July 02, 2012
One of the greatest advancements in the wildlife management field was the advent of radio telemetry equipment. This is where biologists put radio collars on deer and track them with the help of a receiver tuned to a specific frequency.
The technique in finding a radio-collared deer is relatively simple: You point your antenna in the direction of the loudest "beep," take a compass reading, and draw a line on your map. Then you travel around to another location and repeat the same process. Where the two lines intersect is the location of the deer.
With the advent of cellular phone and GPS technology, biologists can now collect thousands of location points from the collars they put on deer. This fine-scale location data is much more precise, and not collecting enough information is a thing of the past. Biologists are now fine-tuning and analyzing home-range data to identify a buck's specific "core" area — the place where he spends 50 percent or more of his time.
Using trail camera data, Dr. Grant Woods believes better food and habitat equates to smaller home ranges. In other words, big-timber bucks will have a larger home range than bucks living in agricultural lands. Additionally, it's important to remember all bucks are individuals. Often, biologists report averages on home range size, when certain bucks can be all over the map. Hunting these bucks is troublesome, and it's likely they are more susceptible to other hunters.
Years ago we believed that once a buck was 2½-years-old, his home range was static or firmly established. New data indicates this may not be true for all bucks. Research has shown 63 percent of adult bucks take off on excursions outside their home range, specifically during the rut. Why this happens, no one knows.
Dr. Mark Conner, from Chesapeake Farms in Maryland, has performed some groundbreaking home-range characteristics and buck-movement studies. Conner and his graduate students from North Carolina State were trying to figure out the sporadic movements of bucks during the hunting season by using GPS collars to follow the deer. For whatever reason, during the rut, many of the bucks they were following just packed up and left their established home range. Then, within 24 hours, they returned.
As Woods says, "Since a substantial percentage of mature bucks make these trips outside of their core area during the rut, many don't know the likely locations of danger as well as they do in their core area. With people, accidents usually happen when we are doing something outside our routine. When bucks take these excursions outside their normal core areas they expose themselves to dangers€¦arrows!"
Why these short-term excursions of bucks occur is a mystery. But, Conner's work indicated 40 percent of his bucks moved out of their home range during the pre-rut time period (October 15-November 4), while 58 percent moved during the primary rut (November 5-25).
Interestingly, the bucks that took off during the pre-rut moved primarily at night. In fact, only 30 percent moved during the daytime hours, whereas during the rut, 73 percent of the bucks moving did so primarily during the day. Most likely, this has to do with thermoregulation or daytime temperatures. In other words, since the bucks during the pre-rut had their winter coats on, it was simply more comfortable for them to travel during cooler, nighttime hours.
Although you may think these movements were simply random, Conner believes they are made on purpose. Exactly why this occurs, he doesn't know. But they most likely had to do with exploratory or actual breeding urges. One buck moved three separate times. From September 7 to 23, the buck was sedentary, and then he took off for parts unknown. From October 20 to November 18, the buck was stagnant. Then, like before, he took off for the second time. Finally, his third home-range shift occurred December 27 through 29. Because ample agricultural food sources were readily available to his bucks, Conner doesn't believe it was entirely food or habitat related.
This data led me to micro-analyze Conner's data. We all know deer movements throughout their home range are dynamic. For example, deer will frequent one area more than others during specific times of the year. We see this when they change their feeding or bedding areas because of habitat changes, hunting pressure, predation, weather, or a host of other factors. Although this may not be true for every deer herd, I've come to believe deer will frequently move their core area — possibly up to five times — during the hunting season.
The first change in core area occurs when a buck sheds his velvet. This is when hormones turn bucks into different animals. Hunters see this in early September when they pin down a buck, only to be humbled by hardly ever seeing the buck again once he sheds his velvet. The second change in core area occurs when the acorns start to drop. Whether it's a boom or a bust year, these little sweet nuts move deer to concentrated areas. Although not always the case, most white oaks drop their nuts earlier than red oaks (exceptions include burr and post oak). Thus, in some areas you can further split this core area into two periods (white and red oak locations).
Once the acorns are depleted, a deer's core area switches over to agricultural crops such as when corn and beans are maturing. Since this will be the last chance to acquire any fat storage for the winter, deer cling to these areas. The acorn and crop core areas reflect what Dr. Woods was saying about highly preferred habitats.
Then the rutting time period comes into play, during which deer move their core area around what may be called "breeding areas." This also correlates to when trees lose the majority of their leaves, often referred to as the "leaf-off" period. If there is a core area that consists of deer breeding, this may explain why Conner's collared deer made excursions completely out of their home range during the rut. In fact, on three occasions Conner's bucks made repeat excursions to the same locations during the rut. Or maybe this is one reason why so may scrapes and rubs are located in the exact same area from year to year.
The last change in core area has to do with the post-rut or winter cover. At this time of year, screening or thermal cover are paramount in conserving needed body fats and energy. Thus, daytime movements are much more predictable.
Please note, this information about dynamic core areas may sound valid, but it is not proven. I'd be neglectful if I didn't mention this is simply my interpretation of certain deer herds.
The takeaway message for a bowhunter is simple: We shouldn't be afraid to move our treestand or camera locations to pick up where the bucks have shifted their core areas.