Supranivean travel of snowshoe hares on Niwot Ridge

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

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

3. Snowshoe Hare LepusAmericanusof 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)

4. 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

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

6. 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

7. 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

8. 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

10. 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 0.079 g/cm)

11. Results

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

13. 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

14. H2 Figure 3 R Squared = 0.1201 P-value = 0.10280 Not significant

15. H3 Figure 4 R squared = -0.05885 P-value = 0.6896 Not Significant

16. 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

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

18. 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

19. 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…

20. Key References • Attributes 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 (Lepusamericanus): A technical conservation assessment. Ellsworth, Ethan and Timothy Reynolds. 2006. USDA Forest Service, Rocky Mountain Region. • Key article

21. Questions? Questions?