Influence of ambient temperature on the phenology of the greater mouse-eared bat (Myotis myotis).

In order to assess the consequences of climate change and evaluate its impacts on wildlife, it is essential to do so on a species-specific level. It is assumed that changes in the ambient temperature influence energy consumption as well as food availability and thus foraging behavior, reproduction, survival, and therefore population dynamics in bats. Based on this assumption, the present study aims to gain insights into the roosting and breeding behavior of the greater mouse-eared bat (Myotis myotis) in relation to changes of the ambient temperature. For this purpose, we investigated the effect of ambient temperature on the phenology of the greater mouse-eared bat by using activity data of the bats collected using light barriers at the maternity roosts. The light barrier used in this study is a system that detects the interruption of two light beams, for example, by a flying bat, and displays it as an electrical signal. The investigations have shown that the higher the winter temperatures, the earlier the greater mouse-eared bats returned to the roosts to form the maternity colony; however, this was only true for ambient temperatures below 0.5°C,birth season started earlier at higher spring temperatures,the dissolution of maternity roosts occurred earlier with earlier birth season and at higher ambient temperatures during lactation. The results revealed that ambient temperature has an influence on the phenology of the greater mouse-eared bat. Depending on the respective life history stage, an increase in ambient temperature can have a positive or negative effect on the fitness of the animals. In recent years, mild winters have been recorded more frequently, which can have an influence on the behavior of bats. Warm winters within certain limits seem to lead to an earlier formation of the maternity colony, which can be positive or negative for the bats depending on persistent weather conditions and thus insect availability. In the course of climate change, we can also expect earlier spring events and an increase in spring temperature, as well as hot spells in summer. These warm springs and summers seem to lead to an earlier beginning of births, a faster development of the juveniles and an earlier dissolution of the maternity roost. An advance of reproductive activities can be assumed to increase the chance to survive the following winter in both mothers and their young, as they have more time to build up sufficient energy reserves for hibernation before winter starts. Due to the climatic changes, phenological changes of the bats be expected. This study highlights that in order to understand the impact of climate change on biodiversity, it is necessary to investigate in detail effects on a species-specific level and also to consider direct and indirect effects of ambient temperature on different life history stages.

How weather triggers the emergence of bats from their subterranean hibernacula.

Hibernation is one of the most important behaviours of bats of the temperate zone. During winter, when little food or liquid water is available, hibernation in torpor lowers metabolic costs. However, the timing of emergence from hibernation is crucial for the resumption of the reproductive process in spring. Here, we investigate the spring emergence of six bat species or pairs of bat species of the genera Myotis and Plecotus at five hibernation sites in Central Europe over 5 years. Using generalized additive Poisson models (GAPMs), we analyze the influence of weather conditions (air and soil temperature, atmospheric pressure, atmospheric pressure trend, rain, wind, and cloud cover) as predictors of bat activity and separate these extrinsic triggers from residual motivation to emerge from hibernation (extrinsic factors not studied; intrinsic motivation). Although bats in a subterranean hibernaculum are more or less cut off from the outside world, all species showed weather dependence, albeit to varying degrees, with air temperature outside the hibernaculum having a significant positive effect in all species. The residual, potentially intrinsic motivation of species to emerge from their hibernacula corresponds to their general ecological adaptation, such as trophic specialization and roosting preferences. It allows the definition of three functional groups (high, medium and low residual activity groups) according to the degree of weather dependence of spring activity. A better knowledge of the interplay of extrinsic triggers and residual motivation (e.g., internal zeitgebers) for spring emergence will help to understand the flexibility of a species to adapt to a changing world.

The soundscape of swarming: Proof of concept for a noninvasive acoustic species identification of swarming Myotis bats.

Bats emit echolocation calls to orientate in their predominantly dark environment. Recording of species-specific calls can facilitate species identification, especially when mist netting is not feasible. However, some taxa, such as Myotis bats can be hard to distinguish acoustically. In crowded situations where calls of many individuals overlap, the subtle differences between species are additionally attenuated. Here, we sought to noninvasively study the phenology of Myotis bats during autumn swarming at a prominent hibernaculum. To do so, we recorded sequences of overlapping echolocation calls (N = 564) during nights of high swarming activity and extracted spectral parameters (peak frequency, start frequency, spectral centroid) and linear frequency cepstral coefficients (LFCCs), which additionally encompass the timbre (vocal "color") of calls. We used this parameter combination in a stepwise discriminant function analysis (DFA) to classify the call sequences to species level. A set of previously identified call sequences of single flying Myotis daubentonii and Myotis nattereri, the most common species at our study site, functioned as a training set for the DFA. 90.2% of the call sequences could be assigned to either M. daubentonii or M. nattereri, indicating the predominantly swarming species at the time of recording. We verified our results by correctly classifying the second set of previously identified call sequences with an accuracy of 100%. In addition, our acoustic species classification corresponds well to the existing knowledge on swarming phenology at the hibernaculum. Moreover, we successfully classified call sequences from a different hibernaculum to species level and verified our classification results by capturing swarming bats while we recorded them. Our findings provide a proof of concept for a new noninvasive acoustic monitoring technique that analyses "swarming soundscapes" by combining classical acoustic parameters and LFCCs, instead of analyzing single calls. Our approach for species identification is especially beneficial in situations with multiple calling individuals, such as autumn swarming.