October 18, 2011
By Brian Murphy, QDMA
Despite the hot, muggy, “dog days” of summer, July and August are special months for the avid whitetail hunter. Bucks are formed in bachelor groups and are highly visible as they frequent agricultural fields and other high quality food sources. This provides opportunities to asses the number, age and antler quality of bucks in your area. This becomes even more exciting when several quality bucks are sighted on your hunting property. However, this excitement often turns to disappointment and frustration as these bucks magically disappear once the hunting season begins. Did they leave, become nocturnal, or go “underground” as many hunters believe? Thankfully, advancements in technology have enabled wildlife researchers to gain a better understanding of buck movements.
Overview of Maryland Study
Equipped with radio-collars that monitor hourly GPS locations, researchers in Maryland recently discovered many new aspects of buck home range and movements. The study took place at Chesapeake Farms, a 3,300-acre wildlife and agricultural research site on the eastern shore of Maryland owned by DuPont Corporation. The research effort was led by James Tomberlin, graduate student from North Carolina State University; Dr. Mark Conner, Manager of Chesapeake Farms; and Dr. Richard Lancia, Wildlife and Fisheries Program Coordinator with North Carolina State University.
Chesapeake Farms has been managed under Quality Deer Management (QDM) guidelines since 1994 and boasts a fairly balanced adult sex ratio of 1.5 does per buck and an older buck age structure with more than half of all bucks harvested being 3.5 years of age or older. Approximately 50 percent of the property is forested, 33 percent is cropland and the remainder is ponds, marshes, hedgerows, and other areas managed for wildlife and hunting.
From 2003 to 2005, researchers darted 18 bucks that were 2.5 years old or older and equipped them with GPS radio-collars, which recorded their location and movements 24 hours a day, seven days a week. This information was used to determine buck home range size, core area use and excursions, or unusual movements outside of their home range.
Buck Home Range and Core Area Use
Previous studies have revealed significant variation in buck home range size according to age, habitat type, deer density, buck age structure, and more. Therefore, the following results should be viewed with caution, especially if the habitat or composition of your deer herd is significantly different than those on Chesapeake Farms.
In this study, the average home range size of mature bucks was approximately 700 acres. However, taken alone, this information can be misleading. First, there was considerable variation in home range size among individual bucks. This echoes previous studies which suggest some bucks are “homebodies” while others are “travelers.”
Second, there was considerable seasonable variation, with home range size being largest during the rut and smallest during summer. This is not surprising given a buck’s drive to breed as many does as possible during the rut and the lack of need to move during the summer, except between bedding and feeding areas. Many bucks also exhibited significant shifts within their home ranges between seasons. For example, many bucks that spent nearly every moment on or adjacent to an agricultural field during the summer shifted their home ranges a mile or more away during the breeding season. Researchers believed that changes in forage availability was likely responsible for the shift, as agricultural crops at Chesapeake Farms were harvested during early fall and mast crops in nearby hardwood forest areas became available. This could explain why many hunters in agricultural areas don’t see the bucks they watched all summer during the hunting season.
Finally, and perhaps most important to hunters, the average size of a buck’s core area, or where he spent at least 50 percent of his time, was only around 100 acres. Like home range size, core area size also varied seasonally and was largest during the rut and smallest during summer. Surprisingly, during the rut, bucks spent 50% or more time in only 16 percent of their home ranges! Given that their study also confirmed that buck activity was lowest during daylight hours, it is not surprising why many mature bucks seem to disappear during the hunting season.
These findings also stress the need for hunters to identify a buck’s core area - or areas - during the hunting season. This is best accomplished through hunter observations and the use of game cameras. However, just because you took dozens of photos of a particular buck in August doesn’t mean that’s where he will be during November. Remember, within their home ranges, bucks often shift core areas seasonally. Therefore, to harvest a particular buck, you likely will need to shift your hunting areas as well. Bottom line, while the locations of those August photos might be the best place to harvest that buck during early archery season, they may be among the least likely spots to take him later in the season.
During summer, daily buck movements tended to be short trips from bedding to feeding areas, but this changed dramatically during the breeding season. Beginning during the pre-rut, several bucks covered large portions of their home ranges and then returned to their core areas within 8-30 hours.
Additionally, 58 percent of bucks also made excursions outside of their home ranges during the rut, often staying in the new locations 6-24 hours before returning to their home ranges. While unsure, researchers speculated that these bucks likely were in pursuit of an estrous doe. These seemingly random excursions outside of a buck’s normal home range could explain how some bucks that have never been seen or photographed previously seem to magically appear and either get harvested or vanish, never to be seen again on the property.
Another interesting finding was the change in time of day the excursions occurred. During both the pre-rut and post-rut periods approximately 70% of excursions occurred during nighttime hours; whereas during the peak rut, 70% occurred during daylight hours. This certainly helps explain the increased visibility of bucks by hunters during the rut.
So, where do all the big bucks go? From this study it’s clear there are numerous reasons why a hunter doesn’t cross paths with a particular buck during the hunting season. For example, where a buck spends his summer or early fall may be drastically different from where he will be during the rut. Also, a buck’s core area is smaller than previously believed. If you are not hunting within or very near this core area, you risk hunting locations that are never or rarely used by a given buck. Furthermore, except during the rut, a mature buck moves little during daylight hours except for brief periods during early morning and late evening.
To make matters worse, researchers at Chesapeake Farms also confirmed that at least some bucks have the ability to pattern hunters. They compared GPS locations of buck movements to those of their permanent hunting stands where all hunting occurred. For example, not once during daylight hours did one 3.5-year-old buck pass within shootable distance of any of these stands during the hunting season. However, at night he used them like mile markers on a highway and was frequently recorded in their immediate vicinity. Unless this buck made a mistake, he had become essentially “unkillable,” at least by hunters on Chesapeake Farms.
Collectively, the findings of this study confirm what ardent whitetail hunters already knew - harvesting mature whitetails, especially with bow and arrow, is among the most difficult hunting challenges. However, armed with this new Whitetail Science, hopefully you can stack the odds a bit more in your favor this hunting season.
Brian Murphy is a wildlife biologist and CEO of the Quality Deer Management Association (www.QDMA.com). He also has been an avid bowhunter for more than 30 years.