Effects of roost specialization on extinction risk in bats

Mapping global conservation priorities and habitat vulnerabilities for cave-dwelling bats in a changing world

Research and media attention is disproportionately focused on taxa and ecosystems perceived as charismatic, while other equally diverse systems such as caves and subterranean ecosystems are often neglected in biodiversity assessments and prioritisations. Highlighting the urgent need for protection, an especially large fraction of cave endemic species may be undescribed. Yet these more challenging systems are also vulnerable, with karsts for example losing a considerable proportion of their area each year. Bats are keystone to cave ecosystems making them potential surrogates to understand cave diversity patterns and identify conservation priorities. On a global scale, almost half (48 %) of known bat species use caves for parts of their life histories, with 32 % endemic to a single country, and 15 % currently threatened. We combined global analysis of cave bats from the IUCN spatial data with site-specific analysis of 1930 bat caves from 46 countries to develop global priorities for the conservation of the most vulnerable subterranean ecosystems. Globally, 28 % of caves showed high bat diversity and were highly threatened. The highest regional concentration of conservation priority caves was in the Palearctic and tropical regions (except the Afrotropical, which requires more intensive cave data sampling). Our results further highlight the importance of prioritising bat caves by incorporating locally collected data and optimising parameter selection (i.e., appropriate landscape features and threats). Finally, to protect and conserve these ecosystems it is crucial that we use frameworks such as this to identify priorities in species and habitat-level and map vulnerable underground habitats with the highest biodiversity and distinctiveness.

The role of forest structure and composition in driving the distribution of bats in Mediterranean regions

Forests are key native habitats in temperate environments. While their structure and composition contribute to shaping local-scale community assembly, their role in driving larger-scale species distributions is understudied. We used detailed forest inventory data, an extensive dataset of occurrence records, and species distribution models integrated with a functional approach, to disentangle mechanistically how species-forest dependency processes drive the regional-scale distributions of nine forest specialist bats in a Mediterranean region in the south of Spain. The regional distribution patterns of forest bats were driven primarily by forest composition and structure rather than by climate. Bat roosting ecology was a key trait explaining the strength of the bat-forest dependency relationships. Tree roosting bats were strongly associated with mature and heterogeneous forest with large trees (diameters > 425 mm). Conversely, and contrary to what local-scale studies show, our results did not support that flight-related traits (wing loading and aspect ratio) drive species distributional patterns. Mediterranean forests are expected to be severely impacted by climate change. This study highlights the utility of disentangling species-environment relationships mechanistically and stresses the need to account for species-forest dependency relationships when assessing the vulnerability of forest specialists towards climate change.

Disparate roost sites drive intraspecific physiological variation in a Malagasy bat

Many species are widely distributed and individual populations can experience vastly different environmental conditions over seasonal and geographic scales. With such a broad ecological reality, datasets with limited spatial and temporal resolution may not accurately represent a species and could lead to poorly informed management decisions. Because physiological flexibility can help species tolerate environmental variation, we studied the physiological responses of two separate populations of Macronycteris commersoni, a bat widespread across Madagascar, in contrasting seasons. The populations roost under the following dissimilar conditions: either a hot, well-buffered cave or within open foliage, unprotected from the local weather. We found that flexible torpor patterns, used in response to prevailing ambient temperature and relative humidity, were central to keeping energy budgets balanced in both populations. While bats’ metabolic rate during torpor and rest did not differ between roosts, adjusting torpor frequency, duration and timing helped bats maintain body condition. Interestingly, the exposed forest roost induced extensive use of torpor, which exceeded the torpor frequency of overwintering bats that stayed in the cave for months and consequently minimised daytime resting energy expenditure in the forest. Our current understanding of intraspecific physiological variation is limited and physiological traits are often considered to be fixed. The results of our study therefore highlight the need for examining species at broad environmental scales to avoid underestimating a species’ full capacity for withstanding environmental variation, especially in the face of ongoing, disruptive human interference in natural habitats.

Roosting ecology of endangered plant-roosting bats on Okinawa Island: Implications for bat-friendly forestry practices

Roosting information is crucial to guiding bat conservation and bat-friendly forestry practices. The Ryukyu tube-nosed bat Murina ryukyuana (Endangered) and Yanbaru whiskered bat Myotis yanbarensis (Critically Endangered) are forest-dwelling bats endemic to the central Ryukyu Archipelago, Japan. Despite their threatened status, little is known about the roosting ecology of these species and the characteristics of natural maternity roosts are unknown. To inform sustainable forestry practices and conservation management, we radio-tracked day roosts of both species in the subtropical forests of Okinawa's Kunigami Village District. We compared roost and roost site characteristics statistically between M. ryukyuana nonmaternity roosts (males or nonreproductive females), maternity roosts, and all M. yanbarensis roosts. Generalized linear models were used to investigate roost site selection by M. ryukyuana irrespective of sex and age class. Lastly, we compiled data on phenology from this and prior studies. Nonreproductive M. ryukyuana roosted alone and primarily in understory foliage. Murina ryukyuana maternity roosts were limited to stands >50 years old, and ~60% were in foliage. Myotis yanbarensis roosted almost entirely in cavities along gulch bottoms and only in stands >70 years old (~1/3 of Kunigami's total forest area). Murina ryukyuana maternity roosts were higher (4.3 ± 0.6 m) than conspecific nonmaternity roosts (2.3 ± 0.5 m; p < .001) and M. yanbarensis roosts (2.7 ± 0.5 m; not significant). Model results were inconclusive. Both species appear to be obligate plant roosters throughout their life cycle, but the less flexible roosting preferences of M. yanbarensis may explain its striking rarity. To conserve these threatened bats, we recommend the following forestry practices: (a) reduce clearing of understory vegetation, (b) refrain from removing trees along streams, (c) promote greater tree cavity densities by protecting old-growth forests and retaining snags, and (d) refrain from removing trees or understory between April and July, while bats are pupping.

Roost selection by Mauritian tomb bats (Taphozus mauritianus) in Lilongwe city, Malawi - importance of woodland for sustainable urban planning

Increasing urbanisation has led to a greater use of artificial structures by bats as alternative roost sites. Despite the widespread presence of bats, roost availability may restrict their distribution and abundance in urban environments. There is limited quantitative information on the drivers of bat roost selection and roosting preferences, particularly in African bats. We explore the factors influencing roost selection in the Mauritian tomb bat (Taphozous mauritianus), within an urban landscape in Lilongwe city, Malawi. Eight building and five landscape features of roosts were compared with both adjacent and random control buildings throughout the city. Bat occupied buildings were situated closer to woodland (mean 709m) compared to random buildings (mean 1847m) but did not differ in any other landscape features explored. Roosts were situated on buildings with larger areas and taller walls, suggesting bats select features for predator-avoidance and acoustic perception when leaving the roost. Bats preferred buildings with exposed roof beams which may provide refuge from disturbance. Whilst roosts are situated more often on brick walls, this feature was also associated with landscape features, therefore its importance in roost selection is less clear. These results are indicative that T. mauritianus selects roosts at both the building and landscape level. The selectivity of T. mauritianus in relation to its roost sites implies that preferred roosts are a limited resource, and as such, conservation actions should focus on protecting roost sites and the woodland bats rely on.

Implications of non-native species for mutualistic network resistance and resilience

Resilience theory aims to understand and predict ecosystem state changes resulting from disturbances. Non-native species are ubiquitous in ecological communities and integrated into many described ecological interaction networks, including mutualisms. By altering the fitness landscape and rewiring species interactions, such network invasion may carry important implications for ecosystem resistance and resilience under continued environmental change. Here, I hypothesize that the tendency of established non-native species to be generalists may make them more likely than natives to occupy central network roles and may link them to the resistance and resilience of the overall network. I use a quantitative research synthesis of 58 empirical pollination and seed dispersal networks, along with extinction simulations, to examine the roles of known non-natives in networks. I show that non-native species in networks enhance network redundancy and may thereby bolster the ecological resistance or functional persistence of ecosystems in the face of disturbance. At the same time, non-natives are unlikely to partner with specialist natives, thus failing to support the resilience of native species assemblages. Non-natives significantly exceed natives in network centrality, normalized degree, and Pollination Service Index. Networks containing non-natives exhibit lower connectance, more links on average, and higher generality and vulnerability than networks lacking non-natives. As environmental change progresses, specialists are particularly likely to be impacted, reducing species diversity in many communities and network types. This work implies that functional diversity may be retained but taxonomic diversity decline as non-native species become established in networks worldwide.

Trait-dependent tolerance of bats to urbanization: a global meta-analysis

Urbanization is a severe threat to global biodiversity, often leading to taxonomic and functional homogenization. However, current urban ecology research has focused mostly on urban birds and plants, limiting our ability to make generalizations about the drivers of urban biodiversity globally. To address this gap, we conducted a global meta-analysis of 87 studies, including 180 bat species (Chiroptera) from urban areas in Asia, Australia, Europe, North and South America. We aimed to (i) understand the importance of functional traits and phylogeny in driving changes in urban bat assemblages, and (ii) assess the capacity of traits for predicting which types of species are most sensitive to urbanization. Our results indicate that species-specific functional traits explain differences in the intensity of urban habitat use. Urban tolerance mainly occurred within the open and edge space foraging and trawling species as well as in bats with flexible roosting strategies. In addition, across bioregions and independent of phylogeny, urban tolerance correlated with higher aspect ratio, a trait enabling fast flight but less agile manoeuvres during aerial food acquisition. Predictive success varied between bioregions, between 43 and 83%. Our analysis demonstrates that the local extinction of bat species in urban areas is non-random, trait-based and predictable, allowing urban landscape managers to tailor local conservation actions to particular types of species.

Social communication in bats

Bats represent one of the most diverse mammalian orders, not only in terms of species numbers, but also in their ecology and life histories. Many species are known to use ephemeral and/or unpredictable resources that require substantial investment to find and defend, and also engage in social interactions, thus requiring significant levels of social coordination. To accomplish these tasks, bats must be able to communicate; there is now substantial evidence that demonstrates the complexity of bat communication and the varied ways in which bats solve some of the problems associated with their unique life histories. However, while the study of communication in bats is rapidly growing, it still lags behind other taxa. Here we provide a comprehensive overview of communication in bats, from the reasons why they communicate to the diversity and application of different signal modalities. The most widespread form of communication is the transmission of a signaller's characteristics, such as species identity, sex, individual identity, group membership, social status and body condition, and because many species of bats can rely little on vision due to their nocturnal lifestyles, it is assumed that sound and olfaction are particularly important signalling modes. For example, research suggests that secretions from specialized glands, often in combination with urine and saliva, are responsible for species recognition in several species. These olfactory signals may also convey information about sex and colony membership. Olfaction may be used in combination with sound, particularly in species that emit constant frequency (CF) echolocation calls, to recognize conspecifics from heterospecifics, yet their simple structure and high frequency do not allow much information of individual identity to be conveyed over long distances. By contrast, social calls may encode a larger number of cues of individual identity, and their lower frequencies increase their range of detection. Social calls are also known to deter predators, repel competitors from foraging patches, attract group mates to roost sites, coordinate foraging activities, and are used during courtship. In addition to sound, visual displays such as wing flapping or hovering may be used during courtship, and swarming around roost sites may serve as a visual cue of roost location. However, visual communication in bats still remains a poorly studied signal modality. Finally, the most common form of tactile communication known in bats is social grooming, which may be used to signal reproductive condition, but also to facilitate and strengthen cooperative interactions. Overall, this review demonstrates the rapid advances made in the study of bat social communication during recent years, and also identifies topics that require further study, particularly those that may allow us to understand adaptation to rapidly changing environmental conditions.

The bats of Rio Grande do Norte state, northeastern Brazil

Abstract Rio Grande do Norte is one of the smallest states in Brazil but has a rich diversity of ecosystems, including Caatinga vegetation, remnants of Atlantic Forest, coastal habitats, mangroves and large karstic areas with caves. However, its chiropteran fauna is little known, and the state contains conspicuous gaps of information on the occurrence and distribution of bats in Brazil. In order to reduce this information gap, based on a review of scientific literature and regional mammal collections, we list 42 species of bats, including new occurrences for 13 species and discussion on their conservation status. Results show that more than half (54%) of the recorded species are phyllostomid bats, and about one third of the bats in the state roosts in underground cavities. The Caatinga harbored the highest bat richness in the state, including the occurrence of four vulnerable species (Furipterus horrens, Lonchorhina aurita, Natalus macrourus and Xeronycteris vieirai). The Atlantic Forest needs to be more sampled, including mangroves, coastal habitats and areas of Caatinga in the central region of the state (Borborema highlands), which are virtually unsurveyed. Although the recent increase of studies on bats in the state, future studies should complement conventional mistnetting with active roost search and bioacoustical records in order to obtain better data for unraveling the bat fauna of Rio Grande do Norte.

Effect of roost choice on winter torpor patterns of a free-ranging insectivorous bat

Gould’s wattled bat (Chalinolobus gouldii) is one of only three native Australian mammals with an Australia-wide distribution. However, currently no data are available on the thermal physiology of free-ranging C. gouldii. Therefore, we aimed to quantify the effect of roost choice on daily skin temperature fluctuations during winter in C. gouldii living in an agricultural landscape in a temperate region. Ambient conditions consisted of long periods below 0°C and snow. Some individuals roosted high in dead branches whereas one individual roosted in a large cavity located low in a live tree. Torpor was employed on every day of the study period by all bats, with bouts lasting for over five days. The skin temperature of individuals in the dead branches tracked ambient temperature, with skin temperatures below 3°C on 67% of bat-days (lowest recorded –0.2°C). In contrast, the individual in the tree cavity maintained a larger skin-ambient temperature differential, likely influenced by the internal cavity temperature. Our study presents the lowest skin temperature recorded for a free-ranging Australian microbat and reveals that roost choice affects the thermal physiology of C. gouldii, ensuring survival during periods of cold weather and limited food supply.