Lutra 54(2)_Grol et al_2011

The influence of a Christmas market on hibernating bats in a man-made limestone cave

It is generally acknowledged that human activity in bat hibernacula can disturb hibernating bats and that such activities need to be appropriately managed. The intensive commercial exploitation of limestone excavations during bats’ hibernation period may be in conflict with the micro-environmental conditions that bats need to hibernate. The Fluweelengrot is a limestone quarry in the south of Limburg (the Netherlands). From 1997 onwards it has hosted a Christmas market that attracts over 100,000 people each November and December. The presence of so many visitors and fifty or so illuminated stalls drastically changes the microclimate of part of the cave system for 4-5 weeks. The parts of the cave system occupied by the Christmas market experience a temporary increase in substrate (ceiling) temperatures of 5-8 °C (with a maximum recorded temperature of 20.1 °C). To investigate the possible impact of the Christmas market on hibernating bats in the Fluweelengrot, we examined annual bat census data between the years 1980 and 2010. Data was divided into two periods: before the Christmas market (1980- 1997) and during the Christmas market (1998-2010). From 1980 to 2010 seven species were found hibernating in the Fluweelengrot of which five were present in sufficient numbers to calculate trend indices. These were compared with the average indices in 89 other limestone quarries in south Limburg. For the whiskered/Brandt’s bat (Myotis mystacinus and/or M. brandtii) and Geoffroy’s bat (Myotis emarginatus), the trends in the number of individuals recorded in the Fluweelengrot were significantly less favourable than in other caves in south Limburg. In the absence of changes in other variables this suggests that the Christmas market has a negative impact on these species. Trends in the numbers of recorded pond bats (Myotis dasycneme), Daubenton’s bats (Myotis daubentonii) and Natterer’s bats (Myotis nattereri) did not differ significantly between the Fluweelengrot and other caves in the area. However a comparison of the distribution of these species of bats before (1990-1997) and during the Christmas market showed a significant shift in their distribution to parts further from the site of the Christmas market. The distribution of the whiskered/Brandt’s bat and Geoffroy’s bat was similar before and after the start of the Christmas market. Increasing commercial exploitation in a number of the marl caves in the south of Limburg is a cause of concern. Given the major importance of these caves as hibernacula for bats, including three species protected under Annex II of the EU Habitats Directive, we propose that impact assessment studies should be carried out to investigate the potential effects of human activities on hibernating bats in the caves.