Multiple climatic and landscape drivers have been linked to variations in bat body size and wing functional traits. Most previous studies used proxies rather than actual climate and land-use data, and their interactions are rarely explored. We investigate whether higher summer average temperatures are driving decreasing bat body size as predicted by Bergmann's rule or increasing appendage size as per Allen's rule. We also explore whether temperature or resource availability (namely forest cover) is responsible for changes in wing functional traits. Using land-use data from historical maps and national statistics combined with climatic data, we assessed the effect of temperature and resource availability on bat morphology. We used 464 museum specimens of three bat species (Eptesicus nilssonii, Pipistrellus pygmaeus, and Plecotus auritus), spanning 180 years, across a 1200 km latitudinal gradient. We found no evidence of higher summer average temperatures driving decreases in body size in bats. Jaw sizes of P. auritus and P. pygmaeus changed over time but in different directions. The geographical variation of forest cover was also related to differences in wing functional traits in two species. Crucially, there was a significant antagonistic interactive effect of forest and temperature on tip index in P. pygmaeus whereby above 14.5°C the relationship between forest and tip index actually reversed. This could indicate that higher temperatures promote more pointed wings, which may provide energetic benefits. Our results show the importance of including both climatic and land-use variables when assessing trends in bat morphology and exploring interactions. Encouragingly, all three species have shown an ability to adapt their body size and functional traits to different conditions, and it could demonstrate their potential to overcome future negative impacts of climate and land-use change. 

Habitat fragmentation increases the proportion of forest borders in the landscape and many forest borders lose their structural complexity due to modern forestry practices.  However, remnants of structurally complex deciduous forests can remain as ecotones between plantations and agricultural fields. In this study we used terrestrial laser scanning to measure structural complexity of different forest borders, measured microclimate and surveyed bats and macro-moths to understand how these taxa are affected. Our aim is to disentangle the main drivers, direct or indirect, that influence bat and moth assemblages. We studied 79 forest borders, and surrounding landscapes and compared them with adjacent agricultural fields and coniferous plantations. Overall, we found less bat activity and lower macro-moth diversity in simple compared to complex borders. Using structural equation modelling, we show the contrasting responses of forest-specialist bats and moths to structural complexity; with bats responding positively and moths negatively. We found similar divergent results in relation to understorey openness; with increasing forest-specialist bat activity but a lower diversity of forest-specialist moths in more open borders. Understorey vegetation also appears to regulate microclimate with more open borders being warmer and less humid. This has a potential knock-on effect for bats as they favoured borders that were warmer and more humid. Surrounding land-cover was more important than structural complexity for generalist species; with increasing generalist bat activity due to a higher proportion of local deciduous forest cover and increasing generalist moth diversity in landscapes with more forest borders. Overall, these complex relationships between forest structure, microclimate and landscape factors, coupled with divergent responses of both taxa highlight their diverse ecological needs. Therefore, we highlight the importance of managing forest borders to retain complexity and connectivity within multifunctional landscapes.

Sympatric bat species can co-exist and avoid interspecific competition via niche differentiation. Detecting dietary differences can be achieved by comparing dietary niches of sympatric and allopatric populations.  If dietary overlap is higher in sympatry versus allopatry, co-occurrence may be altering the dietary niche of the species. Our study region offers an excellent opportunity to investigate this because two species, Eptesicus nilssonii and Pipistrellus pygmaeus, occur sympatrically across southern Sweden and E. nilssonii occurs allopatrically in the north. We analysed droppings from 19 roosts: six P. pygmaeus, seven E. nilssonii located in the known distribution of P. pygmaeus (sympatric) and six roosts located outside the known range of P. pygmaeus (allopatric). We used DNA metabarcoding to assess dietary overlap and dietary niche breadth in both species. We found a high dietary overlap between E. nilssonii and P. pygmaeus at all taxonomic levels of prey. The dominate prey orders in the three bat populations were Ephemeroptera (Mayflies) and one Diptera species (Cranefly); five species from these orders accounted for >70% of all reads. When using quantitative relative read abundance data at the species level the interspecific overlap was higher than the intraspecific overlap. We find a consistent but not significant pattern that E. nilssonii populations co-occurring with P. pygmaeus have the narrowest dietary niche breadth. This could indicate that the co-occurrence with P. pygmaeus is having an impact on prey selection for sympatric E. nilssonii populations.  What is most interesting is that both bat species’ diets are heavily dominated by only five species. These are all currently common insect species and most likely indicates opportunistic foraging on abundant insect populations. However, if these currently abundant insect species decline under climate and land-use change this could be detrimental for bats in the future.

Many species of European bat almost exclusively roost in buildings, show high roost fidelity and likely select roosts based on the configuration of the surrounding landscape. However, our knowledge of roost selection in bat populations at northern latitudes is limited. To understand how landscape context across different spatial scales drives roost selection of three bats species (Eptesicus nilssonii, Pipistrellus pygmaeus and Plecotus auritus) in the northern part of their distribution. Citizen science was used to identify 92 roosts of three bat species in buildings across their known range in Sweden. Species were identified by a combination of molecular methods, photographic identification and expert knowledge. We used land-cover maps to compare the amount of different land-cover types at multiple scales with random points in the landscape using conditional logistic regression. The amount of deciduous forest was the most important land-cover type associated with roost location for all three bat species. The landscape scale varied depending on different foraging guilds. For a long-range echolocator (Eptesicus nilssonii) deciduous forest was associated with roost location up to 500 m from the roost, whereas for short- (Plecotus auritus) and mid-range echolocators (Pipistrellus pygmaeus) deciduous forest up to 2000 m was a strong predictor of roost location. The location of P. auritus roosts was also positively associated with the amount of open habitat up to 1000 m from the roost and mixed forest up to 250 m had a negative effect. This study demonstrates the value of utilizing a citizen science approach to understand roost selection over a large geographical range. Our results highlight the importance of deciduous forest for roost selection in three bat species at the northern extent of their range. Maintaining and increasing the amount of deciduous forest close to maternity roosts and potential but unoccupied roosts will benefit these bat species.