpeckers prevented the overgrowth of old cavities by calluses, which keep cavities accessible to bats. We suggest that woodpeckers may be the most important providers of suitable roosts for forest bats in Central Europe. Roosts were found in both economically valuable trees ( Quercus robur and Tilia cordata) and less valuable tree species ( Salix fragilis and Alnus glutinuosa). Economically valuable trees in our study area were long-lived and likely provide roosting habitat for longer periods but matured at a greater age. However, less economically valuable trees reached maturity and started to decay in a relatively short time, which may provide suitable cavities at a younger age. Maintaining both types of trees within forests may help provide suitable roosting oportunities for tree-dwelling bats in the Czech Republic.