Supranivean travel of snowshoe hares on Niwot Ridge

Marieta BialekEBIO 4100Winter Ecology Spring 2012

Layout of Presentation

IntroductionBackground

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.

SnowMorphological 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

H1The depth of the track will increase as stride increases, due to force pushing down on snow to jump further

H2Tracks will be deeper at lower densities because at lower densities snow is harder to move through

H3Strides will be longer at higher densities because less energy is lost to the snow and more can be used for the jump

MethodsMaterials: 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

LimitationsUncertainty 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 0.079 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 = 0.07492

P-value = 0.1589

Figure 2: Only strides > 85 cm

R squared = 0.03066

P-value = 0.2808

Not significant

H2

Figure 3

R Squared = 0.1201

P-value = 0.10280

Not significant

H3Figure 4

R squared = -0.05885

P-value = 0.6896

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 ReferencesAttributes of forest strips used by snowshoe hare in winter within clear-cut boreal landscapes. Potvin, François, Normand Bertrand, Jean Ferron. 2005. Canadian Journal of Forest Research, 35:(10) 2521-2527

Ecology of Snowshoe Hares in the Central Rocky Mountains. Dolbeer, Richard, William R. Clark. 1975.The Journal of Wildlife Management, 39(3): 535-549

Effect of moonlight on winter activity of snowshoe hares. Gilbert, B., Stan Boutin. 1991. Arctic and Alpine Research, 23:(1) 61-65

-methods

The Geometry of a population cycle: a mechanistic model of snowshoe hare demography. Kingi, Aaron and William Schaffer. 2001. Ecology, 82(3): 814-830

Snowshoe Hare (Lepus americanus): A technical conservation assessment. Ellsworth, Ethan and Timothy Reynolds. 2006. USDA Forest Service, Rocky Mountain Region.

Key article

Questions?

Questions?