Living in a seasonal environment poses challenges for small mammals, such as bats, reliant on insects as their primary food source. Bats may adeptly navigate these energetic challenges by reducing their metabolism and body temperature, entering a state of torpor. Particularly during the winter, bats remain torpid for extended periods, but are dependent on sufficient energy reserves to survive until spring. With the onset of autumn and declining temperature, bats face the challenge of building their fat deposits during a time of decreasing food availability. Bats may therefore transition to cooler roosts to initiate torpor, thereby reducing energy expenditure. However, little is still known about torpor use or roost selection by bats in autumn. This study explores the factors influencing roost selection and torpor use and --duration in two bat species during this critical transition period between the breeding and overwintering season. We show that date in autumn is a stronger driver of torpor use than prevailing ambient temperature, and that bats employ specific strategies in which they first increase daytime torpor use before also increasing the use of nighttime torpor during the pre-hibernation fattening period, most likely to facilitate rapid fat accumulation. Notably, bats commenced nighttime torpor use after spending entire days in torpor. These findings underscore the dynamic nature of torpor and the energy-saving strategies employed during the crucial pre-hibernation period, marking the transition from summer to winter.

A document by Kati Suominen. Click on the document to view its contents.

Climatic and anthropogenic impacts have determined the extinction of species in the past and are also the main factors shaping their present distribution ranges. Geographic range size – a biogeographic variable commonly used to assess population abundance, survival, and conservation status – varies with latitude. According to Rapoport’s rule, range size typically increases with latitude in mammals. Bats differ from other groups of mammals with regards to numerous morphological, physiological, and behavioral adaptations of sensory and motor systems. Nevertheless, bats are a suitable group for evaluating the rule because they show a strong latitudinal gradient in species richness. Our aim was to investigate the distribution patterns of European bat fauna based on two biogeographic variables 1) geographical range size and 2) average latitude of their distribution range, and investigate whether species traits characteristic to bats, mobility and hibernation, are associated with variation in range size and latitudinal distribution. We collected geographical data and species trait data on 44 European bat species from the literature. We discovered that range size and average latitude of distribution range follows Rapoport’s rule to a high degree in bats. Additionally, traits related to hibernation and movement behavior, more specifically hibernation breadth (indicating how widely a species utilizes different types of hibernacula) and mobility (based on seasonal movements), are associated with large distribution ranges and could affect northerly ranges in European bats. Range size does not only assist in directing conservation of threatened species, but it also provides insights into fundamental processes such as dispersal and adaptation. Our results emphasize that knowledge on the relationship between traits and species distribution is important for understanding current distribution patterns and could work as background information for predictive models on the effect of future landscape changes.

The distribution ranges and spatio-temporal patterns in the occurrence and activity of boreal bats are yet largely unknown due to their cryptic lifestyle and lack of suitable and efficient study methods. We approached the issue by establishing a permanent passive-acoustic sampling setup spanning the area of Finland to gain an understanding on how latitude affects bat species composition and activity patterns in northern Europe. The recorded bat calls were semi-automatically identified for three target taxa; Myotis spp., Eptesicus nilssonii or Pipistrellus nathusii and the seasonal activity patterns were modeled for each taxa across the seven sampling years (2015–2021). We found an increase in activity since 2015 for E. nilssonii and Myotis spp. For E. nilssonii and Myotis spp. we found significant latitude -dependent seasonal activity patterns, where seasonal variation in patterns appeared stronger in the north. Over the years, activity of P. nathusii increased during activity peak in June and late season but decreased in mid season. We found the passive-acoustic monitoring network to be an effective and cost-efficient method for gathering bat activity data to analyze spatio-temporal patterns. Long-term data on the composition and dynamics of bat communities facilitates better estimates of abundances and population trend directions for conservation purposes and predicting the effects of climate change.