Clarification of local causes for lesser horseshoe bat extinction in the Bavarian-Tyrolean Alpine region

Abstract

Once widespread in Europe, the lesser horseshoe bat (Rhinolophus hipposideros) suffered massive population declines in the second half of the 20th century and became extinct in some countries. For future conservation programs, it is important to understand the major causes of extinction. Here, we compared extinct and extant populations in Bavaria (Germany) and Tyrol (Austria) concerning the availability of roof trusses as roosts, as well as concerning heavy metals found in feces (lead, Pb; cadmium, Cd), persistent organic pollutants in the air of the roosts (lindane, dichlorodiphenyldichloroethane, dichlorodiphenyldichloroethylene, dichlorodiphenyltrichloroethane (DDT), and pentachloroanisole), landscape parameters (broadleaf forest, cropland, urbanisation), and light-pollution proxies (minimum and maximum radiance). We did not detect any recolonisation in extinct populations. One third of the buildings concerned are currently inaccessible for R. hipposideros because of closed entrances. Most roosts contained residues of lindane and pentachloroanisole, some of DDT. Pb and Cd concentrations were significantly higher for extinct than for extant colonies; these contaminations may at least partly explain the lack of recolonisation for the two thirds of buildings with open entrances. None of the parameters analyzed correlated significantly with the size of extant colonies. For further insight in the conservation biology of the lesser horseshoe bat in the Greater Alpine Space, assessment of transitional and hibernation roosts, linear habitat elements around roosts, and food availability in the face of insect decline will be necessary.