Low foraging rates drive large insectivorous bats away from urban areas

Abstract

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.

Bats in the spotlight : Spatiotemporal response of foraging and commuting bats to anthropogenic light at night

“…Bats are able to fly dozens of kilometres to commute to their foraging areas (Haarsma and Siepel, 2014) or even thousands of kilometres during migration (Petersons, 2004). This high capacity for mobility throughout the landscape makes them very sensitive and vulnerable to habitat loss and fragmentation caused by multiple anthropogenic pressures, such as urbanisation (Avila-Flores and Fenton, 2005;Lintott et al, 2016;Russo and Ancillotto, 2015;Stidsholt et al, 2024), intensive farming (Frey-Ehrenbold et al, 2013;Park, 2015), wind turbines (Ellerbrok et al, 2022;Gaultier et al, 2023;McKay et al, 2024), solar farms (Barré et al, 2023a;Tinsley et al, 2023) and artificial light at night (Laforge et al, 2019;Stone et al, 2015;Voigt et al, 2021). Thus, bats provide a very good study case of the effect of artificial light on nocturnal species in terms of habitat loss and fragmentation.…”

“…Our findings show that artificial light provides predictable food resources in time and space for synanthropic bats (Chapters 3 and 4). In urban settings, insects are less numerous and distributed over greater distances, providing less food for bats (Stidsholt et al, 2024). Studying the response of bats to artificial light along a gradient from rural to urban habitat would help to disentangle the effect of light and urbanisation in order to adapt outdoor lighting according to the habitat composition.…”