Microtus Gregalis Research Articles

Fauna and landscapes of the Southern Minusinsk basin (southern Siberia) at the end of the late pleistocene

The paleolandscapes of the first half of MIS 2 or the Last Glacial Maximum (LGM) were reconstructed based on the study of the first mammoth fauna locality in the Abakan River valley and comparison with other localities in the South Minusinsk Basin. The sediments in the geological section of Uytag are represented by interlayers of silts, underlain and overlain by sandstone rock slack fragment, interpreted as weakly eroded deluvium. The study of the Uytag locality made it possible to clarify the time and range of distribution in southern Siberia of some mammal species Ovis ammon, Equus ferus, Marmota baibacina, Sicista subtilis, Lagurus lagurus and Microtus gregalis, as well as Pleistocene bird Aquila chrysaetos. The age of the locality is confirmed by radiocarbon dating. The species composition of the fauna is similar to other localities in the region of this age. All known localities and single finds of faunal remains indicate a wide development of open steppe landscapes in the South Minusinsk Basin during the LGM.

Fauna and Landscapes of the Southern Minusinsk Basin (Southern Siberia) at the End of the Late Pleistocene.

Paleolandscapes of the first half of MIS 2 or the Last Glacial Maximum (LGM) were reconstructed based on the study of the first mammoth fauna locality found in the Abakan River valley and a comparison with other localities of the South Minusinsk Basin. Sediments of the Uytag geological section under study included silt interlayers underlain and overlain by sandstone rock slack fragments and were interpreted as weakly eroded diluvium. Studies of the Uytag locality made it possible to clarify the time and range of distribution in southern Siberia for several mammals (Ovis ammon, Equus ferus, Marmota baibacina, Sicista subtilis, Lagurus lagurus, and Microtus gregalis) and the Pleistocene bird Aquila chrysaetos. The age of the locality was confirmed by radiocarbon dating. The species composition of the Uytag fauna was similar to that of other localities of the same age and region. All known localities and single finds of faunal remains indicate that open steppe landscapes were widely developed in the South Minusinsk Basin during the LGM.

Investigation and genetic polymorphism analysis of rodents infected with Echinococcus in Ili Prefecture, Xinjiang Uygur Autonomous Region, China.

Alveolar echinococcosis (AE) is a life-threatening disease in humans caused by the larval stage of Echinococcus multilocularis. Domestic animals, dogs, foxes, and small mammals constitute the circular chain of AE. To evaluate the infection, distribution, and genetic polymorphism of AE in the Ili Prefecture (Nilka, Xinyuan and Zhaosu), we conducted this survey. In June and July 2018, 267 small mammals were captured using water-infusion and mousetrap methods. Combined pathogenic and molecular biological methods were used to observe the histopathology of Echinococcus carried by rodents, amplify the mitochondrial nad1 gene of the pathogen, and investigate the genotype and haplotype diversity of Echinococcus in rodents in Ili Prefecture. Morphological identification revealed that these captured small mammals belonged to three species, with Microtus gregalis being the dominant species (183/267). Pathological and molecular biological results confirmed that E. multilocularis was the pathogen of echinococcosis in small mammals, with an infection rate of 15.73% (42/267). Among the three areas sampled, the highest infection rate of rodents was 25.45% (14/55) in Nilka County. However, there was no significant difference in the infection rates between regions (χ2 = 5.119, p > 0.05). Of the three captured rodent species, M. gregalis had the highest infection rate of 17.49% (32/183), but there was no significant difference in infection rates between the rodent species (χ2 = 1.364, p > 0.05). Phylogenetic analyses showed that the nad1 gene sequences obtained in this study clustered in the same clade as isolates from China. These isolates contained 21 haplotypes (Hap_1-21); Hap_2 was the most common haplotype (9/42). Furthermore, haplotype diversity (0.925 ± 0.027) and nucleotide diversity (0.01139 ± 0.00119) were higher in the Ili Prefecture than in other regions, indicating that population differentiation was high. Tajima's D and Fu's Fs tests were negative (p > 0.10), indicating that the population had expanded. The low fixation index (Fst) ranged from 0.00000 to 0.16945, indicating that the degree of genetic differentiation was different among different populations. In summary, Ili Prefecture is a high incidence area of AE, and Microtus spp. may play an important role in the transmission of AE in this area. The results of this study provide basic data for further study of the molecular epidemiology, genetic differences, and control of E. multilocularis in the Ili Prefecture, Xinjiang.

Environmental and climatic inferences for Marine Isotope Stage 2 of southern Belgium (Meuse valley, Namur Province) based on rodent assemblages

The environmental and climatic conditions of the Late Pleistocene of Southern Belgium are here determined for the final part of Marine Isotope Stage 3 (MIS 3) and for MIS 2 on the basis of a study of rodent assemblages. This paper provides a synthesis of several sets of environmental and climatic data from Late Pleistocene sites, all of which are located in southern Belgium. One has previously been published (Caverne Marie-Jeanne), and seven are unpublished (Cavernes de Goyet, Trou des Nutons, Trou du Frontal, Trou de Chaleux, Grotte la Chefalize, Trou du Chêne, and Trou du Sureau). The habitat weighting and quantified ecology methods are applied to rodent material housed in the Royal Belgian Institute of Natural Sciences (RBINS, Brussels), and previous radiocarbon dates are updated, in order to reconstruct past environments. Among all the sites under analysis, the quantified ecology method shows that Trou de Chaleux corresponds to the coldest temperatures and lowest precipitation. Trou de Chaleux, with a chronology between ca. 15,964–14,014 cal yr B.P., could probably be placed in Greenland Stadial 2 (GS2) or Heinrich Event 1 (HE1). It has a rodent assemblage associated with a predominance of open dry and rocky formations, the most abundant species being the collared lemming and the narrow-headed vole. These data are found to coincide with previous studies carried out on the large-mammal, herpetofaunal, and avifaunal associations of the site, as well as on small-mammal associations from other sites in southern Belgium with similar chronology, such as Grotte Walou. Taken together, this indicates that these latest Pleistocene intervals in southern Belgium were characterized by harsh climatic and environmental conditions. In contrast, the other assemblages under study yielded much more heterogeneous results, frequently inconsistent with an attribution to the Pleistocene. This is likely to be a result of their admixture with Holocene material due to recent intrusions.

Mapping small mammal optimal habitats using satellite-derived proxy variables and species distribution models.

Small mammal species play an important role influencing vegetation primary productivity and plant species composition, seed dispersal, soil structure, and as predator and/or prey species. Species which experience population dynamics cycles can, at high population phases, heavily impact agricultural sectors and promote rodent-borne disease transmission. To better understand the drivers behind small mammal distributions and abundances, and how these differ for individual species, it is necessary to characterise landscape variables important for the life cycles of the species in question. In this study, a suite of Earth observation derived metrics quantifying landscape characteristics and dynamics, and in-situ small mammal trapline and transect survey data, are used to generate random forest species distribution models for nine small mammal species for study sites in Narati, China and Sary Mogul, Kyrgyzstan. These species distribution models identify the important landscape proxy variables driving species abundance and distributions, in turn identifying the optimal conditions for each species. The observed relationships differed between species, with the number of landscape proxy variables identified as important for each species ranging from 3 for Microtus gregalis at Sary Mogul, to 26 for Ellobius tancrei at Narati. Results indicate that grasslands were predicted to hold higher abundances of Microtus obscurus, E. tancrei and Marmota baibacina, forest areas hold higher abundances of Myodes centralis and Sorex asper, with mixed forest-grassland boundary areas and areas close to watercourses predicted to hold higher abundances of Apodemus uralensis and Sicista tianshanica. Localised variability in vegetation and wetness conditions, as well as presence of certain habitat types, are also shown to influence these small mammal species abundances. Predictive application of the Random Forest (RF) models identified spatial hot-spots of high abundance, with model validation producing R2 values between 0.670 for M. gregalis transect data at Sary Mogul to 0.939 for E. tancrei transect data at Narati. This enhances previous work whereby optimal habitat was defined simply as presence of a given land cover type, and instead defines optimal habitat via a combination of important landscape dynamic variables, moving from a human-defined to species-defined perspective of optimal habitat. The species distribution models demonstrate differing distributions and abundances of host species across the study areas, utilising the strengths of Earth observation data to improve our understanding of landscape and ecological linkages to small mammal distributions and abundances.

An Invisible Boundary between Geographic Ranges of Cryptic Species of Narrow-Headed Voles (Stenocranius, Lasiopodomys, Cricetidae) in Transbaikalia

The narrow-headed vole species complex is represented by Lasiopodomys gregalis and L. raddei, which probably diverged at the beginning of the Middle Pleistocene and came into secondary contact in the Transbaikal region. The current study analyzed mitochondrial gene cytochrome b, nuclear gene BRCA1, and microsatellite data and was aimed at clarifying geographic ranges of these species and searching for hybrid zones between them. It turned out that the geographic range of L. raddei is almost surrounded by that of L. gregalis; these species are strictly parapatric without a single detected sympatry zone. Although in none of the tested populations did the BRCA1 genotyping contradict the pattern revealed by mitochondrial cytb, microsatellite loci showed traces of hybridization in several populations. Results of species distribution modeling indicated that these species are characterized by quite similar (caused by the same environmental factors), but nevertheless significantly different, ecological preferences.

Ancient DNA of narrow-headed vole reveal common features of the Late Pleistocene population dynamics in cold-adapted small mammals.

The narrow-headed vole, collared lemming and common vole were the most abundant small mammal species across the Eurasian Late Pleistocene steppe-tundra environment. Previous ancient DNA studies of the collared lemming and common vole have revealed dynamic population histories shaped by climatic fluctuations. To investigate the extent to which species with similar adaptations share common evolutionary histories, we generated a dataset comprised the mitochondrial genomes of 139 ancient and 6 modern narrow-headed voles from several sites across Europe and northwestern Asia covering approximately the last 100 thousand years (kyr). We inferred Bayesian time-aware phylogenies using 11 radiocarbon-dated samples to calibrate the molecular clock. Divergence of the main mtDNA lineages across the three species occurred during marine isotope stages (MIS) 7 and MIS 5, suggesting a common response of species adapted to open habitat during interglacials. We identified several time-structured mtDNA lineages in European narrow-headed vole, suggesting lineage turnover. The timing of some of these turnovers was synchronous across the three species, allowing us to identify the main drivers of the Late Pleistocene dynamics of steppe- and cold-adapted species.

Narrow-Headed Voles Species Complex (Cricetidae, Rodentia): Evidence for Species Differentiation Inferred from Transcriptome Data

The narrow-headed vole complex includes two cryptic species, Lasiopodomys raddei and L. gregalis, and three allopatrically-distributed lineages with obscure taxonomic ranks within the latter. Based on the RNA-seq data of 12 specimens, the current study aims to find the molecular mechanisms of intraspecies differentiation and, in particular, reproductive isolation between analyzed groups. According to the results of the GO-enrichment analysis, about a hundred biological processes associated with genes with contrasting SNPs for L. gregalis and L. raddei were identified. Among them, processes of interspecific interactions, defense responses, responses to external stimuli, and the perception of chemical stimuli and smell were identified, indicating the likely existence of pre-copulatory behavioral and physiological mechanisms that contribute to reproductive isolation between cryptic species. An evaluation of the ratio of non-synonymous substitutions to synonymous ones showed evidence of selection in L. raddei compared to L. gregalis for a large part of the analyzed genes. Among the analyzed genes, genes with both weakening and intensifying selection were found.

Mammal extinction facilitated biome shift and human population change during the last glacial termination in East-Central Europe

The study of local extinction times, together with the associated environmental and human population changes in the last glacial termination, provides insights into the causes of mega- and microfauna extinctions. In East-Central (EC) Europe, groups of Palaeolithic humans were present throughout the last glacial maximum, but disappeared suddenly around 15,200 cal BP. In this study cave sediment profiles dated using radiocarbon techniques and a large set of mammal bones dated directly by AMS 14C were used to determine local extinction times. These were, in turn, compared to changes in the total megafauna population of EC Europe derived from coprophilous fungi, the Epigravettian population decline, quantitative climate models, pollen and plant macrofossil inferred climate, as well as to biome reconstructions. The results suggest that the population size of large herbivores decreased in the area after 17,700 cal BP, when temperate tree abundance and warm continental steppe cover both increased in the lowlands. Boreal forest expansion started around 16,200 cal BP. Cave sediments show the decline of narrow-headed vole and arctic lemming populations specifically associated with a tundra environment at the same time and the expansion of the common vole, an inhabitant of steppes. The last dated appearance of arctic lemming was at ~ 16,640 cal BP, while that of the narrow-headed vole at ~ 13,340, and the estimated extinction time of woolly mammoth was either at 13,830 (GRIWM) or 15,210 (PHASE), and reindeer at 11,860 (GRIWM) or 12,550 cal BP (PHASE). The population decline of the large herbivore fauna slightly preceded changes in terrestrial vegetation, and likely facilitated it via a reduction in the intensity of grazing and the concomitant accumulation of plant biomass. Furthermore, it is possible to conclude that the Late Epigravettian population had high degree of quarry-fidelity; they left the basin when these mammals vanished.

Environmental changes in the Middle Urals during Briansk interstadial: Makhnevskaya-2 cave (MIS 3, Russia)

The results of the comprehensive study of zoogenic deposits in the Makhnevskaya-2 Cave (the north of the Middle Urals) made it possible to reconstruct gradual changes in the flora and fauna of the local territory during the Middle Valdai (Briansk) interstadial (MIS 3). The formation of deposits passed through three stages, which differ in proportions of tundra, steppe, and forest vegetation components as well as in proportions of multiple taxa Dicrostonyx torquatus, Microtus gregalis, Lemmini gen. The dental morphological characteristics of two species of rodents (Dicrostonyx torquatus, Microtus gregalis) helped identify biostratigraphic markers of the studied period of the Late Pleistocene.

Non-analogue communities in the Italian Peninsula during Late Pleistocene: The case of Grotta del Sambuco

The study of faunal communities of the past, and how they have changed to become what they are now, is fundamental to the understanding of the changes in ecosystems that we are witnessing and that are coming in the future. In this paper, we present the small mammal assemblage from Grotta del Sambuco (Massa Marittima, Grosseto), belonging to two archaeologic stratigraphic Units, 5 and 6, both dated to Marine Isotope Stage 2. The assemblage from Unit 6 can be defined as “non-analogue”, due to the occurrence of the Narrow-headed Vole Lasiopodomys anglicus and the Southern Birch Mouse Sicista subtilis. Non-analogue communities (i.e., with no equivalent in present time) are frequent during Late Pleistocene in the Italian Peninsula. Starting with Grotta del Sambuco, we describe some of the different factors leading to the origins and disappearance of past non-analogue small mammal assemblages in Italy. Climatic changes and the consequent shifts in geographic distributions of the species play a major role in shaping these communities, eventually leading to extirpation and extinction of cold- or continental-adapted species.

Synanthropic rodent fauna of Eastern Transbaikalia in the early 21st century

The article provides information on the synanthropic rodent fauna of Eastern Transbaikalia. In 2017–2020 the city of Chita, the town of Baley and small settlements of Zabaykalsky krai were surveyed. True synanthropes: the house mouse and the brown rat are most abundant in residential landscapes. Natural populations of the house mouse are typical for coastal biotopes of the steppe zone, and the brown rat is typical for forest-steppe zone of Zabaykalsky krai. In Chita (administrative centre of Zabaykalsky krai) the share of the brown rat in rodent communities has considerably increased in recent decades. There is an extension of the brown rat’s habitat in the area of Baikal-Amur Mainline. Optional synanthropes: striped field mouse, striped dwarf hamster, Maximowicz’s vole, and narrow-headed vole are less important in residential landscapes of the region. In the beginning of the 21st century the field mouse is extending its habitat to the disjunct zone to the west of Transbaikalia: it is now common in the residential area of the town of Baley. Penetration of another optional synanthropic species recorded in the neighbouring Siberian regions – the East European vole – has not been detected.

Влияние промышленного загрязнения на структуру популяций животных Северного Казахстана

The study was conducted in the spring-summer period of 2021 on the territory of the Pavlodar region. The authors studied the number of populations, sex, and age belonging of small mammals. Gero crushers and trap grooves with cones were used on the technogenic territory near the Pavlodar aluminum and Kazakhstan electrolysis plants. 173 animals were obtained: 104 in the background areas and 69 in technogenic territories. The animals belong to 15 species of two orders: Rodents and Insectivores. As a result of the research, a decrease in species richness (<0.695) and species diversity (<0.228) was noted, the dominance of Microtus gregalis (42) and Sicista subtilis (26.1) in areas subject to anthropogenic load was noted. The number of males participating in inbreeding in the territories near factories increases in the steppe mouse and narrow-crusted vole (67%), compared with the control (33%). At the control sites, there were fewer mature females (42%) than at the technogenic ones (58%). The fecundity of females (the number of embryos) is lower in the control area (±5.28) compared to the technogenic zone (±6.1).

МОРФОЛОГИЯ ПЕРВОГО НИЖНЕКОРЕННОГО ЗУБА MICROTUS GREGALIS (RODENTIA, ARVICOLINAE) ИЗ СРЕДНЕГО НЕОПЛЕЙСТОЦЕНА ПРЕДАЛТАЙСКОЙ РАВНИНЫ

In this paper morphological structure of the first lower molar m1 tooth of the narrow-skulled vole from alluvial deposits of the Pre-Altai Plain Middle Neo-Pleistocene is described. Morphological study of the vole remains showed that they belong to the modern species Microtus gregalis. At the same time, the study sample showed significant differences, both in morphological structure and in the size of the first lower molar, in comparison with the recent representatives of the same territory. The set of morphological and morphometric data shows that the studied voles occupy an intermediate position between M. gregaloides of the Early and M. gregalis of the Late Neo-Pleistocene. The ratio of m1 morphotypes also showed the relative primitiveness of the M. gregalis sampling. Morphological study of remains of the narrow-skulled vole from the Solonovka, Petropavlovskoe and Malinovka-4 locations confirmed the previously determined age for sediments containing the remains of microtheriofauna.

Hunting behaviour in arvicoline rodents

In laboratory experiments, purposeful predatory inter-relations with moving insects have been revealed and described in three species of herbivorous voles: the East European vole, the narrow-headed vole, and the Tuva silver vole. The appearance of the full hunting stereotype in these species does not require preliminary experience, which indicates its innate nature. The hunting behaviour of the Tuva silver vole differed from that of the East European vole and narrow-headed vole, which probably reflects the phylogenetic relationships between these species.

Incisor microwear of Arctic rodents as a proxy for microhabitat preference

Changing environmental conditions in the Arctic make it important to document and understand habitat preferences and flexibility of vulnerable high-latitude mammals. Indirect proxies are especially useful for elusive species, such as rodents. This study explores incisor microwear as an indicator of variation in behavior and microhabitat use in Siberian lemmings (Lemmus sibiricus) and narrow-headed voles (Lasiopodomys gregalis) from the Yamal Peninsula, Russia. Fifty-nine individuals were sampled at four sites along a latitudinal gradient from forest-tundra ecotone to high-Arctic tundra. Lemmings are present at the northernmost site, voles at the southernmost site, and both species at the middle two. Lemmus sibiricus prefers wet, mossy lowland, whereas La. gregalis favors drier thickets and more open microhabitats and burrows underground. Feature-based analyses indicate higher densities of features and more uniformly oriented striations for voles than lemmings at sites with both species. The species also differ significantly in microwear texture attributes suggesting larger features for lemmings, and smaller ones, but more of them, for voles. While no texture differences were found between sites within species, voles from sites with open tundra have higher striation densities than those from the forest-tundra ecotone. Furthermore, lemmings from open tundra sites have higher striation densities than those from the water-saturated, moss-covered northernmost site. While microhabitat preferences and burrowing by voles likely contribute to differences between species, variation within seems to reflect habitat variation given differences in abrasive loads between sites. This suggests that incisor microwear patterning can be used to track microhabitat differences among Arctic rodent populations.

Signatures of genetic isolation of the three lineages of the narrow-headed vole Lasiopodomys gregalis (Cricetidae, Rodentia) in a mosaic steppe landscape of South Siberia

Geographic isolation is among the most important factors initiating speciation in mammals. The narrow-headed vole Lasiopodomys gregalis is a widely distributed species in steppe habitats of South Siberia that are highly fragmented by mountain ranges. There are three major mostly allopatric mitochondrial lineages of L. gregalis described throughout the distribution range that most plausibly split in the Middle Pleistocene. This study applies the analysis of five microsatellite loci and species distribution modelling to understand the patterns of isolation and migration between L. gregalis populations in South Siberia and in particular in Tuva basin where all three lineages occur simultaneously. Microsatellite analysis supported the population differentiation revealed previously, with three clusters corresponding to mitochondrial lineages and indicated that gene flow between them is strongly limited. There were only traces of hybridisation in the population near the contact zone of lineages B and C. SDM analysis predicted only a small number of potential contact zones between L. gregalis lineages and barriers corresponding to landscape heterogeneity. We presume that the forested mountain ranges act as the main insurmountable barriers to gene flow between major genetic lineages of L. gregalis.

РЕКОНСТРУКЦИЯ ЛАНДШАФТОВ ПРЕДАЛТАЙСКОЙ РАВНИНЫ В ПОЗДНЕМ НЕОПЛЕЙСТОЦЕНЕ ПО ДАННЫМ ФАУНЫ МЕЛКИХ МЛЕКОПИТАЮЩИХ

Reconstructions of landscape features at the end of the Middle and Late Neopleistocene were carried out based on the study of the small mammal’s fauna. Faunal data indicate a wide development of steppetype landscapes on the Pre-Altai Plain in the interval from MIS 6 to the beginning of MIS 2. Both in warm and cold seasons, gophers predominated among small mammals in the region; striped hamsters, jerboas, zokors, southern birch mouses, narrow-headed voles and lemmings were less common. All these species are typical inhabitants of open biocenoses of the steppe or tundra-steppe type. Reconstructions based on microteriofauna materials are in good agreement with the study of fossil soils of the Pre-Altai Plain. Fossil soils show the development of steppe and forest-steppe landscapes during periods of warming. During the cold stages, loess deposits accumulated in the region, which can be considered as indicators of cryoarid steppes.

Assessing molar wear in narrow-headed voles as a proxy for diet and habitat in a changing Arctic

This paper investigates the potential of mesoscale tooth wear (mesowear, chipping, facets, and other wear attributes) in rodents as a proxy for Arctic habitat. It presents a pilot study of narrow-headed voles, Microtus gregalis, at three sites along a latitudinal gradient of ecological subzones in the Yamal Peninsula of the Russian Arctic. These sites include Kharp in the forest–tundra ecotone, Erkuta in the low Arctic, and Sabetta at the border between the low and the high Arctic. A total of 117 specimens were included and eight variables were used to characterize mesoscale tooth wear. Results show significant differences between the sites, suggesting that these variables can distinguish populations from different subzones. Kharp has the flattest tooth wear, whereas Sabetta has the most M1 occlusal relief and dentin exposure. These results are consistent with and interpreted in the light of published experimental work on captive voles. In addition, the Kharp sample has the tallest M1 crowns, whereas Sabetta has the most vertically implanted M1s. The general directional trends toward separation of values by latitude of samples suggests that mesoscale wear in hypselodont rodents (those with open-rooted, ever-growing molar teeth) reflects variation in food abrasivity and, by extension, may be valuable for tracking habitat and ecological changes in the Arctic.

Number and Distribution of the Narrow-Headed Vole Lasiopodomys gregalis (Pallas, 1779) (Cricetidae, Rodentia) in Western Siberia

According to the data collected in the second half of summer for the period from 1954 to 2016 in the flat and mountainous parts of Western Siberia, the distribution and number of the narrow-headed vole in the zonal and provincial aspects were analyzed. Based on the cluster analysis of the matrix of similarity coefficients of abundance indicators obtained by averaging the initial data by years and groups of geobotanical maps units, the classification of habitats according to the favorable environmental conditions degree for the vole is made. The averaged samples are divided into five types of favorability: from optimal, where the abundance of the species is highest in the whole studied area, to extreme, where it is not encountered. In the South of the West Siberian plain narrow-headed vole prefers steppes, and in the subarctic tundras – communities of river valleys. In the Altai and Kuznetsk-Salair mountain regions it is most common in the subalpine light forests, tundras and tundra-steppe of the North-Western and SouthEastern Altai. On average, this vole prefers open habitats in Western Siberia. According to the classification and the structural graph, the dependence of the vole abundance on a number of factors and their inseparable combinations (enviromental and anthropogenic regimes) was revealed. The greatest connection with its distribution in the habitats of Western Siberia is traced for heat and water availability. On the plain, the number of this vole increases from the middle taiga, where it is found only once, to the subzone of the subarctic tundras in the North and to the forest-steppe and steppe zones in the South. In the mountains its more in the South-Eastern Altai, where a relatively high proportion of the most favorable for narrow-headed vole habitats.