New deer-counting formula more reliable
9/21/2003Projecting the number of deer in a state is something akin to predicting the path of a hurricane - it is an inexact science, but one that is improving with better data and diagnostic tools.
A demonstration of improvements in both arenas came last week with both federal meteorologists' ability to track and forecast Hurricane Isabel, and with the Ohio Division of Wildlife's ability to estimate deer numbers.
It is the latter topic, of course, that is of concern here and it turns out that the Buckeye State has been harboring a significantly higher number of deer than previously thought.
Last year the state was said to harbor a record 575,000 deer, based on projections from a formula that had its roots in the 1960s.
But a recalculation of that number using an improved formula puts last year's record-size herd in the neighborhood of 685,000. The 2002 all-seasons hunting bag, determined by actually counting deer checked in, as required by law, was a record of 204,652.
In addition, the forecast size of the pre-hunting Ohio herd this fall is almost as high as a year ago: 681,000 deer.
The Ohio Division of Wildlife is predicting an all-seasons bag of 185,000 to 195,000 deer, assuming normal weather and numbers of hunters.
“Our previous model was based on a formula that used data primarily from the deer-gun hunting season,” explained Dave Risley, executive administrator of wildlife management and research for the division.
“Hunting methods have changed with the times, and steadily growing numbers of successful archery and muzzleloading hunters have caused us to revise our method of estimating the deer population.”
The older model for estimating deer numbers was OK for monitoring trends in populations, up or down, but it underestimated actual numbers.
The new, much higher estimates do not mean any immediate changes in deer hunting regulations, said Mike Tonkovich, a wildlife division biologist.
But the new formula, called an accounting-style population model, will give deer biologists a clearer picture of where deer numbers are headed, even county by county.
The latter will be particularly true, Tonkovich said, under abnormal circumstances - from unusual weather to a sudden swing in the number of hunters afield - or in accommodating changes in hunter behavior. He explains it this way:
The older harvest-driven model was based on the buck kill during the shotgun season, when, traditionally, 80 per cent of the state's deer harvest occurred.
But over the last 10 years the numbers and success rates of bowhunters and primitive weapons hunters - the latter being principally those using muzzleloading or “black powder” rifles - have increased dramatically.
Nowadays only 60 per cent of the total annual bag comes during shotgun season.
So it is clear that the old gun-season, buck-harvest-based formula now could fail to account for a lot of deer.
Also, the older method was not able to account for unusual conditions - say, very bad weather during gun season, which in turn led to a lower-than-expected bag.
For instance, Tonkovich said, assume biologists expected a bag of 1,000 deer in a given county and, because of bad weather only 300 deer are taken.
That means 700 more deer than expected will move into next year in that county.
The new formula will “carry forward” such surpluses into the next season's management considerations, whereas the old system, based only on harvest, would have assumed the county had far fewer deer than projected and management plans could be adjusted too conservatively.
The new accounting model also includes harvest during the archery and muzzleloader seasons, in addition to the gun season, by county.
It incorporates birth rates as well. Risley said that along with the new model, biologists will increase the number of post-season winter deer surveys to provide a secondary means of estimating deer density.
The deer kill in motor-vehicle collisions and crop-damage culls also is taken into account, along with factors for predation and poaching kills.
In any case, Tonkovich stresses that the annual published deer-herd estimate is an index, a relative and not an absolute number.
It is impossible to count every deer, any more than it is every duck, or walleye, or yellow perch.
The important thing with the new model is having as solid an “opening balance” in the checking account as possible, Tonkovich said.
For if that number is significantly off-base, every other calculation would be off as well. So in arriving at that base or starting figure, “we took a long time.”
Deer densities vary from 25 to 35 per square mile in southeast and east-central regions of the state, and 5 to 10 per square mile in central and western regions.
Perfect hunting weather and unrestricted Sunday hunting last year led to the record bag, and the state deer herd remains high-quality and healthy, the division says.
Testing in 2002 found no evidence in Ohio of chronic wasting disease or tuberculosis - both problems in some states.
The first deer season, archery, opens Oct.4 and continues through Jan.31. A new youth gun-deer season is set statewide for Nov.22-23. The statewide gun season will be Dec.1-7, and the statewide muzzleloader season will be Dec.27-30. A special area primitive weapons hunt for bucks only is set for Oct.20-25 at Salt Fork, Shawnee, and Wildcat Hollow public hunting areas.