Climate-induced changes in the small mammal communities of the Northern Great Lakes Region

We use museum and other collection records to document large and extraordinarily rapid changes in the ranges and relative abundance of nine species of mammals in the northern Great Lakes region (white-footed mice, woodland deer mice, southern red-backed voles, woodland jumping mice, eastern chipmunks, least chipmunks, southern flying squirrels, northern flying squirrels, common opossums). These species reach either the southern or the northern limit of their distributions in this region. Changes consistently reflect increases in species of primarily southern distribution (white-footed mice, eastern chipmunks, southern flying squirrels, common opossums) and declines by northern species (woodland deer mice, southern red-backed voles, woodland jumping mice, least chipmunks, northern flying squirrels). White-footed mice and southern flying squirrels have extended their ranges over 225 km since 1980, and at particularly well-studied sites in Michigan's Upper Peninsula, small mammal assemblages have shifted from numerical domination by northern species to domination by southern species. Repeated resampling at some sites suggests that southern species are replacing northern ones rather than simply being added to the fauna. Observed changes are consistent with predictions from climatic warming but not with predictions based on recovery from logging or changes in human populations. Because of the abundance of these focal species (the eight rodent species make up 96.5% of capture records of all forest-dwelling rodents in the region and 70% of capture records of all forest-dwelling small mammals) and the dominating ecological roles they play, these changes substantially affect the composition and structure of forest communities. They also provide an unusually clear example of change that is likely to be the result of climatic warming in communities that are experienced by large numbers of people.     

Small mammal mycophagy in hemiboreal forest communities of Lithuania

The diets of small mammals in different hemiboreal spruce-dominated, oak-dominated and mixed forests in western part of Lithuania were studied by examination of fungal spores in fresh fecal pellets of caught animals. In the diets of mice (Apodemus spp.), bank voles (Myodes glareolus), and common and pygmy shrews (Sorex araneus and S. minutus), 22 different fungal taxa were identified, 15 of which were hypogeous fungi. The sporocarp abundance and the spores in fecal samples of Elaphomyces fungi prevailed in study area during this investigation. Although most of the captured individuals consumed fungi, the consumption varied among small mammal species. The data show that the fungi were more frequent and taxonomically diverse in Myodes glareolus than in Apodemus spp. diets. The study provided evidence that the fungal component in the diets of insectivorous Sorex species is more diverse than previously known. The availability of sporocarps and the fungal component in the diets of small mammals showed seasonal effects. Annual hypogeous and epigeous sporocarp abundances did not vary significantly across forest types. The significant difference in mycophagy was observed across all forest cover types, with the greatest fungal diversity in fecal samples collected in mixed coniferous-deciduous tree stands.     

Effects of Logging Pattern and Intensity on Squirrel Demography

ABSTRACT We examined the effect of harvesting intensity and pattern on red squirrels (Tamiasciurus hudsonicus), northern flying squirrels (Glaucomys sabrinus), and yellow-pine chipmunks (Tamias amoenus) in mature inland Douglas-fir (Pseudotsuga menziesii glauca) forests in south-central British Columbia, Canada. We sampled squirrels 1 year before harvesting through 4 years after harvesting and estimated population parameters using open-population models. Relative to unharvested stands, each of the 3 species showed a strong response to tree removal. From 2 years to 4 years after logging, red squirrel density was 40% (SE = 7.1) lower in stands with 50% basal-area tree removal. From 1 year and up to 4 years after logging, northern flying squirrel density averaged 60% (SE = 5.2) lower in harvested treatments regardless of intensity or pattern of logging. In contrast, density of yellow-pine chipmunks increased markedly with increased logging intensity. Beginning 3 years after logging, yellow-pine chipmunk density was 734% (SE = 269) greater in stands with 50% basal-area tree removal. In the short term, harvesting intensity was a more important determinant of squirrel density than harvesting pattern. Retaining >10 m² per ha of live residual stand structure in mature inland Douglas-fir forests maintained habitat for forest-dependent species such as red squirrels and northern flying squirrels, albeit at lower densities.     

Spatial distribution of red-backed voles of the genus <Emphasis Type="Italic">Myodes</Emphasis> in the Khanka Plain,Primorskii Krai

The authors present new data on spatial-temporal distribution of the northern red-backed vole (Myodes rutilus Pallas) and the large-toothed redback vole (M. rufocanus Sundervall) for the main habitat types in the Khanka Plain, Primorskii Krai. Data on seasonal and long-term abundance for 2003-2005 are reported. The study was stimulated by contradictory data on the distribution of the Myodes voles in the Khanka Plain.     

Introduced Siberian chipmunks are more heavily infested by ixodid ticks than are native bank voles in a suburban forest in France

By serving as hosts for native vectors, introduced species can surpass native hosts in their role as major reservoirs of local pathogens. During a 4-year longitudinal study, we investigated factors that affected infestation by ixodid ticks on both introduced Siberian chipmunks Tamias sibiricus barberi and native bank voles Myodes glareolus in a suburban forest (Forêt de Sénart, Ile-de-France). Ticks were counted on adult bank voles and on adult and young chipmunks using regular monthly trapping sessions, and questing ticks were quantified by dragging. At the summer peak of questing Ixodes ricinus availability, the average tick load was 27-69 times greater on adult chipmunks than on adult voles, while average biomass per hectare of chipmunks and voles were similar. In adult chipmunks, individual effects significantly explained 31% and 24% of the total variance of tick larvae and nymph burdens, respectively. Male adult chipmunks harboured significantly more larvae and nymphs than adult females, and than juveniles born in spring and in summer. The higher tick loads, and more specifically the ratio of nymphs over larvae, observed in chipmunks may be caused by a higher predisposition - both in terms of susceptibility and exposure - to questing ticks. Tick burdens were also related to habitat and seasonal variation in age- and sex-related space use by both rodents. Introduced chipmunks may thus have an important role in the dynamics of local vector-borne pathogens compared with native reservoir hosts such as bank voles.     

Historic hybridization and persistence of a novel mito-nuclear combination in red-backed voles (genus Myodes)

Background  

The role of hybridization in generating diversity in animals is an active area of discovery and debate. We assess hybridization across a contact zone of northern (Myodes rutilus) and southern (M. gapperi) red-backed voles using variation in skeletal features and both mitochondrial and nuclear loci. This transect extends approximately 550 km along the North Pacific Coast of North America and encompasses 26 populations (n = 485). We establish the history, geographic extent and directionality of hybridization, determine whether hybridization is ongoing, and assess the evolutionary stability of novel genomic combinations.     

Mycophagy by small mammals in the coniferous forests of North America: nutritional value of sporocarps of Rhizopogon vinicolor, a common hypogeous fungus

We evaluated the nutritional value of sporocarps of Rhizopogon vinicolor, a common hypogeous fungus in the coniferous forests of North America, for two small mammal species: the Californian red-backed vole (Clethrionomys californicus) and the northern flying squirrel (Glaucomys sabrinus). Although the nitrogen concentration of sporocarps was high, much of it was in non-protein form or associated with cell walls, suggesting that it may be of low nutritional value or protected from mammalian digestive enzymes. Sporocarps also had high concentrations of cell wall constituents, indicating low availability of digestible energy. When fed a diet of this fungus alone in a controlled feeding experiment both mammal species lost a small amount of body mass. Digestibilities of dry matter, nitrogen, cell wall constituents and energy from sporocarps by both species were lower than the digestibilities of other food types by other similarly sized small mammals. Red-backed voles digested the various components of sporocarps at least as well as the flying squirrels, even though they were almost six-fold smaller in body mass. This observation supports the notion that red-backed voles, like other microtine rodents, have morphological and physiological adaptations of the digestive system that are postulated to permit greater digestion of fibrous diets than predicted on the basis of body size. Despite this, our results re-affirm previous conclusions that hypogeous fungi are only of moderate nutritional value for most small, hindgut-fermenting mammals. Future studies should focus on the importance of mixed-species of fungi in the diet of small mammalian mycophagists. Accepted: 4 December 1998     

Bot fly parasitism of the red-backed vole: host survival,infection risk,and population growth

Parasites can play an important role in the dynamics of host populations, but empirical evidence remains sparse. We investigated the role of bot fly (Cuterebra spp.) parasitism in red-backed voles (Myodes gapperi) by first assessing the impacts of the parasite on the probability of vole survival under stressful conditions as well as on the reproductive activity of females. We then identified the main factors driving both the individual risk of infection and the abundance of bot flies inside red-backed voles. Finally, we evaluated the impacts of bot fly prevalence on the growth rate of vole populations between mid-July and mid-August. Thirty-six populations of red-backed voles were sampled in the boreal forest of Québec, Canada. The presence and the abundance of parasites in voles, two host life history traits (sex and body condition), three indices of habitat complexity (tree basal area, sapling basal area, coarse woody debris volume), and vole abundance were considered in models evaluating the effects of bot flies on host populations. We found that the probability of survival of red-backed voles in live traps decreased with bot fly infection. Both the individual risk of infection and the abundance of bot flies in red-backed voles were driven mainly by vole abundance rather than by the two host life history traits or the three variables of habitat complexity. Parasitism had population consequences: bot fly prevalence was linked to a decrease in short-term growth rate of vole populations over the summer. We found that bot flies have the potential to reduce survival of red-backed voles, an effect that may apply to large portions of populations. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Seasonal regulation in fluctuating small mammal populations: feedback structure and climate

We studied fluctuating populations of six small mammal species in the Appalachian Plateau of Pennsylvania, USA for 20 yr. We analyzed the feedback structure of these species using statistical time series models for spring and autumn abundances. All species showed a seasonal density-dependent structure, and in five of them first-order feedbacks were dominant in winter and summer. Instead, southern red-backed voles ( Clethrionomys gapperi ) showed a different feedback structure during winter and summer. In three species ( C. gapperi , Napaeozapus insignis and Peromyscus maniculatus ), environmental factors were more important during summer, while the opposite pattern was found in Blarina brevicauda and Tamias striatus . Snowfall influenced positively the winter population growth rates of southern red-backed voles, white-footed mice, woodland jumping mice and eastern chipmunks. We found seasonal differences in the effects of the small mammals assemblage on population growth rates of the two Peromyscus species. The common feedback structure between seasons observed in most of the species, particularly among voles and mice, points to a different feedback structure from northern cyclic small mammals. We conclude that a seasonal feedback structure dominated by intra- and inter-specific competitive interactions may be at the basis of the population dynamics of these species.     

Seedling responses to decreased snow depend on canopy composition and small‐mammal herbivore presence

Winter is becoming warmer and shorter across the northern hemisphere, and reductions in snow depth can decrease tree seedling survival by exposing seedlings to harmful microclimates. Similarly, herbivory by small mammals can also limit the survival and distribution of woody plants, but it is unclear whether winter climate change will alter small‐mammal herbivory. Although small‐scale experiments show that snow removal can either increase or decrease both soil temperatures and herbivory, we currently lack snow‐removal experiments replicated across large spatial scales that are needed to understand the effect of reduced snow. To examine how winter herbivory and snow conditions influence seedling dynamics, we transplanted Acer saccharum and Tsuga canadensis seedlings across a 180 km latitudinal gradient in northern Wisconsin, where snow depth varied seven‐fold among sites. Seedlings were transplanted into one of two herbivory treatments (small‐mammal exclosure, small‐mammal access) and one of two late‐winter snow removal treatments (snow removed, snow unmanipulated). Snow removal increased soil freeze‐thaw frequency and cumulative growing degree‐days (GDD), but the magnitude of these effects depended on forest canopy composition. Acer saccharum survival decreased where snow was removed, but only at sites without conifers. Excluding small mammals increased A. saccharum survival at sites where the small‐mammal herbivore Myodes gapperi was present. Excluding small mammals also increased T. canadensis survival in plots with < 5 cm snow. Because variation in canopy composition and M. gapperi presence were important predictors of seedling survival across the snow‐depth gradient, these results reveal complexity in the ability to accurately predict patterns of winter seedling survival over large spatial scales. Global change scenarios that project future patterns of seedling recruitment may benefit from explicitly considering interactions between snow conditions and small‐mammal winter herbivory.     

Gene conversion in the mitochondrial genome on interspecific hybridization in voles of the <Emphasis Type="Italic">Clethrionomys</Emphasis> genus

The phenomenon of interspecific hybridization accompanied by transfer of the mitochondrial genome from the northern red-backed vole (Clethrionomys rutilus) to the bank vole (Cl. glareolus) in northeastern Europe is well known already for 25 years. However, the possibility of recombination between homologous segments of maternal and paternal mtDNAs of the voles during fertilization was not previously studied. Analysis of data on variability of nucleotide sequences of the mitochondrial gene for cytochrome b in populations of red-backed and bank voles in the area of their sympatry has shown that as a result of interspecific hybridization, the mitochondrial gene pool of bank voles contains not only mtDNA haplotypes of red-backed vole females, but also mtDNA haplotypes of bank voles bearing short nucleotide tracts of red-backed vole mtDNA. This finding supports the hypothesis that an incomplete elimination of red-backed vole paternal mtDNA during the interspecific hybridization between bank vole females and red-backed vole males leads to the gene conversion of bank vole maternal mtDNA tracts by homologous ones of mtDNA of red-backed vole males.     

Olfactory orientation of the truffle beetle, Leiodes cinnamomea

Although the truffle beetle, Leiodes cinnamomea, inflicts substantial damage to the ripe stage of fruiting bodies of the economically important black truffle (Tuber melanosporum), it is not attracted by ripe truffle odours. Rather, male beetles are attracted to infested truffles only in the presence of female beetles, suggesting that the former employ a pheromone to locate truffles over short distances. In contrast, female beetles show no attraction to infested or uninfested truffles, suggesting that they employ other cues, possibly linked to odours emitted by truffles prior to the ripe stage. We hypothesize that the chemical composition of truffle volatiles changes over the life of the truffle fruiting body, being attractive to insects early on and to mammals just prior to decomposition.     

Dampening of population cycles in voles affects small mammal community structure,decreases diversity,and increases prevalence of a zoonotic disease

Long‐term decline and depression of density in cyclic small rodents is a recent widespread phenomenon. These observed changes at the population level might have cascading effects at the ecosystem level. Here, we assessed relationships between changing boreal landscapes and biodiversity changes of small mammal communities. We also inferred potential effects of observed community changes for increased transmission risk of Puumala virus (PUUV) spread, causing the zoonotic disease nephropatica epidemica in humans. Analyses were based on long‐term (1971–2013) monitoring data of shrews and voles representing 58 time series in northern Sweden. We calculated richness, diversity, and evenness at alpha, beta, and gamma level, partitioned beta diversity into turnover (species replacement) and nestedness (species addition/removal), used similarity percentages (SIMPER) analysis to assess community structure, and calculated the cumulated number of PUUV‐infected bank voles and average PUUV prevalence (percentage of infected bank voles) per vole cycle. Alpha, beta, and gamma richness and diversity of voles, but not shrews, showed long‐term trends that varied spatially. The observed patterns were associated with an increase in community contribution of bank vole (Myodes glareolus), a decrease of gray‐sided vole (M. rufocanus) and field vole (Microtus agrestis) and a hump‐shaped variation in contribution of common shrew (Sorex araneus). Long‐term biodiversity changes were largely related to changes in forest landscape structure. Number of PUUV‐infected bank voles in spring was negatively related to beta and gamma diversity, and positively related to turnover of shrews (replaced by voles) and to community contribution of bank voles. The latter was also positively related to average PUUV prevalence in spring. We showed that long‐term changes in the boreal landscape contributed to explain the decrease in biodiversity and the change in structure of small mammal communities. In addition, our results suggest decrease in small mammal diversity to have knock‐on effects on dynamics of infectious diseases among small mammals with potential implications for disease transmission to humans.     

Fine-Scale Habitat Associations of Red-Backed Voles in Boreal Mixedwood Stands

Abstract: To provide habitat for late-successional wildlife species, new ecosystem-based forest management practices aim to retain elements of complex stand structure, including live residual trees, dead wood legacies, and advanced regeneration, within managed stands. Predicting the effectiveness of these strategies is a challenge for species whose habitat relationships may involve multiple factors and can vary among sites. For 2 years, we live-trapped a common, late-successional microtine rodent, the southern red-backed vole (Myodes [formerly Clethrionomys] gapperi), in 40 1.4-ha boreal mixedwood sites in Ontario, Canada. Using a neighborhood-scale modeling approach, we related red-backed vole capture locations to spatially referenced measures of overstory trees, shrubs and saplings, downed woody debris (DWD), and forest floor substrate. We further assessed how associations with these features varied with availability of the features within a site and as a function of stand management history. In spring, red-backed voles were associated with trap stations that had, within a 26-m radius, a dense shrub layer, abundant late-decay DWD, coniferous understory and litter, and possibly, understory vegetation associated with moist conditions. Positive associations with shrub cover, late-decay DWD, and a moisture-associated understory were most apparent in sites in which these elements were scarce (e.g., <1,500 stems/ha of hardwood saplings and short shrubs; <0.8% projected ground cover of late-decay DWD). The importance of late-decay DWD; shade-tolerant, coniferous understory composition; and substrate varied depending on a site's management history, with each feature having a strong positive effect in 47–64-year-old stands that were harvested using horse skidding and weaker effects in both 31–40-year-old stands that were clearcut with mechanical skidding and >80-year-old fire-origin stands. Our models of fine-scale habitat relationships for red-backed voles may be useful in establishing structural retention guidelines suitable for wildlife species dependent on late-successional habitat structure. In this regard, retaining abundant DWD and 10–30% live trees at harvest may be effective management strategies for providing favorable habitat conditions at localized scales.     

Maintenance of small mammals using post-harvest woody debris structures on clearcuts: linear configuration of piles is comparable to windrows

Management of post-harvest woody debris structures (e.g., piles and windrows) may help conserve mammal diversity in commercial forest landscapes. A windrow (continuous woody debris) provides a linear habitat to connect patches and reserves of uncut forest and riparian areas to maintain forest-floor small mammals and allow some of their avian and mammalian predators to access and traverse clearcut openings. However, most post-harvest residues are arranged in independent piles of woody debris (separated by 20–30 m, on average) and we asked if a linear configuration of piles would provide similar habitat conditions for small mammals as that achieved by a windrow of continuous woody debris. We tested two hypotheses (H) that piles of woody debris arranged in a linear configuration, on newly clearcut sites, would (H₁) enhance (a) abundance of the major small mammal species (Myodes gapperi and Microtus spp.), and (b) total abundance, species richness, and species diversity of the forest-floor small mammal community; compared with dispersed (conventional) treatment of woody debris. H₂ predicted that, because of the continuity of habitat, responses of small mammals in windrows would be greater than those in piles of woody debris. Three study areas were monitored in southern British Columbia, Canada, and each had three treatments of woody debris: dispersed, in a linear set of piles, and as a windrow. Forest-floor small mammals were sampled by live-trapping in spring and fall periods from 2010 to 2012. Woody debris in a linear configuration of piles and in windrows enhanced mean abundance of the southern red-backed vole (M. gapperi), total voles, and total abundance of small mammals compared with the dispersed treatment. Small mammal responses were variable between spring and fall periods, but overall mean values ± 95% CIs indicated that abundance of M. gapperi, total voles, and total small mammals were reasonably similar in piles and windrows.     

Intraspecific functional diversity of common species enhances community stability

Common species are fundamental to the structure and function of their communities and may enhance community stability through intraspecific functional diversity (iFD). We measured among‐habitat and within‐habitat iFD (i.e., among‐ and within‐plant community types) of two common small mammal species using stable isotopes and functional trait dendrograms, determined whether iFD was related to short‐term population stability and small mammal community stability, and tested whether spatially explicit trait filters helped explain observed patterns of iFD. Southern red‐backed voles (Myodes gapperi) had greater iFD than deer mice (Peromyscus maniculatus), both among habitats, and within the plant community in which they were most abundant (their “primary habitat”). Peromyscus maniculatus populations across habitats differed significantly between years and declined 78% in deciduous forests, their primary habitat, as did the overall deciduous forest small mammal community. Myodes gapperi populations were stable across habitats and within coniferous forest, their primary habitat, as was the coniferous forest small mammal community. Generalized linear models representing internal trait filters (e.g., competition), which increase within‐habitat type iFD, best explained variation in M. gapperi diet, while models representing internal filters and external filters (e.g., climate), which suppress within‐habitat iFD, best explained P. maniculatus diet. This supports the finding that M. gapperi had higher iFD than P. maniculatus and is consistent with the theory that internal trait filters are associated with higher iFD than external filters. Common species with high iFD can impart a stabilizing influence on their communities, information that can be important for conserving biodiversity under environmental change.     

SHORT-TERM DEMOGRAPHIC RESPONSE OF THE RED-BACKED VOLE TO SPRUCE BEETLE INFESTATIONS IN ALASKA

Abstract: How small mammals are affected by habitat changes caused by forest insect epidemics is largely unknown. Our objective was to determine the influence of spruce beetle (Dendroctonus rufipennis) epidemics on the dynamics of northern red-backed vole (Clethrionomys rutilus) populations approximately 10 years post-infestation. We conducted a mark-recapture study on northern red-backed voles for 2 field seasons in the Copper River Basin, Alaska, USA, where recent beetle infestations were widespread. Using the robust sampling design, we produced estimates of vole abundance, survival, and recruitment in 3 locations that varied in their degree of beetle-induced spruce mortality. Vole abundance inversely related to the level of spruce mortality. Vole recruitment showed a larger contribution from both immigration and in situ reproduction in the low infestation site than in the medium and heavy infestation sites. No differences in vole survival were detectable across the 3 locations with varied beetle-induced spruce mortality levels. Measured vole food resources and protective vegetative cover did not vary greatly across infestation levels. Abundance and recruitment parameters indicate a negative change induced by spruce beetle infestations. However, the effect of beetles was not large enough to cause the variation in vole survival. Spruce mortality levels may need to be over 50% before greatly influencing the habitat and the demographics of northern red-backed voles.     

A review of research on Chinese <Emphasis Type="Italic">Tuber</Emphasis> species

Truffles are abundant in some regions of China. Nevertheless, it was not until the 1980s that Tuber species were discovered by Chinese mycologists. In recent years, international truffle markets have shown an increasing interest in the import of Chinese Tuber. These truffles serve as a complement to European truffles due to their lower prices and their greater availability in a deficit market. However, Chinese truffles have been the subject of fraudulent commercial practices, and these could have a negative effect on truffle culture. These concerns have been behind numerous recent studies designed to obtain detailed information about Chinese Tuber species. Unfortunately, many of these studies are not published in English, and are dispersed throughout the specific local or national bibliography and proceedings of specialized truffle conferences. In view of the need to expand current knowledge of Chinese Tuber species, we present a comprehensive summary of the taxonomy, ecology, mycorrhizae, genetics, biochemistry, and cultivation of Chinese Tuber species. We also provide a synthetic taxonomy and morphological characterization of 16 Chinese Tuber species in order to assist in their verification and monitoring.     

Effect of felling on red fox (Vulpes vulpes) and pine marten (Martes martes) diets in transitional mixed forest in Belarus

In transitional mixed forests in northern and central Belarus the influence of intensified felling on the diets of red foxes Vulpes vulpes L. and pine martens Martes martes L. was investigated in two model forested terrains with sandy and clay top-grounds. A total of 1904 scats of red foxes and 1624 scats of pine martens were analysed over two periods differed by logging rate. When logging rate was conservative, red fox and pine marten diets were found to be similar, but under heavy logging feeding of the predator species shifted. In both model woodlands we found the same pronounced dietary trend of higher consumption of rodents, first of all, Microtus voles. The dietary changes were well related to the registered increase in Microtus vole numbers and total number of rodents in felling areas. The increased preying on rodents caused lower consumption of other food items, particularly medium-sized mammals (year-round) or/and birds or/and fruits (in the warm season) or/and mammalian carrion (in the cold season). In the conditions of intensified felling the food niches of the red fox and pine marten diverged mostly because of the great difference in the species structure of rodents consumed. Red foxes turned to preying on Microtus voles more frequently, but less on bank voles Myodes glareolus; while pine martens increased their taking of Microtus voles, continued foraging for bank voles and began taking slightly more of Apodemus mice. Before heavy logging dietary similarity between the red fox and pine marten was high and did not vary considerably through seasons and study areas, whereas after felling was intensified their diet overlap became lower.     

The Celtic fringe of Britain: insights from small mammal phylogeography

Recent genetic studies have challenged the traditional view that the ancestors of British Celtic people spread from central Europe during the Iron Age and have suggested a much earlier origin for them as part of the human recolonization of Britain at the end of the last glaciation. Here we propose that small mammals provide an analogue to help resolve this controversy. Previous studies have shown that common shrews (Sorex araneus) with particular chromosomal characteristics and water voles (Arvicola terrestris) of a specific mitochondrial (mt) DNA lineage have peripheral western/northern distributions with striking similarities to that of Celtic people. We show that mtDNA lineages of three other small mammal species (bank vole Myodes glareolus, field vole Microtus agrestis and pygmy shrew Sorex minutus) also form a ‘Celtic fringe’. We argue that these small mammals most reasonably colonized Britain in a two-phase process following the last glacial maximum (LGM), with climatically driven partial replacement of the first colonists by the second colonists, leaving a peripheral geographical distribution for the first colonists. We suggest that these natural Celtic fringes provide insight into the same phenomenon in humans and support its origin in processes following the end of the LGM.