Factors affecting presence and relative abundance of the Endangered volcano rabbit Romerolagus diazi, a habitat specialist

Habitat specialists are particularly vulnerable to extinction when habitat conditions are altered. Information on the habitat use of such species is thus important because it provides insight into factors that influence distribution and abundance, which is crucial for conservation. Here, we aimed to identify factors that influence the patterns of presence and abundance of the Endangered volcano rabbit Romerolagus diazi, a rare leporid with a patchy distribution. Through exhaustive sampling of its range in the Sierra Chichinautzin and Sierra Nevada volcanic fields, Mexico, and using generalized linear models, we found that the probability of patch occupancy was higher where bunchgrass cover exceeded 75%, rock cover exceeded 5%, no cattle grazing was observed and human settlements were at least 7 km away. Patches with greater relative abundance were those with similar characteristics, but located at elevations > 3,600 m, and with rock cover < 15%. Cattle grazing was identified as a major threat to local populations of the volcano rabbit, particularly in the Sierra Chichinautzin. Because of the significance of bunchgrasses for this species, the protection of the mountain grasslands is required in both volcanic fields.

Effects of human-made resource hotspots on seasonal spatial strategies by a desert pitviper

Habitat heterogeneity and local resource distribution play key roles in animal search patterns. Optimal strategies are often considered for foraging organisms, but many of the same predictions are applicable to mate searching. We quantified movement and space use by a pitviper to test whether Native Habitats (NH) and human-made Resource Hotspots (RH) facilitate alternative seasonal spatial strategies as a result of critical resources, including potential mating partners, being widely dispersed in NH and clustered in RH. Independent of habitat category, seasonal patterns resembled an intermediate mating system with elements of prolonged male mate-searching and female-defense. However, individuals using primarily NH or RH exhibited alternative strategies. NH rattlesnakes displayed greater movement and larger home ranges than RH rattlesnakes across behavioral seasons. NH males increased movement distances and home ranges during the mating season, while RH males displayed minimal or no seasonal shifts. NH females also elevated movement distances during the mating season, while RH females showed no significant seasonal differences. Despite contrasting spatial patterns, mating success and female-defense effort were not significantly affected by habitat category. This unique study system highlights the potential for interactions among sexual selection, habitat heterogeneity, and behavioral plasticity to facilitate divergent search tactics within populations.

Multiscale habitat relationships of snowshoe hares (Lepus americanus) in the mixed conifer landscape of the Northern Rockies, USA: Cross-scale effects of horizontal cover with implications for forest management

Snowshoe hares (Lepus americanus) are an ecologically important herbivore because they modify vegetation through browsing and serve as a prey resource for multiple predators. We implemented a multiscale approach to characterize habitat relationships for snowshoe hares across the mixed conifer landscape of the northern Rocky Mountains, USA. Our objectives were to (1) assess the relationship between horizontal cover and snowshoe hares, (2) estimate how forest metrics vary across the gradient of snowshoe hare use and horizontal cover, and (3) model and map snowshoe hare occupancy and intensity of use. Results indicated that both occupancy and intensity of use by snowshoe hares increased with horizontal cover and that the effect became stronger as intensity of use increased. This underscores the importance of dense horizontal cover to achieve high use, and likely density, of snowshoe hares. Forest structure in areas with high snowshoe hare use and horizontal cover was characterized as multistoried with dense canopy cover and medium-sized trees (e.g., 12.7-24.4 cm). The abundance of lodgepole pine (Pinus contorta) was associated with snowshoe hare use within a mixed conifer context, and the only species to increase in abundance with horizontal cover was Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa). Our landscape-level modeling produced similar patterns in that we observed a positive effect of lodgepole pine and horizontal cover on both occupancy and use by snowshoe hares, but we also observed a positive yet parabolic effect of snow depth on snowshoe hare occupancy. This work is among the first to characterize the multiscale habitat relationships of snowshoe hares across a mixed conifer landscape as well as to map their occupancy and intensity of use. Moreover, our results provide stand- and landscape-level insights that directly relate to management agencies, which aids in conservation efforts of snowshoe hares and their associated predators.

Climate Tolerances and Habitat Requirements Jointly Shape the Elevational Distribution of the American Pika (Ochotona princeps), with Implications for Climate Change Effects

Some of the most compelling examples of ecological responses to climate change are elevational range shifts of individual species, which have been observed throughout the world. A growing body of evidence, however, suggests substantial mediation of simple range shifts due to climate change by other limiting factors. Understanding limiting factors for a species within different contexts, therefore, is critical for predicting responses to climate change. The American pika (Ochotona princeps) is an ideal species for investigating distributions in relation to climate because of their unusual and well-understood natural history as well as observed shifts to higher elevation in parts of their range. We tested three hypotheses for the climatic or habitat characteristics that may limit pika presence and abundance: summer heat, winter snowpack, and forage availability. We performed these tests using an index of pika abundance gathered in a region where environmental influences on pika distribution have not been well-characterized. We estimated relative pika abundance via scat surveys and quantified climatic and habitat characteristics across two North-Central Rocky Mountain Ranges, the Wind River and Bighorn ranges in Wyoming, USA. Pika scat density was highest at mid-elevations and increased linearly with forage availability in both ranges. Scat density also increased with temperatures conducive to forage plant growth, and showed a unimodal relationship with the number of days below -5°C, which is modulated by insulating snowpack. Our results provide support for both the forage availability and winter snowpack hypotheses. Especially in montane systems, considering the context-dependent nature of climate effects across regions and elevations as well as interactions between climatic and other critical habitat characteristics, will be essential for predicting future species distributions.

Vegetation structure and composition determine snowshoe hare (Lepus americanus) activity at arctic tree line

Snowshoe hares (Lepus americanus Erxleben, 1777) are keystone herbivores supporting many boreal-forest predators. Understanding habitat use of hares can help predict how hares and their predators will be affected by disturbances such as climate change, which will have a particularly strong effect at tree line. We examined hare activity at arctic tree line near Churchill, Manitoba, using fecal pellet transects established in August 2012. We counted all hare fecal pellets at two plots per transect and measured plant abundance and vegetation structure surrounding the plots, then used model selection to determine the combinations of habitat features or plant species that best explained hare activity or presence. Hare pellets occurred at a higher density where tall shrub cover was high. Pellet density also increased with increasing canopy cover, tree size, tree density, visibility, and small shrub cover, but was negatively correlated with medium-sized shrub and herb cover. Hares preferred areas with willow (genus Salix L.) and avoided areas with unpalatable black spruce (Picea mariana (Mill.) Britton, Sterns & Poggenb.). With climate warming, tree line is expected to advance northward and the increased tall shrub and willow cover predicted with increasing temperatures should benefit hares by providing greater predator protection and food.

The landscape of fear: habitat use by a predator (Canis latrans) and its main prey (Lepus californicus and Sylvilagus audubonii)

We evaluated the degree of mutual exclusivity of distributions of coyotes ( Canis latrans Say, 1823) and their main prey (two lagomorph species: the black-tailed jackrabbit, Lepus californicus Gray, 1837, and the desert cottontail rabbit, Sylvilagus audubonii (Baird, 1858)) within the landscape by testing two models. The first assumes that prey seek high resource patches and, subsequently, predators seek prey within these patches, and predicts a high degree of overlap in patch use by both. The second model assumes that predator and prey balance not only food resources but reciprocal levels of predation risk and predation success in making decisions on whether or not to use a patch. This model predicts discordance in patch use between predator and prey. We used a combination of GPS-telemetry and camera-trapping data to assess habitat use patterns of predator and prey. Results from this study support the second model regarding spatial use of the landscape by a predator and its prey. Where the use of the landscape by predators and prey seem to be mediated by environmental constraints, both will adjust their predatory or antipredatory strategies based on these constraints. This results in a partial spatial separation of predator and prey across the landscape, providing patches of relative safety for prey but sufficient areas of overlap for predators to be successful.

Mapping potential core areas for lynx (Lynx canadensis) using pellet counts from snowshoe hares (Lepus americanus) and satellite imagery

We used location data from radio-collared Canada lynx ( Lynx canadensis Kerr, 1792), pellet-count data from snowshoe hares ( Lepus americanus Erxleben, 1777), and cover-type data from satellite imagery to evaluate the relationship between the scale of habitat measurement and the potential for persistence of lynx in northeastern Minnesota, USA, at the southern extent of their range. We counted hare pellets at transects throughout northeastern Minnesota to index hare abundance in cover types. Pellet counts were highest in coniferous forest, regenerating–young forest, and shrubby grassland, and these cover types were greater inside lynx use areas than outside of them. Proportions of regenerating–young forest were greater at scales ≥5 km2. We used these results and satellite imagery to map potential lynx core areas. We predicted that 7%–20% of the study area was suitable for lynx. Areas that we predicted to be suitable for lynx corresponded with known core areas, including those withheld from analyses. To maintain habitat for lynx persistence, forest management should retain current levels of 10- to 30-year-old coniferous forest and include ≥5 km2 areas containing 40% of 10- to 30-year-old coniferous forest. Mapping of potential core areas would be improved if cover-type data from satellite imagery identified conifer regeneration.

An appraisal of the fitness consequences of forest disturbance for wildlife using habitat selection theory

Isodar theory can help to unveil the fitness consequences of habitat disturbance for wildlife through an evaluation of adaptive habitat selection using patterns of animal abundance in adjacent habitats. By incorporating measures of disturbance intensity or variations in resource availability into fitness-density functions, we can evaluate the functional form of isodars expected under different disturbance-fitness relationships. Using this framework, we investigated how a gradient of forest harvesting disturbance and differences in resource availability influenced habitat quality for snowshoe hares (Lepus americanus) and red-backed voles (Myodes gapperi) using pairs of logged and uncut boreal forest. Isodars for both species had positive intercepts, indicating reductions to maximum potential fitness in logged stands. Habitat selection by hares depended on both conspecific density and differences in canopy cover between harvested and uncut stands. Fitness-density curves for hares in logged stands were predicted to shift from diverging to converging with those in uncut forest across a gradient of high to low disturbance intensity. Selection for uncut forests thus became less pronounced with increasing population size at low levels of logging disturbance. Voles responded to differences in moss cover between habitats which reflected moisture availability. Lower moss cover in harvested stands either reduced maximum potential fitness or increased the relative rate of decline in fitness with density. Differences in vole densities between harvested and uncut stands were predicted, however, to diminish as populations increased. Our findings underscore the importance of accounting for density-dependent behaviors when evaluating how changing habitat conditions influence animal distribution.

Transformation of abandoned farm fields into coniferous plantations: Is there enough vegetation structure left to maintain winter habitat of snowshoe hares?

Natural forests will likely be unable to sustainably fulfill society needs for wood fibers and intensively managed plantations could be an alternative source of timber in the future. Abandoned farm fields are often targeted for conversion, as they are already disturbed sites; however, they also represent high-quality habitat for species such as snowshoe hares ( Lepus americanus Erxleben 1777), a keystone mammal in the boreal forest. We evaluated the effect of converting abandoned farm fields (n = 22) to conifer plantations (n = 19) on habitat use by snowshoe hares, using pellet counts and snow-tracking surveys. Both survey techniques yielded similar results: winter habitat use by hares is mostly affected by vegetation cover rather than habitat type. In the short term, plantations do not offer less protective cover than the one found in abandoned farm fields. However, upon reaching a certain height (≥7 m), plantations are mechanically pruned and lose their protective quality. Promoting silvicultural techniques that maintain lateral cover beyond a critical threshold (70%) could preserve the quality of hare habitat for an extended proportion of rotation time of the plantation.

Using faecal pellet counts along transects to estimate quokka (Setonix brachyurus) population density

A study was conducted to determine the validity of using transect counts of faecal pellet groups to estimate population densities of a threatened, macropodid marsupial – the quokka (Setonix brachyurus (Quoy & Gaimard, 1830)). Mark–recapture estimates of population density were regressed against counts of faecal pellet groups at six sites with and three sites without fox control within the northern jarrah forest of Western Australia. Significant linear relationships were found between population density and pellet counts for all sites (r2 = 0.56, P < 0.02) and when all unbaited sites were excluded (r2 = 0.98, P < 0.01). We suggest that this method could be used for broad-scale monitoring of this threatened species.

Habitat preference of Canada lynx through a cycle in snowshoe hare abundance

We assessed habitat preference of a lynx (Lynx canadensis) population through 8 years of a snowshoe hare (Lepus americanus) cycle. Seventy-four percent of our southern Yukon study area was approximately 30-year-old regenerating forest resulting from a large wildfire. The study area was not trapped and lynx density was very high compared with other populations in North America. Contrary to our prediction, there was no discernable shift in habitat preference through the hare cycle; however, our habitat types were coarsely mapped and our radiolocations relatively inaccurate. Lynx may have altered their habitat preferences at finer scales (for patches <2 ha). Lynx showed strong preference for regenerating habitats over mature white spruce (Picea glauca) and alpine–subalpine. Lodgepole pine (Pinus contorta) dominated regenerating stands were preferred over spruce–willow (Salix spp.) stands of equal age. Riparian willow stands were also preferred over mature spruce forest and alpine. Lynx used riparian willow stands more in winter, but we detected no other shifts in habitat preference between snow-free and winter periods. We did not detect any difference in habitat preference between sexes. Independent juveniles made greater use of mature forest and perhaps riparian willow than adults, but no other difference in preference between the two age groups was noted. Lynx preference for regenerating habitat over mature forest suggests that burns will benefit lynx, especially if the regenerating community is pine dominated. Logging will only likely provide similar benefits if a dense pine understory results, which is unlikely in intensively managed stands. The suppression of forest fires in recent decades may have contributed to the decline of lynx numbers in the south of their range.

Estimating low-density snowshoe hare populations using fecal pellet counts

Snowshoe hare (Lepus americanus) populations found at high densities can be estimated using fecal pellet densities on rectangular plots, but this method has yet to be evaluated for low-density populations. We further tested the use of fecal pellet plots for estimating hare populations by correlating pellet densities with estimated hare numbers on 12 intensive study areas in Idaho; pellet counts from extensive transects (n = 615) across northern Idaho enabled rectangular plots (0.155 m2) to be compared with paired small (0.155 m2) and large (1 m2) circular plots (metre-circle plots). Metre-circle plots had higher pellet prevalence, lower sample variance, and lower estimates of pellet density than the other plot types. Transects comprising circular plots required less establishment time, and observer training reduced the pellet-count bias attributable to plot shape. The number of hares occupying intensive study sites was correlated with pellet density on all plot types, but rectangular plots provided a slightly closer linear fit to hare numbers than did metre-circle plots. The relationship between pellet density and hare number may have been curvilinear rather than linear, but linear and nonlinear models provided similar numerical estimates over much of the range of pellet densities. These results indicate that pellet counts are a robust estimator of hare numbers in low-density populations, and that metre-circle plots represent an improvement over standard rectangular plots in terms of unbiased pellet counts, sacrificing little predictive power. We recommend using pellet counts in metre-circle plots for estimating populations of snowshoe hares in their southern distribution.

Estimating snowshoe hare population density from pellet plots: a further evaluation

We counted fecal pellets of snowshoe hares (Lepus americanus) once a year in 10 areas in the southwestern Yukon from 1987 to 1996. Pellets in eighty 0.155-m2 quadrats were counted and cleared each June on all areas, and we correlated these counts with estimates of absolute hare density obtained by intensive mark–recapture methods in the same areas. There is a strong relationship between pellet counts and population density (r = 0.76), and we present a predictive log–log regression to quantify this relationship, which improves on our previously published 1987 regression, particularly at low hare densities. The precision of density estimates can be improved most easily by increasing the number of sets of quadrats in an area (one set = 80 plots), rather than increasing the number of plots counted within one set. The most important question remaining concerns the generality of this relationship for snowshoe hares living in other habitats in the eastern and southern portions of their geographic range.

A geographic analysis of snowshoe hare population demography

Snowshoe hare (Lepus americanus) populations across northern Canada and Alaska undergo 8- to 11-year cycles in numbers, but population trends in southern Canada and the contiguous United States are apparently either weakly cyclic, irruptive, or largely stable. Although the demographic attributes (population density, reproductive rates, and survival rates) of northern and southern hare populations should differ considerably to account for such differential trends, to date limited rangewide analyses of hare demography have been undertaken. I reviewed hunter harvest estimates and basic demographic attributes for hare populations across North America, and assessed the effect of latitude, longitude, and latitude × longitude interaction on the magnitude and variation of such attributes. Harvest estimates tended to be synchronous across the Great Lakes area and along the St. Lawrence River, whereas they varied more dramatically along a westward gradient and in hare populations suspected of being cyclic. Hare densities tended to be higher among apparently noncyclic than cyclic populations at numerical lows, as well as among studies where hare numbers were apparently increasing. Populations from northern latitudes tended to breed later than those in the south, and females from western areas produced larger, but fewer litters, than those from eastern populations; total productivity was similar across geographic areas. Survival rates for both adult and juvenile hares were higher in increasing populations than in decreasing populations. Survival of adults also decreased along a northwest gradient, whereas that of juveniles decreased across a western gradient and with longitude, was lower in apparently noncyclic populations, and was also lower in populations in areas of high lynx (Lynx canadensis) densities. I conclude that, although disparity clearly exists in the trends of various hare populations, the absence of strong latitudinal gradients in demographic attributes fails to support the hypothesis that differential survival/predation is responsible for the regional differences in numerical trends.

Winter diet of marten during a snowshoe hare decline

We examined the winter diet of marten (Martes americana) from northern (65–67°N) and southern (60–62°N) regions of the western Northwest Territories from 1988–1989 to 1993–1994 during a decline in snowshoe hare (Lepus americanus) abundance that started in 1990. We used 4256 marten carcasses collected from trappers to examine changes in diet, productivity, age and sex structure of the harvest, and body and reproductive indices. Arvicoline rodents formed the greatest proportion (41–95% occurrence of total prey items) of the annual winter diet in both regions and snowshoe hares constituted 1–39% of prey items. Snowshoe hares constituted 3–64% of the diet when expressed as biomass. Dietary proportions of arvicolines increased and snowshoe hares decreased with time in the northern region but not in the southern region. Female marten took proportionately more arvicolines and males took more snowshoe hares. Juvenile marten took proportionately more snowshoe hares, while adults took more arvicolines. The proportion of juvenile marten in the harvest declined in both regions between 1991–1992 and 1993–1994. The ratio of juveniles to adult females in the harvest also declined with time in the southern region but not in the northern region. The amount of omental fat declined with time for most age and sex classes. Ovulation rates (as determined by counts of corpora lutea) declined with time among yearlings, and among adults from the southern region but not in the northern region. In utero litter size did not change. We suggest that the snowshoe hare population cycle has a significant impact on marten populations in the northern boreal forest.