Elmeros M, Brinkløv SMM, Fjederholt ET, Fjederholt S, Møller JD, Skalshøi MR, Uebel AS & Baagøe HJ 2022. Udflyvningen af flagermus fra Mønsted og Daugbjerg kalkgruber i foråret 2022. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 30 s. - Videnskabelig rapport nr. 519. http://dce2.au.dk/pub/SR519.pdf
Large numbers of Daubenton’s bats (Myotis daubentonii) and pond bats (Myotis dasycneme) use the limestone mines in Mønsted and Daugbjerg in Denmark for hibernation every winter. The mines are also resting sites for Brandt’s bat (Myotis brandtii), Natterer’s bat (Myotis nattereri) and brown long-eared bats (Plecotus auritus). Favourable conditions in the mines are essential for the conservation status of bat populations. The numbers of hibernating bats in the two mines were assessed in 2003 and 2009. To obtain up-to-date data about the population size of pond bats and Daubenton’s bats in the two hibernacula and of the other species hibernating in the mines, we trapped bats emerging from the mines with harp traps from sunset and five hours into the night 14 nights over nine weeks in the spring of 2022.
At the mines in Mønsted, we caught 907 Daubenton’s bats, 427 pond bats, 20 Natterer’s bats, three Brandt's bats and two brown long-eared bats. The number of hibernating pond bats in Mønsted was estimated to 2100-2500 individuals. The number of hibernating Daubenton’s bats was estimated to 4500-6000 individuals. The estimated number of hibernating pond bats in Mønsted in 2022 was about 50 % lower than in 2009. The present estimate is comparable to the estimated population size of pond bats in the first survey in 2003. The estimated number of hibernating Daubenton’s bats in 2022 was also about 50 % lower than in 2009. The present number of hibernating Daubenton’s bats was also lower than the estimated numbers in the first survey in 2003. An automatic bat counter (a light barrier trap) at the main entrance hole to the mines in Mønsted indicate that the number of hibernating bats has been declining gradually since 2014.
At the mines in Daugbjerg 2576 Daubenton’s bats, 737 pond bats, 28 Brandt's bats and three Natterer’s bats were caught. The number of hibernating pond bats in Daugbjerg was estimated to 3600-4400 individuals and the number of hibernating Daubenton’s bats was 13,000-15,000 individuals. The number of hibernating pond bats in Daugbjerg Kalkgruber in 2022 was slightly higher than in 2009 and 2003, while there has been a slight decline in the number of hibernating Daubenton’s bats since 2009.
The national monitoring programme for bats has not detected any declines in the distribution or occurrence of pond bats or Daubenton’s bats in recent years, and numbers in other large hibernacula are stable or increasing. Hence, the declines in bat populations in Mønsted and of Daubenton’s bats in Daugbjerg must be due to changes in the conditions in these hibernacula.
To restore and ensure the favourable status of the hibernating bat populations and the mines’ status as hibernation sites for bats of national and international importance, there must be a greater focus on ensuring optimal conditions for the bats. E.g. human activities, events and other disturbances should be restricted more during the period when bats are resting in the mines. Furthermore, minimal risk of mortality must be ensured in the catchment area of the pits, e.g. from wind turbines, in order to ensure the ecological functionality of the mines as hibernacula for large numbers of bats.