Bats now have a “new” threat, the gray rat (Rattus norvegicus). A study led by Leibniz Institute for Evolution and Biodiversity Science (Germany) has in fact demonstrated through irrefutable observations that these rodents, one of the most widespread and harmful invasive species in the world, can attack birds, even in the two most critical phases, during swarming and hibernation, when they are most vulnerable.
Our new study provides the first systematic evidence of gray rats (Rattus norvegicus) preying on bats at two landmass hibernation sites,” writes first author Mirjam Knörnschild in a Facebook post. “Using infrared and thermal imaging, we documented rats ambushing M. daubentonii and M. nattereri as they landed, and also intercepting bats near the entrance to the hibernaculum in flight. At one site alone, we found more than 50 bat carcasses hidden by rats
And no, it wasn’t a casual observation, but a repeated and targeted one.
Threats to bats
Unfortunately, many bat species have been in decline for some time due to various factors. As our Ministry of the Environment and Energy Security explains, in fact, the alterations to the natural environment caused by us have caused and are causing a drastic reduction in populations.
Among these, certainly the use of pesticides in agriculture which poisons their food (insects), the increasingly intensive exploitation of the woods to obtain wood and the tourist exploitation of the caves, are among the heaviest alterations, which are causing the loss of a good part of the refuges.
But intensive agriculture also contributes to this disaster: in fact, in addition to causing pollution of internal waters with consequent local extinction of many insect species, it drastically modifies the landscape with the loss of riparian vegetation and hedges of vital importance for them.
A 2024 study then demonstrated another terrible risk for bats, with repercussions also on human health: in particular, a devastating fungal disease has affected bats in the United States, called white nose syndrome (WNS), caused by the fungus Pseudogymnoascus destructansdramatically reduced insectivorous bat populations from 2006 to 2017.
And unfortunately it has had unexpected consequences on human health, in particular an increase in infant mortality. In fact, these animals play a crucial role in the natural control of parasites and their decline has forced farmers to resort to pesticides to protect crops, resulting in an 8% increase in infant mortality in the most affected areas.
Approximately 1,334 deaths have been attributed to this chain of events, demonstrating how biodiversity loss can negatively affect public health. The economic impact of WNS has been significant, with estimates indicating agricultural losses totaling approximately $26.9 billion in the affected counties.
Why gray rat predation worries scientists (and what can be done)
Brown rats are among the most widespread and harmful invasive predators in the world. On the islands, they have pushed birds, reptiles and small mammals to the brink of extinction. Our results show that they also pose a threat to bats in densely populated urban environments on the continent
These observations, which do not seem random, represent an alarm, for which the researchers ask:
Urban mass hibernacula are vital strongholds for bats in temperate regions. Protection of these sites must now include actions against non-native rodents (…) Without such measures, bat conservation efforts may suffer, even in otherwise protected sites
The work was published on Global Ecology and Conservation.
Sources: Mirjam Knörnschild/Facebook / Global Ecology and Conservation
