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Effect of winter phases on Survival of Subnivean Mammals

Explore the effects of pre-nival, nival, thaw, and post-nival phases on subnivean mammals' survival, considering temperatures, precipitation, and threats in each phase. Learn about the implications on meadow voles and weasels. Discover the challenges and adaptations in different winter conditions. |

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Effect of winter phases on Survival of Subnivean Mammals

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  1. Effect of winter phases on Survival of Subnivean Mammals Kevin Kohler Winter Ecology 2008 Mountain Research Station, University of Colorado, Boulder

  2. Redefining “Winter” Pre-Nival From onset of freezing temperatures until establishment of permanent snowpack Nival From establishment of a permanent snowpack until precipitation no longer falls as snow Thaw The period of snowmelt Post-Nival From the end of snow melt until the chance of frost has passed

  3. What types of conditions and threats do these different phases of winter pose upon overwintering subnivean mammals? Mean Temperature vs. Height Colder Warmer

  4. Meadow Vole Distribution

  5. Pre-Nival Conditions • Re-radiation frosts • Sub-freezing temperatures • Precipitation in the form of rain • Threats • Surface frosts present barrier to burrowing • Saturation of soil threaten burrows • Vulnerability to predation

  6. Effect of min temps and precip on meadow voles Min Temps Two Deaths Precip Five Deaths

  7. Nival Conditions • Precipitation primarily snow • Temperatures primarily below freezing • Threats are reduced • Snow cover provides protection from cold • Temps in subnivean zone stable • Snow density relatively low • Fewer potential preditors

  8. Deaths Thermal Index Snow Depth

  9. Thaw Conditions • Precip primarily rain • Lowest portion of snowpack often saturated • Depth of snowpack reduced • Snowpack undergoes firnification • Threats • Threats resemble pre-nival conditions • Saturation at depth endangers tunnels • Soil very likely to be saturated preventing burrowing • Increased vulnerability to predation

  10. Post-Nival Conditions • Precip mostly rain • Reradiation frost associated with clear nights • Soils wet or saturated • Threats • Protection of subnivean tunnels gone • Burrowing difficult due to frost and saturation • Increased vulnerability to predation

  11. Weasels! • Weasels shown to detect location of prey quite accurately in subnivean • Long thin shape ideal for hunting in subnivean but poor for conserving heat • Weasels are not well adapted to cold variable temps outside of subnivean • Weasels are more sucseptable to avian predators like owls when forced out of subnivean

  12. Hypotheses Weasels are not as effective of hunters outside of tunnels. Weasel mortality is higher during pre-nival, thaw, and post-nival, than during nival.

  13. Citations 1. Arctic and Alpine Research 1991 Effect pf Abiotic Factors on the Overwintering Success of the Meadow Vole vol. 23 pp 45- 52 2. Corn J and M. G. Raphael 1991 Predicting Marten Winter Habitat Requirements Laramie Wyo. pp21 3. S.C. Forrest, M.G Raphael 1989 Winter Resting Site Ecology of Marten in Central Rocky Mountains J Wildl. 53 pp191-196 4. Sherbern and Bissonette 1994 Marten Access Point Use J. Wldl 58(3)

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