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The days are getting shorter, the temperatures are dropping. Numerous animals are migrating south, others are seeking their hibernacula - including bats. However, while hibernation is becoming shorter and shorter for many animals due to climate change, researchers at the University of Greifswald have now published findings that Daubenton’s bats (Myotis daubentonii) are now entering hibernation a whole month earlier than they did 13 years ago.

The remarkable thing is that the bats do not increase their fat reserves despite the change. This means that they have to survive an additional month on the same energy reserves. This poses a potential challenge to their survival as climate change progresses.

These surprising results come from a long-term study in which over 4,000 bats belonging to two species in the region around Münster (Nordrhein-Westfalen) were individually tagged with small RFID transponders and monitored at their hibernaculum with automatic recording devices. The recorded data provide information on when each of the tagged animals arrived at the hibernaculum and when it left again in spring.

Two species - two contrasting reactions to climate change
In addition to the Daubenton’s bats, Natterer’s bats (Myotis nattereri) also hibernate in the 60-metre well shaft. However, the two species show completely different reactions to climate change: the Natterer’s bat reacts to the increasingly warmer and shorter winters by shortening its hibernation periods, similar to other hibernating mammals.

So why does the Daubenton’s bat sleep longer in contrast to the general trend of shorter hibernation periods? Dr. Gabriella Krivek from the University of Greifswald suspects: “Of course, other species besides bats are also reacting to climate change. The Daubenton’s bat's main prey are insects that spend their larval stage in the water and hatch in large numbers at the same time - providing ideal hunting conditions. These events are linked temporally to the seasonal warming of water bodies and are thus now also occurring earlier in the year as temperatures rise due to climate change. As a result, it might be hard for Daubenton’s bats to find food from earlier on in autumn and therefore they are entering hibernation earlier.”

Hibernation strategies can have an impact on long-term survival
“The phenology - in the case of bats, the start and end of the annual hibernation period - adapts surprisingly quickly to climate change in the bat species studied. As temperatures are continuing to rise, the contrasting hibernation strategies could have a significant impact on the long-term survival of the species we studied,” says Frauke Meier, doctoral candidate at the University of Greifswald and lead author of the study together with Dr. Gabriella Krivek. She continues: “To make matters worse, it is young animals in particular, which generally have a higher mortality rate in winter than adults, that seem to be less able to adapt to the new conditions. In their first year, they go to their hibernacula later than the adults. In the absence of food, this can contribute to an even lower chance of survival.” However, further research is needed to clarify the exact connections between the temporal shifts in hibernation and the fitness of each individual animal, or the development of the entire population.

Impact on nature conservation
“The results are of particular importance for nature conservation,” says Dr. Gabriella Krivek. In Germany, for example, bats are protected by laws that restrict human access to hibernacula between 1 October and 31 March. However, the new results show that this period no longer fully covers the hibernation phase of Daubenton’s bats and it should therefore be adjusted. At the same time, the extended activity period of the Natterer’s bat, a species that rests in trees and hunts in forests outside of the hibernation periods, should be taken into account in autumn and spring, especially by those in the forestry industry.

Further information
The study was performed by Gabriella Krivek & Frauke Meier, Gerald Kerth & Jaap van Schaik from the University of Greifswald and Leo Grosche from the Niedersächsischer Landesbetrieb für Wasserwirtschaft, Küsten- und Naturschutz, Hanover, and published in Global Change Biology.
One Species Hibernates Shorter, the Other Longer: Rapid but Opposing Responses to Warming Climate in Two Sympatric Bat Species Gabriella Krivek, Frauke Meier, Leo Grosche, Gerald Kerth, Jaap van Schaik First published: 2 October 2025 / https://doi.org/10.1111/gcb.70531
https://zoologie.uni-greifswald.de/en

Contact at the University of Greifswald
Dr. Gabi Krivek
Zoological Institute and Museum
Loitzer Straße 26, 17489 Greifswald, Germany
Tel.: +49 3834 420 4358
gabriella.krivek@uni-greifswald.de