Insectivorous Bats Research Articles

A 50-million-year-old, three-dimensionally preserved bat skull supports an early origin for modern echolocation

Bats are among the most recognizable, numerous, and widespread of all mammals. But much of their fossil record is missing, and bat origins remain poorly understood, as do the relationships of early to modern bats. Here, we describe a new early Eocene bat that helps bridge the gap between archaic stem bats and the hyperdiverse modern bat radiation of more than 1,460 living species. Recovered from ∼50 million-year-old cave sediments in the Quercy Phosphorites of southwestern France, Vielasia sigei's remains include a near-complete, three-dimensionally preserved skull-the oldest uncrushed bat cranium yet found. Phylogenetic analyses of a 2,665 craniodental character matrix, with and without 36.8 kb of DNA sequence data, place Vielasia outside modern bats, with total evidence tip-dating placing it sister to the crown clade. Vielasia retains the archaic dentition and skeletal features typical of early Eocene bats, but its inner ear shows specializations found in modern echolocating bats. These features, which include a petrosal only loosely attached to the basicranium, an expanded cochlea representing ∼25% basicranial width, and a long basilar membrane, collectively suggest that the kind of laryngeal echolocation used by most modern bats predates the crown radiation. At least 23 individuals of V.sigei are preserved together in a limestone cave deposit, indicating that cave roosting behavior had evolved in bats by the end of the early Eocene; this period saw the beginning of significant global climate cooling that may have been an evolutionary driver for bats to first congregate in caves.

Multiple synchro-tuning chirplet transform

Time-frequency analysis (TFA) is an effective tool for characterizing non-stationary signals. Due to the limited time-frequency resolution capability, traditional TFA methods cannot achieve the optimal time-frequency representation (TFR). Based on the post-processing technique, a novel TFA method named multiple synchro-tuning chirplet transform (MSTCT) is proposed to obtain high-resolution and robust TFR for non-stationary signals. The MSTCT first estimates the spectral energy, instantaneous frequency (IF), and chirp rate (CR) of non-stationary signals with high time-frequency resolution, enabling precise energy localization on the time-frequency plane. Then, a multiple reassignment procedure is proposed to concentrate the blurry time-frequency energy and yield a better TFR. Moreover, benefiting from the multiple squeezing mechanism in the frequency axis, the MSTCT holds the potential to reconstruct the signal with high accuracy. Both the simulation results and the real-world experiment using the bat echolocation data demonstrate that the proposed MSTCT algorithm achieves superior performance in the time-frequency resolution, noise immunity, and reconstruction capability compared to the state-of-art linear TFA methods.

The marked dextro-dominance causes accentuated morphophysiological variations in the female reproductive organs of the bat Molossus molossus

Molossus molossus is an insectivorous molossid bat that is important in the control of nocturnal insects. It is the nominal and the most representative species of the family. However, there are few studies about its reproduction. Thus, this study aimed to evaluate variations of its female reproductive organs during the different reproductive phases. Twenty adult females, divided into four sample groups (non-reproductive, early and advanced pregnancy and lactation), were submitted to morphological and morphometric analyses. Results show that the female reproductive system of M. molossus is composed of ovaries, a short bicornuate uterus, slightly convoluted uterine tubes and vagina. The system presents a distinct morphofunctional asymmetry, with a marked dextro-dominance. The right ovaries of all analyzed groups (NON, P1, P2, and LAC) showed follicles at different stages of development, a large number of interstitial glands and a small, but persistent corpus luteum. Ovulation is simple, unilateral and preferential, occurring exclusively in the right ovary. Follicular development in the left ovary usually does not pass the secondary stage. Implantation is fundic and preferential, occurring exclusively in the right uterine horn. The placenta is formed with two distinct chorioallantoic portions, one diffuse endotheliochorial, which covers the entire uterine cavity and regresses in the final stages of pregnancy, and the principal discoidal hemochorial portion, formed in the implantation site. The uterine cervix presents a pseudostratified epithelium, while the vagina has a little keratinized stratified epithelium, which does not accentually vary in the different reproductive stages, but can disrupt and shed in some cases.

Providing water sources to insectivorous bats for conservation biological control in arid date plantations

Balance between the high demand for agricultural production and the negative environmental impact of intensive agriculture requires the development of sustainable agricultural approaches. One such approach is conservation biological control (CBC), which aims at enhancing pest suppression by using natural enemies, such as predators and parasites. Insectivorous bats are considered as potential natural enemies for CBC of insect agricultural pests. Bats drink from open water sources and forage above them, hence we hypothesized that supplementation of artificial water pools adjacent to desert date plantations might promote the activity and species richness of insectivorous bats in this habitat, thereby contributing to pest suppression. We predicted that bats will be more attracted to the pools during summer, when other water sources are scarce, than during spring. In addition, we explored the effect of water supplements on the desert bat community structure. Eight pools were installed in a date plantation in the hyper-arid Arava valley, Israel. Bats were acoustically monitored during three experimental stages: 1) before filling the pools with water; 2) while the pools held water and 3) after emptying them. The lesser date moth (Batrachedra amydraula), a major date pest, was monitored using pheromone traps in parallel with the experimental stages. We found that the pools increased bat activity in summer, but not in spring, while species richness was not affected in either season. The local bat community structure was significantly altered while the pools held water, but not due to increased activity of synanthropic Mediterranean species at the expense of local desert species. The number of individuals of the lesser date moth near the pools decreased with the increase in bat activity. Our results support the idea that seasonal water supplementation enhances bat activity in arid farmlands with potential contribution to pest control and the actual contribution to pest suppression should be further quantified. We suggest that the integration of small artificial pools to promote agricultural pest predation by bats may help reduce crop loss and potentially contribute to the conservation of desert bat communities by adding water sources.

Eptesicus innoxius (Chiroptera: Vespertilionidae)

Abstract Eptesicus innoxius (Gervais, 1841) is a vespertilionid bat commonly known as harmless brown bat or harmless serotine. It is a small bat, with woolly, short dorsal fur (5–6 mm), that is brown to pale grayish brown; the sagittal and lambdoidal crests are very low or absent. Eptesicus innoxius occurs in lowlands west of the Andes, with a geographic distribution restricted to northwestern and southern Ecuador, and northwestern Peru, at elevations from sea level to 1,200 m. It is listed as “Near Threatened” (NT) by the International Union for Conservation of Nature because of a suspected population reduction due to a significant decline of habitat where the species occurs.

Contrasting laboratory and field outcomes of bat-moth interactions.

Predator-prey interactions are important but difficult to study in the field. Therefore, laboratory studies are often used to examine the outcomes of predator-prey interactions. Previous laboratory studies have shown that moth hearing and ultrasound production can help prey avoid being eaten by bats. We report here that laboratory behavioural outcomes may not accurately reflect the outcomes of field bat-moth interactions. We tested the success rates of two bat species capturing moths with distinct anti-bat tactics using behavioural experiments. We compared the results with the dietary composition of field bats using next-generation DNA sequencing. Rhinolophus episcopus and Rhinolophus osgoodi had a lower rate of capture success when hunting for moths that produce anti-bat clicks than for silent eared moths and earless moths. Unexpectedly, the success rates of the bats capturing silent eared moths and earless moths did not differ significantly from each other. However, the field bats had a higher proportion of silent eared moths than that of earless moths and that of clicking moths in their diets. The difference between the proportions of silent eared moths and earless moths in the bat diets can be explained by the difference between their abundance in bat foraging habitats. These findings suggest that moth defensive tactics, bat countertactics and moth availability collectively shape the diets of insectivorous bats. This study illustrates the importance of using a combination of behavioural experiments and molecular genetic techniques to reveal the complex interactions between predators and prey in nature.

Integrative taxonomy and evolutionary history reveal cryptic diversity in Myotis riparius (Chiroptera: Vespertilionidae)

Abstract Myotis riparius is an insectivorous bat species widely distributed in the Neotropics with evident geographical variation in morphological traits. We conducted an integrative study using mitochondrial DNA, qualitative and quantitative morphology, and current and past species distribution models to investigate the variation, population structure, and distributional limits within M. riparius populations. Phylogenetic inferences indicated that M. riparius is monophyletic, and populations are divided into geographically structured clades that split during the middle Pleistocene. There is no shared haplotype between geographical populations and strong evidence of partial restriction in gene flow. Morphological and morphometric variations revealed subtle distinctions among different populations, but little correspondence with molecular analysis. The distribution models indicated that M. riparius is associated with forest environments, with discontinuity between populations from South American ecoregions. Past distribution modelling, however, indicated that M. riparius had a larger distribution range in the Last Glacial Maximum than currently. Results of modelling and genetic analyses indicated that M. riparius consisted of a large, widespread, and panmictic (meta)population until the middle Pleistocene, when environmental changes driven by climatic dynamics fragmented and isolated the populations. Myotis riparius is here considered a complex of at least four allopatric and parapatric cryptic evolutionary units.

Biosonar sampling strategies in frequency-modulated echolocating bats

Echolocating bats dynamically control multiple aspects of their biosonar emissions (emission rate, frequency, bandwidth, duration, and direction) in parallel as a function of their surroundings and current goals. As environments become more difficult to navigate and tasks become more complex, bats converge on sampling strategies that have less variability in the timing and spatial changes of their echolocation. We investigated these biosonar dynamics within a virtual echo target presentation paradigm where we challenged big brown bats sitting on a platform to localize a single echo target, which was either stationary or moved unpredictably in azimuth. Acoustic clutter was also added at varying distances to investigate its effect on their sampling strategies during the task. Bats modified their biosonar strategies differently depending on the distance of added acoustic clutter and the distance that a target shifted, and individuals tended to converge on similar strategies. We also show that certain perceptual contexts can lead to unexpected biosonar strategies in individual bats, such as the use of longer-duration emissions with less emission ‘clustering’ when localizing a virtual target against nearby clutter.

Where do Egyptian fruit bats fly when auditory and visual spatial information conflicts?

Egyptian fruit bats, Rousettus aegyptiacus, present a distinct opportunity to unravel the relative contributions of auditory and visual stimuli for navigation. This species has evolved lingual echolocation, but also uses rod vision to navigate. Echolocation and visual gaze are anchored to the head, but the bat's active control over sonar beam aim, ear, and eye position can influence sampling of sensory space. We investigated the relative weighting of echolocation and vision in free-flying Egyptian fruit bats. In this experiment, we used stereo IR video and microphone array recordings to quantify the bat’s trajectory, head direction and sonar beam as it flew to a landing perch. We introduced sensory conflict by equipping the bats with goggles fit with prisms that shifted visual images by 23 degrees to the left or right. In control trials, prisms were replaced with clear or light-blocking lenses. When bats were presented with conflicting visual and echolocation information, they flew in the direction of the prism shift and often missed the perch. Preliminary analyses of sonar beam aim suggests that their navigation is largely guided by vision. These findings underscore the dominant role of vision in bats that have also evolved auditory specializations to operate in darkness.

Food Habit, Spatial, and Dietary Niche Overlap of Three Sympatric Insectivorous Bats (Chiroptera) in the West Region of Cameroon

Food Habit, Spatial, and Dietary Niche Overlap of Three Sympatric Insectivorous Bats (Chiroptera) in the West Region of Cameroon

Insectivorous bats in Indian rice fields respond to moonlight, temperature, and insect activity

ContextRice, India’s most widely grown crop, suffers substantial and increasing yield loss to insect pests. Insectivorous bats are known suppressors of insect pests, providing significant economic value to agricultural systems worldwide, yet their ecology in Indian agricultural landscapes is poorly understood.ObjectivesWe assess the influence of key biotic and abiotic factors on the activity of insectivorous bats over the growing season and within a night in a rice cultivation landscape.MethodsPassive acoustic recorders were used to track bat activity in a rice field in the Sonitpur district of Assam, India. We used generalised linear mixed models to analyse the effect of temperature, insect activity, and moonlight intensity on the activity of six bat sonotypes. We also used a multimodal analysis to describe the within-night activity patterns of these sonotypes.ResultsMinimum nightly temperature and moonlight intensity had a positive and negative influence, respectively, on the activity of six bat sonotypes, while the activity of four bat sonotypes increased with insect activity. Within-night activity showed one of two patterns: three sonotypes displayed a dusk peak in activity, while the three other sonotypes were active through the night.ConclusionThe potential to maximise natural pest control in agricultural landscapes can only be realised through understanding the ecology of natural enemies in these landscapes. Our findings suggest that bats in rice fields are tracking insects over a season and within a night, pointing to a valuable ecosystem service in Indian agriculture that is yet to be quantified.

Increased bat hunting at polluted streams suggests chemical exposure rather than prey shortage

Streams and their riparian areas are important habitats and foraging sites for bats feeding on emergent aquatic insects. Chemical pollutants entering freshwater streams from agricultural and wastewater sources have been shown to alter aquatic insect emergence, yet little is known about how this impacts insectivorous bats in riparian areas. In this study, we investigate the relationships between the presence of wastewater effluent, in-stream pesticide toxicity, the number of emergent and flying aquatic insects, and the activity and hunting behaviour of bats at 14 streams in southwestern Germany. Stream sites were located in riparian forests, sheltered from direct exposure to pollutants from agricultural and urban areas. We focused on three bat species associated with riparian areas: Myotis daubentonii, M. cf. brandtii, and Pipistrellus pipistrellus. We found that streams with higher pesticide toxicity and more frequent detection of wastewater also tended to be warmer and have higher nutrient and lower oxygen concentrations. We did not observe a reduction of insect emergence, bat activity or hunting rates in association with pesticide toxicity and wastewater detections. Instead, the activity and hunting rates of Myotis spp. were higher at more polluted sites. The observed increase in bat hunting at more polluted streams suggests that instead of reduced prey availability, chemical pollution at the levels measured in the present study could expose bats to pollutants transported from the stream by emergent aquatic insects.

Extensive Survey and Analysis of Factors Associated with Presence of Antibodies to Orthoebolaviruses in Bats from West and Central Africa.

The seroprevalence to orthoebolaviruses was studied in 9594 bats (5972 frugivorous and 3622 insectivorous) from Cameroon, the Democratic Republic of Congo (DRC) and Guinea, with a Luminex-based serological assay including recombinant antigens of four orthoebolavirus species. Seroprevalence is expressed as a range according to different cut-off calculations. Between 6.1% and 18.9% bat samples reacted with at least one orthoebolavirus antigen; the highest reactivity was seen with Glycoprotein (GP) antigens. Seroprevalence varied per species and was higher in frugivorous than insectivorous bats; 9.1-27.5% versus 1.3-4.6%, respectively. Seroprevalence in male (13.5%) and female (14.4%) bats was only slightly different and was higher in adults (14.9%) versus juveniles (9.4%) (p < 0.001). Moreover, seroprevalence was highest in subadults (45.4%) when compared to mature adults (19.2%), (p < 0.001). Our data suggest orthoebolavirus circulation is highest in young bats. More long-term studies are needed to identify birthing pulses for the different bat species in diverse geographic regions and to increase the chances of detecting viral RNA in order to document the genetic diversity of filoviruses in bats and their pathogenic potential for humans. Frugivorous bats seem more likely to be reservoirs of orthoebolaviruses, but the role of insectivorous bats has also to be further examined.

A genome assembly of the Yuma myotis bat, Myotis yumanensis.

The Yuma myotis bat (Myotis yumanensis) is a small vespertilionid bat and one of 52 species of new world Myotis bats in the subgenus Pizonyx. While M. yumanensis populations currently appear relatively stable, it is one of 12 bat species known or suspected to be susceptible to white-nose syndrome, the fungal disease causing declines in bat populations across North America. Only two of these 12 species have genome resources available, which limits the ability of resource managers to use genomic techniques to track the responses of bat populations to white-nose syndrome generally. Here we present the first de novo genome assembly for Yuma myotis, generated as a part of the California Conservation Genomics Project. The M. yumanensis genome was generated using a combination of PacBio HiFi long reads and Omni-C chromatin-proximity sequencing technology. This high-quality genome is one of the most complete bat assemblies available, with a contig N50 of 28.03 Mb, scaffold N50 of 99.14 Mb, and BUSCO completeness score of 93.7%. The Yuma myotis genome provides a high-quality resource that will aid in comparative genomic and evolutionary studies, as well as inform conservation management related to white-nose syndrome.

Bat activity is related to habitat structure and time since prescribed fire in managed pine barrens in New England.

Several insectivorous bat species are found in New England, yet research on them is still scarce. Current research shows the ecological importance of bats due to their control of insect populations, but they are endangered by habitat loss and White Nose Syndrome, among other threats. Pine barrens are an uncommon ecosystem found in New England that supports other rare taxa and could be important for these bat species. With hand-held audio recorders, we surveyed for bats in Montague Plains Wildlife Management Area in Massachusetts and Concord Pine Barrens in New Hampshire in June 2022. Our study objectives were to (1) describe the most common bat species and (2) compare bat activity across different habitat types at two managed pine barrens in New England. In particular, we examined bat activity related to habitat type (scrub oak, mature pitch pine, treated pitch pine, hardwood forest), habitat structure (i.e., canopy closure), time since prescribed fire, and path width. We analyzed our data through generalized linear modeling and logistic regression. Overall, we were able to measure the presence of five out of the nine total species found in the area, including the endangered Myotis lucifugus (little brown bat). We recorded 293 bat calls, with the majority of calls from big brown bats (71%). We found significant differences (p<0.05) in bat activity in relation to time since prescribed fire and habitat structure. The index of bat activity was greatest in pitch pine and hardwood forests and lowest in scrub oak and treated pitch pine habitats. With preliminary data, we also found that silver-haired bat presence was influenced by habitat type, with more detections at survey points in hardwood forests. These findings demonstrate the importance of pine barrens as an ecosystem that supports bats in New England. According to the activity of bats in our study, closed canopy and mature pitch pine habitats may be prioritized in conservation efforts at managed barrens for bat species. Further research is recommended to better understand the relationship between prescribed fires, which are common in managed barrens, and bat activity.

Landscape features drive insectivorous bat activity in Indian rice fields

ContextInsectivorous bats have been shown to control a number of agricultural insect pests. As bats exhibit species-specific responses to the surrounding landscape, tied closely to their morphology and foraging mode, the activity and distribution patterns of bats, and consequently the ecosystem services they provide, are influenced by the landscape characteristics.ObjectivesThis study aims to determine which features in the landscape surrounding rice fields influence the activity levels of insectivorous bats, and at what scales they are most influential.MethodsWe collected acoustic recordings to determine activity levels of seven bat sonotypes in rice fields surrounded by a variety of land-cover types in the Nagaon district of Assam, India. Using this, we determined the most important set of features in the surrounding landscape, and the scales at which had the strongest impact, for each sonotype.ResultsOur results suggest that tree cover variables are the most important predictors of bat activity in rice fields. Distance to nearest forest, area of forest within 1 km, distance to nearest forest edge, and landscape heterogeneity influenced all five of the analysed bat sonotypes. Also important were the amount of urban land within 1 km, which exerted a negative effect on the activity of one sonotype, and moonlight activity, which negatively influenced the activity levels of one sonotype.ConclusionOur results demonstrate that when flying over rice fields, bat activity is most influenced by presence and proximity of trees. Therefore, increasing tree cover in agricultural landscapes will increase bat activity and likely the level of pest control.

Detection of novel coronaviruses from dusky fruit bat (Penthetor lucasi) in Sarawak, Malaysian Borneo.

Sarawak has one of the highest diversity of fruit bats species (family Pteropodidae) in Malaysia, with 19 species described. Most coronavirus (CoV) studies have mainly focused on insectivorous bats, resulting in a lack of information on CoVs present in frugivorous bats. In addition, bat CoV surveillance activities are lacking in Malaysia. Our study focuses on determining the presence of bat CoVs in dusky fruit bat (Penthetor lucasi). Guano samples belonging to P. lucasi were collected from Wind Cave Nature Reserve. The samples were screened for the presence of CoVs using validated hemi-nested consensus RNA-dependent RNA polymerase consensus primers. The bat CoV positivity rate was 38.5% (n=15/39), with the viruses belonging to two subgenera: Alphacoronavirus (α-CoV) and Betacoronavirus (β-CoV). Phylogenetic analysis revealed that CoVs from 14 samples of P. lucasi belong to the genus α-CoV and may represent previously described genetic lineages in insectivorous bats in Wind Cave. However, only one sample of P. lucasi was detected with β-CoV which is closely related to subgenus Nobecovirus, which is commonly seen in frugivorous bats. This study provides the first available data on CoVs circulating in P. lucasi.

Dietary analysis of eight insectivorous bats (Chiroptera) from Puting Bato Cave Complex, Burdeos, Polillo Island, Philippines

Food habits of eight insectivorous bat species from Puting Bato Cave Complex, Polillo Island, were examined. Fecal samples collected from eight species of cave-dwelling insectivorous bats contained culled fragments from seven prey taxa (six insect orders and one fish prey). Lepidoptera, Coleoptera, and Hymenoptera were the most consumed group in both percentage volume and percentage frequency. The diet of Hipposideros diadema, H. pygmaeus, Rhinolophus arcuatus, and R. philippinensis mostly concurs with previous studies but with varying proportions. Baseline information on the diets of H. coronatus, M. paululus, R. macrotis, and R. rufus is provided in this study.

First record of leucism in two species of insectivore bats (Chiroptera) from San Luis province, Argentina

El leucismo se define como la falta total o parcial de pigmentación en el cuerpo, exceptuando las partes blandas. Este desorden podría afectar la supervivencia y el éxito reproductivo del animal. En este trabajo se reporta el primer caso de leucismo en Eptesicus furinalis y Tadarida brasiliensis en la provincia de San Luis, Argentina. Para cada especie, se colectó un macho con leucismo, registrándose coloración atípica en el pelaje dorsal y ventral, mientras que los ojos y las membranas tuvieron coloración normal. Comunicar estos desórdenes pigmentarios en murciélagos es fundamental como punto de partida para futuras investigaciones etológicas, ecológicas y genéticas.

The nose knows: a review of the diversity, form, and function of the external and internal features of the bat nose

Dr. M. Brock Fenton has been intrigued by the diversity of bats throughout his long career, and has combined his research and photography skills to capture the extensive morphological diversity found across the order Chiroptera. In this paper, we honour Brock’s fascination with diversity by conducting a review of the external and internal characteristics of the bat nose, a morphological feature that Brock’s photographs have beautifully captured in many bat species. Specifically, we explore variation in form and function of the bat rostrum and its role in respiration, echolocation, and olfaction in bats, with an emphasis on the noseleaves of nasal-emitting echolocators, as well as how turbinate morphology may be impacted by nasophonation. While our review is not an extensive dive into all that is known about bat noses, our goal is to highlight the diversity we see in form across the order Chiroptera while exploring how function has been shaped by selection, particularly in relation to mode of echolocation signal emission.