In Europe, many migratory bat species hibernate in tree hollows. Indeed, the fact that tree roosts are quite susceptible to cold temperatures due to their bad insulation forces Northeuropean populations of these species to migrate to central and western Europe, where ambient conditions are more favourable. However, natural tree roosts are scarce in managed forests because of intense silcivulture. In current forest management, trees do not survive until the age when natural hollows and crevices develop. However, these natural hollows are essential as roosts for the populations of bat migrants. We studied the catchment area of artificial bat roosts that are set up in some managed forests to support migratory species (see picture to the right, (c) Tobais Teige).
Some of these artifical roosts harbor large numbers of migratory bats such as noctule bats (Nyctalus noctula). The opened box seen in the left picture ((c) Tobias Teige) shows a cluster of hibernating noctule bats. Artificial hibernacula are sometimes opened during winter for census counts. In our study, we asked what the catchment area of noctule bats is when hibernating in such artificial roosts. We used a stable isotope approach and assigned noctule bats to either sedentary or migratory populations according to the stable hydrogen isotope ratios in fur keratin.
Our study shows for the first time that artificial bats can provide winter shelter for both sedentary and migratory individuals. The artifical roosts from the Berlin area (red triangle) hosted some individuals that came from distant populations as far as Eastern Poland or the Russian enclave of Kaliningrad (green area on map shown in picture to the right). We conclude that artifical hibernacula may be important substitutes for missing tree hollows in intensively managed forests. Artifical bat boxes also provide the possibilty to monitor populations effectively due to the easy access. However, natural roosts are more valuable than artifical roosts for migratory bats because they are usually at higher height above ground and because old trees may provide multiple shelters for bats over time. Bat boxes have to be monitored and maintained regularly to offer a safe hibernacula for bats.
Many bat species are highly threatened, mostly because of habitat destruction. Over the past few years, we have contributed to efforts to protect the Yasuní Biosphere Reserve in Ecuador, one of the most diverse places on earth. Our field work has revealed that the rainforest of the Yasuní Biosphere Reserves likely harbors more than 120 species of bats. This is paralleled by world richness records for amphibians, reptiles and trees. For more information about the biodiversity of Yasuni forest read the pdf for download (Bass et al. 2010 PLoSONE).
A few years ago, the Ecuadorian president Rafael Correa has launched the Yasuní-ITT initiative to protect the forest of Yasuni Biosphere Reserve from oil exploration and drilling. His argument is to raise funds equivalent to the value of the raw oil found below Yasuní Biosphere Reserve so that oil companies can be stopped from further oil exploration. According to most recent press releases, the financial goal has not yet been reached and it is not secured that the 850 million barrels of oil are kept underground in Yasuní National Park’s Ishpingo-Tambococha-Tiputini (ITT) oil fields. Even though the German parliament agreed to financially contribute to the Yasuni-ITT initiative a few years ago, the government has recently refused to add money in support of this innovative approach in preserving our global biodiversity .