Global change is altering the hibernation physiology and behavior of bats, according to a study carried out over twenty years and led by the University of Barcelona. With increasingly milder winters, bats accumulate fewer fat reserves in autumn, reduce their hibernation period and leave their winter roost earlier. These changes could alter the migratory pattern of bats and the phenology of their seasonal movements. The study has been carried out in the largest colony of bats known in Catalonia, which is located in the Sant Llorenç del Munt i l’Obac Natural Park. It is made up of about 17,000 specimens of the cave bat (Miniopterus schreibersii), a migratory species that gathers in large colonies, especially in winter.
The work, published in the journal Scientific Reports, is signed by the experts Marc López-Roig and Jordi Serra-Cobo, from the Faculty of Biology and the Biodiversity Research Institute (IRBio) of the UB, and Eduard Piera, from the Generalitat of Catalonia.
Adapt to increasingly milder and shorter winters
Everything indicates that bats are adapting to a warmer climate, with milder and shorter winters. In temperate latitudes, bats accumulate large amounts of reserves in the form of fat during the fall to cope with the hibernation period, which usually runs from mid-December to the end of February.
«The accumulated fat reserves must be important enough to be able to survive the entire hibernation period without eating. However, as a result of relatively shorter winters and higher temperatures than decades ago, bats do not gain as much weight in autumn as they used to do years ago, because they do not need as many reserves to get through the winter,” explains the professor. Jordi Serra-Cobo, from the Department of Evolutionary Biology, Ecology and Environmental Sciences of the UB.
These body changes are evident in both sexes, although females have a lower body condition than males, both at the beginning and end of hibernation and during the active period (March). «This fact could have effects on the reproduction of the species, since a poor body condition of the females could negatively affect pregnancy and lactation. However, in our latitudes, females have enough time between the end of hibernation and the start of reproduction to regain weight and have an optimal body condition for reproduction,” details Marc López-Roig.
Hibernate in increasingly warmer caves
Global change also affects the arrangement of bats in their winter roost. “Usually, the bat colony was located in the final chamber of the cave – the hibernation chamber – located 65 meters deep, with a relatively constant temperature – around 7ºC – during the months of December and January.”
«The work confirms how the hibernation chamber takes longer to cool down compared to previous years. This delay affects the hibernation of bats because they do not find the optimal temperatures to be able to hibernate until the end of January or beginning of February. Thus, bats seek the coldest spaces close to the entrance to the winter roost and are exposed to a greater risk of predation (for example, by genets),” highlights López, Roig.
Migratory routes in the process of change
With an increasingly shorter hibernation, bats begin activity earlier compared to other years, migratory movements advance and arrive at spring roosts earlier. If there are late cold spells when spring arrives, bats may not be prepared to deal with periods of low temperatures. These changes could also have implications for the conservation and management of the species. «The migratory routes and seasonal movements of cave bats are very well documented in Catalonia. In recent years, new locations have been identified on these routes, but some of the important known refuges have also been lost or altered,” says Serra-Cobo.
For example, it is known that, in a hibernation shelter in the Tarragona region, the increase in interior temperature prevented the cave bat from hibernating. The loss of this refuge as a hibernation site modified the migration of this species and altered some of the migratory routes in southern Catalonia.
How will it affect pest control in the natural environment?
Global change could also alter the ecological function of bats, which are decisive for the control of insect pests and vectors of infectious diseases in the natural environment. How could all these changes affect the biological cycle of their prey?
«Everything indicates that the phenology of certain insect species has also advanced with climate warming. “This would coincide with the end of hibernation in bats, so the impact of shortening hibernation would be less if these two events were synchronized.”
All bat species can be affected by climate change, but the magnitude of the impact can be very different between groups of bats with different biogeographic patterns. “Mediterranean species, adapted to climatic conditions with higher temperatures, could be less vulnerable to climate warming than species from more Nordic or boreal latitudes,” the team concludes.
