Influence of forest structure on the abundance of snowshoe hares in western Wyoming

Snowshoe hares (Lepus americanus) are a primary prey species for Canada lynx (Lynx canadensis) in western North America. Lynx management plans require knowledge of potential prey distribution and abundance in the western United States. Whether even-aged regenerating forests or multi-storied forests contain more snowshoe hares is currently unknown. During 2006–2008, we estimated snowshoe hare density in 3 classes of 30–70-year-old lodgepole pine (Pinus contorta) and 4 classes of late seral multi-storied forest with a spruce (Picea engelmannii)-fir (Abies lasiocarpa) component in the Bridger-Teton National Forest, Wyoming. We recorded physiographic variables and forest structure characteristics to understand how these factors influence abundance of snowshoe hares. In many instances, snowshoe hares were more abundant in late seral multi-storied forests than regenerating even-aged forests. Forest attributes predicting hare abundance were often more prevalent in multi-storied forests. Late seral multi-storied forests with a spruce–fir component and dense horizontal cover, as well as 30–70-year-old lodgepole pine with high stem density, were disproportionately influential in explaining snowshoe hare densities in western Wyoming. In order to promote improved habitat conditions for snowshoe hares in this region, management agencies should consider shifting their focus towards maintaining, enhancing, and promoting multi-storied forests with dense horizontal cover, as well as developing 30–70-year-old lodgepole pine stands with high stem density that structurally mimic multi-storied forests. © 2012 The Wildlife Society.     

Relationship Between Fecal Pellet Counts and Snowshoe Hare Density in Western Wyoming

ABSTRACT Snowshoe hares (Lepus americanus) are an important prey species for Canada lynx (Lynx canadensis) and are considered critical for lynx population persistence. Determination of snowshoe hare distribution and abundance is needed by land management agencies for lynx conservation. An accepted approach for estimating snowshoe hare abundance is the use of fecal-pellet plot counts. Locally derived regression equations are preferred for accurate calibration of pellet counts to snowshoe hare density due to local differences in pellet deposition and decomposition. We used linear regression to examine correlations between snowshoe hare density, as determined by mark–recapture estimates, and pellet plot counts on both uncleared plots and annually cleared plots on the Bridger-Teton National Forest, western Wyoming, USA. We found significant correlations between snowshoe hare density estimates and fecal pellet counts for both uncleared and annually cleared pellet counts; however, the relationship was stronger (higher r) when using pellet counts from annually cleared plots. In addition, we found that adjusting the buffer size by omitting hard habitat edges (not used by hares) around trapping grids improved correlations between snowshoe hare density and fecal pellet counts for both uncleared plots and annually cleared plots. Though precision is sacrificed when using uncleared plots, they may be useful as a coarse index of habitat use by snowshoe hares. Our derived regression equations may be useful to identify important foraging habitat for Canada lynx in western Wyoming. Land managers responsible for conserving snowshoe hare habitat in western Wyoming may use these equations to monitor changes in hare populations among habitats and during prescribed management actions.     

Population Estimates of Snowshoe Hares in the Southern Rocky Mountains

Abstract: In 1999 Canada lynx (Lynx canadensis) were reintroduced to the southern Rocky Mountains and in 2000 the species was listed as threatened under the Endangered Species Act in the contiguous United States (Colorado Division of Wildlife 2000, U.S. Fish and Wildlife Service 2000). To better evaluate the progress of this reintroduction, we conducted field studies to estimate population densities of snowshoe hares (Lepus americanus), the primary prey of lynx in Colorado, USA. We conducted our field studies in southwestern Colorado in winters 2002 and 2003. We estimated population densities in forested stands of mature Engelmann spruce (Picea engelmannii)-subalpine fir (Abies lasiocarpa) and mature lodgepole pine (Pinus contorta) using mark-recapture data and 3 methods for estimating effective area trapped: half trap interval, mean maximum distance moved (MMDM), and half MMDM. In Engelmann spruce-subalpine fir, we found density estimates ranged from 0.08 ± 0.03 (SE) hares/ha to 1.32 ± 0.15 hares/ha and in lodgepole pine, density estimates ranged from 0.06 ± 0.01 hares/ha to 0.34 ± 0.06 hares/ha, depending on year and method used for estimating effective area trapped. Our density estimates are similar to those reported at the low phase of the hare cycle in populations to the north (<0.1–1.1 hares/ha), where Canada lynx persist (Hodges 2000a). Although density estimates are a useful comparative tool, they depend upon methods used to estimate effective area trapped. Therefore, we urge caution in comparing our density estimates with those from other areas, which may have used dissimilar methods. We also examined effects of temperature and moon phase on capture success of snowshoe hares; extremely low temperatures affected capture success but moon phase did not. Capture success can be improved by trapping snowshoe hares at temperatures above their lower critical temperature (T_lc). If abundance estimates are derived from mark-recapture studies then effects of temperature should be included when modeling capture probabilities.     

Precommercial forest thinning alters abundance but not survival of snowshoe hares

Anthropogenic landscape modification is a major threat to global biodiversity and ecosystem integrity. Thus, land use practices that reconcile human needs with protection of species and ecological processes are of interest. Precommercial forest thinning (PCT) is a land use practice that is believed to be less ecologically disruptive than other silvicultural approaches (e.g., clear-cutting). The impacts of PCT on wildlife populations are not well understood, however, and the effects of this practice on individual animals have not been rigorously examined. Accordingly, we investigated short-term population and individual responses of snowshoe hares (Lepus americanus) to PCT in western Oregon during 2001–2002. We live-trapped hares (n = 143) seasonally and equipped them with mortality-sensitive radio-collars on 3 manipulated sites that were precommercially thinned and on 3 undisturbed controls. We also quantified the activity (movement rates) of all collared hares using an automated data-logger. As a result, we were able to document the effects of PCT on hare abundance, individual survival, and daily movement. Thinning significantly reduced hare abundance relative to that on control sites, but had no effect on individual mortality or activity. We infer, therefore, that a portion of the hares on thinned sites dispersed to adjacent habitat, where they survived as well as conspecifics on both control and manipulated sites but were unavailable for subsequent capture. We conclude that PCT affects hare density in the short-term (i.e., at least in the first few years post-treatment) largely via altered behavior. Thus, if the immediate impacts of this practice on hare populations are to be minimized, thinned stands should be imbedded in a habitat matrix that facilitates the occupancy of individuals dispersing from disturbed patches. © 2012 The Wildlife Society.     

Is Size of Fecal Pellets a Reliable Indicator of Species of Leporids in the Southern Rocky Mountains?

Abstract: In the southern Rocky Mountains, USA, snowshoe hares (Lepus americanus) and mountain cottontails (Sylvilagus nuttallii) are syntopic. Previous researchers used size of fecal pellets to identify leporid species in the Southern Rockies, a common criterion for identifying species of cervids. We measured 655 fecal pellets from 10 mountain cottontails and 2,374 fecal pellets from 23 snowshoe hares. We found no relationship between the body weight of mountain cottontails and the size of their fecal pellets (r = 0.04, F = 0.01, P = 0.91) but found one for snowshoe hares (r = 0.48, F = 9.3, P = 0.005). Although the 2 species differed in the size of their fecal pellets, the difference between means (1.2 mm) was sufficiently small to require measuring individual pellets and is only applicable to individuals of adult size. Although fecal pellet counts may be used to estimate presence and relative abundance of snowshoe hares in the absence of syntopic leporids, where multiple species of leporids are syntopic this method may yield misleading results.     

Canada lynx occurrence and forest management in the Acadian Forest

We evaluated patterns of occurrence and non-occurrence for Canada lynx (Lynx canadensis) across a 16,530-km² study area in Maine to provide a better understanding of lynx habitat selection and habitat ecology on commercially managed forestlands in the Acadian Forest. Because of the influence of forest structure on lynx habitat selection and abundance of their primary prey, the snowshoe hare (Lepus americanus), and to improve our ability to build robust models, we used habitat information derived from a time series of Landsat satellite imagery spanning the period 1973–2004. We defined and mapped 10 forest types based on forest harvest history, time since harvest, and current forest condition. We compared a suite of models to evaluate relative influences of forest composition, habitat patch configuration, and hare density on habitat selection by lynx at the landscape scale. Occupied areas had greater average hare densities and percentage of mature conifer. Average hare density in occupied areas (0.74 hares/ha) was greater than in unoccupied areas (0.62 hares/ha), but was less than previous research has suggested may be necessary to support lynx populations in the southern portion of the species' range. No occupied areas occurred where average hare density was <0.5 hares/ha. Average hare density at the landscape-scale was strongly influenced by amount of high-quality hare habitat (i.e., conifer or mixedwood regenerating forest, 15–35 yr post-harvest). Edge density between mature conifer and high-quality hare habitat was substantially greater in occupied areas compared to unoccupied areas. Juxtaposition of those 2 forest types may provide edge habitat where lynx experience easier travel and improved access to prey in landscapes with extensive areas of high-quality hare habitat where travel and access may be somewhat limited by high understory stem density. Probability of occurrence declined nonlinearly with changes in hare density and percent mature conifer forest in the landscape; thus, suitability of currently occupied landscapes could change markedly with future changes in landscape-level hare densities and changing habitat associated with forest management. Where lynx conservation is a priority, we recommend that managers focus on creating and maintaining a minimum of 27% high-quality hare habitat within 100-km² areas to promote landscape-scale hare densities >0.5 hares/ha. © The Wildlife Society, 2013     

Short‐term response of snowshoe hares to western larch restoration and seasonal needle drop

Old‐growth western larch has been degraded throughout much of its historic range due to extensive timber harvest and fire suppression. We examined the effects of a restoration treatment of western larch on snowshoe hares, a denizen of the boreal forest serving as a focal animal species to indicate the health of the restored ecosystem. We implemented a restoration treatment using “doughnut thinning” to accelerate development of old‐growth attributes in larch stands and simultaneously examined the short‐term effects on snowshoe hare density, survival, and movement. Although typical forest management activities tend to have adverse effects on hares especially in the short term, we found that the restoration treatment did not affect hare density or survival in the short term. In addition, despite significant decreases in cover coinciding with the larch needle drop, we found evidence of year‐round immigration into larch stands by hares suggesting larch stands are suitable year‐round hare habitat. Taken together, our findings suggest that a larch restoration treatment designed to accelerate the development of old‐growth attributes can be implemented so as to have no measurable short‐term detrimental effects on hares.     

Using Pellet Counts to Estimate Snowshoe Hare Numbers in Minnesota

Abstract: We calibrated snowshoe hare (Lepus americanus) numbers with pellet counts in Minnesota, USA, to understand the relationship between hare numbers and pellets in the central portion of the hare range. We found a strong and significant correlation between hare numbers and pellet counts using either linear or functional regression with either annual or semiannual pellet counts. Equations we developed using linear or functional regression predicted >1 hare/ha at similar pellet-density thresholds. These equations can be used to efficiently identify habitats that support hare numbers necessary for Canada lynx (Lynx canadensis) persistence in Minnesota.     

ASSESSMENT OF POTENTIAL BIAS WITH SNOWSHOE HARE FECAL PELLET-PLOT COUNTS

Abstract: The fecal pellet-plot method has been used extensively for snowshoe hare (Lepus americanus) population studies across the species' range, but potential biases associated with the technique have not been addressed adequately. We studied hare pellet-plots in northern Idaho to quantify pellet decomposition rates across environmental gradients, and conducted feeding trials on captive hares to assess the role of diet on pellet production rates. We found that across our study area pellet numbers tended to be higher on plots with high vegetative cover, which likely was a reflection of hare habitat choice rather than lesser pellet decomposition in such habitat. A pellet decomposition experiment indicated that pellet persistence was negatively related to moisture level, and that pellets produced by hares during summer decomposed more quickly than those from winter. We found that only 19% of fecal pellets collected from plots located across northern Idaho were produced by hares during winter. There was a correlation between pellet numbers from plots that were pre-cleared 1 year earlier and estimated numbers of hares on 6 study areas. A similar correlation was lacking for pellet counts from uncleared plots, implying that hare population estimation via pellet-plot counts should involve plot pre-clearing. In captive studies, juvenile hares produced slightly fewer pellets per day per gram of food ingested than adults, but pellet production was similar across diets comprised of 10 different browse species. We conclude that for our study area the fecal pellet-plot method may be subject to notable pellet decomposition bias, and therefore recommend that use of the method elsewhere across the species' range be preceded by assessment of both the pellet-hare density relationship and pellet decomposition rates across habitats.     

Effects of Precommercial Thinning on Snowshoe Hares in Maine

Abstract: Snowshoe hares (Lepus americanus) are an important prey species and a dominant herbivore across much of their North American range, and researchers have questioned the influences of forestry practices that alter habitat for hares and the potential community-level effects on carnivores. We examined the effects of precommercial thinning (PCT) from 1 to 11 years posttreatment on snowshoe hares. In the commercial forests of northern Maine, USA, we counted and cleared hare pellets twice a year during 2001 and 2002 on >46 km of pellet transects across 30 regenerating conifer stands (17 treated with PCT) previously treated with an aerial application of herbicide. We compared densities of snowshoe hare pellets among 3 development classes with (1 yr after thinning, 6 yr after thinning, and 11 yr after thinning) and without thinning (stands with a similar history of clearcut and herbicide treatment but no thinning). During both years, densities of hares were lower in stands treated with PCT than in similar unthinned stands across the 3 development classes and during both leaf-off and leaf-on seasons (P < 0.001). Within both thinned and unthinned stands, hare density was greatest in stands in the 1-year development class when compared to the 6-year and 11-year development classes, but a statistical difference (P = 0.048) among classes was evident only during leaf-off seasons. Precommercial thinning was associated with densities of snowshoe hares that were approximately half of those in similar unthinned stands up to at least 11 years posttreatment; however, thinned stands may retain densities of hares greater than stands managed using other forest harvesting regimes. Our results apply to core portions of stands with crop trees spaced at 1.8–2.4-m intervals following complete overstory removal and herbicide treatment. We advocate caution when applying our results to other thinning regimes or across broader spatial scales.     

Winter Prey Selection of Canada Lynx in Northwestern Montana

ABSTRACT The roles that diet and prey abundance play in habitat selection of Canada lynx (Lynx canadensis) in the contiguous United States is poorly understood. From 1998–2002, we back-tracked radiocollared lynx (6 F, 9 M) for a distance of 582 km and we located 86 kills in northwestern Montana, USA. Lynx preyed on 7 species that included blue grouse (Dendragapus obscurus), spruce grouse (Canachites canadensis), northern flying squirrel (Glaucomys sabrinus), red squirrel (Tamiasciurus hudsonicus), snowshoe hare (Lepus americanus), least weasel (Mustela nivalis), and white-tailed deer (Odocoileus virginianus). Snowshoe hares (69 kills) accounted for 96% (4-yr average, range = 94–99%) of prey biomass during the sample period. Red squirrels were the second-most-common prey (11 kills), but they only provided 2% biomass of the winter diet. Red squirrels contributed little to the lynx diet despite low hare densities. A logistic regression model of snowshoe hare, red squirrel, and grouse abundance, as indexed by the number of track crossings of use and available lynx back-tracks, was a significant (Wald statistic = 19.03, df = 3, P < 0.001) predictor of habitat use. As we expected, lynx (P < 0.001) selected use-areas with higher snowshoe hare abundance compared to random expectation. However, the red squirrel index had a weak (P = 0.087) negative relationship to lynx use, and grouse was nonsignificant (P = 0.432). Our results indicate that lynx in western Montana prey almost exclusively on snowshoe hares during the winter with little use of alternative prey. Thus, reductions in horizontal cover for hares would degrade lynx habitat.     

Of lemmings and snowshoe hares: the ecology of northern Canada

Two population oscillations dominate terrestrial community dynamics in northern Canada. In the boreal forest, the snowshoe hare (Lepus americanus) fluctuates in cycles with an 8-10 year periodicity and in tundra regions lemmings typically fluctuate in cycles with a 3-4 year periodicity. I review 60 years of research that has uncovered many of the causes of these population cycles, outline areas of controversy that remain and suggest key questions to address. Lemmings are keystone herbivores in tundra ecosystems because they are a key food resource for many avian and mammalian predators and are a major consumer of plant production. There remains much controversy over the role of predation, food shortage and social interactions in causing lemming cycles. Predation is well documented as a significant mortality factor limiting numbers. Food shortage is less likely to be a major limiting factor on population growth in lemmings. Social interactions might play a critical role in reducing the rate of population growth as lemming density rises. Snowshoe hares across the boreal forest are a key food for many predators and their cycles have been the subject of large-scale field experiments that have pinpointed predation as the key limiting factor causing these fluctuations. Predators kill hares directly and indirectly stress them by unsuccessful pursuits. Stress reduces the reproductive rate of female hares and is transmitted to their offspring who also suffer reduced reproductive rates. The maternal effects produced by predation risk induce a time lag in the response of hare reproductive rate to density, aiding the cyclic dynamics.     

Diurnal Habitat Relationships of Canada Lynx in an Intensively Managed Private Forest Landscape in Northern Maine

Abstract In March 2000, Canada lynx (Lynx canadensis) were listed as a federally threatened species in 14 states at the southern periphery of their range, where lynx habitat is disjunct and snowshoe hare (Lepus americanus) densities are low. Forest conditions vary across lynx range; thus, region-specific data on the habitat requirements of lynx are needed. We studied lynx in northern Maine, USA, from 1999 to 2004 to assess quality and potential for forests in Maine to sustain lynx populations. We trapped and radiocollared 43 lynx (21 M, 22 F) during this period and evaluated diurnal habitat selection by 16 resident adult lynx (9 M, 7 F) monitored in 2002. We evaluated lynx selection of 8 habitats at multiple spatial scales, and related lynx habitat selection to snowshoe hare abundance. Lynx preferred conifer-dominated sapling stands, which supported the highest hare densities on our study site (x̄ = 2.4 hares/ha), over all other habitats. The habitats where lynx placed their home ranges did not differ by sex. However, within their home ranges, males not only preferred conifer-dominated sapling stands, but also preferred mature conifer, whereas females singularly preferred conifer-dominated sapling stands. Approximately one-third of Maine's spruce-fir forest and nearly 50% of our study area was regenerating conifer or mixed-sapling forest, resulting from a disease event and intensive forest management (e.g., large clear-cuts). Our findings suggest that current habitat conditions in Maine are better than western montane regions and approach conditions in boreal forests during periods of hare abundance. We recommend that forest landowners maintain a mosaic of different-aged conifer stands to ensure a component of regenerating conifer-dominated forest on the landscape.     

A quantitative analysis of the abundance and demography of European hares Lepus europaeus in relation to habitat type, intensity of agriculture and climate

1. European hares Lepus europaeus have declined throughout Europe since the 1960s. Possible reasons for this include agricultural intensification and changes in climate and predator numbers, but no clear consensus has been reached as to the relative importance of each of these. We aimed to identify factors associated with high and low hare numbers throughout Europe, to determine which could have caused population declines. 2. Results of 77 research papers from 12 European countries were summarized. Relationships between hare density and demographics and habitat, climate, hunting and predator variables were examined and quantified where possible. Temporal changes in factors identified as being associated with high or low numbers of hares were then examined to see if they could explain population declines. 3. Data from pastural habitats were limited, but densities of hares were low. Arable habitats had higher densities than mixed areas in spring, unless farming was intensive in which case densities were similar. In autumn the two habitats had similar densities. Field size, temperature, precipitation and hunting had no effect on density throughout Europe. Fecundity was affected by climate. 4. Arable land, various crops, fallow habitat and temperature were positively associated, and monoculture, precipitation and predators negatively associated with hare abundance. The relationship of field size, pasture and woodland with abundance depended on spatial scale. 5. Habitat changes caused by agricultural intensification are the ultimate cause of hare population declines. Effects of changes in climate or predator numbers are magnified by the loss of high-quality year-round forage and cover. Further research is required on how habitat changes affect fecundity and survival, and to identify which parameters have the greatest impact on population numbers. Farmland management policies that target the re-establishment of some of the habitat diversity lost within fields, farms and landscapes will help to reverse the decline of the European hare.