Supranivean travel of snowshoe hares on Niwot Ridge Marieta Bialek EBIO 4100 Winter Ecology Spring 2012

Layout of Presentation Introduction Background Snowshoe Hare, Relevance to Winter Ecology, Question Hypotheses Methods Results Discussion Key References

Snowshoe Hare Lepus Americanus of the Rocky Mountains Hare populations more heterogeneous in rocky mountain regions Important Habitat: Lodgepole pine forests and engelmann spruce-subalpine fir forests Threat: Climate change affecting precipitation (snow) and thus biotic communities (Ellsworth, Reynolds 2006)

Relevance to Winter Ecology In winter hares are main prey biomass for many predators Consume a large amount of woody forage all winter Constantly deposit fecal pellets on the surface which eventually reach the forest floor, affecting soil nutrient content Snow conditions (i.e., depth and density) play an important role in the types of predators that hunt hares during the winter Thus may influence predation risk (Ellsworth, Reynolds 2006) Coevolution with the lynx for snow travel – morphological adaptations

Cont. Snow Morphological adaptation to snow: feet Mechanism: Reduced snow loading facilitates movement over snow

Question Does the top layer of snow density significantly limit the travel of snowshoe hare? How does the stride length effect the depth of the track? How does the density of the snow effect the depth of the track? Is there a significant relationship between the density of the snow and stride length? Null Hypothesis: There is no significant relationship between stride, density of snow, and the depth of a traveling hare track

Multiple Hypotheses and reasoning H1 The depth of the track will increase as stride increases, due to force pushing down on snow to jump further H2 Tracks will be deeper at lower densities because at lower densities snow is harder to move through H3 Strides will be longer at higher densities because less energy is lost to the snow and more can be used for the jump

Methods Materials: flotation, snow density tools (from the snow pit kit) Two locations: Up Niwot Ridge Road between MRS and Cable Gate Around the mountain research station Recorded measurements after fresh snowfall on two different days Only recorded tracks of larger hares Picked tracks between areas of forage where hare clearly has a destination, moving swiftly For each track: Measure stride, depth (hind feet), density of top layer

Limitations in the methods Limitations Uncertainty how long after the snowfall the hair traveled through over snow, in which conditions could have changed Only two days of measurements, after it snowed Time (more time, more data, greater range of densities to work with) Little variation in snow density (range g/cm)

Results

Hypothesis 1 Figure 1 How length of stride affects depth of track

Hypothesis 1 Figure 1: Plot of all tracks, depth as a function of stride R squared = P-value = Figure 2: Only strides > 85 cm R squared = P-value = Not significant

H2 Figure 3 R Squared = P-value = Not significant

H3 Figure 4 R squared = P-value = Not Significant

Discussion possible conclusions Figure 1: Slower = shorter stride, more time to sink Data not significant, because not a significant range of densities: need more data

Revisit Hypothesis 1 Figure 1 How length of stride affects depth of track

Implications Top layer conditions do not have a significant effect on snowshoe hare travel – they are just too well adapted Perhaps the snow conditions are more important in how they effect supranivean predators Snow conditions (i.e., depth and density) play an important role in the types of predators that hunt hares during the winter. Thus may influence predation risk (Ellsworth, Reynolds 2006) Future study: same experiment for hare predators

Future Research Over a longer period of time, conditions can be assessed, (amount of last snowfall (cm), type of snow (i.e. sugar snow, crust, wet melt, powder) Effect of snow conditions on snowshoe hare travel – what conditions are optimal for the snowshoe hare? Can they move faster on a solid crust than on fresh snow? (measure speed) Studies have shown that hare travel is more efficient on snow than bare ground…

Key References Attributes of forest strips used by snowshoe hare in winter within clear-cut boreal landscapes. Potvin, François, Normand Bertrand, Jean Ferron Canadian Journal of Forest Research, 35:(10) Ecology of Snowshoe Hares in the Central Rocky Mountains. Dolbeer, Richard, William R. Clark The Journal of Wildlife Management, 39(3): Effect of moonlight on winter activity of snowshoe hares. Gilbert, B., Stan Boutin Arctic and Alpine Research, 23:(1) methods The Geometry of a population cycle: a mechanistic model of snowshoe hare demography. Kingi, Aaron and William Schaffer Ecology, 82(3): Snowshoe Hare (Lepus americanus): A technical conservation assessment. Ellsworth, Ethan and Timothy Reynolds USDA Forest Service, Rocky Mountain Region. Key article

Questions?