ABSTRACT Intraspecific differences between the sexes can be as large as those between species, and niche partitioning between sexes may reduce competition for resources during energetically demanding periods. In bats, females are typically larger than males—a pattern attributed to greater reproductive investment (Big Mother hypothesis)—yet the functional implications of this dimorphism for foraging ecology remain poorly understood. We tested the hypothesis that sexual size dimorphism in cranial, wing and forearm morphology provides a functional basis for sex‐specific foraging ecology in Cnephaeus (Eptesicus) serotinus, a European sedentary synanthropic species with pronounced spatial segregation between sexes during the breeding season. Using craniometric measurements (n = 137), wing morphometrics (n = 22) and forearm length from long‐term monitoring (n = 1385) collected in northeastern Ukraine, we found consistent female‐biased dimorphism across all traits. Females were significantly larger in forearm length (+3.2%; Cohen's d = 1.07), with this pattern stable across 12 years of monitoring and consistent between age classes. Wing surface areas showed the greatest dimorphism (14%–15%; d = 1.6–2.0), while wing shape indices did not differ, indicating isometric size scaling consistent with compensation for pregnancy‐related mass increases. Mandibular dimensions related to bite force showed substantial dimorphism (2%–3%; d = 0.8–0.9), suggesting enhanced prey handling capacity in females. These findings are consistent with recent molecular dietary studies documenting sex‐specific prey consumption in other bat species. Our results provide morphological support for the hypothesis that sexual dimorphism enables both flight performance during pregnancy and intraspecific trophic niche partitioning, potentially reducing intersexual competition during reproduction.

Abstract Abdominal hernias in bats are rarely reported in the literature, with most reports evaluating postmortem findings. The present study documents successful surgical management of post‐traumatic abdominal hernias in three vespertilionid bats. Three injured bats (two Nyctalus noctula and one Eptesicus serotinus ) were admitted for veterinary care after sustaining presumed trauma. Clinical examinations and radiography confirmed abdominal wall herniation with intestinal prolapse in all three cases. Surgical intervention was performed under isoflurane anaesthesia, and postoperative management involved analgesic and antibiotic therapy, with gradual feeding reintroduction and symptomatic gastrointestinal medication. All surgeries resulted in successful reduction of the hernias, with postoperative complications (abdominal distension and suture dehiscence). Post‐rehabilitation, all bats were placed into artificial hibernation for eventual release. This study focuses on a small number of cases, limiting generalisability. This report highlights the feasibility of surgical intervention for abdominal hernias in bats, contributing to the veterinary care of these protected species.

Ongoing climate change is rapidly altering winter conditions across Europe. This results in northward range expansions and the establishment of new sedentary populations in migratory volant vertebrates. Here we report the first large winter aggregation of Pipistrellus pygmaeus in central Ukraine - and, to our knowledge, in the entire Eastern European Plain. Over the winters of 2021/22–2024/25, we recorded 11 wintering events involving more than 1200 individuals. The largest was a single hibernaculum in a municipal building in Cherkasy (49.43° N, 31.99° E; central Ukraine), where 231 bats were found alive and approximately 1000 were found dead. The bat colony was strongly female-biased and included both adult and this-year-born individuals; the body mass of bats in March was at its lowest seasonal point, notably lower than summer values. Our findings indicate not only a rapid northward shift in the species’ winter range, but also a reorganization of spatial sexual segregation. This shift may be interpreted as a response to the shortening and warming of winters in the region. Our results highlight the critical importance of systematic winter monitoring of urban hibernating bats to understand the mechanisms and broader ecological consequences of climate-driven range dynamics in bats.

Understanding the immunological profiles of wild bats is crucial for monitoring population health, disease dynamics, and stress responses in changing environments. Here, we present a dataset of 747 blood smear samples collected from 19 European bat species between 2017 and 2023 in Ukraine. For a substantial portion of individuals, red and white blood cell counts were assessed, and for most, differential leukocyte profiles were recorded, including segmented and band neutrophils, lymphocytes, monocytes, eosinophils, and basophils. The dataset is accompanied by rich metadata, which, among other aspects, includes species, sex, age class, life-cycle stage (e.g., hibernation, migration, breeding), capture location, habitat type and others. Most individuals were sampled during the hibernation period in urban environments. The dataset offers a valuable baseline for comparative hematology, eco-immunology, and bat conservation research. By sharing detailed leukocyte profiles and standardized metadata, this dataset facilitates cross-species comparisons, contributes to wildlife health surveillance, and supports future studies on the impacts of environmental stressors and zoonotic risks in European bats.

Environmental changes linked to urbanization influence wildlife health and may increase zoonotic risks. In this study, we examined the impact of urban stressors on the cellular immunity of two bat species, Nyctalus noctula and Eptesicus serotinus, along an urban-natural gradient in Eastern Ukraine. Using white blood cell (WBC) profiles as immunity markers, we found that N. noctula from urban and suburban habitats had significantly higher WBC counts, as well as lymphocyte and neutrophil proportions, compared to individuals from natural areas. Meanwhile, E. serotinus, a species more adapted to urban environments, exhibited lower neutrophil levels and a trend toward reduced neutrophil-to-lymphocyte ratios. These findings suggest species-specific immune responses to urban stressors, with potential implications for wildlife conservation and disease dynamics. Further research is needed to understand long-term physiological adaptations in urban-dwelling bats.

Bats, as exceptionally long-lived small mammals, are at particular risk of metal poisoning due to the tendency of metals to bioaccumulate throughout their lives. In our study, we investigated the general question of how trace metal concentrations change with age in different bat tissues on the example of Pipistrellus kuhlii lepidus, which lives for years in one area and is strongly associated with urban environments. To determine the exact age of the individuals, osteochronology was applied, counting the number of dentine rings in cross-sections of the upper canine tooth of each individual. The age of 57 individuals of P. kuhlii lepidus, representing ca. 10

This study investigated the influence of group size on the hibernation patterns of adult males of Nyctalus noctula during hibernation. Bats were divided into three categories (solitary, groups of six, and groups of sixteen) and nine experimental groups comprising one individual with temperature logger per group (iButton). Skin temperature (Ts) was monitored every five minutes. The results showed that bats in larger groups (the group of sixteen) entered longer and more stable torpor, with no instances of full arousal (Ts >20°C). In contrast, solitary bats exhibited more frequent arousals. All bats entered deep torpor after the first nine days. No significant differences in body mass loss were found between the groups. The findings highlight the importance of group size in reducing arousals during hibernation, and the role of social thermoregulation in conserving energy.

Abstract Environmental pollution and habitat loss and are influencing the health status of wild animals and increase the risk of zoonosis outbreaks. For example, the ongoing urbanisation leads to significant habitat changes and burden of anthropogenic stressors. Bats are a diverse mammalian order occurring in urban areas. In a pilot study, we investigated the general immunity status of two common bat species along urban-natural gradients. We used haematological parameters as cellular immunity indicators and intensity of light pollution as a proxy for urbanisation level (i.e. anthropogenic stress) at the sampling points. We found higher total white blood cell, lymphocytes and neutrophil proportions in Nyctalus noctula from suburban and urban habitats in comparison to those from natural ones. At the same time Eptesicus serotinus, a species commonly living in cities, had a lower neutrophil level and a trend towards lower neutrophil-to-lymphocyte ratio and intoxication index compared to N. noctula which only uses the suburban-urban area seasonally. Our study suggests that the cellular immunity in bats is altered by urban stressors, yet depends on species-specific tolerance. We call for more research in this area and, as precaution principle, conservation of habitats in urban areas in order to mitigate the negative impact of urban stressors on the health of wildlife.

The full-scale war in Ukraine negatively impacted populations of urban and semi-urban animals. This study examines the effects of war-related damages on urban populations of bats in Kharkiv city (NE Ukraine) during 2022. Our findings suggest that 45.1% of buildings used as wintering roosts for N. noctula were either partially damaged or completely destroyed by shellings, which may have led to the direct killing of approximately 7,000 bats. Additionally, the war-damaged urban environments in Kharkiv serve as a deadly trap for bats during the period of autumn migration or swarming. Bats flew into buildings’ interiors through windows that were left open or broken by blast waves, resulting in entrapment. The total number of N. noctula trapped inside buildings damaged by shelling was 2,836 individuals, with a death rate of approximately 30%. The group size of trapped bats was more numerous than in previous years, and the main findings were concentrated in war-damaged districts of the city.

Bats are an endangered group of mammals that are very sensitive to environmental stresses. One of such stress factor is trace metals pollution which threatens populations of insectivorous bats due to their top position in the food webs and exceptionally long life span. In our research Pipistrellus kuhlii was tested as a promising indicator species (urban-dwelling, sedentary, with limited daily home-range) for trace metal exposure of bats. We measured concentrations of Pb, Cu, Zn and Cd in internal and external tissues of bats from the industrial city Mariupol and the village Karlovka, Ukraine, to answer the following questions: (1) Do metal concentrations in soil samples differ between urban and rural areas, and between populations of P. kuhlii from those areas? (2) Does metal contamination differ between individuals of different sexes and ages? (3) Whether fur and/or wing membrane, the two tissues that can be collected from live bats, can be used as proxies of metal contamination in internal tissues (liver, kidney, lung, forearm bones) of P. kuhlii? Metal concentrations in soil samples were significantly higher in the city. Bats from the city accumulated significantly more Cd, Pb and Zn in external tissues than those from the rural area. Females accumulated more Cd than males, and this-year-born did not differ significantly from adult individuals. We did not find, however, significant positive correlations between metal concentrations in external and internal tissues, indicating that external tissues cannot serve as an indicator of the metal contamination of internal tissues in P. kuhlii.

Copulatory behaviours stand as cornerstones of sexual selection, yet they remain mysterious in many species. Because of their nocturnal and elusive lifestyle, the copulatory behaviours of bats have been mostly overlooked1. Several aspects of bat reproduction differ from other mammals (e.g. prolonged sperm storage2, delayed development3). Here, we show that in serotine bats (Eptesicus serotinus) the penis is used as a 'copulatory arm' rather than an intromittent organ, revealing a novel copulatory behaviour in mammals.

Seasonal utilization of urban areas by bats remains inadequately explored. This study aimed to comprehensively survey the species composition and population dynamics of bats during both the breeding season (May–July) and autumn migration season (August–September) within a large urban area, specifically Kharkiv city, Ukraine. We conducted multiyear data collection from 2014 to 2016, employing a combination of acoustic recordings, mist-netting, and registration of opportunistically found bats. The results revealed the identification of seven bat species using all methods (Eptesicus serotinus, Nyctalus noctula, N. leisleri, Pipistrellus pygmaeus, P. kuhlii, P. nathusii, and Vespertilio murinus), with notable differences in species composition between the studied periods. During the migration season, N. noctula was a numerically predominant species, while P. kuhlii and E. serotinus were the most abundant during the breeding season. The urban core bat population during the breeding season primarily consisted of males and solitary reproductive females, mainly represented by P. kuhlii and E. serotinus. Acoustic recording data indicated that N. noctula actively avoided the urban core during the breeding season, but was more common on the city periphery. In contrast, during the migration season, the city experienced a significant surge in bat abundance, both in general and specifically among noctule bats, with their numbers increasing tenfold compared to the breeding season. Moreover, a considerable number of young individuals were observed during the migration season. These findings provide evidence that bats tend to avoid the urban core in large cities at temperate latitudes during the breeding season but actively utilize urban areas during autumn migration. Understanding the seasonal preferences and movements of bats in urban environments is crucial for effective conservation and management strategies.

Bats are of high conservational status in most European countries. All bats are under legal protection in Ukraine and included in the national Red Data Book. However, bats remain one of the least studied groups of mammals in Ukraine. Their cryptic lifestyle limits the possibilities of direct observations and, as a result, data on bat distribution are incomplete. Wildlife rehabilitation centres accumulate a plethora of records of wild animals and those data may significantly contribute to knowledge on the species range, phenology and habitat preferences.This paper presents the data accumulated from over a decade of work by the Ukrainian Bat Rehabilitation Center (formerly The Bat Rehabilitation Center of Feldman Ecopark), the premier organisation engaged in the rescue and rehabilitation of bats across Ukraine. In addition to in-person data collected by Ukrainian Bat Rehabilitation Center staff, the Center also accepts observations of bat encounters from citizens. The Center's dataset boasts over 20,000 distinct observations, which are the subject of this paper.This dataset, spanning 2011-2022, contains a total of 20,948 records of bat findings, 19,024 of which consist of records directly identified by UBRC team members. The remaining 1924 observations were provided by citizens through helpline. Data on 16 species and one subspecies have been collected. The highest number of records belongs to Nyctalusnoctula (n = 15889), followed by Eptesicusserotinus (n = 2017) and Pipistrelluskuhliilepidus (n = 2001). Less than 10% of these records have been previously published; the rest are presented in this paper for the first time. The dataset is particularly rich in information on bats in human settlements and is (to the best of the authors' knowledge) the largest dataset on bats within human-modified landscapes ever collected from the territory of Eastern Europe. The entire dataset is available through the Global Biodiversity Information Facility (GBIF).

Abstract Copulatory behaviours stand as cornerstones of sexual selection, yet they remain mysterious in many species, especially in bats. An extremely large penile erection with a heart-shape terminal swelling has been observed in the serotine bat (Eptesicus serotinus). The engorgement of the erectile tissues could take place after penetration to generate a copulatory lock. Alternatively, the erected penis, long and mobile, could be used to pass by the protective tail membrane to reach the vulva. In the latter scenario, the penis may however not be able to penetrate the vagina. In order to find out which of the two scenarios occurs, we investigated the morphology of female and male genitalia of E. serotinus. We found that the vagina is more than seven times shorter than the erected penis, supporting that the penis is used as a copulatory arm rather than an intromittent organ. We could confirm our hypothesis with direct observations of copulations. During mating, the male grasps the female in a dorsoventral position. The male probes the female’s ventral part with its erected penis until the penis is tightly pushed against the vulva. Afterward, the pair stops moving and can hold the position for several hours. In addition, the timing of copulations, which exhibits a peak in October, implies that visits to swarming sites throughout the year may serve other functions besides mating. This research reveals a novel copulatory behaviour that has not been previously documented in mammals and sheds light on the poorly understood area of bat reproduction.

Hibernation patterns of European bat species, especially those that hibernate above ground, remain under-explored. Our study focused on Nyctalus noctula, a common species among above-ground hibernating bats. We conducted the study on 22 individuals, manipulating group size and sex-age ratio in a captive setting, and recorded skin temperature data using temperature loggers. Bats hibernating in groups awoke less frequently and had more prolonged torpor bouts than solitary hibernating bats. The latter cooled faster during periods of arousal, but their time in the warming and euthermic stages was similar to that of individuals hibernating in groups. A general linear model (GLM) analysis revealed that all the factors we examined, including ambient temperature, sex, age, group size, and body mass, significantly affected the likelihood of a bat being in a state of hibernation or arousal. Young females with high body mass and hibernating in a group had a notably higher probability of arousal. Bats in groups maintained skin temperature (Ts) above 0 degrees C, while it dropped around 0 degrees C in some solitary hibernating bats. However, median Ts was similar in all bat groups. Body mass was higher in females compared to males and in adult bats compared to sub-adults. We hypothesized that adult males have greater fat reserves and can afford a longer total arousal time to effectively seek a mate and mating compared to sub-adult males with low body mass. Heavier females used more fat for more frequent arousals to reduce the negative metabolic consequences of hibernation for fast conception and successful pregnancy in spring. At the same time, sub-adult males entered the wintering period with lower body mass and balanced the use of energy resources for survival and mating. It seems that N. noctula, as an above-grounded hibernator, benefits more from group hibernation than solitary hibernation.

Cities or urban areas are the new types of landscapes that have rapidly developed in the Anthropocene and generally mimic mountains and rock habitats. Such areas attract different vertebrate species that naturally prefer rocky habitats, for example, bats, which are common animal inhabitants of the cities in the Northern Hemisphere. Here we review records of four bat species (Hypsugo savii, Plecotus austriacus, Pipistrellus nathusii and P. pygmaeus) inhabiting human settlements in Ukraine, encompassing the period from 2011 to 2022. Over the last 20 to 30 years, the winter range of P. nathusii has shifted 200-300 km north, and now covers all Black Sea coast steppe regions of continental Ukraine. The Pl. austiacus range most likely covers the whole territory of Ukraine. We documented the first factual records of H. savii in continental Ukraine and the first winter records of P. pygmaeus for the country. Our observations clearly demonstrate colonization of newly formed urban landscapes by bats species from different ecological groups. Therefore, bats, same as some other mammalian species, can be considered beneficiaries of urbanization and urban heat islands.

Winter counting of bats in hibernacula is one of the main methods of estimating their population trends in Europe. However, it is not always possible for humans to identify and count all bats in the maze of big karstic caves or abandoned mines. Previously we notice a significant fluctuation in the numbers of bat species and individuals in sandstone mines located in the Kharkiv region (NE Ukraine), and hypothesized that a significant undercount happened due to the hiding of bats in deep crevices of sandstone. Here using a camera trap placed inside a mine (September 17-19, 2017) we tested this hypothesis. Firstly we identified significant levels of bat flight activity where no roosting bats had been observed through conventional visual survey methods. The proportion of identified bats (Myotis group and Plecotus auritus) on footage was similar to that obtained by usual winter counts. Finally, we filmed and documented cases of crawling bats inside the deep crevices in the wall depths. We ventured to make an extrapolation of bat numbers in a mine on the basis of autumn-spring mist-netting data, and our evidence that they do hide in crevices. Our observations clearly demonstrate that hiding bat behaviour in mines might result in an underestimation of the real number of hibernating bats in sand-stone mines.

Eastern European broadleaved forests north of the 50th degree of latitude serve as a core breeding area for most migratory bat species wintering in Eastern and Central Europe. The southern border of this region has faced an increase in clear-cutting intensity in recent decades. We conducted a standardized mist-netting survey on eleven heterogeneous oak forest plots in order to assess how land cover types and forest age affect abundance, diversity and the breeding of bats. We found that abundance indices and species richness increased from upland plots surrounded by agricultural lands to riverine or waterside plots with high forest cover. Particularly large mature forests older than 90 years positively affected the breeding activity of bats, their abundance indices and overall species richness. Regarding species associations with specific habitats, we found that Myotis brandtii, Nyctalus leisleri and Pipistrellus pygmaeus were mainly found in mature deciduous forest stands, while Plecotus auritus appeared to be the only species tolerating clearcuts and young stands. Forest-dwelling species such as Nyctalus noctula and Pipistrellus nathusii were additionally associated with water habitats. Thus, the combination of mature forests and water sources is essential in shaping Eastern European assemblages of forest bat species.