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

Abstract

Article Figures and data Abstract Editor's evaluation eLife digest Introduction Results Discussion Materials and methods Data availability References Decision letter Author response Article and author information Metrics Abstract Predators that target multiple prey types are predicted to switch foraging modes according to prey profitability to increase energy returns in dynamic environments. Here, we use bat-borne tags and DNA metabarcoding of feces to test the hypothesis that greater mouse-eared bats make immediate foraging decisions based on prey profitability and changes in the environment. We show that these bats use two foraging strategies with similar average nightly captures of 25 small, aerial insects and 29 large, ground-dwelling insects per bat, but with much higher capture success in the air (76%) vs ground (30%). However, owing to the 3–20 times larger ground prey, 85% of the nightly food acquisition comes from ground prey despite the 2.5 times higher failure rates. We find that most bats use the same foraging strategy on a given night suggesting that bats adapt their hunting behavior to weather and ground conditions. We conclude that these bats use high risk-high gain gleaning of ground prey as a primary foraging tactic, but switch to aerial hunting when environmental changes reduce the profitability of ground prey, showing that prey switching matched to environmental dynamics plays a key role in covering the energy intake even in specialized predators. Editor's evaluation This study presents important findings on the hunting strategies and energy intake of bats in the wild. It combines several methods (biologging, captive experiment, and DNA metabarcoding) to provide convincing evidence for the claims. With detailed data and analyses on foraging ecology, this work will be of broad interest to animal ecologists. https://doi.org/10.7554/eLife.84190.sa0 Decision letter Reviews on Sciety eLife's review process eLife digest Bats are the only mammals capable of powered flight and therefore need a high calorie intake to survive. They hunt at night using the echoes made by their own calls to navigate and locate prey. Bats can use different tactics to hunt for food: hawking involves catching prey on the wing and requires fast aerial manoeuvring and more intense echolocation calls, while gleaning involves listening for movements of ground and water dwelling prey as the bat hovers. Some bat species specialise as hawkers or gleaners but maintain the ability to hunt with both methods. With the ever-growing impact of human activities on their habitats, it is important to understand how adaptable bats feeding habits are to changes in their environment. To find out more, Stidsholt et al. studied greater mouse-eared bats, which primarily feed by gleaning. To understand how this species chooses feeding strategies they fitted bats with tiny backpacks that could record the animal’s location and foraging behaviour. They could also monitor prey sizes by recording the sounds of the bats chewing. Stidsholt et al. found that, although these bats tried to catch prey on the ground more often than in the air, they were actually more successful as airborne hunters. Despite this, gleaning was still a more profitable strategy for them, because the body mass of ground prey is higher than for airborne prey. Gleaning gave the bats a higher calorie intake, even though their capture rate was lower. Although feeding habits differed slightly between individual bats on a given night of monitoring, there were much larger changes in behaviour between different feeding nights. This shows that, although this species of bat prefers gleaning, they will switch strategies to hawking as their environment changes, for example if there is more airborne prey, or if rainfall makes it hard to hear movements on the ground. Bats tended to get enough calories for their needs but did not catch more prey than they needed to survive. Stidsholt et al. concluded that greater mouse-eared bats change their feeding strategy based on prey availability and size, as well as the bat’s environment. Their study provides an important insight into how bats fit into the ecosystem and how adaptable bats might be to changes in their habitat. Introduction For many predators, the ability to switch between multiple prey types is key to surviving dynamics in prey availability. While some prey types are only available sequentially e.g., over seasons, others are available simultaneously and predators must choose when to switch between them. In these situations, predators are predicted to ignore low profitability prey when more profitable prey are present and abundant, and only switch prey type if there is a perceived prospect of increased profitability (i.e. more energy gained per time unit of hunting) (Stephens and Krebs, 1986). However, testing such fundamental predictions of prey switching in the wild are greatly complicated by the difficulties of measuring encounter rates and capturing successes to estimate prey profitability of individual predator-prey interaction (Sih and Christensen, 2001). Here, we use a biologging approach on echolocating bats as a model organism to investigate how prey profitability influences the foraging strategies of a wild predator known to target prey inhabiting two different habitats (Arlettaz, 1996). Bats are widespread and abundant predators that serve important roles in ecosystems across the globe (Kunz et al., 2011). Their evolutionary success is due to the unique combination of echolocation and powered flight (Teeling et al., 2005) allowing them to avoid visual predators by feeding at night, thereby gaining unfettered access to food sources that include insects, small vertebrates, fruit, nectar, pollen, and blood (Simmons, 2005). Within the mosaic of foraging niches they exploit, echolocating bats are categorized into three main foraging strategies: the ancestral mode of capturing prey on the wing (hawking), and the derived modes of trawling prey from water surfaces or gleaning prey, nectar, or fruit from ground and trees (Schnitzler and Kalko, 2001). To aid these specialized hunting strategies, each guild of bats has evolved specific adaptations in echolocation signals, auditory systems, morphology, and flight mechanics (Norberg and Rayner, 1987; Fenton, 1990; Schnitzler and Kalko, 2001). Despite such specialism, recent research has shown that foraging style is not monotypic within species: gleaning bats occasionally capture aerial prey (Bell, 1982; Fenton, 1990; Ratcliffe and Dawson, 2003; Ratcliffe et al., 2006; Hackett et al., 2014), while insect-gleaning bats may seasonally target nectar or fruit (Aliperti et al., 2017) or vice versa (Herrera M. et al., 2001). These changes in foraging style presumably track the relative abundance of preferred versus alternative food sources, broadening the ecological roles of bats and providing a degree of resilience in the face of changing resources. However, owing to the complexity of studying detailed hunting behaviors in the wild, it is not clear why or when specialized bats switch foraging strategies. To address this, we asked whether bats adapt their hunting strategies continuously to maintain net intake or if switching is the last resort when preferred prey are unavailable. To do so, we used miniaturized biologging devices to track the hunting behavior of greater mouse-eared bats. This species primarily captures ground-dwelling arthropods by passively listening for their movements (i.e. gleaning, Video 1; Video 2; Arlettaz, 1996), and is, therefore, specialized for gleaning: broad, short wings enable their take-off from the ground, and weak echolocation calls avoid alerting prey while also allowing the bat to hear rustling sounds of surface-dwelling prey. Nonetheless, like many other gleaning bats, greater mouse-eared bats have maintained the ancestral ability to use echolocation to capture aerial prey on the wing (i.e. hawking, Video 3; Video 4; Video 5; Stidsholt et al., 2021), requiring that they switch to intense calls to detect small prey, and maintain the capability to maneuver fast in 3D space to track evasive prey. While call intensity can be adjusted to fit different strategies, the morphological and anatomical specializations for ground gleaning must affect the efficiency of these bats as aerial hawkers. We, therefore, predicted that these bats would prefer gleaning whenever it was profitable, and would only switch to aerial hunting when environmental conditions led to poor energy intake rates when gleaning. Specifically, we tested the hypotheses that (1) although sensorimotor adaptation to gleaning comes at the cost of a reduced ability to capture aerial prey, bats continue to rely on both foraging strategies to cover their energy intake; (2) bats prefer the foraging strategy with the highest prey profitability; and (3) bats maintain their energy intake by adapting their foraging strategies to the habitat and environment. To test these hypotheses, we used miniaturized biologging devices to track the hunting behavior of 34 greater mouse-eared bats (Stidsholt et al., 2019). These tags recorded the bats’ echolocation behavior, three-dimensional movement patterns, GPS locations (N=7 of 34 bats) and mastication sounds after prey captures Video 6 as a proxy for foraging success. We complemented these data with DNA metabarcoding of feces from co-dwelling con-specifics (N=54 bats) to identify prey species and sizes. This combined biologging and DNA metabarcoding approach allowed us to quantify strategy switching in a wild predator as a function of prey profitability and habitat. Video 1 Download asset This video cannot be played in place because your browser does support HTML5 video. You may still download the video for offline viewing. Download as MPEG-4 Download as WebM Download as Ogg A bat captures prey on the ground in a forest floor reconstructed in a flight room while carrying a tag. We used these laboratory experiments to ground truth in the wild data. Video 2 Download asset This video cannot be played in place because your browser does support HTML5 video. You may still download the video for offline viewing. Download as MPEG-4 Download as WebM Download as Ogg Synchronized audio and acceleration data of a ground capture in the wild. Here, the mating song of the targeted bush cricket is audible and can be clearly seen in the spectrogram. Video 3 Download asset This video cannot be played in place because your browser does support HTML5 video. You may still download the video for offline viewing. Download as MPEG-4 Download as WebM Download as Ogg A trained greater mouse-eared bat captures a tethered moth. We used these video recordings to ground truth the data from the wild. Video 4 Download asset This video cannot be played in place because your browser does support HTML5 video. You may still download the video for offline viewing. Download as MPEG-4 Download as WebM Download as Ogg One minute of aerial hunting by a wild greater mouse-eared bat. The 3D flight pattern is reconstructed from the sensor data on the tag and is shown in white. Each aerial prey attack is marked as circles color-coded according to foraging success (green = success vs red = failure). Video 5 Download asset This video cannot be played in place because your browser does support HTML5 video. You may still download the video for offline viewing. Download as MPEG-4 Download as WebM Download as Ogg Aerial capture in the lab with a tag. We trained bats to catch tethered moths or mealworms with and without tags in a dark flight room while filming their behavior with an infrared camera. Video 6 Download asset This video cannot be played in place because your browser does support HTML5 video. You may still download the video for offline viewing. Download as MPEG-4 Download as WebM Download as Ogg Mastication of a bat is used to determine success ratios and prey sizes. The audible mastication sounds of the greater mouse-eared bats were used to determine successful prey attacks, and to measure the relative prey sizes between foraging strategies. Results To categorize the foraging strategies used by wild bats, we analyzed one night of sound and movement data from each of 34 female, greater mouse-eared bats (Myotis myotis). All bats commuted from the colony or release site to one or several foraging grounds before returning back to the roost before dawn (Figure 1ABC). Since, we used two different types of biologging devices with different sensors, foraging bouts were defined either as flight intervals of more than 50 s with a high variation in heading based on accelerometer and magnetometer data, or as intervals of an area-restricted search for tags including GPS (N=7 bats). Figure 1 with 4 supplements see all Download asset Open asset Greater mouse-eared bats tagged on different nights show wide variation in foraging strategy and success. (A-C) The jerk (differential of on-animal recorded acceleration) reveals the overall movement of the bat by showing periods of no movement (rest) and strong movement (flight) for three different bats (summed values for Bat ID 25, 5, and 30 as depicted in panel D) and two different travel modes (commuting (dark gray) vs foraging (light gray)). We marked all prey attacks as either hawking (blue diamonds) or gleaning (green circles) by visual and auditory inspection of the sound and movement data. Prey captures were classified by audible mastication sounds as successful (yellow edge) or failures (black edge). The bats exemplified here either primarily gleaned (A), primarily hawked (B), or used both strategies in alternating bouts (C). ( D–E) Successful (D) and unsuccessful (E) prey attacks of all bats (N=34) grouped according to the night of tagging for aerial hawking (blue) and gleaning (green). Stars mark the bats equipped with GPS tags; A, B, and C mark the bats depicted in panels A-C. (F–G) The success ratio (F) reveals the percentage of all attacks that were successful per bat per night (dots), while attack rates (G) reveal the number of foraging attacks per minute for each bat per night (dots) with more than one prey attack per foraging strategy for aerial hawking (blue) and gleaning (green) along with kernel densities and boxplots. Foraging success and number of prey attacks according to foraging strategy A total of 3917 attacks on prey (Figure 1D,E) were recorded with most bats capturing prey both on the ground by passively gleaning prey (Figure 1—figure supplement 1), and by pursuing prey mid-air by aerial hawking (Figure 1—figure supplement 2). However, four bats exclusively gleaned, while two bats only hawked (Figure 1D,E). The dominant foraging strategy used per bat per night seemed to be affected by the night of tagging indicating that bats tagged on the same nights choose the same foraging strategy (Figure 1D,E, Figure 1—figure supplement 3, N, N=10 nights, 1–9 bats tagged per night; LMM; testing if the ratio between ground:aerial captures was explained by the night of tagging Supplementary file 1g). The bats attacked food more often on the ground (mean: 80 attacks per individual per night, quartiles: 26–110) than in the air (mean: 36 attacks, quartiles: 7–70; GLMM, Poisson distribution, p=0.002, Supplementary file 1, Figure 1D), but the proportion of attacks that were successful (i.e. success ratio) based on audible mastication sounds following prey captures were more than double in the air (mean: 76%, quartiles: 71–88) than on ground (30%, quartiles: 25–40; Supplementary file 1, Figure 1F, Figure 1—figure supplement 4). This led to on average 25 (quartiles: 10–33) aerial and 29 (quartiles: 5–53) ground insects caught per bat per night (Figure 1D). The bats attacked prey more often on the ground (35 s between captures, quartiles: 17–70 s) compared to in the air (51 s between attacks, quartiles: 31–111, LMM, p<0.00001) (Figure 1G). Thus, bats caught prey much more reliably in the air, but attacked ground prey more often and devoted more foraging time to ground gleaning. The effect of habitat on foraging strategies We next used GPS tracks from seven bats to investigate the behavioral and ecological factors that influence foraging success. Specifically, we tested if movement style (i.e. commuting vs actively searching for prey defined via the Lavielle method Hurme et al., 2019, Figure 2—figure supplement 1) and habitat (i.e. forest vs open fields, Figure 2) affected the success ratio and prey attacks. The GPS-tagged bats also predominantly caught prey in separate foraging bouts that were each dedicated to either hawking (Figure 2A, blue diamonds) or gleaning (Figure 2A, green circles) (Figure 2—figure supplement 2). However, almost half of all aerial prey was captured during commuting (47% of total aerial captures; Figure 2—figure supplement 1). When gleaning, the bats attacked the same total number of prey in forest and open field habitats (field: 207 vs forest: 221 attacks in total, Figure 2C), but with more attacks per bout when gleaning above fields (field: 25 vs forest: 14 attacks/bout). Moreover, gleaning in open fields was twice as successful as in forest habitats (success ratio of 48% per foraging bout with more than two prey attacks in open fields vs 12% in the forest, Figure 2E, Supplementary file 1). In contrast, when capturing insects in the air, the attack rates and success ratios were consistently high and unaffected by habitat (Figure 2DF, LMM, Supplementary file 1). Figure 2 with 2 supplements see all Download asset Open asset Habitat influences the foraging success of greater mouse-eared only when gleaning. (A) Tracks of seven bats with GPS tags released either at the cave (red star) or at a location nearby (white star) and their foraging behavior: Gleaning (green circles) and hawking (blue diamonds) attacks along with their success (yellow edge) or failure (black edge). (B) The bats were tracked in North-Eastern Bulgaria (white square). C-F: Total prey attacks (CD) and success ratios per foraging bout (EF), for both habitats: open field (blue; G) and forest (magenta; H). Each data point corresponds to one foraging bout. G-H: The two main foraging habitats of greater mouse-eared bats: open fields (G) and the open spaces below the canopy in forests (H). Estimation of prey sizes To estimate prey types and sizes, we first performed DNA metabarcoding analysis on the feces of 54 untagged greater mouse-eared bats from the same colony caught in the morning upon returning from the foraging grounds. The bats target a wide range of prey species spanning 155 OUT (Operational Taxonomic Units) (Figure 3AB), of which ~60% occupy aerial niches (36 families), and ~40% occupy ground niches (23 families; Figure 3A). Ground prey was 2.5 x longer than aerial prey (20 mm (quartiles: 14–28 mm) vs 7 mm (quartiles 4–9 mm), Figure 3C) estimated from measured lengths of representatives of each species from online photo databases covering the same region in Bulgaria. We used length-weight regressions (Straus and Avilés, 2018) for each group to convert body-length to body mass for each prey type. For this analysis, we used the weighted average of the two most numerous prey types for aerial and ground regression values. Under these assumptions, estimated dry body masses of ground prey were ~20 times heavier than aerial prey (means: 67.5 mg quartiles: 29.7–146.6 mg) vs 3.0 mg (quartiles: 0.7–5.7 mg, Figure 3E, green and blue circles). Figure 3 with 3 supplements see all Download asset Open asset Ground prey is larger than aerial prey and sufficient to offset the lower foraging success ratios of gleaning. (A-B) DNA metabarcoding of feces from 54 greater mouse-eared bats (48 females, six males). Insects were categorized as either ground (green) or aerial (blue). The few prey species (N=5) that are both aerial and ground were omitted from the analysis. Distribution of the targeted prey orders depicted as OTU (Operational Taxonomic Units) between ground (~40%) and aerial (~60%) niches (A) and across taxonomical units in the Arthropoda (B). (C-F): Prey properties and profitability during gleaning (ground prey, green) and aerial hawking (aerial prey, blue), with kernel densities and boxplots. (C) Body lengths of the prey sorted by foraging strategy. (D) Number of mastication sounds identified after each prey capture by an automatic detector (N=244 ground captures and 336 aerial captures across 10 bats). (E) Dry prey body masses of each prey type identified for gleaning via DNA metabarcoding (green circles) (DNA metabarcoding was used as the reference prey body mass for ground captures), and for aerial prey by mastication analysis (blue triangles) and DNA metabarcoding (blue circles). (F) Prey profitability of gleaning or hawking prey calculated from prey body masses from mastication analysis (triangles) or DNA metabarcoding (circles) combined with observed success ratios, handling, and search times (Figure 3—figure supplement 2). The data are plotted for bootstrapped data (N=70 random data points) due to varying sample sizes of each parameter. (G) Total caloric intake per night per bat calculated by multiplying the caloric intake per prey with the number of successful gleaning and hawking prey captures (Figure 1), and compared to the field metabolic rate of a 30 g bat estimated from the literature (O’Mara et al., 2017) (orange). Since DNA metabarcoding does not provide the exact proportion of caught prey items and species, and thus does not allow to calculate the size distribution of caught prey, we performed an analysis of the mastication sounds as an additional proxy for prey size for nine bats with the best signal to noise ratio of the audio data (Tag type A). Greater mouse-eared bats chew all prey while flying irrespective of how they are caught and take longer to masticate larger prey (verified in laboratory feeding experiments, Figure 3—figure supplement 1). We used body length-to-body mass conversions from the DNA metabarcoding of ground prey as the reference prey body mass. We then estimated aerial prey body masses from the difference in chewing durations between ground and aerial prey. Bats chew longer on ground prey than aerial prey, indicated by the ~3 x more mastication sounds detected after each gleaning capture (75, quartiles: 38.5–111.5, Figure 3D) compared to aerial hawking (23, quartiles: 15–55). By applying this ratio to the body mass estimations of gleaning prey, we estimated aerial prey body mass of 21.2 mg on average (quartiles: 9.3–45.9) (Figure 3E, blue triangles). Thus, in the following, we use both a lower and a higher estimate of aerial prey body masses of 3.0 mg (from DNA metabarcoding), and 21.2 mg (from masticating sounds) (Figure 3E). Taking successful prey captures into account and the weighted average of the caloric values of the two most numerous prey types for aerial and ground (25.4 kJ/g dry mass of ground prey Bell, 1990; Zygmunt et al., 2006) and 21.3 kJ/g dry mass of aerial prey (Kurta and Kunz, 1987; Bell, 1990), the bats ingested an average of 60.2 kJ/night/bat (quartiles: 32.1–84.8) based on the lower aerial prey body mass estimates (Figure 3G, solid gray line), and 74.9 kJ/night/bat (quartiles: 55.2–95.7) based on the higher estimates (Figure 3G, shaded gray). Using energy assimilation rates of 50–82% in bats (Kurta et al., 1989; Straus and Avilés, 2018), the bats obtained on average between 30–61 kJ/night per bat (Figure 3G) during the hunting seasons of July to August. Prey profitability The profitability of prey caught by gleaning or hawking for all bats (N=34) was quantified by combining success ratios (Figure 1F), and search and handling times (Figure 3—figure supplement 2) with lower (Figure 3E, circles) and higher estimates of prey body masses (Figure 3E, triangles). The gleaning foraging strategy yielded a profitability of 7.4 J/s (quartiles: 5.6–8.1 J/s, Figure 3F green), while hawking resulted in a lower estimate of 0.5 J/s (quartiles: 0.4–0.54, Figure 3F, blue circles) and a higher estimate of 3.3 J/s (quartiles: 2.8–3.8, Figure 3F, blue triangles). Prey profitability when gleaning is thus 2.3–14 times higher than when aerial hawking. Discussion The small size and high metabolic rate of bats out of hibernation, coupled with a costly locomotion mode, require a high and constant input of energy from foraging (Kleiber, 1947). This, in turn, calls for either stable and narrow food niches or adaptive hunting behaviors that track habitat and prey dynamics. Here, we used biologging and metabarcoding to explore how greater mouse-eared bats chose between two different foraging strategies to cover their high energy intake, and how strategy switching is adapted to habitat and environment. Greater mouse-eared bats are more successful when hawking, but gain more energy from gleaning prey off the ground Since greater mouse-eared bats are a gleaning specialists, we first hypothesized that their sensorimotor adaptation to gleaning would come at the cost of a poorer ability to capture aerial prey during hawking, and that they, therefore, would rely mostly on the ground foraging to cover their energy intake. Our finding that the tagged bats were less successful in gleaning prey from the ground compared to hawking insects mid-air (30 vs 76% success ratio) (Figure 1F) leads us to dismiss that hypothesis. Surprisingly, the high success ratios for greater mouse-eared bats when hawking are on par with observations in the wild for hawking specialist bats (Rydell et al., 2002). Such high success rates are likely facilitated by superfast sensorimotor responses to guide echo-based captures (Stidsholt et al., 2021). But these superfast movements may be less beneficial when gleaning since ground-dwelling arthropods can seek refuge under leaves or twigs if the attack of the bat is not perfectly aimed. In such cases, the bats must rely on tactile and olfactory cues, and their poorer ground locomotion to find the prey (Kolb, 1958), contributing to the low success ratio of gleaning (Supplementary file 1). Despite the disparity in success ratios, tagged bats used both foraging strategies to capture food (Figure 1). During one night of foraging, the bats on average caught a mean of 25 insects in the air and 29 insects on the ground (Figure 1) demonstrating a reliance on both food sources. These numbers are on par with total prey captures of the similar-sized Rhinopoma microphyllum, estimated from buzz counts (Cvikel et al., 2015), but well below the very high feeding rates inferred in a smaller (7–11 g) species (M. daubentonii) (Encarnação and Dietz, 2006). The extra weight of the tags (~3–4 g) (Portugal et al., 2018; Kline et al., 2021) did not appear to strongly impact the number of prey attacks nor the ability to capture food since (i) both tagged (Videos 1 and 5) and un-tagged trained bats quickly learned to intercept aerial and ground prey in the lab with similar success ratios as in the wild (Supplementary file 1), and (ii) the wild tagged bats spent the same amount of time on foraging outside the colony as bats equipped with lighter (0.4 g) telemetry transmitters (Egert-Berg et al., 2018). The discrepancy between the inferred intake of thousands of insects per night from a smaller bat species (Encarnação and Dietz, 2006), and the measured total prey captures in our study is, therefore, more likely to relate to the dramatic difference in prey sizes between the prey species rather than a reduced foraging effort due to tagging effects. Given our measured total prey captures and prey sizes, wild greater mouse-eared bats in our study assimilated an average of 61.4 kJ/night per bat (assuming 82% assimilation) (Figure 3G). This is higher than the estimated field metabolic rate (FMR) of the similar-sized female lesser long-nosed bats (Leptonycteris yerbabuenae) of 40 kJ/day (Goldshtein et al., 2020), but close to the allometric scaling estimate of the FMR of a 30 g bat based on heart rate measurements from wild-tagged 18 g Uroderma bilobatum (FMRM.myo = FMRU.bil * (30 g/18 g)0.7 = 65.5 kJ/day) (O’Mara et al., 2017). Thus, despite making less than 100 prey captures per night, the estimated food intake of the tagged bats matches their predicted FMR. The bats in our study on average reached their predicted energetic requirement in a full night of foraging, but only just so, suggesting either feeding to satiation or perhaps alternatively that they might have little scope to compensate for changes in their environment. Since the bats fly out just after sunset and return early in the morning, they are vulnerable to any disturbance or change in habitat quality that reduces their foraging intake. Moreover, despite selecting only heavy, post-lactating females within the same colony, we measured a wide individual variation in hunting tactics. Tagged bats attacked from 48 to 280 prey during a night of foraging (Figures 1 and 2), demonstrating that continuous recordings from the same individuals are important to quantify the hunting efforts and energy budgets of wild predators, and that extrapolations of food intake from brief observations may result in significant errors in that light. Greater mouse-eared bats prefer larger ground-dwelling prey over aerial prey despite low success ratios The tagged bats attacked prey in the air and on the ground at similar rates, but success ratios for aerial prey were more than twice of those of ground prey (Figure 1F). Moreover, gleaning insects most likely exposes bats to a higher predation risks from ground predators, and a