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The range of Tyto alba overlaps with that of Asio otus in a large part of the Holarctic. Both species are adapted to open-area hunting and prey upon similar species. In contrast to A. otus, data about the diet of T. alba on Crimea and surroundings are extremely scarce. Our study aimed to describe the prey spectrum of T. alba and evaluate at what extant its diet overlaps to that of A. otus. We evaluated diets based on 48 pellets of T. alba and 88 of A. otus collected from January to March 2018 in the Western part of the Crimea Peninsula. Simultaneously, we assessed the availability of small mammal prey by installing 150 spring-loaded bar mousetraps around the collection sites. Small mammals were the main prey in the diet of T. alba and A. otus (99.2% and 100% of all individuals in pellets). The most consumed species of both species was Microtus socialis (52.3% and 74.4% of all individuals). The second most consumed species of T. alba was Crocidura leucodon, an endangered species in Crimea. The diet of T. alba was more diverse than that of A. otus (Shannon diversity Index: 1.1 and 0.76, Simpson Index: 0.51 and 0.31, respectively). However, their diets overlapped widely (Pianka's index = 0.94). The frequency of mammalian prey in traps correlated moderately with that in A. otus pellets (rs = 0.5, p < 0.2), and it deviated from the frequency of mammalian prey in T. alba pellets (rs = -0.05, p < 0.9). The presence of the endangered C. leucodon in the diet of T. alba reinforce the utility of this predator species as a tool to detect threatened or rare small mammals that are not caught by traps and to increase information about their geographical distribution.

In the article the chromosomal complement of the social vole (Microtus socialis parvus Satunin, 1906) from five additional points of the North Caucasus is studied in a comparative aspect. Much attention is given to the distribution of this species taking into account the landscape structure and biotopic allocation. It is concluded that the karyotype of the social vole in the analysed area is not susceptible to polymorphism. The chromosomal complement of all studied individuals is identical in the number and morphology of chromosomes.

The features of the spatial distribution of four species of Mouse-Like rodents (Sylvaemus fulvipectus, Cricetulus migratorius, Microtus socialis, and Dryomys nitedula) in the forest associations of the foothill zone of the Republic of Dagestan are analyzed. Sixteen environmental parameters are selected, of which ten significantly showed interspecific differences. The distribution of rodent species is demonstrated relative to the environmental characteristics taken into account in the descriptions; the preferences and requirements for the environment of each species are revealed. Thus, the yellow-bellied mouse and gray hamster were found at all stations, whereas the forest dormouse and social vole were more selective in their choice of stations. As a result, the width of the spatial niches for the yellow-bellied mouse and gray hamster is greater than that of the forest dormouse and social vole. The results of pairwise comparison of the spatial niches of studied rodent species reveal low values of their overlap.

The intraspecific relations of two species of the subgenus Sumeriomys have been studied: the social vole Microtus socialis and the paradox vole M. paradoxus. The relationships between animals same-sex individuals in the experimental groups, are generally amicable, but the cohabitation of two or more females suppresses reproduction. Groups formed from unfamiliar individuals were characterized by increased aggressiveness, which led to high mortality. The paradox vole was diffed from social vole by higher motor and social activity and greater aggressiveness towards unfamiliar individuals. The vocal behavior of individuals of both species is similar. 30% of contacts between individuals are accompanied by squeaks; males sing in intersex interactions, but this behavior is rare (less than 1% of contacts).

A considerable increase in the social vole population distributed in the northwestern Caspian region (Republic of Kalmykia) in 2014–2016 has been recorded. The average long-term dominance index of the rodent cenosis in 2014–2016 was three times as high as in 2002–2010. The rise in the rodent population was caused by an increase in the reproduction rate due to adequate fodder supplies under favorable climatic conditions. In May 2016, social vole mass migration and deaths were registered; it is a rare phenomenon arising in rodents that may be caused by overdensity of their population. All of the males were first involved in the migration process because of increased intraspecific competition, higher aggression levels, and weaker attachment to the habitats as compared to the females. The mass migration and deaths of social voles in the northwestern Caspian region may reflect the unstable equilibrium dynamics caused by changes in the anthropogenic pressure and land-use system, which interacts with the damping effects in the climate.

Entomoparasitic nematodes are the natural regulators of numbers of fleas – plague vectors in natural plague foci. They have an impact on the intensity of epizootic process, progressing in these foci. Objective of the study is to examine entomoparasitic nematodes from fleas of the souslik and vole, collected in the territory of Povolzhsky Region. Materials and methods. Presented are the results of morphological and genetic analysis of entomoparasitic nematodes, flea parasites – Citellophilus tesquorum, Amphipsylla rossica and Ctenophthalmus secundus, collected from the small ground squirrel Spermophilus pygmaeus and social vole Microtus socialis, respectively. Results and conclusions. Established has been morphological identity of nematode parasitic females isolated from all the three species of fleas, and a high degree of similarity to the previously described Rubzovinema ceratophylla, parasitizing on C. tesquorum fleas. Substantiated has been the belonging of parasitic nematodes isolated from fleas C. tesquorum, А. rossica and C. secundus, to one and the same species, specified as Rubzovinema sp., based on the high percentage of the homology of the nucleotide sequences of rRNA genes (99.3–100 %). This species differs from the previously described monoxenous R. ceratophylla in absence of strict host specificity.

The article addresses the interrelationship between different forms of group varia­bility of craniometrical features according to value of their contribution in the overall morphological disparity of individuals in the population Microtus socialis in southern Ukraine. It is shown that most of the variability of traits determined primarily the age animals and less sex, season, number and density of individuals in the population. Obtained results indicate that the age variability is the base for formation of all other forms of group variability. It is proved that the variability of craniometrical traits in young and subadult voles is determined primarily by size and density of individuals in population (cyclic variability). Second largest impact on the variability of craniometrical features includes season, third – sex whose influence on the variability of traits in young voles was statistically proven. In juvenile voles sex and season affect the variability of linear dimensions and proportions of the skull, while in subadult and adults – mostly in the proportions of the skull and almost no influence on the variability of its linear dimensions. Sexual variability of the craniometrical traits increases markedly with the age of voles.

The results of interspecific crosses of the social vole Microtus socialis with the Altai vole M. obscurus, the East European vole M. rossiaemeridionalis, and the Transcaspian vole M. transcaspicus are presented. The role of the sperm head structure in the reproductive isolation of this species was studied. Hybrids were obtained in five of the six crossing combinations. It is established that significant differences in the sperm head shape in the social vole and in arvalis group species do not prevent fertilization. The sterility of hybrids indicates the existence of postcopulative mechanisms of reproductive isolation.

Expression of sexual differences in social vole populations of virgin steppe reserve “Askania Nova” analyzed in the article. It is established that the severity of the sexual differences of value morphological features depending on the age of the animals and to a lesser degree on the season. В статье проанализировано проявление половых различий в популяции общественной полёвки целинной степи заповедника «Аскания-Нова». Установлено, что степень выраженности половых различий величины морфологических признаков изменчива в зависимости от возраста зверьков и в меньшей степени от сезона.

The study reports on chromosomes in several populations of social voles from south-eastern Europe and the Middle East. The standard karyotypes of individuals of Microtus hartingi and Microtus guentheri originating from both south-eastern Europe and Asia Minor comprised 54 mostly acrocentric chromosomes. However, variation between populations was found in the amount and distribution of C-heterochromatin in certain autosomes and the sex chromosomes. Furthermore, a specific pattern of argyrophilic nucleolar organizer region distribution was recorded in different geographic populations. In a population from Asia Minor, a heterozygous centric fusion of two autosomes was found. The G-banded karyotypes of M. guentheri and Microtus socialis were compared, and tandem fusions of autosomes were suggested as possible mechanism of the divergence. The karyotypes of the nine currently recognized species of social voles are reviewed, and implications of chromosomal data for systematics are evaluated.

The botanical composition and the ratio of various plants in the diet of Microtus socialisPall. were determined by microhistological cuticular-coprological analysis of undigested remains. Microtus socialis disappeared from the zonal plain of the Volga-Ural interfluve in the early 1970s and appeared again in 2009. The role of grains in their nutrition became more important, and the ratio of wormwoods sharply decreased. The feeding patterns observed are caused by the long-term absence of these massive phytophages and reflect significant changes in the habitat over the last 40 years.

The Social Vole Microtus socialis differs from non-socialis voles from Iran by its smaller size and relatively broader inter-orbital region. Discriminant Function Analysis based on 14 cranial measurements classified all Iranian specimens into their actual group (i.e. socialis or non-socialis). A dotted distribution map of M. socialis is provided for Turkey, Syria, Lebanon, Iraq and Iran. Isolated records from Khorassan and Fars, both in Iran, are discussed. Inter-locality variations were significant in dimensions of the tooth-row, diastema, rostrum, bullae and braincase breadth. The postero-internal loop of the second upper molar was either absent or rare; only in voles from Lebanon and Syria was the incidence of this morphotype observed in about one-third of the specimens. Marginal populations seemed to be morphologically most distant.

A comparative analysis of the spatial-ethological structure of social vole (Microtus socialis Pall.) colonies was made on the basis of studies performed in Dagestan (1987–1991) and the southern Kalmyk Republic (1993–1998). Notwithstanding differences in environmental conditions and the extent and forms of anthropogenic impact, the population structure of the species proved to be similar and stable. Irrespective of population density, its core consists of family groups. Specific features of social behavior (aggressiveness toward unfamiliar animals) provide for the protection of home ranges and help to maintain a stable population structure.

Olfactory cues can contain information for discrimination of gender that can affect subsequent social interactions. Social rodents are hypothesized to use more olfactory cues than nonsocial rodents to distinguish males from females. The generality of this hypothesis was tested using the pine vole (Microtus pinetorum), a social vole. We examined nine possible sources of odors. A slide containing an odor from a male and a female was presented to each test subject for 3 min. We recorded the amount of time each test subject spent investigating each odor. Females spent significantly more time investigating male urine and male anogenital odors; however, they did not use any other odor sources to discriminate gender. In contrast, males did not use any odor sources to discriminate gender. Our results do not support the hypothesis that all social rodents use numerous odor sources to discriminate gender. Instead, our results are consistent with the alternative hypothesis that use of odor sources to convey information about gender may differ in rodents that live in different microhabitats.