Emergence time in forest bats: the influence of canopy closure

Extrinsic and intrinsic factors influencing the emergence and return of the Asian particolored bat Vespertilio sinensis to the summer roost

Circadian rhythms play a crucial role in the health and survival of organisms. However, little is known concerning how intrinsic and extrinsic factors affect animal daily rhythms in the field, especially in nocturnal animals. Here, we investigated the first emergence, mid-emergence, and return times of Vespertilio sinensis, and also integrated environmental conditions (temperature, humidity, and light intensity) and biotic factors (reproductive status and predation risk) to determine causes of variation in the activity rhythms of the bats. We found that variation in the first emergence time, the mid-emergence time, and the final return time were distinct. The results demonstrated that the emergence and return times of bats were affected by light intensity, reproductive status, and predation risk in a relatively complex pattern. Light intensity had the greatest contribution to activity rhythms. Moreover, we first investigated the effects of actual predators on the activity rhythms of bats; the results showed that the mid-emergence time of bats was earlier as predators were hunting, but the final return time was later when predators were present. Finally, our results also highlighted the importance of higher energy demands during the lactation in bats to variation in activity rhythms. These results improve our understanding of the patterns and causes of variation in activity rhythms in bats and other nocturnal animals.

Do We Need to Use Bats as Bioindicators?

Simple Summary

Bioindicators are organisms that react to the quality or characteristics of the environment and their changes. They are vitally important to track environmental alterations and take action to mitigate them. As choosing the right bioindicators has important policy implications, it is crucial to select them to tackle clear goals rather than selling specific organisms as bioindicators for other reasons, such as for improving their public profile and encourage species conservation. Bats are a species-rich mammal group that provide key services such as pest suppression, pollination of plants of economic importance or seed dispersal. Bats show clear reactions to environmental alterations and as such have been proposed as potentially useful bioindicators. Based on the relatively limited number of studies available, bats are likely excellent indicators in habitats such as rivers, forests, and urban sites. However, more testing across broad geographic areas is needed, and establishing research networks is fundamental to reach this goal. Some limitations to using bats as bioindicators exist, such as difficulties in separating cryptic species and identifying bats in flight from their calls. It is often also problematic to establish the environmental factors that influence the distribution and behaviour of bats.

Abstract

Bats show responses to anthropogenic stressors linked to changes in other ecosystem components such as insects, and as K-selected mammals, exhibit fast population declines. This speciose, widespread mammal group shows an impressive trophic diversity and provides key ecosystem services. For these and other reasons, bats might act as suitable bioindicators in many environmental contexts. However, few studies have explicitly tested this potential, and in some cases, stating that bats are useful bioindicators more closely resembles a slogan to support conservation than a well-grounded piece of scientific evidence. Here, we review the available information and highlight the limitations that arise in using bats as bioindicators. Based on the limited number of studies available, the use of bats as bioindicators is highly promising and warrants further investigation in specific contexts such as river quality, urbanisation, farming practices, forestry, bioaccumulation, and climate change. Whether bats may also serve as surrogate taxa remains a controversial yet highly interesting matter. Some limitations to using bats as bioindicators include taxonomical issues, sampling problems, difficulties in associating responses with specific stressors, and geographically biased or delayed responses. Overall, we urge the scientific community to test bat responses to specific stressors in selected ecosystem types and develop research networks to explore the geographic consistency of such responses. The high cost of sampling equipment (ultrasound detectors) is being greatly reduced by technological advances, and the legal obligation to monitor bat populations already existing in many countries such as those in the EU offers an important opportunity to accomplish two objectives (conservation and bioindication) with one action.

Diversity and Abundance of Roadkilled Bats in the Brazilian Atlantic Forest

Faunal mortality from roadkill has a negative impact on global biodiversity, and bats are among the roadkilled animals. In South America, the Atlantic Forest covers southeastern Brazil, a region which sustains a large bat diversity. In this biome, the Sooretama reserves are crossed by the federal highway BR-101, one of the busiest in Brazil. We analyzed bats roadkilled along the 25 km stretch of highway that crosses the Sooretama reserves. Data were collected between the years 2010 and 2015. In total, 773 individuals distributed among 47 bat species were roadkilled during this period. The insectivorous feeding guild was the most affected, accounting for 25 species and 74% of the recorded roadkill, and those flying in the open area were the most frequently roadkilled (41.9%). Bat mortality rates did not differ between months of the year. However, the relation between rainy days and roadkill was negative. Monitoring by foot was more efficient than by car for detection of bat carcasses. Radars with a speed limit below 60 km/h reduced the rates of roadkill. The diversity of deceased bats found in this study represents 40% of the known species in the Atlantic Forest, and is the largest among current studies of species killed on highways globally. The present study raises concerns about the high diversity and abundance of roadkilled insectivorous bats and the conservation of these animals in the Neotropical region.

Presence of humans and domestic cats affects bat behaviour in an urban nursery of greater horseshoe bats (Rhinolophus ferrumequinum)

Proximity to humans is a primary stressor for wildlife, especially in urban habitats where frequent disturbance may occur. Several bat species often roost in buildings but while the effects of disturbance inside the roost are well documented, little is known about those occurring in the proximity of roosts. We tested the effects of anthropogenic stressors on bats by monitoring reactions to disturbance in a colony of greater horseshoe bats (Rhinolophus ferrumequinum). We assessed disturbance by recording and quantifying the presence of people, domestic cats and noise sources near the roost. Disturbance outside the roost caused the disruption of roosting clusters; when cats entered the roost, bats decreased indoor flight activity. Emergence timing was delayed when people were close to the roost exit, and the delay increased along with the number of people. The occurrence of a cat increased the degree of group clustering during emergence. Cats entered the roost especially when young bats were present, and bat remains occurred in 30% of the cat scats we examined. We show that the occurence of human activities near roosts and free-ranging domestic cats are important albeit overlooked sources of disturbance.

Vertical stratification in bat assemblages of the Atlantic Forest of south-eastern Brazil

Tropical forests are three-dimensional spaces with species and resources heterogeneously distributed. The vertical stratification of tropical forest biotas has been observed for several organisms and regions, but, surprisingly, the vertical structuring of large areas of important tropical forests, such as Brazil's Atlantic Forest, remains poorly studied. Here, we addressed the use of different Atlantic Forest strata by bats, comparing ensemble composition and relative abundance between the understorey and the canopy. A total of 618 bats belonging to 31 species and four families were recorded, including 11 species of frugivores and seven species of gleaning insectivores, the two trophic guilds predominantly represented in our sampling. Fifteen species were captured exclusively in the canopy, and six exclusively in the understorey, and many of those species were represented by a low number of captures (<5). The bat species composition, richness and relative abundance between canopy and understorey strata varied.Chiroderma villosumwas exclusively captured in the canopy,Artibeus lituratuswas netted predominantly in the canopy andCarollia perspicillataandDesmodus rotunduswere mostly captured in the understorey. Although processes such as resource partitioning between species and ecomorphological constraints may explain the differential use of forest strata, this remains little understood because of the scarcity of data for the Atlantic forest canopies.

Sociality influences thermoregulation and roost switching in a forest bat using ephemeral roosts

In summer, many temperate bat species use daytime torpor, but breeding females do so less to avoid interferences with reproduction. In forest-roosting bats, deep tree cavities buffer roost microclimate from abrupt temperature oscillations and facilitate thermoregulation. Forest bats also switch roosts frequently, so thermally suitable cavities may be limiting. We tested how barbastelle bats (Barbastella barbastellus), often roosting beneath flaking bark in snags, may thermoregulate successfully despite the unstable microclimate of their preferred cavities. We assessed thermoregulation patterns of bats roosting in trees in a beech forest of central Italy. Although all bats used torpor, females were more often normothermic. Cavities were poorly insulated, but social thermoregulation probably overcomes this problem. A model incorporating the presence of roost mates and group size explained thermoregulation patterns better than others based, respectively, on the location and structural characteristics of tree roosts and cavities, weather, or sex, reproductive or body condition. Homeothermy was recorded for all subjects, including nonreproductive females: This probably ensures availability of a warm roosting environment for nonvolant juveniles. Homeothermy may also represent a lifesaver for bats roosting beneath loose bark, very exposed to predators, because homeothermic bats may react quickly in case of emergency. We also found that barbastelle bats maintain group cohesion when switching roosts: This may accelerate roost occupation at the end of a night, quickly securing a stable microclimate in the newly occupied cavity. Overall, both thermoregulation and roost-switching patterns were satisfactorily explained as adaptations to a structurally and thermally labile roosting environment.

Spatial and temporal distribution of bats (Chiroptera) in bright summer nights

Most bat species show plasticity in their choice of habitat and landscape. This study focuses on the distribution and activity of bats along the hillsides and onto the shores of a low salinity marine Norwegian fiord at 62°N. Ultrasound was recorded using D500 detectors in June and July at 42 different sites from the shoreline and up the hillsides to around 200 m. Detectors were placed in well-preserved woodlands. OnlyPipistrellussp., northern batsEptesicus nilssoniiand bats of theMyotisgenus were common. There was a clear non-linear spatial distribution pattern along these slopes, with a pronounced increase in the number of recorded bats at short distances from the shore. On all six nights, the detector closest to the shore had the highest number of recorded bats. A pattern was also seen in bat distribution over time.Pipistrellussp., northern bats andMyotisspecies all had a peak near the shore during the darkest part of the night, which is around 01.35 h in mid-summer at this latitude. At greater distances,Pipistrellussp. and northern bats had a peak around 40 minutes to one hour before the darkest part of the night, respectively. Here,Myotisspp. peaked about an hour after 01.35.

Managing coniferous production forests towards bat conservation

Context Forest management has impacts on bats worldwide. Given that many forest bats are threatened and that bats are important providers of ecosystem services, understanding the effects of forest management practices on their activity is fundamental for the implementation of conservation measures. Despite these important issues, studies on the effects of management practices on bats are scarce. Aims To propose management measures for coniferous production forests, to ensure sustainability of bat populations. Methods We evaluated bat species richness and activity during gestation, lactation and mating/swarming/dispersion seasons in differently managed pine stands to evaluate how vegetation structure influences those variables. Bat activity was surveyed using acoustic monitoring in 28 sampling plots within stands with distinct management records in Portugal. We also sampled arthropods using light traps to ascertain how prey availability influenced bat species richness and activity in those plots. Key results Bat species richness and activity varied along the three phenological seasons and were higher in autumn, when mating, swarming and dispersion from nurseries to hibernacula took place. Prey availability varied, but was higher during the lactation season. We hypothesise that the lower levels of bat species richness and activity registered during that period were due to a reduced availability of roosts, rather than food scarcity. Species richness was positively correlated with canopy cover and prey taxa richness, and negatively associated with dry branches cover. Total bat activity was positively correlated with tree height and prey taxa richness, and negatively associated with dry branches cover. The activity of edge-space foragers was positively associated with average tree height and prey taxa richness, while the activity of open-space foragers was negatively associated with dry branches cover. Conclusions Coniferous production forests are of great importance for bats during the mating/swarming/dispersion season. Canopy cover, dry branches cover, tree height and prey taxa richness influence bat species richness and activity as a whole, particularly the activity of open- and edge- foraging guilds. Implications Based on our results, two straightforward management actions should be implemented in coniferous production forests to increase their value for bat assemblages: the maintenance of old coniferous stands, and the cutting of dry branches at the subcanopy level.

Barriers and benefits: implications of artificial night-lighting for the distribution of common bats in Britain and Ireland

Artificial lighting is a particular problem for animals active at night. Approximately 69% of mammal species are nocturnal, and one-third of these are bats. Due to their extensive movements-both on a nightly basis to exploit ephemeral food supplies, and during migration between roosts-bats have an unusually high probability of encountering artificial light in the landscape. This paper reviews the impacts of lighting on bats and their prey, exploring the direct and indirect consequences of lighting intensity and spectral composition. In addition, new data from large-scale surveys involving more than 265 000 bat calls at more than 600 locations in two countries are presented, showing that prevalent street-lighting types are not generally linked with increased activity of common and widespread bat species. Such bats, which are important to ecosystem function, are generally considered 'light-attracted' and likely to benefit from the insect congregations that form at lights. Leisler's bat (Nyctalus leisleri) may be an exception, being more frequent in lit than dark transects. For common pipistrelle bats (Pipistrellus pipistrellus), lighting is negatively associated with their distribution on a landscape scale, but there may be local increases in habitats with good tree cover. Research is now needed on the impacts of sky glow and glare for bat navigation, and to explore the implications of lighting for habitat matrix permeability.

Tropical secondary forest management influences frugivorous bat composition, abundance and fruit consumption in Chiapas, Mexico

Most studies on frugivorous bat assemblages in secondary forests have concentrated on differences among successional stages, and have disregarded the effect of forest management. Secondary forest management practices alter the vegetation structure and fruit availability, important factors associated with differences in frugivorous bat assemblage structure, and fruit consumption and can therefore modify forest succession. Our objective was to elucidate factors (forest structural variables and fruit availability) determining bat diversity, abundance, composition and species-specific abundance of bats in (i) secondary forests managed by Lacandon farmers dominated by Ochroma pyramidale, in (ii) secondary forests without management, and in (iii) mature rain forests in Chiapas, Southern Mexico. Frugivorous bat species diversity (Shannon H') was similar between forest types. However, bat abundance was highest in rain forest and O. pyramidale forests. Bat species composition was different among forest types with more Carollia sowelli and Sturnira lilium captures in O. pyramidale forests. Overall, bat fruit consumption was dominated by early-successional shrubs, highest late-successional fruit consumption was found in rain forests and more bats consumed early-successional shrub fruits in O. pyramidale forests. Ochroma pyramidale forests presented a higher canopy openness, tree height, lower tree density and diversity of fruit than secondary forests. Tree density and canopy openness were negatively correlated with bat species diversity and bat abundance, but bat abundance increased with fruit abundance and tree height. Hence, secondary forest management alters forests' structural characteristics and resource availability, and shapes the frugivorous bat community structure, and thereby the fruit consumption by bats.

Response of neotropical bat assemblages to human land use

Neotropical bats are sensitive to human-induced habitat changes, and some authors believe bats can be used as bioindicators. In the literature, however, the results are disparate. Some results show bat diversity deceases as disturbance increases, whereas others indicate no effect. Determining the general response patterns of bats when they encounter different degrees of human-induced disturbance across the Neotropics would help to determine their usefulness as bioindicators. In a series of meta-analyses, we compared the occurrence frequency of bat species between well-preserved forests and human-use areas. We obtained data through an extensive review of published peer-reviewed articles, theses, and reports. The overall effect size indicated that human-use areas harbored more bat species than well-preserved forests. Different response patterns emerged when meta-analyses were conducted separately by family, feeding habit, vegetation stratum, and conservation status. Our results suggest that bat assemblages display strong responses to forest loss and land-use change and that the direction and magnitude of these responses depends on the bat group under study and the type of disturbance. Our results are consistent with the idea that bats are useful for assessing the effects of habitat changes in the Neotropics. However, with our meta-analyses we could not detect fine differences in bat feeding habits, especially within Phyllostomidae, or elucidate the effect of landscape configuration.

Do predators influence the behaviour of bats?

Many aspects of animal behaviour are affected by real-time changes in the risk of predation. This conclusion holds for virtually all taxa and ecological systems studied, but does it hold for bats? Bats are poorly represented in the literature on anti-predator behaviour, which may reflect a lack of nocturnal predators specialized on bats. If bats actually experience a world with minimal anti-predator concerns, then they will provide a unique contrast within the realm of vertebrate ecology. Alternatively, such predator-driven behaviour in bats may not yet be fully understood, given the difficulties in working with these highly mobile and nocturnal animals. We provide a wide-ranging exploration of these issues in bat behaviour. We first cover the basic predator-prey information available on bats, both on potential predators and the ways in which bats might perceive predators and respond to attacks. We then cover work relevant to key aspects of bat behaviour, such as choice of daytime roosts, the nature of sleep and torpor, evening roost departures, moonlight avoidance, landscape-related movement patterns, and habitat selection. Overall, the evidence in favour of a strong influence of predators on bat behaviour is equivocal, with the picture clouded by contradictory results and a lack of information on potential predators and the perception of risk by bats. It seems clear that day-active bats run a considerable risk of being killed by diurnal raptors, which are able to capture bats with relative ease. Thus, bats taking advantage of a pulse of insects just prior to sunset are likely taking risks to gain much-needed energy. Further, the choice of daytime roosts by bats is probably strongly influenced by roost safety. Few studies, however, have directly addressed either of these topics. As a group, insectivorous temperate-zone bats show no clear tendency to avoid apparently risky situations, such as activity on moonlit nights. However, some observations are consistent with the idea that predation risk affects choice of movement paths and feeding areas by temperate-zone bats, as well as the timing of roost departures. The behaviour of tropical bats, on the other hand, seems more generally influenced by predators; this is especially true for tropical nectarivores and frugivores, but also for insectivorous bats. Presumably there are more serious predators on bats in the tropics (e.g. specialized raptors or carnivorous bats), but the identity of these predators is unclear. More information is needed to assess fully the influence of predators on bat behaviour. There is much need for work on the ways in which bats perceive predators via auditory, visual, and olfactory cues, and whether bats have some knowledge of the risks posed by different predators. Also needed is information on how predators attack bats and how bats react to attacking predators. Difficult to obtain, but of critical value, will be information on the nature of the predation risk experienced by bats while away from roosts and during the full darkness of night.

Seasonal variation in prey abundance influences habitat use by greater horseshoe bats (Rhinolophus ferrumequinum) in a temperate deciduous forest

The hypothesis that patterns of habitat selection of greater horseshoe bats ( Rhinolophus ferrumequinum (Schreber, 1774)) vary across seasons in a temperate deciduous forest was investigated. Variables associated with potentially important ecological factors for greater horseshoe bats (physical structure of shrub stratum, crown canopy, insect availability, lunar phase, and weather) were collected for different seasons, and 75 sampling sites were established in the Luotong Mountain Nature Reserve in northeast China. Insect abundance was highest in late summer and lowest in late autumn. Poisson generalized linear models showed that the activity of greater horseshoe bats was positively related to the height and density of shrub stratum in late summer, whereas the activity of greater horseshoe bats was associated with insect abundance in early and late autumn. During periods of intermediate prey abundance (early summer), the height and density of shrub stratum, as well as insect abundance, influenced the activity of greater horseshoe bats. Shrub stratum may provide shelter against predation for foraging greater horseshoe bats. These results support our prediction that there was a trade-off between importance of food and cover among seasons for foraging bats. These findings are useful for the conservation and management of greater horseshoe bats.