Low foraging rates drive large insectivorous bats away from urban areas.

Urbanization has significant impacts on wildlife and ecosystems and acts as an environmental filter excluding certain species from local ecological communities. Specifically, it may be challenging for some animals to find enough food in urban environments to achieve a positive energy balance. Because urban environments favor small-sized bats with low energy requirements, we hypothesized that common noctules (Nyctalus noctula) acquire food at a slower rate and rely less on conspecifics to find prey in urban than in rural environments due to a low food abundance and predictable distribution of insects in urban environments. To address this, we estimated prey sizes and measured prey capture rates, foraging efforts, and the presence of conspecifics during hunting of 22 common noctule bats equipped with sensor loggers in an urban and rural environment. Even though common noctule bats hunted similar-sized prey in both environments, urban bats captured prey at a lower rate (mean: 2.4 vs. 6.3 prey attacks/min), and a lower total amount of prey (mean: 179 vs. 377 prey attacks/foraging bout) than conspecifics from rural environments. Consequently, the energy expended to capture prey was higher for common noctules in urban than in rural environments. In line with our prediction, urban bats relied less on group hunting, likely because group hunting was unnecessary in an environment where the spatial distribution of prey insects is predictable, for example, in parks or around floodlights. While acknowledging the limitations of a small sample size and low number of spatial replicates, our study suggests that scarce food resources may make urban habitats unfavorable for large bat species with higher energy requirements compared to smaller bat species. In conclusion, a lower food intake may displace larger species from urban areas making habitats with high insect biomass production key for protecting large bat species in urban environments.

Long-term field study reveals that warmer summers lead to larger and longer-lived females only in northern populations of Natterer's bats.

Animals often respond to climate change with changes in morphology, e.g., shrinking body size with increasing temperatures, as expected by Bergmann's rule. Because small body size can have fitness costs for individuals, this trend could threaten populations. Recent studies, however, show that morphological responses to climate change and the resulting fitness consequences cannot be generalized even among related species. In this long-term study, we investigate the interaction between ambient temperature, body size and survival probability in a large number of individually marked wild adult female Natterer's bats (Myotis nattereri). We compare populations from two geographical regions in Germany with a different climate. In a sliding window analysis, we found larger body sizes in adult females that were raised in warmer summers only in the northern population, but not in the southern population that experienced an overall warmer climate. With a capture-mark-recapture approach, we showed that larger individuals had higher survival rates, demonstrating that weather conditions in early life could have long-lasting fitness effects. The different responses in body size to warmer temperatures in the two regions highlight that fitness-relevant morphological responses to climate change have to be viewed on a regional scale and may affect local populations differently.

Precipitation during two weeks in spring influences reproductive success of first-year females in the long-lived Natterer's bat.

Bats are characterized by low reproductive rates in contrast with most of other small mammals. This makes their populations vulnerable when inclement environmental conditions such as cold and rainy weather impair the reproductive success of females. The fine-scale effect of weather on bats, however, remains largely unknown. Using a sliding window analysis approach on an 18-year individualized dataset on six Natterer's bat (Myotis nattereri) colonies, we investigated the effect of fine-scale weather conditions on age-specific reproductive success. We found that increased precipitation during a short time window in spring strongly reduced the probability of successful reproduction of first-year (FY) females. Our data suggest that this time window is concomitant with implantation or early pregnancy, before substantial investment into embryo development. In addition, larger FY had higher reproductive success, suggesting that reproduction may be condition dependent in young females. Reproductive success of older females was not affected by either weather or individual parameters. Our results show that changes in precipitation pattern may compromise the reproductive success of FY females. Further studies are needed to better understand the impact of weather conditions on reproductive success in long-lived bats under climate change scenarios.