Counting hibernating bats
This year I will try to write a small story about one of my research related activities every month, and this month I will give a small account of the annual hibernating bat census. Every year many volunteers of the Dutch Mammal Society count bats in different places in the Netherlands. If I have time, I try to help Jasja Dekker with counting the bats around Wageningen. There are several different places we visit around Wageningen, namely, two old stone factories, an old ice cellar and several ruins of buildings.
Bats hibernate in winter, most probably due to the low abundance of insects in winter, on which they feed. Some species hibernate all through winter, but some species become active during warmer periods to feed on winter active insects such as winter moths. During hibernation, the bats lower their heart rate and breathing in order to lower their body temperature and metabolism. In this way they can spend days hanging from their feet. Depending on the species they will hibernate in more enclosed or more open spaces varying in moisture level and temperature. Therefore, a good hibernation site for bats has a variety in hiding places at different temperatures and moisture levels, to facilitate a multitude of species.
Today we started at the old stone factory near Rhenen in an area called ‘De Blauwe Kamer’. This stone factory was build around 1900 to fabricate bricks, but was discontinued in 1975. After that, some of the ruins were left, among which part of the big ring furnace. It is in this ring furnace that we count the bats. Although the space is quite large, it is difficult to look into all the cracks and crevices to find the hibernating bats. The ring furnace has openings to the outside, which means that there is a gradient in temperature and moisture level.
We found several species of bat, namely the brown long-eared bat (Plecotus auritus), Daubenton’s bat (Myotis daubentonii), Natterer’s bat (Myotis nattereri) and whiskered bat (Myotis mystacinus). It can be quiet difficult to find the bats in the first place, as you have to look above your head in the dark while trying not to stumble over the rubble that has accumulated over the decades after the factory stopped working.
Next to the stone factory ‘de Blauwe Kamer’, we visited several other sites among which the most notable are the old ice cellar at ‘Oranje Nassau Oord’ between Wageningen and Renkum and the old stone factory near Renkum. The old ice cellar is a fantastic site to look for bats, as the bats are hanging freely on the walls, which makes identification and finding them a lot easier, but which also makes this object more prone to disturbance, as the bats can’t hide away in between the bricks. Unfortunately, my flashes were not working properly at the moment we visited the cellar, so I don’t have any pictures from this site this year. After the cellar we went to several ruins of old buildings at a place called Buunderkamp. Depending on the weather you can find more or less bats here, as the sites are very exposed. Luckily, today was not that cold, so there were still some bats hanging from the ceilings, such as the whiskered bat at the top of this post.
The old stone factory near Renkum is a similar object to the old stone factory ‘De Blauwe Kamer’, but the type of furnaces were different, which results in a lot of small tunnels instead of one large one. These small tunnels are not very suitable for photography, so no pictures from here either.