The fortifications of Langres, in Haute-Marne, and in particular the fort of Cognelot, delight lovers of history, old stones, but also bats. They take up residence there each winter, sure of not being disturbed or driven away, they who are sometimes abused and unloved.
It’s amazing how, when we walk into a dark, narrow, underground place, we tend to imperceptibly lower our voices. Perhaps it is due to the mystery that permeates these places, perhaps it is the fear of upsetting with sounds a silent and still atmosphere, which was there before us and which will be after. In any case, when we descend, on this November morning, the steps which lead us in the underground arteries of the fort du Cognelot, near Chalindrey, in Haute-Marne, each of us murmurs instead of speaking out loud. With me, the keeper of the fort and Guillaume Geneste, project manager for Haute-Marne du conservatory of natural spaces of Champagne-Ardenne. And if we begin this descent into the bowels of the 19th century building, it is because we are looking for bats.
Bats are indeed fond of these fortifications during the winter: they are a suitable habitat for the long hibernation that awaits them. With the thickness of the walls, the temperature remains constantly stable there, the hygrometry also, there are cavities, holes, stones of size which offer a good point of attachment. And above all, there is little passage in winter.
After forming a thick layer of fat in the summer to store up, bats hibernate, putting themselves in a state of deep lethargy. They slow down their metabolism, sometimes up to one or two heartbeats per minute.
If they are awakened, by humans or another animal, they will therefore have to draw heavily on their reserves to fly, rest and then go back to sleep. The risk is that they therefore no longer have enough reserves to end the winter.
Perhaps this is ultimately why we lower our voices in the underground passages, animated by the acute awareness of not disturbing anyone. But as we walked through the darkness by the white glow of our cellphone torches, still no bats. Spiders galore, on walls and ceilings, yes, but nocturnal mammals, no. However, keeping his eyes riveted on the ground, Guillaume Geneste manages to spot their presence: tiny droppings, no bigger than grains of rice, are strewn in various places on the cut stone of the fort. He then raises his flashlight, trying to locate the cavity that could house the object of our research. But nothing. “Maybe it’s still too hot for them to try to hibernate, notes Guillaume Geneste. They are still sometimes seen flying at nightfall. They must still be in the process of perfecting their reserves “.
Create spaces of tranquility
Fort du Cognelot, like all the defensive buildings on the Langres plateau, is home to a large population of bats: the most common are European barbastelles with wide trapezoidal ears and large horseshoe bats, with thick woolly coats. , greyish in color with red undertones on the back. These species, like others, have been endangered since the mid-20th century. “This is mainly due to agricultural intensification and the loss of hunting habitat, explains Aurélie Stoetzel, bats project manager at the conservatory of natural spaces. As they are insectivorous animals, the use of pesticides has greatly reduced their amount of food “. We must therefore compensate, and try to protect at best.
And for this, the conservatory of natural spaces has installed very specific gates at the entrance to certain rooms and tunnels of the fort. Their bars are not vertical but horizontal. Locked, it is behind these doors that we continue our research in the freezing cold of this early winter on the Langrois plateau. “These are bat screens, indicates Guillaume Geneste. The fact that the bars are horizontal allows bats to pass through the grids in mid-flight and therefore not to injure themselves “. The idea is also to reserve some quiet areas for bats by prohibiting access – by the public and other species – to certain areas of the fort.
Because these fortifications attract many curious people, even if their role in the history of France has above all been a deterrent. The large rooms of the Fort du Cognelot, each equipped with its fireplace, the original bread oven and above all the viewpoint over the Langres plateau unleash the imagination and take us on a journey through Haute-Marne which has just emerged from the war of 1870. Today, the fort is the scene of many public and private events and welcomes in particular every year, in October, the witches festival. Preserving areas of tranquility for bats is therefore all the more important since, for them, the sources of disturbance can be numerous.
Bats use the fort especially in winter, so we tell ourselves that it is not necessarily necessary to put it under cover all year round.
The idea is also not to upset the population towards a species with which things do not always go well.
A sometimes difficult cohabitation with the human being
With the destruction of many natural cavities, whether in winter for hibernation or in summer for nesting, bats have tended to find refuge in dwellings and especially in cellars or attics. During hibernation, they are inconspicuous and rarely cause problems for humans. On the other hand, in summer, cohabitation is sometimes more difficult. There is often the fear that bats will proliferate or bring disease. “It’s not always obvious, continues Aurélie Stoetzel. The first thing we do in case of difficult cohabitation is to inform about the cycle of bats, to indicate that there are no particular diseases in the guano (the excrements, note ). It is about informing and reassuring. But when hundreds of bats take up residence next to a room, it can create serious nuisance. We then try to find solutions on a case-by-case basis “.
And sometimes these solutions are difficult to implement, compromise impossible, which increases the pressure on the already endangered species. However, the bat being at the top of the food chain, an entire ecosystem would start to malfunction if there were no more.
It’s a bit of a swallow relay, but at night. They feed on a lot of insects, some of which can cause diseases to trees or plants.
Thus, as a consequence, plant species could end up in turn sick and in danger, and with them, all the fauna and flora associated with them. A “domino” effect that conservationists try to avoid at all costs.
So how do we live with the natural world around us, which sometimes seems hostile, destructive, embarrassing or unapproachable? There aren’t that many solutions, except to learn more, to try to understand the forces that are at play, the beauty, sometimes, of this universe that we cannot really control, and to try, as a human being, every day, to find the right place, our place, within the giant ecosystem in which we live.