Snowshoe Hare (Lepus americanus)

Abstract

Predation risk induces a myriad of behavioral antipredator responses of prey. However, different antipredator behaviors exhibit different degrees of flexibility within a single prey species. Moreover, how predator species composition and traits interact with the flexibility of particular antipredator behaviors to determine spatiotemporal activity patterns of prey remains unknown. We examined geographic variation in multiple behavioral axes of a single prey species, snowshoe hares Lepus americanus, across three different ecosystems in northern North America that differed in the predator guild (Wisconsin, USA, with multiple generalist predators; Isle Royale, Michigan, USA, with a single generalist predator; and Yukon, Canada, with a specialist ambush predator and a generalist predator). We hypothesized that predator species composition and traits would drive divergent behavioral patterns of hares across ecosystems. Using a biologging-based dataset of hare behaviors and a camera-based dataset of predator occurrence collected over multiple winters, we examined diel activity patterns, space use, and movement of hares while accounting for variable environmental conditions. Hares were only slightly less nocturnal (<10%) when faced with a single nocturnal generalist predator (Isle Royale), and they exhibited highly comparable diel activity patterns across all sites. Patterns of spatial risk avoidance of hares were moderately different between the multi-predator systems; hares potentially avoided more lethal predators in Wisconsin and exhibited the opposite patterns of habitat use between daytime and nighttime in Yukon, possibly to avoid the most active predator at each time of day. Additionally, hare movements were shorter and more tortuous where ambush specialist predators were present (Yukon). Our study demonstrates that spatiotemporal risk avoidance of prey can exhibit limited geographic variation, but certain behavioral responses, such as diel activity, may be more conserved across ecosystems.

Abstract

The snowshoe hare (Lepus americanus) is considered a critical keystone species of the boreal and temperate forests of North America. Although their population ecology and evolutionary dynamics have been studied extensively, a lack of high-quality genomic resources has limited molecular insights into their biology. Here, we combined cytogenetic karyotype analysis, PacBio HiFi long-read sequencing (~33× coverage), and chromosome conformation capture (Hi-C) sequencing to generate a phased chromosome-level genome assembly from a male snowshoe hare specimen. The primary haploid assembly is 2.75 Gb, with the 24 largest scaffolds corresponding to individual chromosomes (2n = 48 chromosomes, scaffold N50 = 131 Mb) and containing only 213 gaps. Assembly completeness was high, with 99.6% of mammalian Benchmarking Universal Single-Copy Orthologs recovered. Comparative analysis of this genome with other Lepus species revealed conservation of chromosomal architecture within the genus, while alignment with the European rabbit (Oryctolagus cuniculus) genome identified chromosomal rearrangements consistent with known karyotypic divergence between hares and rabbits. This genome assembly establishes a critical reference for future genomic studies in snowshoe hares and related taxa.
adaptation, comparative genomics, karyotype, Lagomorpha, mammal

Abstract

Research Highlight: Oli, M., Kenney, A., Boonstra, R., Boutin, S., Murray, D., Jung, T., Hines, J., Krebs, C. (2026). Demographic mechanisms of snowshoe hare population cycles in Yukon, Canada. Journal of Animal Ecology. https://doi.org.10.1111/1365-2656.70169. Ecologists have long been intrigued by cycles in population abundances characterizing the dynamics of some wild species. Abundance may follow surprisingly regular cycles, with an increase phase, a peak phase and then a decline phase of more or less the same length. Predator-induced mortality has long been proposed as the main demographic mechanism inducing population cycles, leading most of cycle theory to consider that population cycles result from survival changes only. In this paper, Oli et al. (2025) assessed how the cycles in population abundance of the snowshoe hare (Lepus americanus) in Yukon, observed during 43 years, are driven by survival or reproductive rates of some specific age classes and how their contributions differ according to the cyclic phase. Thanks to the individual monitoring of more than 7000 snowshoe hares and a state-of-the-art capture-mark-recapture modelling framework, they showed different contributions of age-specific vital rates to the population growth rate, depending on the cyclic phase (increase, peak, decline and low phases) and the breeding period considered (early, mid, late and non-breeding periods). For instance, improved breeding probability, litter size and pre-weaning survival played a major role during the increase phases, whereas lower pre-weaning survival explained population decline. They also highlighted a strong interaction between season and cyclic phases, with, for example, at mid-breeding season, a survival in low phases that is close to the survival observed in increase phases. This led to different life-history strategies over the seasons and the phases: the population had a fast strategy in the early breeding season in the increase phase and a slow strategy in the late breeding season and decline phase, demonstrating a high level of plasticity across phases and seasons. The enigma of population cycles is not fully solved yet, but the study by Oli et al. (2025) clearly contributes to improving our mechanistic understanding of population cycles.

Abstract

One hundred years have elapsed since Charles Elton (1924) described the periodic fluctuations in North American snowshoe hare abundance, yet mechanisms underlying 9–11-year population cycles in snowshoe hares continue to be debated.
We applied multistate capture–mark–recapture models to long-term field data (1977–2020) based on >20,000 captures of >7000 unique snowshoe hares (Lepus americanus) from Kluane Lake, Yukon, Canada, to estimate and model state-specific demographic parameters. Juveniles had the lowest and reproductive adult females the highest apparent survival. Apparent survival of all sex-age classes was highest during the mid- and late-breeding seasons and was generally better during the increase phase.
Conditional probability of females transitioning from non-reproductive to reproductive state, and reproductive females remaining in the reproductive state, increased substantially as the population transitioned from low to increase phase throughout the breeding season.
Analysis of stage-structured matrix population models revealed that population-dynamic characteristics were strongly phase-specific, and also varied across seasons, with the increase phases being characterized by high monthly asymptotic population growth rate. Snowshoe hares experienced short stage-specific generation time during the early breeding season across all phases; they experienced relatively long generation time during the increase and low phase of the mid-breeding season, and the increase and peak phase of the late breeding season.
Elasticity analyses showed that asymptotic population growth rate was proportionately most sensitive to changes in survival of adult females across all phases and seasons. However, retrospective life table response experiment analysis showed that rapid growth of the snowshoe hare populations during the increase phase was due to improvements in reproductive transitions and pre-weaning survival, whereas population declines are caused primarily by reduced survival (primarily, pre-weaning survival), with reduced reproductive transitions and smaller litter sizes playing a secondary role.
Our results suggest that cyclic populations of snowshoe hares are characterized by complex demographic and population-dynamic patterns, depending on phase of the cycle and reproductive season, and that different demographic mechanisms underlie rapid population growth during the increase phase, and swift population declines as the population transitions from the peak to the decline phase. Because our study represents the first comprehensive demographic and population-dynamic study of a cyclic population, similar studies would be needed to test the generalities of our conclusions. Whereas density-dependent predation has been shown to be the primary cause of phase-related changes in survival, future research should focus on identifying mechanisms underlying phase-related changes in reproductive parameters.

Global climate change has shifted seasonality, influencing species across multiple scales, from individual traits to community dynamics. I examined these effects on a winter-adapted mammal snowshoe hare (Lepus americanus) at its southern range boundary, a region expected to be vulnerable to climate change. Specifically, I investigated how southern range populations are responding to changing environmental conditions. I examined this across two distinct ecological scales. At the community scale, a 40-year analysis of mainland populations (44º–49ºN) in the Great Lakes region revealed a clear gradient of fading cyclicity, indicating widespread population destabilization likely driven by pressures from shifting seasonality. Additionally, I assessed a hypothesized refugium on Isle Royale National Park. At the population and individual scale, this island population was found to be large, connected, demographically stable, and cyclic, despite lacking the specialized predators thought essential for cycle stability. These results demonstrate how shifting seasonality drives both cyclic collapse and unique persistence at the southern range edge. By integrating analyses across scales from community-wide cycle dynamics to localized refugial stability, I examined both broad scale regional shifts as well as identified Isle Royale as a critical stronghold for the persistence of this climate-vulnerable species.

ABSTRACT
Aim

The regular cycling of animal populations has fascinated ecologists for over a century. Some cycling populations have recently however, exhibited instability, often attributed to climate change. Snowshoe hare (Lepus americanus) cycles are well documented, displaying peaks every 8–11 years. While these cycles have been studied extensively in the core of their distributional range, less is known about snowshoe hare cyclic dynamics along their southern range boundary. We tested the hypotheses that the cycling of southern snowshoe hare populations varies across a latitudinal cline and that populations have exhibited dampening in recent years.
Location

Six latitudinal degrees (44°–49° N) in the Great Lakes region.
Taxon

Snowshoe hare (Lepus americanus).
Methods

Utilising a series of snow track transects across Minnesota and Wisconsin, we examined snowshoe hare cyclicity across a 40-year time series from 1978 to 2022. These transects were grouped into four bands across the Great Lakes region to identify changes across a latitudinal cline. Wavelet analysis was then used to examine shifts in cyclic behaviour across time.
Results

We found evidence of cyclicity across all latitudinal zones and detected a gradient of fading cyclicity along their southern range boundary.
Main Conclusions

Our findings reveal that while snowshoe hare populations along their southern range boundary have previously cycled, in recent years they appear to be destabilising. These observed shifts in cyclic behaviour may be linked to other regional shifts including range contraction and climate change; however, further research investigating the causal mechanisms behind this cyclic loss is needed.

Abstract

Research Highlight: Shiratsuru, S., & Pauli, J. N. (2024). Food-safety trade-offs drive dynamic behavioural antipredator responses among snowshoe hares. Journal of Animal Ecology, DOI: 10.1111/1365-2656.14183. Predation-risk effects are known to be context dependent, with impacts of perceived predation threat on individual antipredator responses, prey population demography, species interactions and community organization hinging on traits of the prey, the predator(s) and setting of the interaction. Yet, few empirical studies to date have simultaneously explored how these three drivers shape contingency in antipredator behaviour, the key first step in the process by which predation-risk effects play out, especially in free-living vertebrates. In a new study, Shiratsuru & Pauli (2024) address this knowledge deficit by showing that snowshoe hares (Lepus americanus) trade foraging for anti-predator vigilance dynamically as a function of winter food availability (a proxy for individual energetic state), the timing and intensity of predator activity, and environmental properties associated with elevated vulnerability to predator-induced mortality, notably including coat colour mismatch caused by variation in snow cover. These results offer new insight into the complexity of predation-risk effects and should serve as a guide for research aiming to better understand the expression of these effects under varying circumstances.

Abstract

Cyclic changes in snowshoe hare (Lepus americanus) fecundity have been attributed to changes in winter forage availability and predation pressure. Disentangling how nutrition and predation pressure affect snowshoe hare physiology is complex. As an herbivore of the northern boreal forests, snowshoe hares cope with extreme seasonal changes in diet, ambient temperature, and energy demands. We examined seasonal variation in the body condition index, blood biomarkers indicative of nutritional status, and fecal cortisol metabolite concentrations, in snowshoe hares across five ecologically distinct times of year in relation to adult survival rates. Snowshoe hares sampled from a high-density population in northern Alaska during 2018 showed decreases in survival and in plasma concentrations of total protein (TP), blood urea nitrogen (BUN), hematocrit (Hct), Chloride (Cl) and glucose during March and October. Increased survival and concentrations of Cl, TP, BUN, Hct, sodium (Na) and glucose were observed during August. Decreases in mass and survival from August to October suggest limited forage. Increases in TP, BUN, Hct and glucose in December suggest higher metabolic turnover. Fecal cortisol concentrations were not significantly associated with seasonal nutritional condition. A two-fold increase in mean cortisol was observed during August, potentially associated with energetically costly processes such as increased movement and reproduction. This work provides seasonal observations of snowshoe hare plasma biochemical values (N = 164) indicative of nutritional status, and supports the idea of using a collective biomarker approach to advance our understanding of how seasonality may play a role in snowshoe hare physiology.

ABSTRACT

The North American boreal forest is a massive ecosystem, and its keystone herbivore is the snowshoe hare (Lepus americanus). Hares are exposed to considerable environmental extremes in diet and weather, food availability, and predation risk. Gut microbiomes have been suggested to facilitate adaptive animal responses to environmental change, but severe environmental challenges to homeostasis can also disrupt host-microbiome relationships. To better understand gut microbiome contributions to animal acclimation, we studied the faecal bacterial microbiome of wild hares across two types of extreme environmental change that are integral to their natural history: (1) seasonal transitions between summer and winter, and (2) changes over the ~10 year ‘boom-bust’ population cycles that are characterised by shifting food resource availability and predation pressure. When compared to summer, hares in winter had lower bacterial richness and were depleted in 20 families (including Oxalobacteraceae and Christensenellaceae) but enriched for Ruminococcaceae (a family which contains plant fibre degrading bacteria) alongside nine other bacterial groups. Marked bacterial microbiome differences also occurred across phases of the population cycle. Bacterial microbiomes were lower in richness and compositionally distinct in the peak compared to the increase or decline phases of the population cycle. Direct measures of host physiology and diet quality (faecal fibre contents) most strongly supported food resource availability as a mechanism underlying phase-based differences in bacterial communities, but faecal fibre contents could not fully account for bacterial microbiome variation across phases.

ABSTRACT

Browsing herbivores must consider food digestibility while balancing the intake of multiple nutrients (i.e., protein and energy) simultaneously. Nutritional Geometry (NG) is a framework that is used to assess how nutrients interact to impact animal feeding behavior and body condition. Here, we use NG combined with detailed digestibility trials to evaluate how snowshoe hares (Lepus americanus), a common boreal browser that experiences 10-year population cycles, balance energy and protein. We conducted 65 no-choice and 15 multi-choice feeding trials on 17 hares in Kluane, Yukon (Canada) during the winters of 2022 and 2023. We tested four diets ranging from the low protein (5.6%) and high fiber content of hare winter food (twigs) to the high protein (16.7%) and low fiber content of rabbit chow. We measured daily intake per kg0.75 per day in multi-choice trials and daily intake, weight change, and digestibility in no-choice trials. We analyzed the effect of diet treatment on each response and the effect of protein and energy intake, in both crude and digestible terms, on feeding rates and weight change. In multi-choice trials, hares chose a diet balanced in energy and protein, but with a protein content above that in twigs. On single diets, hares were fed to meet a minimum daily digestible energy intake of approximately 1000 kJ/kg0.75/day, regardless of protein content, after which digestible protein influenced weight change (p = 0.02). We found that hares could maintain their weight after they acquired 6 g of digestible protein per kg0.75/day. Our results suggest that snowshoe hares choose to consume food items on the basis of the interaction between energy and protein, and these choices influence weight change. Our work supports previous hypotheses that declines in twig quality at peak hare densities could contribute to the subsequent increase in over-winter weight loss that occurs during the population crash.

Abstract
Changes in reproduction may be closely linked to population density and often manifest in various behaviours. Thus, variation in behaviours associated with reproduction can provide insights into the mechanisms influencing the distribution and abundance of populations as well as broader community dynamics. We used a combination of occurrence and behavioural data from camera traps to measure variation in the abundance of Canada lynx during two time periods with contrasting abundance of their primary prey, snowshoe hare. Our first objective was to determine if N-mixture models, camera occurrence rates, and behaviours could be used to monitor trends in cyclic abundance. Our second objective was to investigate the underlying environmental and ecological factors influencing lynx reproductive behaviours (cheek-rubbing, scent-marking, and grouping). We found that lynx behaviours and relative abundance were correlated among years and that those relationships varied with the abundance of snowshoe hare. Consistent with our predictions, years with greater abundance of lynx and hare were characterized by increases in cheek-rubbing, scent-marking, and grouping behaviours. Variation in behaviour and estimates of abundance proved to be strong co-occurring indicators of the cyclic population dynamics of Canada lynx. Behaviour can provide valuable insights into the mechanisms (i.e., prey availability, breeding activity) that influence population distributions and abundance.

bstract

Animals balance acquiring food for energy while minimizing their risk of predation, but climate or habitat features can tip the scales. I used snowshoe hare (Lepus americanus) to test how external variables influence foraging and survival. First, I used winter coat-colour mismatch to test the Camouflage Hypothesis. I predicted that white hares mismatched on a snowless winter background would be more vulnerable to predation than matched hares. Instead, mismatched hares had lower mortality risk than matched hares. Temperature and snow depth, not mismatch, influenced survival and foraging behaviour. Next, I tested the Risk Allocation Hypothesis with a novel risk simulation experiment in the context of spring environmental factors. Hares did not allocate risk based on simulated risk or weather conditions. Instead, hares were risk averse as a function of canopy cover. Taken together, my results demonstrate that multiple mechanisms likely impact the energetics-risk balance. Snow depth and canopy cover have direct implications on predation risk, while temperature impacts energetics; however, effects may not be detectable if conditions do not represent an energetic challenge. My work highlights the idiosyncrasies of place considering previous results across the hare range, and contributes to mismatch and behavioural frameworks for a seasonally coat-colour changing species.

Abstract:
The snowshoe hare is well adapted to cold climates. A prey species, the snowshoe hare molts from brown to white pelage in the fall to camouflage against the snow and avoid predation. Pennsylvania’s winters are warming, and average snowfall is declining, causing hares to spend more time in winter-white pelage on a snowless background. Hares in this state of mismatch have higher predation rates. Range contractions tied to winter warming trends have already been observed in southern snowshoe hare populations. Across their range, snowshoe hare are associated with densely vegetated forest that provides visual cover from predators. In Pennsylvania, early-successional hardwood forest is an important cover type for snowshoe hare because the high density of regenerating stems provides both forage and cover. Sufficiently dense forest cover has the potential to offset the increased predation risk of hares in mismatch, but the amount of early-successional forest has been declining in Pennsylvania over several decades. With this dual threat of warming winters and declining early-successional forest cover, the status of the Pennsylvania snowshoe hare population needed to be assessed. I first designed a single-season occupancy study that followed the methods of a previous 2004 study. My goal was to determine if the Pennsylvania snowshoe hare range had contracted since 2004. I created occupancy models fit to field survey data from 2004 and 2023, which showed that a range contraction had occurred, coinciding with declines in winter snowfall. This range contraction was greater than had been predicted by the 2004 study. I further found that occupancy models fit to the 2004 survey data were unable to predict occupancy in 2023, even when exact values for climate and forest conditions in 2023 were used to generate the prediction. This study is one of only a few that have explicitly evaluated species distribution model projections with long-term data sets, and I showed that model projections may be wrong and cannot be reliably evaluated until time has passed and new field data are collected. After identifying the rapid contraction of the snowshoe hare range in Pennsylvania, I designed a second study with the goal of providing guidance to state land managers on managing forests for snowshoe hare. I applied spatially-explicit capture-recapture modeling to non-invasive genetic sampling of fecal pellets on 10 forested sites in northwest Pennsylvania, a region where hare occupancy probabilities were high. I identified forest age class and forest understory density as important forest characteristics related to snowshoe hare population density. Snowshoe hare densities were higher in denser forest understories. Early-successional forest was able to support greater population densities than mature forest for the same forest understory conditions, but I observed the highest snowshoe hare densities in mature forest with mountain laurel and eastern hemlock understories. Under simulations, I showed that both stand-replacing harvest to create early-successional cover and improvement of mature forest understory densities have the potential to increase snowshoe hare population densities. Although the expected increases in hare population density after forest management actions were small, higher population densities are related to lower extinction risks; therefore, forest management can increase the resiliency of the Pennsylvania snowshoe hare population under warming winters by maintaining and increasing population densities.

Abstract

Animals exhibit dynamic movement and activity in response to environmental variation including changes in reproductive opportunities, predation risk, or food availability. Yet, it remains unclear which factors are primary in affecting animal movement, and whether the relative importance of these factors are consistent through time. We tracked snowshoe hares (Lepus americanus) using GPS telemetry during eight summers spanning a hare population cycle (2015–2022) in southwestern Yukon, Canada, to determine associations between environmental variation and hare movement and home range size. Hare density varied 25-fold during the study and home range size increased markedly during low hare density, especially for males. Both sexes retained similar core space use and linearity of movements, but at low densities males had greater and more variable movement rates and time spent travelling. Trail cameras revealed that annual changes in hare movement were also correlated with relative abundance of lynx (Lynx canadensis) and coyotes (Canis latrans). However, hare detection rates within a season were not closely associated with seasonal variation in predator detection. Observed differences between male and female hares in some metrics highlighted that different life histories and reproductive behavior are likely the main drivers of hare movement dynamics. Therefore, fitness rewards associated with successful mate search and reproduction appear to outweigh risks associated with increased movement, even in highly variable environments where costs of prioritizing reproduction-related activities are notably high and variable.

Abstract

Climate change is altering interspecific interactions globally, yet community-level responses are difficult to predict due to both the direct and indirect effects of changing abiotic and biotic conditions. Snowshoe hares (Lepus americanus) are particularly vulnerable to decreasing snow cover and resultant camouflage mismatch. This species shares a suite of predators with alternative prey species including porcupines (Erethizon dorsatum) and ruffed grouse (Bonasa umbellus), and all three species historically exhibited synchronized population dynamics. Recently, the community has become partially disassembled, notably with the loss of snowshoe hares and associated enemy-mediated indirect interactions resulting from declining snow duration. Specifically, we hypothesized that the extirpation of hares in the early 1990s indirectly increased predation pressure on ruffed grouse and porcupines. To test our hypothesis, we experimentally translocated 96 snowshoe hares to a site within a regional ecotone between northern and southern forests where snowshoe hares were recently extirpated and monitored community members before, during, and after translocation. Ruffed grouse were only loosely associated with the biotic interactions that linked porcupines and snowshoe hares, likely due to predation occurring from avian predators and strong negative direct effects of declining winter snow depths. In contrast, predation of neonate porcupines was virtually non-existent following repatriation, compared with periods without hares. This abrupt attenuation of predation did not increase overall survival due to increased non-predation mortality from cold, early spring weather. Porcupines directly benefited from warming winters: decreased snow cover increased adult survival and warmer temperatures around parturition increased maternal condition and reduced non-predation causes of mortality for neonates. Our experimental manipulation suggests that enemy-mediated indirect interactions were likely to be important features of this community; however, climate change has disrupted these interactions, resulting in extirpation of a central prey species (snowshoe hare) and increased predation of an alternative prey species (porcupine). We show complex effects from climate change with some species directly and negatively affected, while others benefited from direct effects of warming winters, but suffered negative effects from indirect interactions. Due to absent snowshoe hares and associated biotic interactions, continued persistence of this community module is unlikely, potentially resulting in altered no-analog communities along trailing edge distributions.

Abstract

Cyclic fluctuations in abundance exhibited by some mammalian populations in northern habitats (“population cycles”) are key processes in the functioning of many boreal and tundra ecosystems. Understanding population cycles, essentially demographic processes, necessitates discerning the demographic mechanisms that underlie numerical changes. Using mark–recapture data spanning five population cycles (1977–2017), we examined demographic mechanisms underlying the 9–10-yr cycles exhibited by snowshoe hares (Lepus americanus Erxleben) in southwestern Yukon, Canada. Snowshoe hare populations always decreased during winter and increased during summer; the balance between winter declines and summer increases characterized the four, multiyear cyclic phases: increase, peak, decline, and low. Little or no recruitment occurred during winter, but summer recruitment varied markedly across the four phases with the highest and lowest recruitment observed during the increase and decline phase, respectively. Population crashes during the decline were triggered by a substantial decline in winter survival and by a lack of subsequent summer recruitment. In contrast, initiation of the increase phase was triggered by a twofold increase in summer recruitment abetted secondarily by improvements in subsequent winter survival. We show that differences in peak density across cycles are explained by differences in overall population growth rate, amount of time available for population growth to occur, and starting population density. Demographic mechanisms underlying snowshoe hare population cycles were consistent across cycles in our study site but we do not yet know if similar demographic processes underlie population cycles in other northern snowshoe hare populations.