The effect of snow cover on lemming population cycles in the Canadian High Arctic

Rising temperatures and changes in the precipitation regime will have a strong impact on the quality of the snow cover in the Arctic. A snow cover of good quality protecting lemmings from cold temperatures and predators is thought to be an important factor for maintaining the cyclic dynamic of their populations in the tundra. We examined if the characteristics of annual fluctuations (amplitude and shape of phases) in brown lemming (Lemmus trimucronatus) density could be determined by snow depth, snow density, sub-nivean temperature and persistence of snow. Using an 18-year time series of brown lemming abundance on Bylot Island in the Canadian Arctic, we tested if snow variables could explain the residual variation between the observed lemming density and the one predicted by models where cyclicity had been accounted for. Our analysis provides support for the hypothesis that snow cover can affect the amplitude and possibly also the periodicity of lemming population cycles in the High Arctic. Summer abundance of brown lemmings was higher following winters with a deep snow cover and a low-density snow pack near the ground but was unaffected by the date of establishment or melting and duration of the snow cover. Two snow variables showed a temporal trend; mean winter snow depth tended to increase and date of establishment of the hiemal threshold occurred earlier over time. These temporal trends, which should be favourable to lemmings, may explain why healthy population cycles have apparently been maintained at our study site contrary to other Arctic sites.     

Delayed and inverse density dependence in a chamois population of the Italian Alps

Both density dependent and density independent factors have been considered important determinants of the dynamics of ungulate populations Intraspecific competition for food and the amount of snow cover were suggested in the past as factors that influence the demographic parameters of the chamois Rupicapra rupicapra We present a 10 yr study on a closed population of the Italian Alps Animals, divided by sex and age class (kid, yearling, subadult, adult, old), were counted over the period 1981–1990 The number of chamois hunted and the number of carcasses found each year and the daily snow height were also available We investigated possible correlations between several demographic parameters and both snow cover and chamois density, accounting for sex- and age-differential mortality and a possible delay in density dependence Results are as follows a) there is no statistically significant correlation between snow cover and demographic rates, b) there is no detectable compensation between natural and hunting-related mortality, c) birth rate is density independent for any time delay, d) when calculated from carcasses, total mortality, mortality of 1-yr-old and older males and females significantly depend on total density with 2 years' lag, while kid mortality is not related to density for any time delay, e) when calculated from censuses, all mortality rates significantly depend on total density with 2 years' lag, although the variance explained by delayed density is definitely smaller for kids, f) nonlinear regression of kid mortality from censuses against density of kids in the same year yields a much higher coefficient of determination and inverse density dependence is evidenced However, determination between delayed and inverse density dependence in kid mortality is impossible, given our dataset In general, results support the hypothesis that intraspecific competition, epidemics and predation, rather than weather, play a role in the dynamics of this ungulate population     

The role of geological substrate for horn growth in ungulates: a case study on Alpine chamois

Ecological factors such as environmental and climatic conditions affect the growth of ornaments in ungulates. Studies about their influence can reveal key information on individual life histories and detect the events that can have important evolutionary consequences. Among the ecological factors commonly thought to play a role in such ecological processes, researches have so far neglected the possible influence of the geological feature which may either promote or restrain the early investment in horn growth. This study takes into consideration a broad range of ecological factors that are expected to affect horn growth and analyses how the substrate (calcareous versus siliceous) could modify the horn size in 1,685 yearling Alpine chamois (Rupicapra rupicapra) which were legally shot during 5 consecutive years in Central-Eastern Italian Alps. Interestingly, we found shorter horns in chamois shot on siliceous than on calcareous substrate, irrespective of the sex, showing how the substrate (and related ecological conditions) may affect horn growth. The substrate interacted with two ecological factors in shaping the horn size, i.e. aspect and snow cover. Differences between horn lengths recorded for chamois shot on these two substrates were less pronounced where South-facing slopes prevailed. During an average winter (about 100 days with more than 10 cm of snow on the ground) chamois horns were longer in individuals using calcareous areas, although the increase of number of days with more than 10 cm of snow on the ground had a stronger impact in reducing horn length in calcareous environment. We demonstrated that substrate, and related ecological conditions, influence horn growth. In ungulate species where ornament size is related to reproductive success, environmental factors, such as geological feature, can thus cause evolutionary consequences in the expression of ornaments and individual fitness.     

Contrasting Effects of Climate Change on Alpine Chamois

Global climate change can affect animal ecology in numerous ways, but researchers usually emphasize undesirable consequences. Temperature increases, for instance, can induce direct physiological costs and indirect effects via mismatches in resource needs and availability. Species living in mountainous regions, however, could experience beneficial effects because winters might become less severe. We examined the potentially opposing effects of climate change during spring, summer, and winter on recruitment in Alpine chamois (Rupicapra rupicapra). We examined initial recruitment (i.e., the ratio of kids to adult females) and net recruitment (i.e., the ratio of yearlings to adult females) of Alpine chamois through the use of linear mixed effects models and data from block count censuses performed across a 1,500-km² study area in the Italian Alps during summer from 2001 to 2015. Initial recruitment was relatively resistant to the effects of climate change, declining slightly over the study period. We suggest that the effects of increased forage availability and lower snow cover in winter may benefit the reproductive output of adult females, compensating for any negative effects of trophic mismatch and higher temperatures during summer. By contrast, net recruitment strongly declined throughout the study period, consistent with the slight decline of initial recruitment and the negative effects of increasing summer temperatures on the survival of kids during their first winter. These negative effects seemed to outweigh positive effects of climate change, even in a species strongly challenged by winter conditions. These findings provide important information for hunted populations; setting more appropriate hunting bags for yearling chamois should be considered. The ecological plasticity of the chamois, which also inhabits low altitudes, may allow a possible evolutionary escape for the species. © 2020 The Wildlife Society.     

Reduced Snow Cover Increases Wintertime Nitrous Oxide (N<Subscript>2</Subscript>O) Emissions from an Agricultural Soil in the Upper U.S. Midwest

Throughout most of the northern hemisphere, snow cover decreased in almost every winter month from 1967 to 2012. Because snow is an effective insulator, snow cover loss has likely enhanced soil freezing and the frequency of soil freeze–thaw cycles, which can disrupt soil nitrogen dynamics including the production of nitrous oxide (N₂O). We used replicated automated gas flux chambers deployed in an annual cropping system in the upper Midwest US for three winters (December–March, 2011–2013) to examine the effects of snow removal and additions on N₂O fluxes. Diminished snow cover resulted in increased N₂O emissions each year; over the entire experiment, cumulative emissions in plots with snow removed were 69% higher than in ambient snow control plots and 95% higher than in plots that received additional snow (P < 0.001). Higher emissions coincided with a greater number of freeze–thaw cycles that broke up soil macroaggregates (250–8000 µm) and significantly increased soil inorganic nitrogen pools. We conclude that winters with less snow cover can be expected to accelerate N₂O fluxes from agricultural soils subject to wintertime freezing.     

Two Different Epidemiological Scenarios of Border Disease in the Populations of Pyrenean chamois (Rupicapra p. pyrenaica) after the First Disease Outbreaks

Since 2001 several outbreaks of a new disease associated with Border disease virus (BDV) infection have caused important declines in Pyrenean chamois (Rupicapra pyrenaica) populations in the Pyrenees. The goal of this study was to analyze the post-outbreak BDV epidemiology in the first two areas affected by disease with the aim to establish if the infection has become endemic. We also investigated if BDV infected wild and domestic ruminants sharing habitat with chamois. Unexpectedly, we found different epidemiological scenarios in each population. Since the disease outbreaks, some chamois populations recuperated quickly, while others did not recover as expected. In chamois from the first areas, prevalence was high (73.47%) and constant throughout the whole study period and did not differ between chamois born before and after the BDV outbreak; in all, BDV was detected by RT-PCR in six chamois. In the other areas, prevalence was lower (52.79%) and decreased during the study period; as well, prevalence was significantly lower in chamois born after the disease outbreak. No BDV were detected in this population. A comparative virus neutralisation test performed with four BDV strains and one Bovine viral diarrhoea virus (BVDV) strain showed that all the chamois had BDV-specific antibodies. Pestivirus antibodies were detected in all the rest of analyzed species, with low prevalence values in wild ruminants and moderate values in domestic ruminants. No viruses were detected in these species. These results confirm the hypothesis that outbreaks of BDV infection only affect the Pyrenean chamois, although other wild ruminants can occasionally be infected. In conclusion, two different scenarios have appeared since the first border disease outbreaks in Pyrenean chamois: on the one hand frequent BDV circulation with possible negative impact on population dynamics in some areas and on the other, lack of virus circulation and quick recovery of the chamois population.     

Male Alpine Chamois Occupy Territories at Hotspots Before the Mating Season

Ungulate mating systems vary broadly both between and within species. Studies on mating systems in different habitats can provide clues to the ecological factors determining this diversity. Despite its abundance in the European Alps and its importance as a game species, surprisingly little is known about the mating system of Alpine chamois Rupicapra rupicapra rupicapra. We tested the hypothesis that adult males first defend mating territories in late spring, when females segregate from males and well before the Nov. rut. In the Gran Paradiso National Park (north‐western Italian Alps), adult males shared a winter range but occupied individual ranges in summer and early autumn. Males were more aggressive to each other in the summer than in the spring. A strong site fidelity from one year to the next was found for the summer and early autumn months. Those males that occupied the same territories both in the summer and during the rut (Nov.) appeared to be at hotspots, attractive to females during the rut because of reduced snow cover. Other males appeared to cluster around these hotspots during the rut. Territories that were first occupied during the summer were visited by more females than those that were not established until the rut began. Our results suggest that the mating system of this population of Alpine chamois consists of the early occupation of clustered mating territories. The early establishment of mating territories in areas frequented by females during the rut may lead to reproductive benefits for male chamois.     

Disentangling demographic effects of red deer on chamois population dynamics

Investigating the impact of ecological factors on sex‐ and age‐specific vital rates is essential to understand animal population dynamics and detect the potential for interactions between sympatric species. We used block count data and autoregressive linear models to investigate variation in birth rate, kid survival, female survival, and male survival in a population of Alpine chamois Rupicapra rupicapra rupicapra monitored over 27 years within the Stelvio National Park, Central Italian Alps, as function of climatic variables, density dependence, and interspecific competition with red deer Cervus elaphus. We also used path analysis to assess the indirect effect of deer abundance on chamois growth rate mediated by each demographic parameter. Based on previous findings, we predicted that birth rate at [t] would negatively relate to red deer abundance at year [t − 1]; survival rates between [t] and [t + 1] would negatively relate to red deer abundance at year [t − 1] and to the interactive effect of winter precipitation at [t + 1] and chamois density at [t]. Our results showed that birth rate was positively related to spring–summer precipitation in the previous year, but this effect was hampered by increasing red deer abundance. Kid and female survival rates were negatively related to the combined effect of chamois abundance and winter precipitation. Male and female survival rates were negatively related to lagged red deer abundance. The path analysis supported a negative indirect effect of red deer abundance on chamois growth rate mediated by birth rate and female survival. Our results suggest that chamois population dynamics was largely explained by the synergistic effect of density dependence and winter harshness, as well as by interspecific competition with red deer, whose effects were seemingly stronger on the kid–female segment of the population.     

Lignin Degradation in Foliar Litter of Two Shrub Species from the Gap Center to the Closed Canopy in an Alpine Fir Forest

To understand the effects of forest gaps on lignin degradation during shrub foliar litter decomposition, a field litterbag experiment was conducted in an alpine fir (Abies faxoniana) forest of the eastern Tibet Plateau. Dwarf bamboo (Fargesia nitida) and willow (Salix paraplesia) foliar litterbags were placed on the forest floor from the gap center to the closed canopy. The litterbags were sampled during snow formation, snow coverage, snow melting and the growing season from October 2010 to October 2012. The lignin concentrations and loss in the litter were measured. Over 2 years, lignin loss was lower in the bamboo litter (34.64–43.89%) than in the willow litter (38.91–55.10%). In the bamboo litter, lignin loss mainly occurred during the first decomposition year, whereas it occurred during the second decomposition year in the willow litter. Both bamboo and willow litter lignin loss decreased from the gap center to the closed canopy during the first year and over the entire 2-year decomposition period. Compared with the closed canopy, the gap center showed higher lignin loss for both bamboo and willow litter during the two winters, but lower lignin loss during the early growing period. Additionally, the dynamics of microbial biomass carbon during litter decomposition followed the same trend as litter lignin loss during the two winters and growing period. These results indicated that alpine forest gaps had significant effects on shrub litter lignin loss and that reduced snow cover during winter warming would inhibit shrub lignin degradation in this alpine forest.     

Overwintering stress of Vaccinium vitis-idaea in the absence of snow cover

A snow manipulation experiment aimed to assess risks of direct freezing injury, freeze-induced dehydration and winter desiccation in the absence of snow cover on lingonberry (Vaccinium vitis-idaea). Frames with sheet-plastic sides and removable lids were used in this experiment for two purposes: to prevent accumulation of snow in mid-winter and to provide extra heat during early spring. Leaves were analyzed for frost hardiness, tissue water content and osmotic concentrations, and photoinhibition (Fv/Fm) during the period from the 10th of February to the 7th of April. The natural snow accumulation was low indicated by a minor difference in minimum temperatures between the frame treatment and naturally snow-covered plots. The heating effect of the frames started gradually at the end of February along with increasing solar elevation angles, and was highest at the beginning of April. Frost hardiness peaked in March as a consequence of cold periods, but it was practically lost by the beginning of April. Tissue water content decreased gradually at first, becoming greatly decreased later due to the extra heat. In accordance, the tissue osmotic concentrations increased first gradually, followed by a dramatic increase. Photoinhibition increased uniformly with increasing solar radiation, but at the end showed a sharp increment within a few days, obviously also indicating the effect of heating. It was concluded that neither lethal freezing stress nor significant freeze-induced dehydration occurred during the experiment. However, plants that overwintered without snow suffered from severe winter desiccation injuries due to the combination of solar heat and frozen soil. Although the desiccation stress was possibly a lethal factor, it was preceded by long-term and continued photoinhibition. It was concluded that during overwintering, chamaephyte species may suffer from both freezing and winter desiccation in the absence of protecting snow cover. However, during mild winters provided by climatic change scenarios, the risk of winter desiccation will be more probable. In relation to the future climate, it was concluded that winter desiccation and photoinhibition may develop gradually during a snowless winter and would, even if they did not reach a lethal level by themselves, possibly reduce frost hardiness.     

Effects of climate and snow depth on Bromus tectorum population dynamics at high elevation

Invasive plants are thought to be especially capable of range shifts or expansion in response to climate change due to high dispersal and colonization abilities. Although highly invasive throughout the Intermountain West, the presence and impact of the grass Bromus tectorum has been limited at higher elevations in the eastern Sierra Nevada, potentially due to extreme wintertime conditions. However, climate models project an upward elevational shift of climate regimes in the Sierra Nevada that could favor B. tectorum expansion. This research specifically examined the effects of experimental snow depth manipulations and interannual climate variability over 5 years on B. tectorum populations at high elevation (2,175 m). Experimentally-increased snow depth had an effect on phenology and biomass, but no effect on individual fecundity. Instead an experimentally-increased snowpack inhibited population growth in 1 year by reducing seedling emergence and early survival. A similar negative effect of increased snow was observed 2 years later. However, a strong negative effect on B. tectorum was also associated with a naturally low-snow winter, when seedling emergence was reduced by 86%. Across 5 years, winters with greater snow cover and a slower accumulation of degree-days coincided with higher B. tectorum seedling density and population growth. Thus, we observed negative effects associated with both experimentally-increased and naturally-decreased snowpacks. It is likely that the effect of snow at high elevation is nonlinear and differs from lower elevations where wintertime germination can be favorable. Additionally, we observed a doubling of population size in 1 year, which is alarming at this elevation.     

Clinging on to alpine life: Investigating factors driving the uphill range contraction and population decline of a mountain breeding bird

Climate change and anthropogenic nitrogen deposition are widely regarded as important drivers of environmental change in alpine habitats. However, due to the difficulties working in high‐elevation mountain systems, the impacts of these drivers on alpine breeding species have rarely been investigated. The Eurasian dotterel (Charadrius morinellus) is a migratory wader, which has been the subject of uniquely long‐term and spatially widespread monitoring effort in Scotland, where it breeds in alpine areas in dwindling numbers. Here we analyse data sets spanning three decades, to investigate whether key potential drivers of environmental change in Scottish mountains (snow lie, elevated summer temperatures and nitrogen deposition) have contributed to the population decline of dotterel. We also consider the role of rainfall on the species' wintering grounds in North Africa. We found that dotterel declines—in both density and site occupancy of breeding males—primarily occurred on low and intermediate elevation sites. High‐elevation sites mostly continued to be occupied, but males occurred at lower densities in years following snow‐rich winters, suggesting that high‐elevation snow cover displaced dotterel to lower sites. Wintering ground rainfall was positively associated with densities of breeding males two springs later. Dotterel densities were reduced at low and intermediate sites where nitrogen deposition was greatest, but not at high‐elevation sites. While climatic factors explained variation in breeding density between years, they did not seem to explain the species' uphill retreat and decline. We cannot rule out the possibility that dotterel have increasingly settled on higher sites previously unavailable due to extensive snow cover, while changes associated with nitrogen deposition may also have rendered lower lying sites less suitable for breeding. Causes of population and range changes in mountain‐breeding species are thus liable to be complex, involving multiple anthropogenic drivers of environmental change acting widely across annual and migratory life cycles.     

雪被斑块对高山森林两种灌木凋落叶质量损失的影响

高山/亚高山森林灌木层植物凋落物的分解对于系统物质循环等过程具有重要意义, 并可能受到冬季不同厚度雪被斑块下冻融格局的影响。该文采用凋落物分解袋法, 研究了高山森林典型灌层植物华西箭竹(Fargesia nitida)和康定柳(Salix paraplesia)凋落物在沿林窗-林下形成的冬季雪被厚度梯度(厚型雪被斑块、较厚型雪被斑块、中型雪被斑块、薄型雪被斑块、无雪被斑块)上在第一年不同关键时期(冻结初期、冻结期、融化期、生长季节初期和生长季节后期)的质量损失特征。在整个冻融季节, 华西箭竹和康定柳凋落叶的平均质量损失分别占全年的(48.78 ± 2.35)%和(46.60 ± 5.02)%。冻融季节雪被覆盖斑块下凋落叶的失重率表现出厚型雪被斑块大于薄型雪被斑块的趋势,而生长季节无雪被斑块的失重率明显较高。尽管如此, 华西箭竹凋落物第一年分解表现出随冬季雪被厚度增加而增加的趋势, 但康定柳凋落物第一年失重率以薄型雪被斑块最高, 而无雪被斑块最低。同时, 相关分析表明冻融季节凋落叶的失重率与平均温度和负积温呈极显著正相关, 生长季节凋落叶的失重率与所调查的温度因子并无显著相关关系, 但全年凋落物失重率与平均温度和正/负积温均显著相关。这些结果清晰地表明, 未来冬季变暖情境下高山森林冬季雪被格局的改变将显著影响灌层植物凋落物分解, 影响趋势随着物种的差异具有明显差异。     

The Impact of Winter Meteorological Parameters on Abundance of the Grey Partridge <Emphasis Type="Italic">Perdix perdix</Emphasis> in the Southern Ural Steppe

In the winter periods from 1994 to 2017, the grey partridge average abundance in the steppe zone of the southern Urals was significantly negatively correlated with some meteorological parameters (the snow cover height, precipitations, snow density). At the same time, in the subsequent summer period, these winter parameters (including the mean air temperature) had no influence on the bird number. Indeed, the harsh and snowy winters did not affect the grey partridge abundance in the reproductive period. We believe that migrations from the breeding area or nomadic movements of these birds occurred in the most extreme winters.     

The impact of snow accumulation on a heath spider community in a sub-Arctic landscape

Patterns of snow cover across the Arctic are expected to change as a result of shrub encroachment and climate change. As snow cover impacts both the subnivean environment and the date of spring melt, these changes could impact Arctic food webs by altering the phenology and survival of overwintering arthropods, such as spiders (Araneae). In this field study, we used snow fences to increase snow cover across a series of large (375 m²) heath tundra plots and examined the effects on the local spider community during the following growing season. Fences increased snow cover and delayed melt on the treatment plots, paralleling the conditions of nearby shrub sites. Frequent sampling over the season revealed that increased snow cover did not affect spider abundance across different genera nor did it affect overall community composition. Further, our snow treatment did not affect the dates when plots achieved seasonal catch milestones (25, 50, 75 % of total seasonal catch). Increased winter snow cover did, however, produce higher body masses in adults and juveniles of the dominant species Pardosa lapponica (Lycosidae), beginning immediately after snow melt until midway through the growing season. In addition, ovary/oocyte mass of mature P. lapponica females was significantly higher on treatment plots during the peak reproductive period. This is the first experimental manipulation study to report a significant effect of landscape-level changes to winter snow cover on the biomass of an Arctic macroarthropod.     

Recolonization following past persecution questions the importance of persistent snow cover as a range limiting factor for wolverines

Globally, climate is changing rapidly, which causes shifts in many species' distributions, stressing the need to understand their response to changing environmental conditions to inform conservation and management. Northern latitudes are expected to experience strongest changes in climate, with milder winters and decreasing snow cover. The wolverine (Gulo gulo) is a circumpolar, threatened carnivore distributed in northern tundra, boreal, and subboreal habitats. Previous studies have suggested that wolverine distribution and reproduction are constrained by a strong association with persistent spring snow cover. We assess this hypothesis by relating spatial distribution of 1589 reproductive events, a fitness-related proxy for female reproduction and survival, to snow cover over two decades. Wolverine distribution has increased and number of reproductive events increased 20 times in areas lacking spring snow cover during our study period, despite low monitoring effort where snow is sparse. Thus, the relationship between reproductive events and persistent spring snow cover weakened during this period. These findings show that wolverine reproductive success and hence distribution are less dependent on spring snow cover than expected. This has important implications for projections of future habitat availability, and thus distribution, of this threatened species. Our study also illustrates how past persecution, or other factors, that have restricted species distribution to remote areas can mask actual effects of environmental parameters, whose importance reveals when populations expand beyond previously restricted ranges. Overwhelming evidence shows that climate change is affecting many species and ecological processes, but forecasting potential consequences on a given species requires longitudinal data to revisit hypotheses and reassess the direction and magnitude of climate effects with new data. This is especially important for conservation-oriented management of species inhabiting dynamic systems where environmental factors and human activities interact, a common scenario for many species in different ecosystems around the globe.     

Snow depth does not affect recruitment in a low-density population of boreal woodland caribou (<Emphasis Type="Italic">Rangifer tarandus caribou</Emphasis>)

Winter snow depth may be an important driver of annual variability in recruitment of ungulate calves, and low calf recruitment has been implicated as a factor in declining boreal caribou (Rangifer tarandus caribou) populations. We used 11 consecutive years (2006–2016) of aerial survey data to document calf recruitment in a low-density population of boreal woodland caribou in the Northwest Territories, Canada. We measured snow depth in winter and tested two hypotheses: (1) that calf recruitment was lower in winters with greater snow depth and (2) that calf recruitment was lower following winters with greater snow depth (1-year time lag). Recruitment, the number of calves/adult female in March, ranged twofold from 0.23 to 0.45, and snow depth also ranged twofold from 41 to 85 cm. Yet, we found no support for the hypothesis that late-winter snow depth in the current or previous year was inversely related to calf recruitment.     

Snow conditions as an estimator of the breeding output in high-Arctic pink-footed geese Anser brachyrhynchus

The Svalbard-breeding population of pink-footed geese Anser brachyrhynchus has increased during the last decades and is giving rise to agricultural conflicts along their migration route, as well as causing grazing impacts on tundra vegetation. An adaptive flyway management plan has been implemented, which will be based on predictive population models including environmental variables expected to affect goose population development, such as weather conditions on the breeding grounds. A local study in Svalbard showed that snow cover prior to egg laying is a crucial factor for the reproductive output of pink-footed geese, and MODIS satellite images provided a useful estimator of snow cover. In this study, we up-scaled the analysis to the population level by examining various measures of snow conditions and compared them with the overall breeding success of the population as indexed by the proportion of juveniles in the autumn population. As explanatory variables, we explored MODIS images, satellite-based radar measures of onset of snow melt, winter NAO index, and the May temperature sum and May thaw days. To test for the presence of density dependence, we included the number of adults in the population. For 2000–2011, MODIS-derived snow cover (available since 2000) was the strongest indicator of breeding conditions. For 1981–2011, winter NAO and May thaw days had equal weight. Interestingly, there appears to have been a phase shift from density-dependent to density-independent reproduction, which is consistent with a hypothesis of released breeding potential due to the recent advancement of spring in Svalbard.     

Demographic response of tundra small mammals to a snow fencing experiment

Snow cover is a key environmental component for tundra wildlife that will be affected by climate change. Change to the snow cover may affect the population dynamics of high‐latitude small mammals, which are active throughout the winter and reproduce under the snow. We experimentally tested the hypotheses that a deeper snow cover would enhance the densities and winter reproductive rates of small mammals, but that predation by mustelids could be higher in areas of increased small mammal density. We enhanced snow cover by setting out snow fences at three sites in the Canadian Arctic (Bylot Island, Nunavut, and Herschel Island and Komakuk Beach, Yukon) over periods ranging from one to four years. Densities of winter nests were higher where snow depth was increased but spring lemming densities did not increase on the experimental areas. Lemmings probably moved from areas of deep snow, their preferred winter habitat, to summer habitat during snow melt once the advantages associated with deep snow were gone. Our treatment had no effect on signs of reproduction in winter nests, proportion of lactating females in spring, or the proportion of juveniles caught in spring, which suggests that deep snow did not enhance reproduction. Results on predation were inconsistent across sites as predation by weasels was higher on the experimental area at one site but lower at two others and was not higher in areas of winter nest aggregations. Although this experiment provided us with several new insights about the impact of snow cover on the population dynamics of tundra small mammals, it also illustrates the challenges and difficulties associated with large‐scale experiments aimed at manipulating a critical climatic factor.     

Snow tracking reveals different foraging patterns of red foxes and pine martens

Red fox (Vulpes vulpes) shares similar prey preferences and co-occurs with several other carnivores, and is together with pine marten (Martes martes), the most common mesocarnivore in the northern boreal forest. Voles are important prey for both species, but it is unclear to what extent they compete for the same food resources in winter. Here, we use 2139 km and 533 km of meticulous snow tracking of red foxes and pine martens to evaluate their food niches. We measured hunting and digging behaviour, whether successful or not, and the effect of snow depth and temperature. Pine martens were restricted to forested habitats, whereas red foxes used a wide range of habitats. Red foxes were found to dig more often than pine martens, 0.67 vs. 0.39 digging events per kilometre. Hunting was less common and similar in both species, about 0.1 hunting event per kilometre. Pine martens were more efficient in hunting and finding food remains compared to red foxes. Increasing snow depth reduced hunting success and also reduced dig success of red foxes. Food niche overlap was small. Red foxes used mostly voles and carrion remains of ungulates, whereas pine martens used cached eggs and small birds. We suggest that caching eggs is an important strategy for pine martens to survive winter in northern latitudes. Snow depth was important for capturing voles, and thick snow cover appeared to mask the effect of vole peaks. Intensified land use, as clear-cutting and leaving slaughter remains from harvest, will benefit red foxes on the expense of pine martens. The ongoing climate change with warmer winters and less snow will likely further benefit the red fox.