Monday, October 26, 2009

OPINION: Counting Deer in Wisconsin

How many deer are in Wisconsin? It depends on who you ask. From a recent story:

A debate continues to rage between Wisconsin hunters and the Department of Natural Resources over the true number of deer in the state. Hunters have repeatedly argued the deer population is dropping. The DNR counters saying there are too many deer in Wisconsin and the agency is studying a plan to extend the deer hunting season.

The debate is not new. What is new is some vehicle collision data that can be brought to bear on the question.

Now, hunters say they have the proof they need, a study that reportedly shows car-deer crashes in Wisconsin has dropped and has been dropping for years. Joe Terrien of MJ Collision Center in Bellevue has seen the numbers drop first hand. "Six years ago, we saw at least on deer hit a day. Now we're seeing two a week."

A collision data seems like a good source of data, at least at the level of a township. But does this hold up statewide?

Data from the Department of Transportation seem to confirm the drop. In 2003, a peak year according to the DOT there were more than 20 thousand car deer crashes reported by the State Patrol. Since then, the numbers are trending lower.

You can look at the 2008 DoT Report here. I do not think there is much ammunition to give credence to the hunters saying deer populations are down. Here is data showing the relationship between deer-vehicle collisions in Wisconsin from 1993 to 2008. Do you see a trend? Because there isn't one.

What does this mean? The interpretation is ambiguous. If you think deer densities should correlate with deer crashes, you would probably be suspect of the crash estimates, the deer population estimates, or both.

But DNR Spokesperson Kieth Warnke denied the connection between less deer and less car deer crashes."I don't think they reflect a magnitude of change in deer population state wide." Warnke does not deny the numbers in the study. But The DNR and DOT say there could be other factors involved. They give examples such as the bad economy is keeping many drivers off the roads and that may be responsible for the lower numbers.

I don't think Keith is correct here, either. His reasoning is correct, but he seems to exclude fewer deer as an explanation. The ideal approach to estimating population trends should incorporate all sources of data, but of course that is easier said than done.

In the final analysis, the exact number of deer does not really matter. If you are a hunter, what matters is seeing a deer during deer season. If you are a driver, what matters is not colliding with deer. Actual population estimates are nothing more than a tool to help population managers do their job. By this measure, the current SAK model, with all its flaws, does a reasonable job. That is not to say the DNR cannot do better. However, I think this latest salvo from the disgruntled deer hunters association has missed its target.

Source: NBC26

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