DComeaux wrote:SpinnerMan wrote:Check the snow line.
How many years following, lets use 1980, do you think you'd find "sustained" snow cover within the area I've marked on your map during duck season?
nsm_depth_current_National.jpg
Sustained for how long?
The depth matters. My chart only has inches of snow over most of Canada. Your figure doesn't distinguish between an inch of snow or a foot of snow. Having an inch is very different than having a foot.
Your figure shows snow over all of Iowa and northern Missouri, but little in the Dakotas in Christmas 1997. If that was a foot of snow over Iowa and northern Mo, that will move birds. If it's an inch, it won't.
The species matters as well. The snow doesn't have any impact on divers. It doesn't have any effect on species that don't eat on dry land. It also doesn't have effect on species that don't include northern regions in their wintering range.
My point is that need to consider more than just temperature. Both snow and temperature have an impact.
But yes, you need to look at the average number of days that there is snow cover in that region above a certain depth. I'll bet the number of mallards you see is correlated with that. Snow moves birds
too is my point. And it seems, no scientific info, just how it seems to me, that the number of days where we get the snow we need is less than it used to be.
DComeaux wrote:From my recollection, major fronts weren't considered near as important in years past as they are today.
My suspicion is that you are probably correct. I believe part of the reason is that the snow pattern has shifted. But there are other things like decades of high hunting pressure on all birds that go south versus staying north were the season is closed. More open water up north. More food available up north (not just flooded corn, but all sources which I think are far bigger). To over come these other factors that have shifted away from your favor, you need more snow and more hard cold which we seem to have less of at least at the times it matters.
Just many factors to consider. All of them seem to be shifting unfavorably for hunting hardy species at the southern edge of their winter range.