Wind energy production in forests conflicts with tree-roosting bats

Oak woodlands and urban green spaces: Landscape management for a forest-affiliated bat, the Leisler's bat (Nyctalus leisleri)

European forests have been intensively managed for a long time, threatening many forest-bound wildlife species, such as the Leisler's bat (Nyctalus leisleri). This rare species has been observed in deciduous forests, but we lack conclusive landscape-scale management recommendations for continental Europe. We therefore tracked the movements of 32 adult Leisler's bats from three local colonies with miniaturised Global Positioning System (GPS) loggers in two consecutive summers in a landscape that consists of a mosaic of woodland, forest plantations and farmland in Germany and in which wind energy production is expanding. We then analysed the habitat preferences of bats and how they interact with local wind turbines using an integrated step selection function in which we differentiated between roosting, commuting and foraging. Most spatial positions of Leisler's bats overlapped with the rotor-swept zone of local wind turbines, indicating that this species may be vulnerable at turbines. Further, Leisler's bats preferred oak woodlands and urban spaces, but avoided coniferous forests. For roosting, Leisler's bats preferred urban areas, probably because old trees were available along lanes or in churchyards. We call for careful landscape-scale management of oak woodlands and urban green spaces, particularly the preservation of old trees to support populations of Leisler's bats and other forest-affiliated bats. Furthermore, wind turbines should be sited well away from Leisler's bat colonies, as the flight altitude of Leisler's bats overlaps with the operating range of wind turbines, putting them at risk of being attracted to wind turbines during foraging trips.

Large and high-altitude foraging ranges suggests importance of Wrinkle-lipped free-tailed bats (Mops plicatus) for consuming dispersing pest insects

The tropical bat Mops plicatus feeds primarily on planthoppers, a major pest for rice farmers in Southeast Asia. This bat may help limit the spread of planthoppers by feeding on wind-dispersed individuals at high altitudes, providing an important ecosystem service. However, its foraging behavior during peak planthopper activity remains poorly understood. Therefore, we examined the three-dimensional foraging behavior of M. plicatus using miniaturized Global Positioning System loggers during peak emergence of planthoppers. We predicted that bats would spend most foraging time at high altitudes (i.e., > 110 m above ground), and use relatively large foraging ranges. Furthermore, we predicted that low-altitude flights would occur in paddy fields and high-altitude flights above forested sites on mountain ridges. Six of the 11 tracked bats used large foraging areas, covering between 40 to 1,740 km2 during a single night. The median distance bats traveled per foraging trip was 60 km (range 27-217 km), with a median maximum distance from the cave roost of 26 km (range 13-95 km). Bats flew at a median altitude of 146 m above ground, yet occasionally reached more than 1,600 m above ground. Our results confirmed that M. plicatus foraged primarily at high altitudes for about 57% of their time. They preferred paddy fields and forests while avoiding water bodies. With its high-altitude flights and preference for planthoppers as prey, M. plicatus could help limit the spread of a major rice pest in Southeast Asia. Protecting this bat species could help support rice harvests throughout the region.

The trans-european catchment area of common noctule bats killed by wind turbines in France

Wind turbines used to combat climate change pose a green-green dilemma when endangered and protected wildlife species are killed by collisions with rotating blades. Here, we investigated the geographic origin of bats killed by wind turbines along an east-west transect in France to determine the spatial extent of this conflict in Western Europe. We analysed stable hydrogen isotopes in the fur keratin of 60 common noctule bats (Nyctalus noctula) killed by wind turbines during summer migration in four regions of France to predict their geographic origin using models based on precipitation isoscapes. We first separated migratory from regional individuals based on fur isotope ratios of local bats. Across all regions, 71.7% of common noctules killed by turbines were of regional and 28.3% of distant origin, the latter being predominantly females from northeastern Europe. We observed a higher proportion of migratory individuals from western sites compared to eastern sites. Our study suggests that wind-turbine-related losses of common noctule bats may impact distant breeding populations across whole Europe, confirming that migratory bats are highly vulnerable to wind turbines and that effective conservation measures, such as temporary curtailment of turbine operation, should be mandatory to protect them from colliding with the rotating blades of wind turbines.

Effects of tag mass on the physiology and behaviour of common noctule bats

BACKGROUND

External tags, such as transmitters and loggers, are often used to study bat movements. However, physiological and behavioural effects on bats carrying tags have rarely been investigated, and recommendations on the maximum acceptable tag mass are rather based on rules of thumb than on rigorous scientific assessment.

METHODS

We conducted a comprehensive three-step assessment of the potential physiological and behavioural effects of tagging bats, using common noctules Nyctalus noctula as a model. First, we examined seasonal changes in body mass. Second, we predicted and then measured potential changes in flight metabolic rate in a wind tunnel. Third, we conducted a meta-analysis of published data to assess effects of different tag masses on the weight and behaviour of bats.

RESULTS

Individual body mass of common noctules varied seasonally by 7.0 ± 2.6 g (range: 0.5-11.5 g). Aerodynamic theory predicted a 26% increase in flight metabolic rate for a common noctule equipped with a 3.8 g tag, equating to 14% of body mass. In a wind tunnel experiment, we could not confirm the predicted increase for tagged bats. Our meta-analysis revealed a weak correlation between tag mass and emergence time and flight duration in wild bats. Interestingly, relative tag mass (3-19% of bat body mass) was not related to body mass loss, but bats lost more body mass the longer tags were attached. Notably, relatively heavy bats lost more mass than conspecifics with a more average body mass index.

CONCLUSION

Because heavy tags (> 3 g) were generally used for shorter periods of time than lighter tags (~ 1 g), the long-term effects of heavy tags on bats cannot be assessed at this time. Furthermore, the effects of disturbance and resource distribution in the landscape cannot be separated from those of tagging. We recommend that tags weighing 5-10% of a bat's mass should only be applied for a few days. For longer studies, tags weighing less than 5% of a bat's body mass should be used. To avoid adverse effects on bats, researchers should target individuals with average, rather than peak, body mass indices.

Toward solving the global green-green dilemma between wind energy production and bat conservation

Wind energy production is growing rapidly worldwide in an effort to reduce greenhouse gas emissions. However, wind energy production is not environmentally neutral. Negative impacts on volant animals, such as bats, include fatalities at turbines and habitat loss due to land-use change and displacement. Siting turbines away from ecologically sensitive areas and implementing measures to reduce fatalities are critical to protecting bat populations. Restricting turbine operations during periods of high bat activity is the most effective form of mitigation currently available to reduce fatalities. Compensating for habitat loss and offsetting mortality are not often practiced, because meaningful offsets are lacking. Legal frameworks to prevent or mitigate the negative impacts of wind energy on bats are absent in most countries, especially in emerging markets. Therefore, governments and lending institutions are key in reconciling wind energy production with biodiversity goals by requiring sufficient environmental standards for wind energy projects.

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.

Conservation: Tracking bats around wind turbines

Alternative energy is essential for a green future but comes at a high risk for animals. New research shows that forest-based wind turbines may create an ecological trap for bats that typically are repelled by wind turbines.