Echolocating bats prefer a high risk-high gain foraging strategy to increase prey profitability

Fast vocal-motor tracking of escaping prey in echolocating bats

BACKGROUND

Echolocating bats face an intense arms race with insect prey that can detect bat calls and initiate evasive maneuvers. Their high closing speeds and short biosonar ranges leave bats with only a few 100 ms between detection and capture, suggesting a reactive sensory-motor operation that might preclude tracking of escaping prey. Here we test this hypothesis using greater mouse-eared bats (Myotis myotis) as a model species. With high-resolution biologging tags, we recorded bats hunting aerial prey in the wild and we also collected data from trained conspecifics in the laboratory facing simulated prey escapes of various speeds and distances.

RESULTS

We show that wild bats employed flexible buzz durations during hunting. In the laboratory, such dynamic vocal responses were driven by moving targets, where faster and longer movements led to longer buzzes. During these buzzes, the bats engaged in acute vocal-motor tracking via increased call intervals within 240 ms of evasive prey maneuvers.

CONCLUSIONS

Echolocating bats can track evasive prey via a fast vocal-motor feedback loop allowing them to expand their acoustic depth of field. This echo-guided sensory adjustment contributes to the hunting superiority of bats as the most formidable insectivorous predator of the night skies.

Trait responses, nonconsumptive effects, and the physiological basis of Helicoverpa armigera to bat predation risk

Predation reduces the population density of prey, affecting its fitness and population dynamics. Few studies have connected trait changes with fitness consequences in prey and the molecular basis and metabolic mechanisms of such changes in bat-insect systems. This study focuses on the responses of Helicoverpa armigera to different predation risks, focusing on echolocating bats and their calls. Substantial modifications were observed in the nocturnal and diurnal activities of H. armigera under predation risk, with enhanced evasion behaviors. Accelerated development and decreased fitness were observed under predation risks. Transcriptomic and metabolomic analyses indicated that exposure to bats induced the upregulation of amino acid metabolism- and antioxidant pathway-related genes, reflecting shifts in resource utilization in response to oxidative stress. Exposure to bat predation risks enhanced the activity of DNA damage repair pathways and suppressed energy metabolism, contributing to the observed trait changes and fitness decreases. The current results underscore the complex adaptive strategies that prey species evolve in response to predation risk, enhancing our understanding of the predator-prey dynamic and offering valuable insights for innovative and ecologically informed pest management strategies.

Bats integrate multiple echolocation and flight tactics to track prey

The ability of "target tracking," such as keeping a target object in sight, is crucial for various activities. However, most sensing systems experience a certain degree of delay due to information processing, which challenges accurate target tracking. The long history of studies on animal behavior has revealed several tactics for it, although a systematic understanding of how individual tactics are combined into a strategy has not been reached. This study demonstrates a multifaceted tracking strategy in animals, which mitigates the adverse delay effects with small implementation costs. Using an active-sensing bat to measure their sensing state while chasing natural prey, we found that bats use a tracking strategy by combining multiple echolocation and flight tactics. The three echolocation tactics, namely the predictive control of sensing direction accompanied by adjusting the sensing rate and angular range, produce a direct compensation effect. Simultaneously, the flight tactic, the counter maneuver, assists echolocation by stabilizing the target direction. Our simulation results demonstrate that these combined tactics improve tracking accuracy over a wide range of delay constraints. In addition, a concise rule based on the angular velocity between bats and targets explains how bats control these tactics, suggesting that bats successfully reduce the burden of multitasking management. Our findings reveal the sophisticated strategy in animals' tracking systems and provide insights into understanding and developing efficiently integrated strategies in target tracking across various disciplines.

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.

Calibrated microphone array recordings reveal that a gleaning bat emits low-intensity echolocation calls even in open-space habitat

Echolocating bats use ultrasound for orientation and prey capture in darkness. Ultrasound is strongly attenuated in air. Consequently, aerial-hawking bats generally emit very intense echolocation calls to maximize detection range. However, call levels vary more than tenfold (>20 dB) between species and are tightly linked to the foraging strategy. The brown long-eared bat (Plecotus auritus) is a primarily gleaning, low-amplitude species that may occasionally hawk airborne prey. We used state-of-the-art calibrated acoustic 3D-localization and automated call analysis to measure P. auritus' source levels. Plecotus auritus emits echolocation calls of low amplitude (92 dB rmsSPL re. 20 µPa at 10 cm) even while flying in open-space. While P. auritus thus probably benefits from delayed evasive manoeuvres of eared insects, we propose that low-amplitude echolocation did not evolve as an adaptive countermeasure, but is limited by morphological constraints.