PRINCIPLES AND PATTERNS OF BAT MOVEMENTS: FROM AERODYNAMICS TO ECOLOGY

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.

Bat Motion can be Described by Leap Frogging

We present models of bat motion derived from radio-tracking data collected over 14 nights. The data presents an initial dispersal period and a return to roost period. Although a simple diffusion model fits the initial dispersal motion we show that simple convection cannot provide a description of the bats returning to their roost. By extending our model to include non-autonomous parameters, or a leap frogging form of motion, where bats on the exterior move back first, we find we are able to accurately capture the bat's motion. We discuss ways of distinguishing between the two movement descriptions and, finally, consider how the different motion descriptions would impact a bat's hunting strategy.

A global systematic review of frugivorous animal tracking studies and the estimation of seed dispersal distances

Seed dispersal is one of the most important ecosystem functions globally. It shapes plant populations, enhances forest succession, and has multiple, indirect benefits for humans, yet it is one of the most threatened processes in plant regeneration, worldwide. Seed dispersal distances are determined by the diets, seed retention times and movements of frugivorous animals. Hence, understanding how we can most effectively describe frugivore movement and behaviour with rapidly developing animal tracking technology is key to quantifying seed dispersal. To assess the current use of animal tracking in frugivory studies and to provide a baseline for future studies, we provide a comprehensive review and synthesis on the existing primary literature of global tracking studies that monitor movement of frugivorous animals. Specifically, we identify studies that estimate dispersal distances and how they vary with body mass and environmental traits. We show that over the last two decades there has been a large increase in frugivore tracking studies that determine seed dispersal distances. However, some taxa (e.g. reptiles) and geographic locations (e.g. Africa and Central Asia) are poorly studied. Furthermore, we found that certain morphological and environmental traits can be used to predict seed dispersal distances. We demonstrate that flight ability and increased body mass both significantly increase estimated seed dispersal mean and maximum distances. Our results also suggest that protected areas have a positive effect on mean seed dispersal distances when compared to unprotected areas. We anticipate that this review will act as a reference for future frugivore tracking studies, specifically to target current taxonomic and geographic data gaps, and to further explore how seed dispersal relates to key frugivore and fruit traits.

Flight performance and wing morphology in the bat Carollia perspicillata: biophysical models and energetics

Studies on functional performance are important to understand the processes responsible for the evolution of diversity. Morphological trait variation within species influences the energetic cost of locomotion and impacts life history traits, with ecological and evolutionary consequences. This study examined wing morphology correlates of flight performance measured by energetic expenditure in the Seba's short-tailed bat, Carollia perspicillata. In the flight experiments, nature caught bats (59 females, 57 males) were allowed to fly for 3 min in a room. After each flight, thermographic images were taken to measure body temperature, and biophysical models were used to calculate sensible heat loss as a measure of energetic expenditure. Wing morphological traits were measured for each individual and associated with heat loss and power required to fly on performance surfaces. Wing morphological traits explained 7-10% of flight energetic cost, and morphologies with the best performance would save the energy equivalent to 9-30% of total daily requirements. The optimal performance areas within the C. perspicillata morphospace were consistent with predicted selection trends from the literature. A trade-off between demands for flight speed and maneuverability was observed. Wing loading and camber presented sexual dimorphism. These morphological differences are likely associated with more economical but less maneuverable flight in females, leading them to fly more often in open areas along the forest edge. Our findings demonstrate how small scale changes in wing morphology can affect life history strategies and fitness.

Can reintroduction of beavers improve insect biodiversity?

Ecosystem engineering species, such as beavers, may help the restoration of biodiversity. Through the building of dams and lodges and altering the natural hydrology, beavers change the habitat structure and create multiple habitats that facilitate a wide variety of other organisms including terrestrial invertebrate communities. Here we study the effect of beaver reintroduction in Klosterheden in Denmark on biomass of flying invertebrates and diversity of moths. Further, aerial photos were used to assess riparian structure and productivity using the normalized difference vegetation index (NDVI). Our findings show that the presence of beavers affected flying invertebrate biomass, but that this was dependent on time of the year. Further, a strong effect of presence of beavers was found on diversity of moths. The results also show an increase in vegetation productivity and structural heterogeneity at sites with presence of beavers. Overall, our results demonstrate the importance of beavers as important ecosystem engineers that affect invertebrate species composition and abundance, as well as riparian structure and productivity.

Linking changes in individual specialization and population niche of space use across seasons in the great evening bat (Ia io)

BACKGROUND

The niche breadth of an animal population comprises both within-individual and between-individual variation (individual specialization). Both components can be used to explain changes in population niche breadth, and this has been extensively investigated in dietary niche dimension studies. However, little is known about how changes in food resources or environmental factors across seasons affect changes in individual and population space use within the same population.

METHODS

In this study, we used micro-GPS loggers to capture the space use of individuals and of a population of the great evening bat (Ia io) in summer and autumn. We used I. io as a model to investigate how individual spatial niche breadth and spatial individual specialization affect changes in population niche breadth (home range and core area sizes) across seasons. Additionally, we explored the drivers of individual spatial specialization.

RESULTS

We found that the population home range and the core area of I. io did not increase in autumn when insect resources were reduced. Moreover, I. io showed different specialization strategies in the two seasons: higher spatial individual specialization in summer and lower individual specialization but broader individual niche breadth in autumn. This trade-off may maintain the dynamic stability of the population spatial niche breadth across seasons and facilitate the population response to changes in food resources and environmental factors.

CONCLUSIONS

Like diet, spatial niche breadth of a population also may be determined by a combination of individual niche breadth and individual specialization. Our work provides new insights into the evolution of niche breadth from the spatial dimension.

Insights into the formation and diversification of a novel chiropteran wing membrane from embryonic development

BACKGROUND

Through the evolution of novel wing structures, bats (Order Chiroptera) became the only mammalian group to achieve powered flight. This achievement preceded the massive adaptive radiation of bats into diverse ecological niches. We investigate some of the developmental processes that underlie the origin and subsequent diversification of one of the novel membranes of the bat wing: the plagiopatagium, which connects the fore- and hind limb in all bat species.

RESULTS

Our results suggest that the plagiopatagium initially arises through novel outgrowths from the body flank that subsequently merge with the limbs to generate the wing airfoil. Our findings further suggest that this merging process, which is highly conserved across bats, occurs through modulation of the programs controlling the development of the periderm of the epidermal epithelium. Finally, our results suggest that the shape of the plagiopatagium begins to diversify in bats only after this merging has occurred.

CONCLUSIONS

This study demonstrates how focusing on the evolution of cellular processes can inform an understanding of the developmental factors shaping the evolution of novel, highly adaptive structures.

Estimation of Japanese encephalitis virus infection prevalence in mosquitoes and bats through nationwide sentinel surveillance in Indonesia

Indonesia belongs to endemic areas of Japanese encephalitis (JE), yet data regarding the true risk of disease transmission are lacking. While many seroprevalence studies reported its classic enzootic transmission, data related to the role of bats in the transmission of JE virus are limited. This current study aimed to identify the potential role of bats in the local transmission of the JE virus to aid the ongoing active case surveillance in Indonesia, in order to estimate the transmission risk. Mosquitoes and bats were collected from 11 provinces in Indonesia. The detection of the JE virus used polymerase chain reaction (PCR). Maps were generated to analyze the JE virus distribution pattern. Logistic regression analysis was done to identify risk factors of JE virus transmission. JE virus was detected in 1.4% (7/483) of mosquito pools and in 2.0% (68/3,322) of bat samples. Mosquito species positive for JE virus were Culex tritaeniorhynchus and Cx. vishnui, whereas JE-positive bats belonged to the genera Cynopterus, Eonycteris, Hipposideros, Kerivoula, Macroglossus, Pipistrellus, Rousettus, Scotophilus and Thoopterus. JE-positive mosquitoes were collected at the same sites as the JE-positive bats. Collection site nearby human dwellings (AOR: 2.02; P = 0.009) and relative humidity of >80% (AOR: 2.40; P = 0.001) were identified as independent risk factors for JE virus transmission. The findings of the current study highlighted the likely ongoing risk of JE virus transmission in many provinces in Indonesia, and its potential implications on human health.

Rodents Prefer Going Downhill All the Way (Gravitaxis) Instead of Taking an Uphill Task

We directly tested whether, when given the choice to ascend or descend, rodents would favor traveling downwards or upwards. The test incorporated different rodent species that dwell in different habitats and display different life and motor styles. Testing was performed in a three-dimensional Y-maze in which the basis was horizontal and, by rotating it, one arm of the maze could be pointing upwards at a certain angle and the other arm pointed downwards at the same angle. All the tested species displayed a general preference for descent, with rodents from complex habitats being less affected by inclination compared with rodents from flatlands. Unlike laboratory rats, wild species traveled greater distances along the lower compared to the upper maze arm. All the rodents initially tended to travel the entire length of the inclined maze arms, but such complete trips decreased with the increase in inclination. When introduced into the maze from top or bottom, flatland dwellers traveled mainly in the entry arm. Overall, when given the choice to ascend or descend, all the tested species displayed a preference to descend, perhaps as attraction to the ground, where they usually have their burrows.

Movements of three mormoopid bat species (Chiroptera, Mormoopidae) among three underground roosts in southeastern Mexico

The movement of individuals between roosts allows gene flow and influences the spatial distribution, dynamics, and genetic structure of populations. The objectives of this study were to describe the patterns of movement of the bats Mormoops megalophylla, Pteronotus fulvus, and Pteronotus mesoamericanus, between a mine (La Mina) and two caves (El Apanguito and Cerro Huatulco) and explore some drivers for the movements in Oaxaca, México using capture-recapture methods. From July 2016 to June 2017, we captured 5082 individuals (2369 P. fulvus, 1868 P. mesoamericanus, and 845 M. megalophylla). We obtained 292 recaptures, including 57 recaptures represented inter-roost movements (34 by P. fulvus, 18 by P. mesoamericanus, and 5 by M. megalophylla). Brownie’s Multistate model showed that the movements among roosts were species-specific and were determined only by the roost occupied before capture for P. mesoamericanus, by the roosts used before and after capture for P. fulvus, or only by seasonality for M. megalophylla. The results showed that the reproductive condition could have influenced the movements between roosts in the three mormoopids, mainly due to the formation of maternity colonies of P. mesoamericanus and P. fulvus in the El Apanguito cave and exclusive colonies of M. megalophylla males in Cerro Huatulco. Due to the importance of the reproductive events that occur in the roosts studied, we suggest that the three roosts should be considered as part of the group of Important Sites for the Conservation of Bats in the state of Oaxaca.

Sing or Jam? Density-Dependent Food Competition Strategies in Mexican Free-Tailed Bats (Tadarida brasiliensis)

Organisms compete for food in many ways, but it is often difficult to know why they use certain competition strategies over others. Bats compete for food either through aggression coupled with food-claiming signals or by actively interfering with a competitor’s sensory processing during prey pursuit (i.e., jamming). It is not known why these different behaviors are exhibited. I studied food competition between Mexican free-tailed bats (Tadarida brasiliensis) at foraging sites in Arizona and New Mexico using passive acoustic recording, insect sampling and 3-D infrared videography with or without supplemental lighting that concentrated prey. Bat activity was quantified by the number of recorded echolocation calls, while feeding behavior was indicated by feeding buzzes. Two competitive behaviors were observed—song, which was produced by bats chasing conspecifics, and sinFM calls, which jam echolocation of competitors pursuing prey. Song production was most common when few bats were present and feeding at low rates. In contrast, jamming signals were most common with many bats present and feeding at high rates. Supplemental lighting increased the numbers of bats, feeding buzzes and sinFM calls, but not song. These results indicate that bats employ different strategies—singing and chasing competitors at low bat densities but jamming competitors at high bat densities. Food claiming signals (song) may only be effective with few competitors present, whereas jamming can be effective with many bats at a foraging site. Multiple competition strategies appear to have evolved in bats that are used under different densities of competitors.

From Protein to Pandemic: The Transdisciplinary Approach Needed to Prevent Spillover and the Next Pandemic

Pandemics are a consequence of a series of processes that span scales from viral biology at 10-9 m to global transmission at 106 m. The pathogen passes from one host species to another through a sequence of events that starts with an infected reservoir host and entails interspecific contact, innate immune responses, receptor protein structure within the potential host, and the global spread of the novel pathogen through the naive host population. Each event presents a potential barrier to the onward passage of the virus and should be characterized with an integrated transdisciplinary approach. Epidemic control is based on the prevention of exposure, infection, and disease. However, the ultimate pandemic prevention is prevention of the spillover event itself. Here, we focus on the potential for preventing the spillover of henipaviruses, a group of viruses derived from bats that frequently cross species barriers, incur high human mortality, and are transmitted among humans via stuttering chains. We outline the transdisciplinary approach needed to prevent the spillover process and, therefore, future pandemics.

Predicting migration routes for three species of migratory bats using species distribution models

Understanding seasonal variation in the distribution and movement patterns of migratory species is essential to monitoring and conservation efforts. While there are many species of migratory bats in North America, little is known about their seasonal movements. In terms of conservation, this is important because the bat fatalities from wind energy turbines are significant and may fluctuate seasonally. Here we describe seasonally resolved distributions for the three species that are most impacted by wind farms (Lasiurus borealis (eastern red bat), L. cinereus (hoary bat) and Lasionycteris noctivagans (silver-haired bat)) and use these distributions to infer their most likely migratory pathways. To accomplish this, we collected 2,880 occurrence points from the Global Biodiversity Information Facility over five decades in North America to model species distributions on a seasonal basis and used an ensemble approach for modeling distributions. This dataset included 1,129 data points for L. borealis, 917 for L. cinereus and 834 for L. noctivagans. The results suggest that all three species exhibit variation in distributions from north to south depending on season, with each species showing potential migratory pathways during the fall migration that follow linear features. Finally, we describe proposed migratory pathways for these three species that can be used to identify stop-over sites, assess small-scale migration and highlight areas that should be prioritized for actions to reduce the effects of wind farm mortality.

At Least Seven Distinct Rotavirus Genotype Constellations in Bats with Evidence of Reassortment and Zoonotic Transmissions

The increased research on bat coronaviruses after severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV) allowed the very rapid identification of SARS-CoV-2. This is an excellent example of the importance of knowing viruses harbored by wildlife in general, and bats in particular, for global preparedness against emerging viral pathogens.

Bats host many viruses pathogenic to humans, and increasing evidence suggests that rotavirus A (RVA) also belongs to this list. Rotaviruses cause diarrheal disease in many mammals and birds, and their segmented genomes allow them to reassort and increase their genetic diversity. Eighteen out of 2,142 bat fecal samples (0.8%) collected from Europe, Central America, and Africa were PCR-positive for RVA, and 11 of those were fully characterized using viral metagenomics. Upon contrasting their genomes with publicly available data, at least 7 distinct bat RVA genotype constellations (GCs) were identified, which included evidence of reassortments and 6 novel genotypes. Some of these constellations are spread across the world, whereas others appear to be geographically restricted. Our analyses also suggest that several unusual human and equine RVA strains might be of bat RVA origin, based on their phylogenetic clustering, despite various levels of nucleotide sequence identities between them. Although SA11 is one of the most widely used reference strains for RVA research and forms the backbone of a reverse genetics system, its origin remained enigmatic. Remarkably, the majority of the genotypes of SA11-like strains were shared with Gabonese bat RVAs, suggesting a potential common origin. Overall, our findings suggest an underexplored genetic diversity of RVAs in bats, which is likely only the tip of the iceberg. Increasing contact between humans and bat wildlife will further increase the zoonosis risk, which warrants closer attention to these viruses.

Seed dispersal by Neotropical bats in human-disturbed landscapes

Abstract In human-modified landscapes, where large bird and mammal species are often functionally extinct, bats are the main seed dispersers. However, the role of seed dispersal by bats for the maintenance of habitat dynamics in fragmented landscapes is still not understood, with information lacking on landscape-level effects of plant–bat interactions. We present some key topics related to spatial ecology of bats and discuss the potential influence of habitat fragmentation on several aspects of seed dispersal by Neotropical bats. We suggest that future studies need to evaluate bat–plant networks along habitat-loss and fragmentation gradients at the landscape level, including changes in land-cover types and habitat structural complexity, going beyond patch-based analysis. By advancing on the comprehension of ecosystem functioning in fragmented landscapes, we will better understand the bat-modulated seed-dispersal process, supporting regeneration and restoration programs that benefit from bat-based functions.

Patterns of foraging activity and fidelity in a southeast Asian flying fox

BACKGROUND

Improved understanding of the foraging ecology of bats in the face of ongoing habitat loss and modification worldwide is essential to their conservation and maintaining the substantial ecosystem services they provide. It is also fundamental to assessing potential transmission risks of zoonotic pathogens in human-wildlife interfaces. We evaluated the influence of environmental and behavioral variables on the foraging patterns of Pteropus lylei (a reservoir of Nipah virus) in a heterogeneous landscape in Cambodia.

METHODS

We employed an approach based on animal-movement modeling, which comprised a path-segmentation method (hidden Markov model) to identify individual foraging-behavior sequences in GPS data generated by eight P. lylei. We characterized foraging localities, foraging activity, and probability of returning to a given foraging locality over consecutive nights. Generalized linear mixed models were also applied to assess the influence of several variables including proxies for energetic costs and quality of foraging areas.

RESULTS

Bats performed few foraging bouts (area-restricted searches) during a given night, mainly in residential areas, and the duration of these decreased during the night. The probability of a bat revisiting a given foraging area within 48 h varied according to the duration previously spent there, its distance to the roost site, and the corresponding habitat type. We interpret these fine-scale patterns in relation to global habitat quality (including food-resource quality and predictability), habitat-familiarity and experience of each individual.

CONCLUSIONS

Our study provides evidence that heterogeneous human-made environments may promote complex patterns of foraging-behavior and short-term re-visitation in fruit bat species that occur in such landscapes. This highlights the need for similarly detailed studies to understand the processes that maintain biodiversity in these environments and assess the potential for pathogen transmission in human-wildlife interfaces.

Evolution of Flight Muscle Contractility and Energetic Efficiency

The powered flight of animals requires efficient and sustainable contractions of the wing muscles of various flying species. Despite their high degree of phylogenetic divergence, flight muscles in insects and vertebrates are striated muscles with similarly specialized sarcomeric structure and basic mechanisms of contraction and relaxation. Comparative studies examining flight muscles together with other striated muscles can provide valuable insights into the fundamental mechanisms of muscle contraction and energetic efficiency. Here, we conducted a literature review and data mining to investigate the independent emergence and evolution of flight muscles in insects, birds, and bats, and the likely molecular basis of their contractile features and energetic efficiency. Bird and bat flight muscles have different metabolic rates that reflect differences in energetic efficiencies while having similar contractile machinery that is under the selection of similar natural environments. The significantly lower efficiency of insect flight muscles along with minimized energy expenditure in Ca2+ handling is discussed as a potential mechanism to increase the efficiency of mammalian striated muscles. A better understanding of the molecular evolution of myofilament proteins in the context of physiological functions of invertebrate and vertebrate flight muscles can help explore novel approaches to enhance the performance and efficiency of skeletal and cardiac muscles for the improvement of human health.

Individual specialization in the use of space by frugivorous bats

Natural populations are not homogenous systems but sets of individuals that occupy subsets of the species' niche. This phenomenon is known as individual specialization. Recently, several studies found evidence of individual specialization in animal diets. Diet is a critical dimension of a species' niche that affects several other dimensions, including space use, which has been poorly studied under the light of individual specialization. In this study, which harnesses the framework of the movement ecology paradigm and uses yellow-shouldered bats Sturnira lilium as a model, we ask how food preferences lead individual bats of the same population to forage mainly in different locations and habitats. Ten individual bats were radiotracked in a heterogeneous Brazilian savanna. First, we modelled intraspecific variation in space use as a network of individual bats and the landscape elements visited by them. Second, we developed two novel metrics, the spatial individual specialization index (SpatIS) and the spatial individual complementary specialization index (SpatICS). Additionally, we tested food-plant availability as a driver of interindividual differences in space use. There was large interindividual variation in space use not explained by sex or weight. Our results point to individual specialization in space use in the studied population of S. lilium, most probably linked to food-plant distribution. Individual specialization affects not only which plant species frugivores consume, but also the way they move in space, ultimately with consequences for seed dispersal and landscape connectivity.

Decision making in foraging bats

Foraging is a complex and cognitively demanding behavior. Although it is often regarded as a mundane task, foraging requires the continuous weighting and integration of many sources of information with varying levels of credence. Bats are extremely diverse in their ecology and behavior, and thus demonstrate a wide variety of foraging strategies. In this review, we examine the different factors influencing the decision process of bats during foraging. Technological developments of recent years will soon enable real-time tracking of environmental conditions, of the position and quality of food items, the location of conspecifics, and the bat's movement history. Monitoring these variables alongside the continuous movement of the bat will facilitate the testing of different decision-making theories such as the use of reinforcement learning in wild free ranging bats and other animals.

Flowers up! The effect of floral height along the shoot axis on the fitness of bat-pollinated species

BACKGROUND AND AIMS

Bat-pollination is an important system in terms of occurrence and distribution, although it remains little studied. Thus, the role of particular flower traits in this interaction remains uncertain. Flower height along the shoot axis, associated with flower exposure, has often been deemed a key trait in this system, but its effect on fitness has not previously been assessed. We aimed to test its role and propose that taller flowers attain higher fitness due to a higher degree of accessibility and conspicuity to foraging bats.

METHODS

We assessed the effect of floral height on bat visiting rates to individual flowers of Crescentia cujete (Bignoniaceae), a cauliflorous model bat-pollinated species with a marked gradient in flower height along the shoot axis. Additionally, we tested the effect of this variable on seed/ovule ratio measurements from seven other species from different families along a herb-tree gradient. Hypotheses were tested through mixed-effect linear models.

KEY RESULTS

Bat visiting rates varied positively as a function of flower height in C. cujete, but significance was found only for the subset of flowers located on the trunk, closer to the ground. Similarly, seed/ovule ratios were positively correlated with flower height only for the three species with the shortest statures along the height gradient and shortest average floral heights. These results suggest that proximity to the ground, associated with herbaceous or bushy surrounding vegetation, may be an obstacle to the foraging of nectar-feeding bats, which in turn should explain the morphological convergence of inflorescence length and exposure strategies of short-statured bat-pollinated plants.

CONCLUSIONS

Flower height has a species-specific effect on plant fitness. This study provides a novel numerical perspective to the role of an unexplored trait in bat-pollination, and has elucidated some aspects of the adaptive importance of flower height based on limitations imposed by ecologically complex pollinators.

Ecology and Host Identity Outweigh Evolutionary History in Shaping the Bat Microbiome

This study is the first to provide a comprehensive survey of bacterial symbionts from multiple anatomical sites across a broad taxonomic range of Afrotropical bats, demonstrating significant associations between the bat microbiome and anatomical site, geographic locality, and host identity—but not evolutionary history. This study provides a framework for future systems biology approaches to examine host-symbiont relationships across broad taxonomic scales, emphasizing the need to elucidate the interplay between host ecology and evolutionary history in shaping the microbiome of different anatomical sites.

Recent studies of mammalian microbiomes have identified strong phylogenetic effects on bacterial community composition. Bats (Mammalia: Chiroptera) are among the most speciose mammals on the planet and the only mammal capable of true flight. We examined 1,236 16S rRNA amplicon libraries of the gut, oral, and skin microbiota from 497 Afrotropical bats (representing 9 families, 20 genera, and 31 species) to assess the extent to which host ecology and phylogeny predict microbial community similarity in bats. In contrast to recent studies of host-microbe associations in other mammals, we found no correlation between chiropteran phylogeny and bacterial community dissimilarity across the three anatomical sites sampled. For all anatomical sites, we found host species identity and geographic locality to be strong predictors of microbial community composition and observed a positive correlation between elevation and bacterial richness. Last, we identified significantly different bacterial associations within the gut microbiota of insectivorous and frugivorous bats. We conclude that the gut, oral, and skin microbiota of bats are shaped predominantly by ecological factors and do not exhibit the same degree of phylosymbiosis observed in other mammals.

IMPORTANCE This study is the first to provide a comprehensive survey of bacterial symbionts from multiple anatomical sites across a broad taxonomic range of Afrotropical bats, demonstrating significant associations between the bat microbiome and anatomical site, geographic locality, and host identity—but not evolutionary history. This study provides a framework for future systems biology approaches to examine host-symbiont relationships across broad taxonomic scales, emphasizing the need to elucidate the interplay between host ecology and evolutionary history in shaping the microbiome of different anatomical sites.

Neuroethology of bat navigation

Once a year about 15 million Mexican free-tailed bats (Tadarida brasiliensis) migrate up to 1,500 kilometers from wintering grounds, seamlessly flying over the Mexican border to enter the United States. Their destination is the Bracken Cave in southern Texas, which will be their summer home between the months of March through October. While residing there, these bats emerge every night at dusk from the narrow 100-foot-wide opening of this enormous cave and begin their nightly commute to foraging grounds located up to 50 kilometers away. Upon arrival, they will spend the night hunting for insects in mid-air while providing a valuable service to local farmers by keeping crop pests in check. Close to the break of dawn, as the night of hunting comes to an end, these bats will begin making their trip back to the roost.

Nine years of Indiana bat (Myotis sodalis) spring migration behavior

The endangered Indiana bat (Myotis sodalis) congregates in large hibernation groups in winter and travels after spring emergence to form summer maternity colonies, but information on migration behavior in this species remains limited to mostly band recovery observations. We tracked female Indiana bats in spring migration toward summer grounds using aerial radiotelemetry. Adult female Indiana bats were radiotagged in spring from 2009 through 2017, with 15 individuals successfully tracked to summer grounds and an additional 11 bats located in summer grounds via aerial telemetry after migration was complete. This resulted in the location of 17 previously unknown summer grounds for female Indiana bats, including adding Georgia, Alabama, and Mississippi to the summer maternity range. Two of the colonies identified in this study were south of the previously known southernmost colony in Tennessee, expanding the summer maternity range for the species by 178 km. Time-stamped location fixes along the migration path provided information about nightly and overall distances traveled, duration of travel, migration speed, and weather-related influences on bat behavior. Bats traveled 164.6 ± 26.2 km (± SE) on average from hibernacula to summer grounds and were migrating for an average of 7.3 ± 1.4 calendar nights. Bats alternated between foraging and traveling throughout each night of their migration route. Nightly migration rate was 9.9 ± 0.8 km/h and bats were active on the landscape for an average of 6.1 ± 0.4 h/night. Lower nighttime temperatures and lower barometric pressure correlated with use of layover areas during a migration night. Understanding bat behavior during migration can provide pertinent information for land managers to consider in efforts to conserve potential migration corridors, foraging areas, and roosting habitats of species in decline.

Flight costs in volant vertebrates: A phylogenetically-controlled meta-analysis of birds and bats

Flight costs play an important role in determining the behavior, ecology, and physiology of birds and bats. Mechanical flight costs can be estimated from aerodynamics. However, measured metabolic flight costs (oxygen consumption rate) are less accurately predicted by flight theory, either because of (1) variation in flight efficiency across species, (2) variation in how basal costs interact with flight costs or (3) methodological biases. To tease apart these three hypotheses, we conducted a phylogenetically-controlled meta-analysis based on data from birds and bats. Birds doing short flights in a lab had higher metabolic rates than those with sustained flapping flight. In turn, species that used sustained flapping flight had a higher metabolic rate than those that flew primarily via gliding. Models accounting for relatedness (phylogeny) explained the data better than those that did not, which is congruent with the idea that several different flight Bauplans have evolved within birds and bats. Focusing on species with sustained flapping flight, for which more data are currently available, we found that flight cost estimates were not affected by measurement methods in both birds and bats. However, efficiency increased with body mass and decreased with flight speed in both birds and bats. Basal metabolic rate was additive to flight metabolic rate in bats but not birds. We use these results to derive an equation for estimating metabolic flight costs of birds and bats that includes variation in whole animal efficiency with flight speed and body mass.

Experienced Migratory Bats Integrate the Sun's Position at Dusk for Navigation at Night

From bats to whales, millions of mammals migrate every year. However, their navigation capacity for accomplishing long-distance movements remains remarkably understudied and lags behind by five decades compared to other animals [1, 2]-partly because, unlike for other taxa, such as birds and sea turtles, no small-scale orientation assay has so far been developed. Yet recently, bats became a model to investigate which cues mammals use for long-range navigation, and, surprisingly for nocturnal animals, sunset cues, and particularly polarized-light cues, appear to be crucial for calibration of the magnetic-compass system in non-migratory bats [3-5]. This does not appear to hold for a species of migratory bat, however [6], and thus the nature of the information used by migratory bats for navigation remains unclear. Here, we asked whether the position of the solar disk per se is relevant for compass orientation in a migratory bat, Pipistrellus pygmaeus. Using a new experimental assay that measures takeoff orientation, we tested the orientation of bats exposed to a shifted sunset azimuth using a mirror at dusk. Bats exposed to a 180°-rotated azimuth of the setting sun and released after translocation during the same night shifted their heading direction by ∼180° compared to control bats. However, first-year migrants had no clear orientation either as controls or after the same treatment. This suggests that learning the migratory direction is a key component in the navigational system of naive bats in this species. Our study provides rare evidence for the specific cues and mechanisms that migratory mammals use for navigation.

Flight patterns in zoo-housed fruit bats (Pteropus spp.)

Maintaining the capacity for sustained flight in captivity is a key goal for the management of threatened fruit bats. We developed quantifiable descriptions of flight complexity and used them to assess the suitability of an enclosure for two species of fruit bat of differing size, the large Livingstone's fruit bat, Pteropus livingstonii, and the smaller Rodrigues fruit bat, Pteropus rodricensis, in a two-part study. In Phase 1, Rodrigues fruit bats flew more often than Livingstone's fruit bats and although the majority of flights in both species were linear, Rodrigues fruit bats were more likely to display complex flight paths involving turns, while flights by Livingstone's fruit bats were more likely to end in a crash-landing than Rodrigues fruit bat flights. The enclosure may therefore not have been large enough for Livingstone's fruit bats to display a full range of flight behavior over longer distances. In Phase 2, juvenile Livingstone's fruit bats ( < 3 years old) flew more than twice as often as younger adults (3-10 years old) did. Older adult Livingstone's fruit bats over the age of 10 years were not observed to fly. We could not separate out the effects of age, weight and environment during development as these factors were strongly correlated in our study; future work in this area will be very important in understanding the factors that affect flight in captive bats, and how it can be encouraged by appropriate enclosure design.

A fully autonomous terrestrial bat-like acoustic robot

Echolocating bats rely on active sound emission (echolocation) for mapping novel environments and navigating through them. Many theoretical frameworks have been suggested to explain how they do so, but few attempts have been made to build an actual robot that mimics their abilities. Here, we present the ‘Robat’—a fully autonomous bat-like terrestrial robot that relies on echolocation to move through a novel environment while mapping it solely based on sound. Using the echoes reflected from the environment, the Robat delineates the borders of objects it encounters, and classifies them using an artificial neural-network, thus creating a rich map of its environment. Unlike most previous attempts to apply sonar in robotics, we focus on a biological bat-like approach, which relies on a single emitter and two ears, and we apply a biological plausible signal processing approach to extract information about objects’ position and identity.

Many animals are able of mapping a new environment even while moving through it for the first time. Bats can do this by emitting sound and extracting information from the echoes reflected from objects in their surroundings. In this study, we mimicked this ability by developing a robot that emits sound like a bat and analyzes the returning echoes to generate a map of space. Our Robat had an ultrasonic speaker mimicking the bat’s mouth and two ultrasonic microphones mimicking its ears. It moved autonomously through novel out-doors environments and mapped them using sound only. It was able to negotiate obstacles and move around them, to avoid dead-ends and even to recognize if the object in front of it is a plant or not. We show the great potential of using sound for future robotic applications.

Changing resource landscapes and spillover of henipaviruses

Old World fruit bats (Chiroptera: Pteropodidae) provide critical pollination and seed dispersal services to forest ecosystems across Africa, Asia, and Australia. In each of these regions, pteropodids have been identified as natural reservoir hosts for henipaviruses. The genus Henipavirus includes Hendra virus and Nipah virus, which regularly spill over from bats to domestic animals and humans in Australia and Asia, and a suite of largely uncharacterized African henipaviruses. Rapid change in fruit bat habitat and associated shifts in their ecology and behavior are well documented, with evidence suggesting that altered diet, roosting habitat, and movement behaviors are increasing spillover risk of bat-borne viruses. We review the ways that changing resource landscapes affect the processes that culminate in cross-species transmission of henipaviruses, from reservoir host density and distribution to within-host immunity and recipient host exposure. We evaluate existing evidence and highlight gaps in knowledge that are limiting our understanding of the ecological drivers of henipavirus spillover. When considering spillover in the context of land-use change, we emphasize that it is especially important to disentangle the effects of habitat loss and resource provisioning on these processes, and to jointly consider changes in resource abundance, quality, and composition.