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

Are bats tracking climate change? Long-term monitoring reveals phenology shifts and population trends of forest bats

Climate change is altering wildlife assemblages, although limited long-term data hinders understanding of its impacts. Bats are widely reported to be good models for studying climate change effects due to their sensitivity to temperature and migration patterns. Here we use forest bats as models to investigate how climate and interspecific interactions may affect wildlife species in the long-term, by monitoring populations of sympatric noctules over three decades. We aimed at understanding how climate influences fluctuations in population size and phenology, as well as assessing the role of interactions among sympatric species in shaping population trends. We investigated the long-term effects of climate change on forest bat species coexisting in the same mountainous area in central Italy. Through bat-box monitoring analysis, we examined population trends, phenological changes, and potential interspecific interactions. Overall, populations of all three species exhibited a significant increase, although fluctuations were largely driven by precipitation patterns. Specifically, cumulative yearly precipitation affected population sizes of all species, with N. leisleri additionally influenced by minimum yearly temperatures and by the presence of N. lasiopterus. We also documented phenological shifts, particularly in N. leisleri, with males advancing their arrival as early as February, and females delaying to late summer and autumn, leading to a significant decline in seasonal intersex overlap. Interspecific interactions also apparently shaped population trends, with N. lasiopterus showing a positive association with N. noctula, and N. leisleri being displaced from areas with increasing presence of N. lasiopterus. These findings indicate that forest bats may alter their ecology in response to climate change, yet inconsistently among species and between sexes, with potentially negative effects upon interspecific interactions and individual reproductive success. Besides, we highlight the importance of long-term monitoring programs in understanding the multifaceted effects of climate change on bat populations in forest ecosystems, particularly in mountain habitats.

Bats surf storm fronts during spring migration

Long-distance migration, common in passerine birds, is rare and poorly studied in bats. Piloting a 1.2-gram IoT (Internet of Things) tag with onboard processing, we tracked the daily location, temperature, and activity of female common noctules (Nyctalus noctula) during spring migration across central Europe up to 1116 kilometers. Over 3 years, 71 bats migrated tens to hundreds of kilometers per night, predominantly with incoming warm fronts, which provided them with wind support. Bats also showed unexpected flexibility in their ability to migrate across a wide range of conditions if needed. However, females leaving toward the end of the season showed higher total activity per distance traveled, a possible cost for their flexible migration timing.

Molecular Insights Into the Sensory Adaption of the Cave-Dwelling Leech Sinospelaeobdella wulingensis to the Karst Cave Environment

Karst caves are a unique environment significantly different from the external environment; adaptation of cave-dwelling animals to the cave environment is often accompanied by shifts in the sensory systems. Aquatic and terrestrial leeches have been found in the karst caves. In this study, we conducted a transcriptome analysis on the cave-dwelling leech Sinospelaeobdella wulingensis. A total of 29,286 unigenes were obtained by assembling the clean reads, and only 395 genes are differentially expressed in winter and summer samples. Two piezo-type mechanosensitive ion channels (Piezos), eight transient receptor potential channels (TRPs), and six ionotropic glutamate receptors (iGluRs) were identified in the transcriptome. These channels/receptors are transmembrane proteins sharing conserved structural features in the respective protein families. SwPiezo1 shares high identity with Piezos in non-caving leeches. SwiGluRs are conserved in protein sequence and share high identities with homologous proteins in other leeches. In contrast, SwTRPs belong to different subfamilies and share diverse identities with TRPs in other species. Gene expression analysis showed that two SwPiezos, five SwTRPs, and one SwiGluR are abundantly expressed in both winter and summer samples. These results suggest that SwPiezos, SwTRPs, and SwiGluRs are candidate sensory channels/receptors that may have roles in mechanosensory and chemosensory systems. High expression levels of Piezo and TRP genes imply a mechanosensory adaptation of S. wulingensis to the hanging living style in caves. Furthermore, enrichment of sensory genes in the oral sucker indicates the important role of this tissue in response to environmental stimuli. Similar gene expression profiles in winter and summer samples imply a stable physiological status of S. wulingensis in the cave environment.

Mountain caves of the central region of Veracruz: A vertebrate biodiversity reservoir in a Neotropical hotspot

The mountain region of central Veracruz, Mexico hosts a large system of karst and volcanic caves that are unexplored. In particular, the vertebrates that inhabit these subterranean ecosystems are unknown. This study evaluated the diversity of mammals, birds, reptiles, amphibians, and fish in three environments (euphotic, disphotic, and aphotic) of 16 caves of different geological origin (12 karst caves and 4 volcanic caves) distributed along an altitudinal gradient (300-2400 m a.s.l.). We found a richness of 242 vertebrate species (184 birds, 30 mammals, 15 reptiles, 12 amphibians, and 1 fish) and an abundance of a total of 11,323 individuals (4,969 mammals, 6,483 birds, 36 reptiles, 27 amphibians, and 5 fish). The richness of all vertebrate classes was higher in karst than in volcanic caves. Vertebrate diversity was also higher at mid-altitudes between 600-899 m a.s.l. Diversity varied between environments, where bird and reptile richness was higher in the euphotic environment, while mammal and amphibian diversity was higher in the aphotic environment. The similarity in the composition of vertebrate species does not depend on the distance between karstic and volcanic caves. Volcanic and karst caves shared on average up to 70% and 55% of vertebrate species, which indicates that only 30% and 45% of species, respectively, is different in each cave type. Given the vulnerability and fragility of these subterranean ecosystems, as well as the important diversity that they contain, we recommend including the caves of the central region of Veracruz in the conservation agenda of local governments and communities. Community-based conservation can help ensure the presence of vertebrate species in the caves of this region.

Quantifying long-term phenological patterns of aerial insectivores roosting in the Great Lakes region using weather surveillance radar

Organisms have been shifting their timing of life history events (phenology) in response to changes in the emergence of resources induced by climate change. Yet understanding these patterns at large scales and across long time series is often challenging. Here we used the US weather surveillance radar network to collect data on the timing of communal swallow and martin roosts and evaluate the scale of phenological shifts and its potential association with temperature. The discrete morning departures of these aggregated aerial insectivores from ground-based roosting locations are detected by radars around sunrise. For the first time, we applied a machine learning algorithm to automatically detect and track these large-scale behaviors. We used 21 years of data from 12 weather surveillance radar stations in the Great Lakes region to quantify the phenology in roosting behavior of aerial insectivores at three spatial levels: local roost cluster, radar station, and across the Great Lakes region. We show that their peak roosting activity timing has advanced by 2.26 days per decade at the regional scale. Similar signals of advancement were found at the station scale, but not at the local roost cluster scale. Air temperature trends in the Great Lakes region during the active roosting period were predictive of later stages of roosting phenology trends (75% and 90% passage dates). Our study represents one of the longest-term broad-scale phenology examinations of avian aerial insectivore species responding to environmental change and provides a stepping stone for examining potential phenological mismatches across trophic levels at broad spatial scales.

Bat responses to climate change: a systematic review

Understanding how species respond to climate change is key to informing vulnerability assessments and designing effective conservation strategies, yet research efforts on wildlife responses to climate change fail to deliver a representative overview due to inherent biases. Bats are a species-rich, globally distributed group of organisms that are thought to be particularly sensitive to the effects of climate change because of their high surface-to-volume ratios and low reproductive rates. We systematically reviewed the literature on bat responses to climate change to provide an overview of the current state of knowledge, identify research gaps and biases and highlight future research needs. We found that studies are geographically biased towards Europe, North America and Australia, and temperate and Mediterranean biomes, thus missing a substantial proportion of bat diversity and thermal responses. Less than half of the published studies provide concrete evidence for bat responses to climate change. For over a third of studied bat species, response evidence is only based on predictive species distribution models. Consequently, the most frequently reported responses involve range shifts (57% of species) and changes in patterns of species diversity (26%). Bats showed a variety of responses, including both positive (e.g. range expansion and population increase) and negative responses (range contraction and population decrease), although responses to extreme events were always negative or neutral. Spatial responses varied in their outcome and across families, with almost all taxonomic groups featuring both range expansions and contractions, while demographic responses were strongly biased towards negative outcomes, particularly among Pteropodidae and Molossidae. The commonly used correlative modelling approaches can be applied to many species, but do not provide mechanistic insight into behavioural, physiological, phenological or genetic responses. There was a paucity of experimental studies (26%), and only a small proportion of the 396 bat species covered in the examined studies were studied using long-term and/or experimental approaches (11%), even though they are more informative about the effects of climate change. We emphasise the need for more empirical studies to unravel the multifaceted nature of bats' responses to climate change and the need for standardised study designs that will enable synthesis and meta-analysis of the literature. Finally, we stress the importance of overcoming geographic and taxonomic disparities through strengthening research capacity in the Global South to provide a more comprehensive view of terrestrial biodiversity responses to climate change.

Assessing future shifts in habitat suitability and connectivity to old-growth forests to support the conservation of the endangered giant noctule

Background

Suitable climate and availability of habitats for roosting, foraging, and dispersing are critical for the long-term persistence of bat species. The giant noctule (Nyctalus lasiopterus) represents one of the lesser-known European bats, especially regarding the environmental factors which shape its distribution.

Methodology

We integrated climate-based ecological niche models with information about topography and rivers' network to model weighted suitability for N. lasiopterus in the western Palearctic. The weighted suitability map was then used to estimate connectivity among the distinct occurrence localities of N. lasiopterus, as well as from these latter towards European old-growth forests, under current conditions and different combinations of future timeframes (2030, 2050, 2070) and shared socioeconomic pathways (SSPs 3.70 and 5.85).

Results

Current weighted suitability is highest in Andalusia, northern Iberia, southwestern France, peninsular Italy, coastal Balkans and Anatolia, with dispersed suitable patches elsewhere. A north-eastward shift of weighted suitability emerges in the considered future scenarios, especially under SSP 5.85. The major current ecological corridors for N. lasiopterus are predicted within a 'belt' connecting northern Spain and southwestern France, as well as in the Italian Alps. However, following changes in weighted suitability, connectivity would increase in central-eastern Europe in the future. The bioclimatic niche of the western N. lasiopterus populations does not overlap with those of the central and eastern ones, and it only overlaps with climatic conditions characterizing old-growth forests in western Europe.

Conclusions

The outcomes of our analyses would help in designing specific conservation measures for the distinct groups of giant noctule populations, favoring the possibility of range expansion and movement towards forested habitats.