October 28, 2010
There has long been an uneasy truce between wildlife biologists and hunters. Both continually look for answers as to why deer do what they do. And both prefer those explanations to be simple. But each faction is often distrustful of the other's explanations.
Biologists dismiss long-held conventions because they lack scientific data to back them up. Meanwhile, hunters criticize the scientists for lacking practical field experience and good, old-fashioned woodsmanship.
We'll use two long-held beliefs as an example. It was once widely accepted that an individual deer would spend its entire life within an area of roughly one square mile. Conventional wisdom also held that as soon as the guns start going off, those same deer would take off for parts unknown. That also applied to bowhunting, though to a lesser extent.
I'm not sure where that square mile figure came from, but 25 years ago we all believed it. As for the dispersal, some of it was common sense and some was attributable to our own arrogance. It stands to reason deer will try to avoid hunting pressure. And if we stealthy woodsmen can't find them, they must not be there anymore. That is what we believed -- until the radio collar proved us wrong.
When biologists starting fitting radio collars around the necks of deer, we gained vast new insight into their behavior and movement patterns. I assisted a fellow grad student with one study that showed deer -- particularly does -- had much smaller home ranges than we once thought. In good habitat, some deer might spend as much as 90 percent of their time in less than 50 acres.
Of greater interest to hunters were later studies on how deer reacted to hunting pressure.
The early ones were done without radio collars. Researchers simply put hunters inside an enclosure with a known number of deer and recorded success rates and the number of deer sightings. Both quickly tapered off with increased hunting pressure. But the deer didn't leave. They couldn't.
Subsequent radio collar studies conducted on free-range deer found similar results. As hunting pressure increased, success rates and deer sightings dwindled. And despite the fact the deer were free to leave, they didn't. They stayed largely within the same home range but moved less, particularly during daylight hours.
More recently, GPS collars are replacing radio telemetry equipment. Instead of a wildlife technician riding around with a hand-held antenna and recording data twice a day, the GPS collars continuously transmit precise data on location and activity to a desktop computer via satellite.
Gabriel Karns and several other researchers recently used GPS collars to look at the impact of hunting pressure on buck movement at Chesapeake Farms in Maryland. Not surprisingly, they found adult bucks reduced movement during twilight hours and decreased activity during the day once hunting began; and that home range and core area size did not change significantly.
However, they also observed that more intense hunting pressure on surrounding properties caused deer to use the Chesapeake Farms property as a refuge, even though there was also hunting on the farm property. They suggested this showed a "pseudo-refuge" effect. Up to a certain level, the only effect of hunting pressure was reduced buck movement within core areas and home ranges. Past a certain level, deer actually shifted their range from areas of high hunting pressure to areas of lower hunting pressure.
Because the neighboring deer were not collared, the researchers could not determine whether the immigrating deer were actually leaving their traditional home ranges or merely shifting core areas within them. Regardless, Karns concluded, "If you can create a hunting pressure differential, you get a net immigration of deer."
It should be noted the study was conducted around and during the two-week shotgun season. While bowhunting pressure is considerably less, it is hunting pressure nonetheless and will have some effect on deer behavior.
Plug this fresh insight into what we already know about home range size and deer movement and a picture starts to develop. By creating a pressure differential, you can turn your happy hunting grounds into a huntable refuge.
You can do this in several different ways, depending on local circumstances and conditions. If your neighbors gun hunt, you can simply limit your property to bowhunting. If you don't own or lease property, seek out areas where firearms hunting is limited or prohibited. Even within bowhunting-only areas, you can exploit a pressure differential by limiting the amount of hunting pressure your target areas receive.
Hunting pressure differential can be adjusted to a very fine level, including small properties and even single stand locations. In fact, many of you probably already do so simply by rotating stands or holding certain stands in reserve for "special occasions." It may be a very subtle differential, but if you're going after a mature buck, it is often the subtle things that make a noticeable difference.
All of us -- biologists and hunters alike -- knew hunting pressure influenced deer movement. We just didn't know exactly how. We probably never will, either. But thanks to research and field observations, we now have a much better understanding.