ORIGINAL: M.Hensler/PA
RSB, could you pleas answeremy questions above. What environmental factors are we talking about here? Just curious here.
I’m not sure what questions you are referring to unless they are the ones I already answered. I didn’t really talk much about the variables of the environmental factors though so I will do that now.
The annual post season deer populations are greatly influenced by the previous year’s food and winter conditions. When you have a fall with little or no mast crop the deer don’t put on as much weight before the winter sets in. So that alone can be an environmental influence that can and will affect the next year’s deer population. I will explain more about how that actually affects deer populations a bit later in this post.
The next environmental factor that has a serious impact is the depth of the snow cover and the length of any adverse winter snows. In the northern tier and mountainous regions elsewhere across the state once the snow gets deep in the winter the deer are forced off of the ridges and plateaus and into the river and creek valleys to what are typically referred to as wintering grounds. At this point there can be all kinds of good browse or food on the higher ground but it isn’t of any value to the deer because they can’t get to it.
When that happens and deep snow cover locks the deer into primary wintering grounds the deer will seriously impact the available food supply. While that is happening the deer are all losing weight and sometimes that weight lose is significant. If a deer loses over about 1/3 of its body weight it is probably going to die even if the snows disappear and the deer can now find all the food it wants.
But, the real problem is not with winter mortality of the deer, which generally doesn’t happen in great numbers. The real problem comes from reduced fawn survival rates the next spring. When the doe doesn’t have enough high quality food through the winter and the spring she produces an under weight fawn and that fawn then has little chance of surviving after it is born.
To show how much of a factor the poor winter food conditions can have fawn survival I am going to provide some data from a research project in Michigan that was designed to measure the affects that the nutrition of the doe would have on fawn survival rates. To do that they provided various amounts of natural food supply to captive deer and I am going to show the fawn mortality percentages for each group of deer.
Food value……………………………………… ………….fawn mortality
Good winter to good & moderate in spring……………………….12.2 %
Poor winter & good spring……………………………………†¦...35.1 %
Poor winter & moderate spring……………………………………53 .7 %
Poor winter & poor spring……………………………………†¦â€¦92.9 %
These fawn mortality figures are only including loses from nutritional factors and don’t even include any predation. So through in some normal predation and it isn’t too hard to see how much of an affect the length and severity of the winter can have on the next year’s fawn population. If you have two or three years of these harsh environmental years in a row you start getting into a compounding factor and the deer populations drop very rapidly.
I believe that is exactly what we just experienced here in the northern tier and across our more mountainous regions of the southern tier. We just had a year with a good mast crop followed by a more mild winter so I suspect we will also see some deer population improvement this year, but we also have to remember that it was compounding of bad years that got us to the low level and it will take a compounding of years to fully recover from the lean year.
Think of it this way; half of those fawns that died within a few days of being born during the previous three years were button bucks. You will never see nor harvest one of them though because they died soon after being born. The other half were doe fawns and they will never be seen or produce a fawn because they died soon after they were born. The bottom line is that you have to have good fawn recruitment if you want good deer numbers in the future. To have good fawn recruitment you have to have good habitat, but it isn’t even enough to have good habitat unless it is also where the deer need it during the harshest of winter conditions.
Most of those environmental factors we can’t control so all we can do is understand that there will always be some major fluctuations in deer populations resulting from the variables of the environmental factors.
Some things in both life, as in nature, we just have to accept while trying to make the best of them by learning to understand and expect them.