Effect of winter phases on Survival of Subnivean Mammals by KWo6W5

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									   Effect of winter phases on
Survival of Subnivean Mammals
               Kevin Kohler
            Winter Ecology 2008




    Mountain Research Station, University of Colorado, Boulder
                   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
What types of conditions and threats do these
    different phases of winter pose upon
    overwintering subnivean mammals?

             Mean Temperature vs. Height




         Colder                      Warmer
Meadow Vole Distribution
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
    Effect of min temps and precip on meadow voles


Min Temps


                                         Two Deaths


Precip                                          Five Deaths
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
                Deaths
Thermal Index
                         Snow Depth
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
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
              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
              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.
                                    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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