DIETARY VARIATION OF BRAZILIAN FREE-TAILED BATS LINKS TO MIGRATORY POPULATIONS OF PEST INSECTS

All-you-can-eat buffet: A spider-specialized bat species (Myotis emarginatus) turns into a pest fly eater around cattle

Determining the dietary spectrum of European insectivorous bats over time is the cornerstone of their conservation, as it will aid our understanding of foraging behavior plasticity in response to plummeting insect populations. Despite the global decline in insects, a restricted number of arthropod pest species thrive. Yet past research has overlooked the potential of European bats to suppress pests harmful to woodlands or livestock, in spite of their economic relevance. Here we investigated the diet composition, its breeding season variations and pest consumption of an insectivorous bat species (Myotis emarginatus), at the northern edge of its range (Wallonia, Belgium). We also explored the prey ecology to gain insight into the hunting strategies and foraging habitats of this bat species. We used DNA metabarcoding to amplify two COI markers within 195 bat droppings collected in June, July and August, thereby identifying 512 prey taxa predominated by Diptera, Araneae and Lepidoptera. Overall, in 97% of the samples we detected at least one of the 58 potential pest taxa, 41 of which targeting trees. The June samples were marked by a diet rich in orb-weaver spiders, in accordance with the archetypal diet of M. emarginatus bats. However, during the highly energy demanding July-August parturition and lactation period, roughly 55% of the dropping samples contained two cattle fly pests (Stomoxys calcitrans and Musca domestica). Moreover, among the 88 Diptera species preyed upon by M. emarginatus in July and August, these flies accounted for around 50% of the taxa occurrences. This plasticity-the switch from a spider-rich to a fly-rich diet-seems providential considering the dramatic ongoing drop in insect populations but this involves ensuring bat-friendly cattle farming. Our results revealed that bats widely consume pest entomofauna, thereby highlighting their potential role as allies of forest managers and farmers.

High temporal resolution data reveal low bat and insect activity over managed meadows in central Europe

Increasing agriculture and pesticide use have led to declines in insect populations and biodiversity worldwide. In addition to insect diversity, it is also important to consider insect abundance, due to the importance of insects as food for species at higher trophic levels such as bats. We monitored spatiotemporal variation in abundance of nocturnal flying insects over meadows, a common open landscape structure in central Europe, and correlated it with bat feeding activity. Our most important result was that insect abundance was almost always extremely low. This was true regardless of management intensity of the different meadows monitored. We also found no correlation of insect abundance or the presence of insect swarms with bat feeding activity. This suggests that insect abundance over meadows was too low and insect swarms too rare for bats to risk expending energy to search for them. Meadows appeared to be poor habitat for nocturnal flying insects, and of low value as a foraging habitat for bats. Our study highlights the importance of long-term monitoring of insect abundance, especially at high temporal scales to identify and protect foraging habitats. This will become increasingly important given the rapid decline of insects.

Aerospace-foraging bats eat seasonably across varying habitats

Recent research has confirmed the efficiency of insectivorous bats as pest suppressors, underlining the ecological services they offer in agroecosystems. Therefore, some efforts try to enhance bat foraging in agricultural landscapes by acting upon environmental factors favouring them. In this study, we monitored a Miniopterus schreibersii colony, in the southern Iberian Peninsula. We intensively sampled their faeces and analysed them by metabarcoding to describe how the bent-winged bat diet would change with time, and to test whether their most-consumed prey would seasonally depend on different landscapes or habitats. Our results confirm that M. schreibersii are selective opportunist predators of moths, dipterans, mayflies, and other fluttering insects, shifting their diet to temporary peaks of prey availability in their foraging range, including both pest and non-pest insects. Supporting our hypothesis, throughout the year, M. schreibersii consume insects linked to diverse open habitats, including wetlands, grassland, diverse croplands, and woodland. The importance of each prey habitat varies seasonally, depending on their insect phenology, making bats indirectly dependent on a diverse landscape as their primary prey source. Bats' predation upon pest insects is quantitatively high, consuming around 1610 kg in 5 months, of which 1467 kg correspond to ten species. So, their suppression effect may be relevant, mainly in patchy heterogeneous landscapes, where bats' foraging may concentrate in successive outbursts of pests, affecting different crops or woodlands. Our results stress that to take advantage of the ecosystem services of bats or other generalist insectivores, keeping the environmental conditions they require to thrive, particularly a heterogeneous landscape within the colony's foraging area, is crucial.

Pest suppression by bats and management strategies to favour it: a global review

Fighting insect pests is a major challenge for agriculture worldwide, and biological control and integrated pest management constitute well-recognised, cost-effective ways to prevent and overcome this problem. Bats are important arthropod predators globally and, in recent decades, an increasing number of studies have focused on the role of bats as natural enemies of agricultural pests. This review assesses the state of knowledge of the ecosystem services provided by bats as pest consumers at a global level and provides recommendations that may favour the efficiency of pest predation by bats. Through a systematic review, we assess evidence for predation, the top-down effect of bats on crops and the economic value of ecosystem services these mammals provide, describing the different methodological approaches used in a total of 66 reviewed articles and 18 agroecosystem types. We also provide a list of detailed conservation measures and management recommendations found in the scientific literature that may favour the delivery of this important ecosystem service, including actions aimed at restoring bat populations in agroecosystems. The most frequent recommendations include increasing habitat heterogeneity, providing additional roosts, and implementing laws to protect bats and reduce agrochemical use. However, very little evidence is available on the direct consequences of these practices on bat insectivory in farmland. Additionally, through a second in-depth systematic review of scientific articles focused on bat diet and, as part of the ongoing European Cost Action project CA18107, we provide a complete list of 2308 documented interactions between bat species and their respective insect pest prey. These pertain to 81 bat species belonging to 36 different genera preying upon 760 insect pests from 14 orders in agroecosystems and other habitats such as forest or urban areas. The data set is publicly available and updatable.

Investigating the Migratory Behavior of Soybean Looper, a Major Pest of Soybean, through Comparisons with the Corn Pest Fall Armyworm Using Mitochondrial Haplotypes and a Sex-Linked Marker

The Noctuid moth soybean looper (SBL), Chrysodeixis includens (Walker), is an economically important pest of soybean (Glycine max (Linnaeus) Merrill). Because it is not known to survive freezing winters, permanent populations in the United States are believed to be limited to the southern regions of Texas and Florida, yet its geographical range of infestations annually extend to Canada. This indicates annual migrations of thousands of kilometers during the spring and summer growing season. This behavior is like that of the fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), also a Noctuid that is a major global pest of corn. SBL and FAW are projected to have very similar distributions of permanent populations in North America based on climate suitability modeling and the overlap in the distribution of their preferred host plants (corn and soybean). It therefore seems likely that the two species will display similar migratory behavior in the United States. This was tested by identifying genetic markers in SBL analogous to those successfully used to delineate FAW migratory pathways and comparing the distribution patterns of the markers from the two species. Contrary to expectations, the results indicate substantial differences in migratory behavior that appear to be related to differences in the timing of corn and soybean plantings. These findings underscore the importance of agricultural practices in influencing pest migration patterns, in particular the timing of host availability relative to mean seasonal air transport patterns.

Our good neighbors: Understanding ecosystem services provided by insectivorous bats in Rwanda

Bats are prodigious consumers of agricultural and forest pests, and are, therefore, a natural asset for agricultural productivity, suppressing populations of such pests. This study provides baseline information of diet of 143 bats belonging to eight insectivorous bat species from agricultural areas of Rwanda while evaluating the effectiveness of bats as pest suppressors. Using DNA metabarcoding to analyze bat fecal pellets, 85 different insect species were detected, with 60% (n = 65), 64% (n = 11) and 78% (n = 9) found to be agricultural pests from eastern, northern and western regions, respectively. Given the high percentages of agricultural pests detected, we submit that Rwandan insectivorous bats have the capacity for biocontrol of agricultural pests. Rwandan bat populations should be protected and promoted since they may foster higher crop yields and sustainable livelihoods.

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.

Going out for dinner-The consumption of agriculture pests by bats in urban areas

Insectivorous bats provide ecosystem services in agricultural and urban landscapes by consuming arthropods that are considered pests. Bat species inhabiting cities are expected to consume insects associated with urban areas, such as mosquitoes, flying termites, moths, and beetles. We captured insectivorous bats in the Federal District of Brazil and used fecal DNA metabarcoding to investigate the arthropod consumed by five bat species living in colonies in city buildings, and ascertained whether their predation was related to ecosystem services. These insectivorous bat species were found to consume 83 morphospecies of arthropods and among these 41 were identified to species, most of which were agricultural pests. We propose that bats may roost in the city areas and forage in the nearby agricultural fields using their ability to fly over long distances. We also calculated the value of the pest suppression ecosystem service by the bats. By a conservative estimation, bats save US$ 94 per hectare of cornfields, accounting for an annual savings of US$ 390.6 million per harvest in Brazil. Our study confirms that, regardless of their roosting location, bats are essential for providing ecosystem services in the cities, with extensive impacts on crops and elsewhere, in addition to significant savings in the use of pesticides.

Diet of arthropodophagous bats (Mammalia, Chiroptera) from Northwestern Argentina

The diet of arthropodophagous bats can be influenced by several factors. Furthermore, its study is critical for understanding their role in the ecosystem as regulators of arthropod abundance. The aim of this study was to analyze the diet of 12 species beloging to two families of arthropodophagous bats from the Yungas Forests, Northwestern Argentina. We also evaluated differences in diet between well-preserved and disturbed sites, sexes, and seasons. The specimens were collected with mist nets in eight different localities, four well-preserved and four disturbed sites of the Yungas Forests. Through the analysis of feces, arthropod remains were identified until the lowest possible taxonomic level. Volume and frequency of occurrence percentages for each food item and the niche breadth for the species were estimated. A total of 475 samples from 12 species were analyzed and their diet contained arthropods from eight orders and seven families; the highest number of consumed arthropod orders were registered for Eptesicus diminutus. A low niche breadth was recorded in general for all species. The diet was significantly influenced by season and site characteristics only in E. diminutus and E. furinalis, respectively. This showed that bats could modify its diet according to the different habitats and seasons.

Climatic drivers of (changes in) bat migration phenology at Bracken Cave (USA)

Climate change is drastically changing the timing of biological events across the globe. Changes in the phenology of seasonal migrations between the breeding and wintering grounds have been observed across biological taxa, including birds, mammals, and insects. For birds, strong links have been shown between changes in migration phenology and changes in weather conditions at the wintering, stopover, and breeding areas. For other animal taxa, the current understanding of, and evidence for, climate (change) influences on migration still remains rather limited, mainly due to the lack of long-term phenology datasets. Bracken Cave in Texas (USA) holds one of the largest bat colonies of the world. Using weather radar data, a unique 23-year (1995-2017) long time series was recently produced of the spring and autumn migration phenology of Brazilian free-tailed bats (Tadarida brasiliensis) at Bracken Cave. Here, we analyse these migration phenology time series in combination with gridded temperature, precipitation, and wind data across Mexico and southern USA, to identify the climatic drivers of (changes in) bat migration phenology. Perhaps surprisingly, our extensive spatiotemporal search did not find temperature to influence either spring or autumn migration. Instead, spring migration phenology seems to be predominantly driven by wind conditions at likely wintering or spring stopover areas during the migration period. Autumn migration phenology, on the other hand, seems to be dominated by precipitation to the east and north-east of Bracken Cave. Long-term changes towards more frequent migration and favourable wind conditions have, furthermore, allowed spring migration to occur 16 days earlier. Our results illustrate how some of the remaining knowledge gaps on the influence of climate (change) on bat migration and abundance can be addressed using weather radar analyses.

Bat community response to intensification of biomass production for bioenergy across the southeastern United States

Human demand for food, fiber, and space is accelerating the rate of change of land cover and land use. Much of the world now consists of a matrix of natural forests, managed forests, agricultural cropland, and urbanized plots. Expansion of domestic energy production efforts in the United States is one driver predicted to influence future land-use and land management practices across large spatial scales. Favorable growing conditions make the southeastern United States an ideal location for producing a large portion of the country's renewable bioenergy. We investigated patterns of bat occurrence in two bioenergy feedstocks commonly grown in this region (corn, Zea mays, and pine, Pinus taeda and P. elliottii). We also evaluated potential impacts of the three major pathways of woody biomass extraction (residue removal following clearcut harvest, short-rotation energy plantations, and mid-rotation forest thinning) to bat occurrence through a priori land-use contrasts. We acoustically sampled bat vocalizations at 84 sites in the Southeastern Plains and Southern Coastal Plains of the southeastern United States across three years. We found that mid-rotation thinning resulted in positive effects on bat occurrence, and potential conversion of unmanaged (reference) forest to managed forest for timber and/or bioenergy harvest resulted in negative effects on bat occurrence when effects were averaged across all species. The effects of short-rotation energy plantations, removal of logging residues from plantation clearcuts, and corn were equivocal for all bat species examined. Our results suggest that accelerated production of biomass for energy production through either corn or intensively managed pine forests is not likely to have an adverse effect on bat communities, so long as existing older unmanaged forests are not converted to managed bioenergy or timber plantations. Beyond bioenergy crop production, mid-rotation thinning of even-aged pine stands intended for timber production, increases to the duration of plantation rotations to promote older forest stands, arranging forest stands and crop fields to maximize edge habitat, and maintaining unmanaged forests could benefit bat communities by augmenting roosting and foraging opportunities.

Species-specific effects of moonlight on insectivorous bat activity in central Chile

Moonlight intensity influences the activity patterns of bats. Some bat species reduce their activity levels during brighter nights, a phenomenon known as “lunar phobia.” While lunar phobia of bats has been extensively studied in tropical regions, the same is not the case of bats in temperate regions. By using acoustic detectors, we examined differences in the activity of insectivorous bats on nights with different moonlight intensity in an agricultural landscape of central Chile. We also examined the hourly activity patterns throughout the night and how these varied between full and new moon nights. All bat species modified their activity based on the moonlight intensity; however, their effects were species-specific. The activity of Lasiurus varius, L. villosissimus, Myotis chiloensis, and Histiotus montanus was lower during bright nights, while Tadarida brasiliensis was the only species whose activity was higher during bright nights. Hourly activity throughout the night differed between full moon nights and new moon nights in most bat species. During full moon, bats concentrated their activities in the early hours of the nights; a more homogeneous activity pattern was exhibited during new moon night. Our study demonstrates that moonlight affects the activity of bats in Chile, a factor that should be considered when studying bats.

Insectivorous bats as biomonitor of metal exposure in the megalopolis of Mexico and rural environments in Central Mexico

The Megalopolis of Mexico is one of the largest cities in the world and presents substantial problems of metal pollution. Insectivorous bats that inhabit this city are potentially exposed to metals and could therefore serve as a good biomonitor. We collected 70 adult male individuals of Tadarida brasiliensis (Chiroptera: Molossidae) from two areas inside the Megalopolis (Cuautitlán and Xochimilco) and two rural environments in Central Mexico (Tequixquiac and Tlalcozotitlán). We analyzed livers to determine the total concentrations of ten metals by the ICP-MS technique, compared concentrations among study sites to provide evidence of metal exposure, and explored the associations between metals and their accumulation patterns in bats. The hepatic metal concentrations we recorded were generally consistent with those of similar studies in insectivorous bats. Higher concentrations of Cu and Zn in Cuautitlán and Xochimilco bats were associated with vehicular traffic. Higher concentrations of V, Cr, and Co in Tequixquiac bats and Cd in Tlalcozotitlán bats were linked with industrial, agricultural, or sewage sources. Variations in Fe and Mn concentrations were related to geogenic sources or local conditions. Similar Ni and Pb concentrations were linked with strong homeostatic controls or historical pollution. Accumulation patterns showed that all urban bats belonged to a single population with similar degrees of metal exposure, while rural bats belonged to two different populations exposed to different metals. Our results highlight the need to monitor the emissions generated by particular sources in each study site.

Faecal analyses and alimentary tracers reveal the foraging ecology of two sympatric bats

We used three complementary methods to assess the diet of two insectivorous bat species: one an obligate aerial hunter, Miniopterus natalensis, and the other Myotis tricolor whose morphology and taxonomic affiliation to other trawling bats suggests it may be a trawler (capturing insects from the water surface with its feet and tail). We used visual inspection, stable isotope values and fatty acid profiles of insect fragments in bat faeces sampled across five sites to determine the contribution of aquatic and terrestrial arthropods to the diets of the two species. The niche widths of M. tricolor were generally wider than those of Miniopterus natalensis but with much overlap, both taking aquatic and terrestrial insects, albeit in different proportions. The diet of M. tricolor had high proportions of fatty acids (20:5ω3 and 22:6ω3) that are only obtainable from aquatic insects. Furthermore, the diet of M. tricolor had higher proportions of water striders (Gerridae) and whirligig beetles (Gyrinidae), insects obtainable via trawling, than Miniopterus natalensis. These results suggest both species are flexible in their consumption of prey but that M. tricolor may use both aerial hawking and trawling, or at least gleaning, to take insects from water surfaces. The resultant spatial segregation may sufficiently differentiate the niches of the two species, allowing them to co-exist. Furthermore, our results emphasize that using a combination of methods to analyse diets of cryptic animals yields greater insights into animal foraging ecology than any of them on their own.

Insectivorous bats selectively source moths and eat mostly pest insects on dryland and irrigated cotton farms

Insectivorous bats are efficient predators of pest arthropods in agroecosystems. This pest control service has been estimated to be worth billions of dollars to agriculture globally. However, few studies have explicitly investigated the composition and abundance of dietary prey items consumed or assessed the ratio of pest and beneficial arthropods, making it difficult to evaluate the quality of the pest control service provided. In this study, we used metabarcoding to identify the prey items eaten by insectivorous bats over the cotton-growing season in an intensive cropping region in northern New South Wales, Australia. We found that seven species of insectivorous bat (n = 58) consumed 728 prey species, 13 of which represented around 50% of total prey abundance consumed. Importantly, the identified prey items included major arthropod pests, comprising 65% of prey relative abundance and 13% of prey species recorded. Significant cotton pests such as Helicoverpa punctigera (Australian bollworm) and Achyra affinitalis (cotton webspinner) were detected in at least 76% of bat fecal samples, with Teleogryllus oceanicus (field crickets), Helicoverpa armigera (cotton bollworm), and Crocidosema plebejana (cotton tipworm) detected in 55% of bat fecal samples. Our results indicate that insectivorous bats are selective predators that exploit a narrow selection of preferred pest taxa and potentially play an important role in controlling lepidopteran pests on cotton farms. Our study provides crucial information for farmers to determine the service or disservice provided by insectivorous bats in relation to crops, for on-farm decision making.

Agro-ecological options for fall armyworm (Spodoptera frugiperda JE Smith) management: Providing low-cost, smallholder friendly solutions to an invasive pest

Fall armyworm (FAW), a voracious agricultural pest native to North and South America, was first detected on the African continent in 2016 and has subsequently spread throughout the continent and across Asia. It has been predicted that FAW could cause up to $US13 billion per annum in crop losses throughout sub-Saharan Africa, thereby threatening the livelihoods of millions of poor farmers. In their haste to respond to FAW governments may promote indiscriminate use of chemical pesticides which, aside from human health and environmental risks, could undermine smallholder pest management strategies that depend to a large degree on natural enemies. Agro-ecological approaches offer culturally appropriate low-cost pest control strategies that can be readily integrated into existing efforts to improve smallholder incomes and resilience through sustainable intensification. Such approaches should therefore be promoted as a core component of integrated pest management (IPM) programmes for FAW in combination with crop breeding for pest resistance, classical biological control and selective use of safe pesticides. Nonetheless, the suitability of agro-ecological measures for reducing FAW densities and impact need to be carefully assessed across varied environmental and socio-economic conditions before they can be proposed for wide-scale implementation. To support this process, we review evidence for the efficacy of potential agro-ecological measures for controlling FAW and other pests, consider the associated risks, and draw attention to critical knowledge gaps. The evidence indicates that several measures can be adopted immediately. These include (i) sustainable soil fertility management, especially measures that maintain or restore soil organic carbon; (ii) intercropping with appropriately selected companion plants; and (iii) diversifying the farm environment through management of (semi)natural habitats at multiple spatial scales. Nevertheless, we recommend embedding trials into upscaling programmes so that the costs and benefits of these interventions may be determined across the diverse biophysical and socio-economic contexts that are found in the invaded range.

Mercury Bioaccumulation in Two Species of Insectivorous Bats from Urban China: Influence of Species, Age, and Land Use Type

Mercury (Hg) is a widespread, toxic pollutant, and China is the world's largest emitter. We investigated Hg concentrations of fur in Japanese pipistrelles (Pipistrellus abramus) and Chinese noctules (Nyctalus plancyi) from Chengdu, Sichuan Province, in relation to degree of urbanization. Bats were mist-netted in June and July 2013, and the fur was analyzed via atomic absorption. Statistical comparisons were made between ages, species, and site types with unpaired t tests and between Hg concentration and body condition with Spearman's rank correlations. Across sites, adult pipistrelles (n = 10) had significantly greater concentrations than adult noctules (n = 16). Adult N. plancyi (n = 16) had significantly greater concentrations than juvenile N. plancyi (n = 14). Contrary to our predictions, there was no significant difference in Hg values between urban (n = 3) and peri-urban (n = 6) locations for P. abramus. While small sample sizes precluded additional comparisons, the highest value (33 mg/kg) came from an adult female P. abramus in the agricultural area. The relationship between body condition and Hg concentration was insignificant. However, most pipistrelles (7/13) and no noctules (0/31) had concentrations > 10 mg/kg, a threshold associated with disruption of homeostatic control and mobility. All bats had concentrations > 0.2 mg/kg, which is associated with compromised immunity. These are the first published records of contaminant concentrations from bats in China. For future studies, we recommend P. abramus as a regional bioindicator, longer term assessments of pre- and post-exposure effects, and simultaneous assessment of blood and fur Hg concentrations.

Willingness to Pay for Conservation of Transborder Migratory Species: A Case Study of the Mexican Free-Tailed Bat in the United States and Mexico

We estimated U.S. and Mexican citizens' willingness to pay (WTP) for protecting habitat for a transborder migratory species, the Mexican free-tailed bat (Tadarida brasiliensis mexicana), using the contingent valuation method. Few contingent valuation surveys have evaluated whether households in one country would pay to protect habitat in another country. This study addresses that gap. In our study, Mexican respondents were asked about their WTP for conservation of Mexican free-tailed bat habitat in Mexico and in the United States. Similarly, U.S. respondents were asked about their WTP for conservation in the United States and in Mexico. U.S. households would pay $30 annually to protect habitat in the United States and $24 annually to protect habitat in Mexico. Mexican households would pay $8 annually to protect habitat in Mexico and $5 annually to protect habitat in the United States. In both countries, these WTP amounts rose significantly for increasing the size of the bat population rather than simply stabilizing the current bat population. The ratio of Mexican household WTP relative to U.S. household WTP is nearly identical to that of Mexican household income relative to U.S. household income. This suggests that the perceived economic benefits received from the bats is similar in Mexico and the United States, and that scaling WTP by relative income in international benefit transfer may be plausible.

Ongoing changes in migration phenology and winter residency at Bracken Bat Cave

Bats play an important role in agroecology and are effective bioindicators of environmental conditions, but little is known about their fundamental migration ecology, much less how these systems are responding to global change. Some of the world's largest bat populations occur during the summer in the south-central United States, when millions of pregnant females migrate from lower latitudes to give birth in communal maternity colonies. Despite a relatively large volume of research into these colonies, many fundamental questions regarding their abundance-including their intra- and interseasonal variability-remain unanswered, and even estimating the size of individual populations has been a long-running challenge. Overall, monitoring these bat populations at high temporal resolution (e.g., nightly) and across long time spans (e.g., decades) has been impossible. Here, we show 22 continuous years of nightly population counts at Bracken Cave, a large bat colony in south-central Texas, enabling the first climate-scale phenological analysis. Using quantitative radar monitoring, we found that spring migration and the summer reproductive cycle have advanced by approximately 2 weeks over the study period. Furthermore, we quantify the ongoing growth of a newly-established overwintering population that indicates a system-wide response to changing environmental conditions. Our observations reveal behavioral plasticity in bats' ability to adapt to changing resource availability, and provide the first long-term quantification of their response to a changing climate. As aerial insectivores, these changes in bat phenology and propensity for overwintering indicate probable shifts in prey availability, with clear implications for pest management across wider regional agrisystems.

Brazilian free-tailed bats (Tadarida brasiliensis) adjust foraging behaviour in response to migratory moths

Insect migrations represent large movements of resources across a landscape, which are attractive to predators capable of detecting and catching them. Brazilian free-tailed bats (Tadarida brasiliensis (I. Geoffroy, 1824)) consume migratory noctuid moths, which concentrate in favourable winds resulting in aggregations of prey that attract bats hundreds of metres above ground. Although T. brasiliensis are known to feed on these aggregations of migratory moths, changes in their foraging behaviours have not been linked to moth migration events. We investigated possible shifts in the bats’ foraging behaviours when moths are migrating with respect to altitude and moth abundance. We recorded 1104 echolocation call passes of T. brasiliensis at ground level and at altitudes of ∼100 and ∼200 m above ground level. We found proportionally more bat activity at higher altitudes when migratory moth abundance was high. We also found that bats decreased call frequency and bandwidth and increased call duration at higher altitudes and behaved similarly with increasing moth abundance even at ground level. Our results support predictions that bats change foraging behaviour in response to seasonal availability of migratory moths and document alterations in echolocation call parameters that are consistent with optimizing prey detection.

Advances on the group composition, mating system, roosting and flight behaviour of the European free-tailed bat (Tadarida teniotis)

We investigated a large colony of European free-tailed bats (Tadarida teniotis) in Spain, using a combination of capture-mark-recapture data and direct observations. Its social and reproductive organisation is complex and the mating system fits a “resource defence polygyny” model. In spring and autumn, aggressive interactions in flight, defence of roosts and mating songs of males to attract females occurred. According to our results, T. teniotis is organised in “harems” consisting of a dominant male and a variable number of females. In addition the sexual cycle displayed a bimodal reproductive pattern (this is unique and remarkable for European bats). The bimodal pattern coincided with peaks in food availability (moths) at high altitudes. Presumably, roost-guarding activities (patrolling, advertising…) make males less prone to move away (e.g. at higher altitudes and longer distances) from roosts, resulting in differences in prey selection and in altitudinal segregation between sexes. This provides a plausible explanation for the differences in diet (predation of more sedentary vs. high-flying migratory moths) between males and females that has been found in published studies.

Anthropogenic noise changes arthropod abundances

Anthropogenic noise is a widespread and growing form of sensory pollution associated with the expansion of human infrastructure. One specific source of constant and intense noise is that produced by compressors used for the extraction and transportation of natural gas. Terrestrial arthropods play a central role in many ecosystems, and given that numerous species rely upon airborne sounds and substrate‐borne vibrations in their life histories, we predicted that increased background sound levels or the presence of compressor noise would influence their distributions. In the second largest natural gas field in the United States (San Juan Basin, New Mexico, USA), we assessed differences in the abundances of terrestrial arthropod families and community structure as a function of compressor noise and background sound level. Using pitfall traps, we simultaneously sampled five sites adjacent to well pads that possessed operating compressors, and five alternate, quieter well pad sites that lacked compressors, but were otherwise similar. We found a negative association between sites with compressor noise or higher levels of background sound and the abundance of five arthropod families and one genus, a positive relationship between loud sites and the abundance of one family, and no relationship between noise level or compressor presence and abundance for six families and two genera. Despite these changes, we found no evidence of community turnover as a function of background sound level or site type (compressor and noncompressor). Our results indicate that anthropogenic noise differentially affects the abundances of some arthropod families. These preliminary findings point to a need to determine the direct and indirect mechanisms driving these observed responses. Given the diverse and important ecological functions provided by arthropods, changes in abundances could have ecological implications. Therefore, we recommend the consideration of arthropods in the environmental assessment of noise‐producing infrastructure.

Sub-lethal Effects of Chlorpyrifos on Big Brown Bats (Eptesicus fuscus)

We determined dose-response curves for sublethal effects of the organophosphorus (OP) insecticide, chlorpyrifos, on bats. Big brown bats (Eptesicus fuscus, n = 64) were given a single dose of chlorpyrifos (nominal concentrations) of 0, 5, 10, 15, 20, 25, 30, or 60 µg/g body weight and examined at 12 or 24 h after dosing. A second experiment dosed 32 bats with 0 or 60 µg/g body weight and examined 1, 3, 7, or 14 days after dosing. Skin temperature and behavioral changes were recorded, and brain and plasma cholinesterase (ChE) activity were measured. The benchmark dose (BMD10) of chlorpyrifos that altered brain and plasma ChE activity at 24 h was 3.7 and 10.1 µg/g, respectively. The 95 % lower confidence limit for the BMD10 (i.e., BMDL10) was 1.6 and 7.7 µg/g. The best of five models (as determined by AIC) for impaired flight, impaired movement, or presence of tremors provided a BMD10 of 6.2, 12.9, and 7.8 µg/g body weight of chlorpyrifos, respectively. BMDL10 for impaired flight, impaired movement, or presence of tremors was 3.5, 6.6, and 5.3 µg/g body weight, respectively. In the wild, impaired ability to fly or crawl could be life-threatening. Brain and plasma ChE activity remained low for 3 days after dosing. Gradual recovery of enzyme activity was observed by 7 days in survivors. Brain and plasma ChE activity were still significantly lower than that of the control group at 14 days after dosing.

Effects of land use on bat diversity in a complex plantation–forest landscape in northeastern Brazil

In fragmented areas, the persistence of different species depends on their ability to use the surrounding matrix either as a corridor or as a foraging habitat. We assessed how species richness and abundance of Neotropical bats differ among forest fragments and rubber plantations under different management regimes. Our study site was located in a heterogeneous agricultural area in the Atlantic Forest of Bahia, northeastern Brazil. By combining mist netting and acoustic monitoring as complementary techniques, we caught 28 phyllostomid species and recorded 21 aerial insectivorous species, which either forage in open space or close to forests. Open space species were equally abundant and diverse in all land use types. In contrast, assemblages of phyllostomid and aerial insectivorous forest species differed significantly among habitats, with the highest species richness recorded in forest fragments. We identified a number of forest specialists in forest fragments, which indicates a relatively intact bat fauna. In intensively used rubber-cacao plantation, we found surprisingly high bat abundance and diversity, despite the shortage of resources for bats. Our results also indicate that patches of secondary vegetation around rubber plantations are important landscape features for bats and might contribute to the persistence of highly diverse bat assemblages. We suggest that bats do not perceive plantations as a hostile matrix, but probably use them as corridors between forest fragments and patches of secondary vegetation.

Em áreas fragmentadas, a persistência de diferentes espécies depende da habilidade delas em usar a matriz ao redor como um corredor ou hábitat de forrageio. Nós avaliamos como a riqueza de espécies e abundância de morcegos neotropicais diferem entre fragmentos de mata e seringais sob diferentes regimes de manejo. Nossa área de estudo estava localizada em uma área agrícola heterogênea na Mata Atlântica da Bahia, nordeste do Brasil. Combinando capturas em redes com monitoramento acústico como técnicas complementares, capturamos 28 espécies de morcegos filostomídeos e 21 espécies de morcegos insetívoros aéreos, que forrageiam em espaço aberto ou perto de florestas. As espécies de espaço aberto foram igualmente abundantes e diversas em todas as categorias de uso da terra. Por outro lado, comunidades de filostomídeos e insetívoros aéreos de florestas diferiram significativamente entre hábitats, com a maior riqueza de espécies tendo sido registrada em fragmentos de mata. Identificamos muitos especialistas em florestas nos fragmentos de mata, o que sugere que a fauna de morcegos ainda está relativamente intacta. Em plantações mistas de cacau e seringais intensivamente usadas, encontramos uma abundância e riqueza de morcegos surpreendentemente altas, apesar da escassez de recursos para morcegos. Nossos resultados indicam que manchas de vegetação secundária ao redor de seringais são importantes elementos da paisagem para morcegos e podem contribuir para a persistência de comunidades altamente diversas. Sugerimos que morcegos não percebem as plantações como uma matriz hostil, mas provavelmente as usam como corredores entre fragmentos de mata e manchas de vegetação secundária.

Tone-deaf ears in moths may limit the acoustic detection of two-tone bats

Frequency alternation in the echolocation of insectivorous bats has been interpreted in relation to ranging and duty cycle, i.e. advantages for echolocation. The shifts in frequency of the calls of these so-called two-tone bats, however, may also play its role in the success of their hunting behavior for a preferred prey, the tympanate moth. How the auditory receptors (e.g. the A1 and A2 cells) in the moth's ear detect such frequency shifts is currently unknown. Here, we measured the auditory responses of the A1 cell in the noctuid Spodoptera frugiperda to the echolocation hunting sequence of Molossus molossus, a two-tone bat. We also manipulated the bat calls to control for the frequency shifts by lowering the frequency band of the search and approach calls. The firing response of the A1 receptor cell significantly decreases with the shift to higher frequencies during the search and approach phases of the hunting sequence of M. molossus; this could be explained by the receptor's threshold curve. The frequency dependence of the decrease in the receptor's response is supported by the results attained with the manipulated sequence: search and approach calls with the same minimum frequency are detected by the moth at the same threshold intensity. The two-tone bat M. molossus shows a call frequency alternation behavior that may enable it to overcome moth audition even in the mid-frequency range (i.e. 20-50 kHz) where moths hear best.

Market forces and technological substitutes cause fluctuations in the value of bat pest-control services for cotton

Critics of the market-based, ecosystem services approach to biodiversity conservation worry that volatile market conditions and technological substitutes will diminish the value of ecosystem services and obviate the “economic benefits” arguments for conservation. To explore the effects of market forces and substitutes on service values, we assessed how the value of the pest-control services provided by Mexican free-tailed bats (Tadarida brasiliensis mexicana) to cotton production in the southwestern U.S. has changed over time. We calculated service values each year from 1990 through 2008 by estimating the value of avoided crop damage and the reduced social and private costs of insecticide use in the presence of bats. Over this period, the ecosystem service value declined by 79% ($19.09 million U.S. dollars) due to the introduction and widespread adoption of Bt (Bacillus thuringiensis) cotton transgenically modified to express its own pesticide, falling global cotton prices and the reduction in the number of hectares in the U.S. planted with cotton. Our results demonstrate that fluctuations in market conditions can cause temporal variation in ecosystem service values even when ecosystem function – in this case bat population numbers – is held constant. Evidence is accumulating, however, of the evolution of pest resistance to Bt cotton, suggesting that the value of bat pest-control services may increase again. This gives rise to an economic option value argument for conserving Mexican free-tailed bat populations. We anticipate that these results will spur discussion about the role of ecosystem services in biodiversity conservation in general, and bat conservation in particular.

Diet of the insectivorous bat Pipistrellus nathusii during autumn migration and summer residence

Migration is widespread among vertebrates, yet bat migration has received little attention and only in the recent decades has a better understanding of it been gained. Migration can cause significant changes in behaviour and physiology, due to increasing energy demands and aerodynamic constraints. Dietary shifts, for example, have been shown to occur in birds before onset of migration. For bats, it is not known if a change in diet occurs during migration, although breeding season-related dietary preference has been documented. It is known that a diet rich in fats and the accumulation of fat deposits do increase the flight range of migratory bats. Some bat species can be regarded as long-distance migrants, covering up to 2000 km between summer and winter roosting areas. Pipistrellus nathusii (Vespertilionidae), a European long-distant migrant, travels each year along the Baltic Sea from north-eastern Europe to hibernate in central and southern Europe. This study presents data on the dietary habits of migrating Pipistrellus nathusii compared with those during the breeding season. We analysed faecal samples from bats on fall migration caught at the Ornithological Field Station in Pape, Latvia and from samples collected in North-Latvian summer roosts. We applied both morphological identification and molecular methods, as morphological methods also recognize life stages of prey and can contribute frequency data. The diets of bats on migration and breeding bats were similar, with Diptera and Lepidoptera comprising the major prey categories. However, certain prey groups could be explained by the different hunting habitats exploited during migration vs. summer residence.

Bats in a farming landscape benefit from linear remnants and unimproved pastures

Schemes designed to make farming landscapes less hostile to wildlife have been questioned because target taxa do not always respond in the expected manner. Microbats are often overlooked in this process, yet persist in agricultural landscapes and exert top-down control of crop pests. We investigated the relationship between microbats and measures commonly incorporated into agri-environment schemes, to derive management recommendations for their ongoing conservation. We used acoustic detectors to quantify bat species richness, activity, and feeding in 32 linear remnants and adjacent fields across an agricultural region of New South Wales, Australia. Nocturnal arthropods were simultaneously trapped using black-light traps. We recorded 91,969 bat calls, 17,277 of which could be attributed to one of the 13 taxa recorded, and 491 calls contained feeding buzzes. The linear remnants supported higher bat activity than the fields, but species richness and feeding activity did not significantly differ. We trapped a mean 87.6 g (±17.6 g SE) of arthropods per night, but found no differences in biomass between land uses. Wider linear remnants with intact native vegetation supported more bat species, as did those adjacent to unsealed, as opposed to sealed roads. Fields of unimproved native pastures, with more retained scattered trees and associated hollows and logs, supported the greatest bat species richness and activity. We conclude that the juxtaposition of linear remnants of intact vegetation and scattered trees in fields, coupled with less-intensive land uses such as unimproved pastures will benefit bat communities in agricultural landscapes, and should be incorporated into agri-environment schemes. In contrast, sealed roads may act as a deterrent. The "wildlife friendly farming" vs "land sparing" debate has so far primarily focussed on birds, but here we have found evidence that the integration of both approaches could particularly benefit bats.

The foraging ecology of the mountain long-eared bat Plecotus macrobullaris revealed with DNA mini-barcodes

Molecular analysis of diet overcomes the considerable limitations of traditional techniques for identifying prey remains in bat faeces. We collected faeces from individual Mountain Long-eared Bats Plecotus macrobullaris trapped using mist nets during the summers of 2009 and 2010 in the Pyrenees. We analysed their diet using DNA mini-barcodes to identify prey species. In addition, we inferred some basic features of the bat's foraging ecology that had not yet been addressed. P. macrobullaris fed almost exclusively on moths (97.8%). As prey we detected one dipteran genus (Tipulidae) and 29 moth taxa: 28 were identified at species level (23 Noctuidae, 1 Crambidae, 1 Geometridae, 1 Pyralidae, 1 Sphingidae, 1 Tortricidae), and one at genus level (Rhyacia sp., Noctuidae). Known ecological information about the prey species allowed us to determine that bats had foraged at elevations between 1,500 and 2,500 m amsl (above mean sea level), mostly in subalpine meadows, followed by other open habitats such as orophilous grasslands and alpine meadows. No forest prey species were identified in the diet. As 96.4% of identified prey species were tympanate moths and no evidence of gleaning behaviour was revealed, we suggest P. macrobullaris probably forages by aerial hawking using faint echolocation pulses to avoid detection by hearing moths. As we could identify 87.8% of the analysed sequences (64.1% of the MOTUs, Molecular Operational Taxonomic Units) at species level, we conclude that DNA mini-barcodes are a very useful tool to analyse the diet of moth-specialist bats.