Studies in Alabama and Wisconsin shed light on breeding and mortality.
The old saying familiarity breeds contempt might be true for some things, but it doesn’t apply to deer hunters. We can’t seem to get enough information about whitetails, the continent’s favorite big game animal. Results from two new whitetail research projects, each of which remains ongoing, will only fuel the fire.
One of the most interesting things to have appeared recently on the whitetail research scene comes from a 430-acre enclosed research facility near Camp Hill, Ala. Since it opened, Auburn University deer scientists and graduate students have been working diligently to solve some of the thornier puzzles of white-tailed deer behavior and reproduction.
Dr. Steve Ditchkoff, the facility’s research leader, has not only been studying deer for years, but he also was instrumental in raising the money needed to construct and open the facility.
A variety of habitats exist within the enclosure: old pastures, bottomlands, regenerating clearcuts, a pine plantation and hardwood uplands. An all-weather creek runs through the property; and food plots, planted with warm- and cool-season forages, supplement naturally occurring browse and mast species.
“Our goal is to gain intimate knowledge of each individual in the population throughout the animal’s entire life while they maintain natural behaviors,” Ditchkoff says.
He explained there are three types of research methods deer scientists have used traditionally.
The first is studying whitetails in 1- or 2-acre enclosures in which researchers have complete control of the animals. The downside of the pens is deer behavior might not be wholly natural.
The second method uses radio-telemetry collars or implant devices on free-ranging animals. This allows scientists to track the deer, but it doesn’t provide other behavioral data.
The third method is studying hunter-harvested animals by drawing blood and taking measurements, or by making other field observations and tests.
“We’re trying to combine the best of all worlds,” Ditchkoff said. “We want to know every animal, but within a free-range setting so behaviors are realistic and as natural as possible.”
Until now, hunters and scientists have put forth many theories about which deer in a given population do the bulk of the breeding. Conclusions, however, were mostly conjecture, unless the animals had been held in a small pen.
“Is it the largest male? The oldest male? The one with the biggest antlers? The one with the highest levels of testosterone? That is what we were hoping to find out,” Ditchkoff said.
The Auburn facility holds about 100 whitetails. The buck-to-doe ratio is excellent at about 1:1.3. Deer are born there, and they die there, too — all naturally. No animals were brought in to augment the genetics that were already present when the facility’s fence was closed.
Thanks to advances in DNA testing, the Auburn researchers were able to trap each animal in the facility, extract a DNA sample and then freeze-brand identifying information into the hide of the deer so that researchers could tell from a distance which animal was being observed. As fawns were born, researchers trapped them, extracted DNA and were able to determine exactly which buck was the deer’s sire and which doe was its dam.
At first, all age classes of males succeeded in siring fawns, from 1½-year-olds on up. “A few buck fawns even successfully sired offspring,” Ditchkoff commented.
“Older males, as we’d suspected, sired more offspring than did younger males,” Ditchkoff continued. “After three years of data — with more older males in the population — the breeding success of younger males decreased. When the oldest males were 3 1/2 years old, the 1 1/2-year-old bucks were pretty successful as breeders. But as we got more 4 1/2- and 5 1/2-year-old bucks in the population, the younger males had less success.”
Ditchkoff provided the following statistics: When the oldest bucks were 3 1/2 years old, the 1 1/2-year-old bucks did 50 percent of the breeding. When both 3 1/2- and 4 1/2-year-old bucks were present, 1 1/2-year-old bucks sired just 7 percent of that year’s offspring. When 5 1/2-year-old bucks were present, the 1 1/2-year-old males accounted for 0 percent of the offspring.
“We’re not sure yet what the driving factor is in the suppression (of breeding success by younger males), but we believe it is a good thing,” Ditchkoff said. “If breeding is suppressed in younger males, they will be in much better condition coming out of breeding season. That translates into better antler growth in the future. We don’t have any hard data yet; it’s just a guess, but no breeding usually means a higher survival rate, better body condition during the summer and, thus, more resources to devote to antler growth.”
The work at the Auburn facility has only just begun. DNA testing on this population will continue into the future as the researchers attempt to answer questions such as why female deer breed with certain age classes of males. As Ditchkoff said, “Is it antler size? Antler configuration? Testosterone levels? Body size or other genetic factors? We want to find out.”
He emphasized that the research being conducted in the Auburn facility is funded by private donations, and “donations are always appreciated,” he said.
To make a donation, send a check made out to “Auburn University Foundation” at this address:
Dr. Steve Ditchkoff
School of Forestry and Wildlife Sciences
Auburn, AL 36849
Please include “For Deer Research” in the memo line of your check.
WISCONSIN LAUNCHES TWO STUDIES
Over the past several decades, whitetail hunters in Wisconsin have become increasingly concerned about what they perceived to be troubling trends taking place in the state’s deer herd.
Whether rightly or wrongly, hunters weren’t too sure about the accuracy of the S-A-K (the sex-age-kill) estimate that was being used for the deer population modeling system adopted by the state’s Department of Natural Resources.
The orange army made their concerns known, and the eventual result was the commencement of two research projects: the Buck Mortality Study and the Predation and Fawn Recruitment Study, both of which got under way in late 2010.
The first is located in the east-central part of the state in Shawano, Waupaca and Outagamie counties in a locale comprised primarily of farmland interspersed with woodlots. The other study area is located in the northern forest in Sawyer, Price and Rusk counties.
“Part of this effort involved marking lots of deer with radio collars and ear tags,” said Chris Jacques (pronounced Jakes) of the Wisconsin DNR.
Jacques, who came to Wisconsin from South Dakota, originally attempted to capture whitetails by helicopter net-gun. That proved to be “difficult and stressful to the animals here in Wisconsin,” Jacques said, noting that was not the case in the more open habitats of South Dakota. “(Helicopter) capture led to higher than normal mortality, so we have decided not to use helicopters this year. Instead we’ll focus all of our capture efforts on ground trapping techniques, which we hope will minimize stress and subsequent mortality to captured animals.”
Researchers are now using ground traps — box traps, clover traps and drop nets, although Jacques doesn’t rule out a return to helicopters if researchers fail to trap enough deer.
In the first year of the study, 339 adult (18 months or older) and yearling (8 to 10 months) deer were captured.
Of those 339 captures, 151 were adult females, and 86 were subsequently radio-collared. Eighty-three of the radio-collared females also were given vaginal implant transmitters (VIT). Ultra-sound testing had previously determined that 77 of the 83 VIT does (93 percent) were pregnant.
A vaginal implant transmitter is expelled when a doe gives birth, thus providing a signal that researchers can follow to locate birth sites of newly born fawns. The area is then searched intensively for the fawns.
After analyzing data accumulated during the study’s first year, researchers were able to ascertain that hunting, predation and collisions with vehicles are the leading causes of mortality in adult deer in the east-central study area.
“Rather unexpectedly, there also have been some starvation events, particularly in east-central Wisconsin,” Jacques said. “We don’t think the starvation is associated with our handling techniques. We suspect it might be because of a difference in deer densities between the two areas.
“There are 60 to 80 deer per square mile in the east-central area, so maybe more young does are giving birth. The propensity to abandon fawns could be greater for inexperienced mothers than for older does. Vehicle collisions also are a primary source of mortality, so perhaps some starvation events are due to mothers being killed by vehicles.
“It is possible that we might just be picking up on a cause of fawn mortality that is more common than we previously thought,” Jacques concluded.
Eighteen of 48 fawns (38 percent) in the east-central area had died by the end of 2011. Most deaths were caused by predation (33 percent), starvation (33 percent), or collisions with vehicles (17 percent). Coyotes were responsible for five fawn deaths, and a bear was responsible for the other.
In the northern forest, just as hunters had suspected, fawns are dying off at an even greater rate. According to Jacques, 22 fawns, a whopping 73 percent of the 30 fawns that had been radio-collared in that area, died in 2011. Most, 64 percent, were because of predation, primarily by bears and bobcats.
According to Jacques, an independent audit of the S-A-K model of estimating deer populations used by the Wisconsin DNR recommended that a long term radio-telemetry study be conducted across various habitat types to determine whether deer population estimates provided by the agency might be improved.
“The one unknown variable in the S-A-K model that is particularly sensitive to changes over time is known as the buck recovery rate,” Jacques said. “That is the annual percentage of bucks that are dying because of hunting. Historically, we have estimated that quantity using simulation modeling because there was no actual field research that we could use in the model. At the conclusion of this study, we will have empirical estimates of buck mortality derived directly from field research. We can then plug these numbers into the model, thereby improving the accuracy and precision of our S-A-K population estimates, which will make our deer management program better.”
At the conclusion of the first year, researchers had determined that hunter harvest (61 percent) and vehicle collisions (24 percent) were primary causes of adult and yearling deer deaths across east-central Wisconsin. In the northern part of the state, hunter harvest accounted for 38 percent, and predation for 26 percent.
“Very few adult and yearling deer are dying of wolf predation,” according to Jacques, who noted an astonishing rate of scavenging once the animals died. “The scavenging (hampers) our ability to get on (the dead animals) fast enough to determine (with accuracy) what actually caused their deaths. From what we’ve been able to determine, last winter (2010-11) there were five wolf predation events, four of which were button bucks. One adult doe was preyed upon by wolves.
“So far this year (winter of 2011-12) there has been one wolf predation of a 1 1/2-year-old buck.
Researchers also have been collecting some crude movement data as an offshoot of the mortality study. “One interesting thing is we’re seeing many adult bucks are real homebodies,” Jacques said. “One adult buck shot this hunting season was within 200 yards of where he was captured last year. Although sample sizes are limited, adult bucks seem to hang very tight to their home range and move very little between traditional seasonal home ranges (in these study areas).”
The average distance travelled by yearling bucks dispersing from natal ranges was anywhere from 1.5 to 20 miles. “Who knows how far that (long distance) buck would have gone?” Jacques mused. “He was 20 miles away and might have still been travelling when he died as a result of a collision with a vehicle near Green Bay.
Across northern Wisconsin, 66 percent of adult deer did not migrate; in the east-central area, 90 percent did not migrate. Those deer that migrated in the northern forest travelled an average of 3.8 miles and a maximum of 9 miles. Migrants in the eastern farmland travelled an average of 2.7 miles and a maximum of 4.5 miles.
At the end of December 2011, 19 adult males, 22 adult females and eight fawns in northern Wisconsin; and 21 adult males, 25 adult females and 30 fawns in east-central Wisconsin were being monitored weekly to gain even more information that researchers hope to use to improve our knowledge of the ever fascinating white-tailed deer.
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• When the Food Is Gone: Can you help deer through harsh winters without doing more harm than good? This article was published in the July 2012 edition of Buckmasters Whitetail Magazine. Subscribe today to have Buckmasters delivered to your home.