Effect of winter phases on Survival of Subnivean Mammals

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

2. The calender defines winter as a 90 day period between December 21st and March 21st, however it does not make sense to think of winter in this way in regard to organisms. Climatic factors rather than the position of the sun dictate how organisms experience winter. The calender defines winter as a 90 day period between December 21st and March 21st, however it does not make sense to think of winter in this way in regard to organisms. Climatic factors rather than the position of the sun dictate how organisms experience winter.

3. So, given these different phases of winter… Something we have already gone over But I would like to refresh is how temperature changes with depth in the snowpack…So, given these different phases of winter… Something we have already gone over But I would like to refresh is how temperature changes with depth in the snowpack…

4. So I took a look at the effect of these winter phases on the meadow vole, a small overwintering mammal known to make subnivean tunnels. So I took a look at the effect of these winter phases on the meadow vole, a small overwintering mammal known to make subnivean tunnels.

5. Reradiation frosts are when cold clear windless nights radiate off a lot of heat into space and can freeze the ground. Saturation of soil can flood burrows either drowning the subnivean creatures or forcing them to the surface exposing them to other threats like cold temperatures, wind, and predation.Reradiation frosts are when cold clear windless nights radiate off a lot of heat into space and can freeze the ground. Saturation of soil can flood burrows either drowning the subnivean creatures or forcing them to the surface exposing them to other threats like cold temperatures, wind, and predation.

6. Effect of min temps and precip on meadow voles This graph shows very nicely the effect of temperature and precipitation in the form of rain upon meadow vole mortaility. In Ontario Canada a total of 7 voles were placed in a cage and exposed to these conditions during a 7 day period in October. During a period of heavy rains and temperatures around zero two voles died. Two days later when the temp dropped to -6 celcius there was only a trace amount of pricip but the remaining five voles diedThis graph shows very nicely the effect of temperature and precipitation in the form of rain upon meadow vole mortaility. In Ontario Canada a total of 7 voles were placed in a cage and exposed to these conditions during a 7 day period in October. During a period of heavy rains and temperatures around zero two voles died. Two days later when the temp dropped to -6 celcius there was only a trace amount of pricip but the remaining five voles died

7. Snow density is directly related to its ability to act as an insilator which I will explain further in just a second.Snow density is directly related to its ability to act as an insilator which I will explain further in just a second.

8. It is seen here that the thermal index, which is a combination of snow depth and snow density, has a direct effect on vole mortality. We can see that a thermal index below 100 is unsuitable for vole survival. Mortailities occur frequently when the thermal index is below 100 and not at all when it is above 100.It is seen here that the thermal index, which is a combination of snow depth and snow density, has a direct effect on vole mortality. We can see that a thermal index below 100 is unsuitable for vole survival. Mortailities occur frequently when the thermal index is below 100 and not at all when it is above 100.

9. Firnification is basically a process of freeze thaw that metamorphoses snow grains into larger granuals. This not only allows more light into the subnivean, increasing further melting but also increases infiltration into the snow due to the larger grain sizes. This has the effect of threatening the subnivean tunnels of the voles.Firnification is basically a process of freeze thaw that metamorphoses snow grains into larger granuals. This not only allows more light into the subnivean, increasing further melting but also increases infiltration into the snow due to the larger grain sizes. This has the effect of threatening the subnivean tunnels of the voles.

10. This period again has the effect of making it difficult for the voles to find shelter.This period again has the effect of making it difficult for the voles to find shelter.

11. Weasels are a primary predator of meadow voles and also overwinter in the subnivean. Also in a study involving the choice of subnivean entrance point it was shown that weasels will choose entrance points with higher prey density. (and of course their primary prey during the winter are voles). It is uncertain how the weasels locate the voles but it is thought to be auditory, olfactory, or both. Either way it has been shown that they are excellent at locating prey in the subnivean. Weasels are a primary predator of meadow voles and also overwinter in the subnivean. Also in a study involving the choice of subnivean entrance point it was shown that weasels will choose entrance points with higher prey density. (and of course their primary prey during the winter are voles). It is uncertain how the weasels locate the voles but it is thought to be auditory, olfactory, or both. Either way it has been shown that they are excellent at locating prey in the subnivean.

12. Given this information I would like to propose a few possibilities that could be looked into in the future. Given this information I would like to propose a few possibilities that could be looked into in the future.