hunting pressure

When the Hunting Pressure is On: Deer Behavioral Responses to Hunting vs. Sharpshooting

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Controlling overly abundant white-tailed deer populations in residential areas is a monumental problem and invariably leads to controversy. Some residents readily support killing deer by use of controlled hunting or sharpshooting, whereas others prefer nonlethal control methods. As unpopular as it might sometimes be, lethal deer removal produces immediate results and currently is the most efficient way to solve the problem of too many deer.

By John Ozoga

Controlled hunting tends to be the most effective, cost-efficient and proven management tool in both rural and some suburban areas. However, hunting — especially with firearms — is not always feasible, legal or otherwise socially acceptable where deer live in close contact with humans.

Sharpshooting is another option that gives managers even more control in residential areas where gun hunting is either unlawful or impractical. Although it might not be viewed favorably by some hunters, sharpshooting gives managers the ability to remove a greater proportion of the deer in a relatively short time with minimal disturbance.

Given the whitetail’s strict matriarchal social system and strong attachment to their established home range, questions remain as to how remaining animals’ behavior is affected when other members of their family group are suddenly eliminated. Some studies suggest deer remaining after severe population reduction continue to live on their ancestral range, despite very low deer numbers. In contrast, other studies indicate remaining deer shift out of their known home ranges to associate with unrelated deer.

In white-tailed deer, adults exhibit sexual segregation, meaning the adult does and bucks live separately —spatially and socially — except during the rut. The basic social organization among female whitetails is matrilineal, consisting of a family group comprised of a matriarch doe, several generations of her daughters and their fawns. Several such genetically related families share common range and associate seasonally as a cohesive clan.

Females that survive to maturity commonly exhibit superior survival skills and function as group leaders. Close association between mothers, daughters and other female relatives assures that young individuals learn the location of food, water, cover and potential dangers.

hunting pressure

Heavy hunting pressure tends to remove prime-age group leaders, thereby disintegrating the whitetail’s adaptive social system. Logically, intensive harvesting of mature does, in particular, could disrupt normal patterns of whitetail social behavior.

Changes Associated with Population Reduction

The aim of a study, led by University of Connecticut researcher Scott Williams, was to quantify and compare changes in deer behavior associated with drastic population reduction as the result of controlled hunting vs. sharpshooting. The investigators theorized that socially isolated deer would be inclined to leave their traditional range, interact with members of other matrilineal groups and establish new core ranges … “to accommodate the new social network.”

The Connecticut based researchers conducted their study at Duke Farms, a 4.2 square mile area located in Hillsborough, New Jersey. A 1.1 square mile portion of the area, referred to as the Park, was enclosed by fence. The remaining 3.1 square miles, referred to as the Farm, was unfenced.

Both properties held more than 200 deer per square mile, causing severe overbrowsing and considerable deer-human conflicts. Prior to this study, managers of the estate decided to eliminate all deer from the fenced-in Park via sharpshooting and reduce Farm deer densities with controlled hunting.

In late November 2004, researchers captured 20 deer reflecting the local sex-age composition (eight adult does, four adult bucks and eight fawns) both within the Park and Farm. Each deer was fitted with a global positioning system (GPS) collar. Deer captured on the Farm were marked with high-visibility paint to prevent hunter harvest of study animals. Radio-collared deer were tracked from Nov. 15, 2004, through Feb. 27, 2005.

A total of 215 uncollared Park deer (about 92% of the herd) were removed by sharpshooters during a seven-day period in January 2005. Free-ranging Farm deer were subjected to a series of intensive controlled shotgun hunts during November and December 2004 (totaling 11 days), during which time 392 deer (about 66% of the herd) were harvested.

Home range and core areas of activity were calculated for Park deer pre-shoot, during the week of sharpshoot and post-shoot. Home range and core areas for Farm deer subjected to controlled hunts were determined weekly for the same intervals for comparison.

Controlled Hunting Effects

Deer subjected to controlled hunting (Farm deer) exhibited an increase in average home range size during periods of hunting and a reduction in home range size in the absence of hunting. Mean weekly home range size was highest during the week that included a six-day hunt, but then decreased sharply post-hunt (544 acres vs. 170 acres, respectively).

The researchers, citing numerous supporting data from other studies, suggest that hunted deer increased their home range size in seeking refuge from hunters on unhuntable portions of the adjacent properties. Typically, intensively hunted deer are more mobile, traverse larger areas, are found farther from roads, increase their nocturnal activity and make greater use of dense cover during periods of hunting compared to periods of nonhunting.

Although the investigators didn’t say so, these findings indicate that hunted adult deer in this study were familiar with more than just their normal home range and quickly sought refuge where they were safe from disturbance. Likewise, deer resumed use of their normal home range once the human threat passed.

Keep in mind, however, that controlled hunting reduced the Farm deer populations by only 66%. Given the initial likelihood of complex family groups, this means most deer surviving the controlled hunt were not deprived of close kin — hence, were not socially isolated.

Sharpshooting Effects

Compared to controlled hunting survivors, those deer surviving sharpshooting responded differently to the effects of population reduction. Likely due to the shooting techniques employed and the fact that nearly 92% of the deer were killed, most of the deer remaining following sharpshooting were probably sole surviving members of their former ancestral clan.

Sharpshooters were given more control over their methods of deer removal. They harvested deer at night, over bait, from treestands or a vehicle, but only took shots (generally to the head or neck) that would assure a clean kill. In addition, sharpshooters permitted large groups of deer to dissipate before any animals were harvested, so that other animals would not witness the killing and would more likely remain “naive” for harvest at a later time.

Since radio-collared deer surviving the sharpshooting harvest did not increase their home range size substantially during the harvest period, sharpshooting techniques were presumably less behaviorally disruptive than controlled hunting methods. Interestingly, those deer surviving the sharpshooting harvest showed a significant increase in home range size and regrouped with unrelated deer post-shoot. In contrast, deer subjected to controlled hunting returned to their traditional range, retained associations with family members and did not expand their range post hunt.

Social Effects

While not as gregarious as some other members of the deer family — such as mule deer and elk — whitetails are by no means antisocial. Although their degree of sociality might vary regionally, depending upon environmental pressures, more and more study evidence indicates that the very foundation of the whitetail’s social system is the matriarchy. Female whitetails occupy home ranges adjacent to, and often overlapping that of their mothers, and interact with female relatives seasonally.

Female whitetails less than 2 years old, in particular, have a strong drive to achieve and maintain compatible associations with other mature does. If their mothers or other close female relatives are not available, then they might disperse considerable distances to find these associates. Such social interactions are of interest to managers because behaviors can be learned through successive generations.

hunting pressure

Since deer socially isolated as the result of the sharpshooting regrouped with unrelated females post-harvest, the researchers concluded the following: “The social nature of white-tailed deer can override the [inborn] survival mechanism of high home range site fidelity. We argue that white-tailed deer may rely more on their social network for survival purposes than previously thought.”

Although the authors of this study did not site a previous study of mine, I reported similar results. I mimicked social isolation for some deer in my Cusino enclosure studies by removing all female relatives of some does during the annual winter trapout. By the next autumn, all socially isolated yearling does had formed a strong social bond with the nearest doe that would tolerate her presence, generally an older isolate mother. By the breeding season, there was no significant difference in group size among isolate does as compared to those with intact family groups (4.8 deer vs. 4.5 deer, respectively).

Other researchers have also found greater likelihood of dispersal among young female whitetails in areas where antlerless deer are intensively harvested and the female age structure is heavily skewed to young animals. Although such social disruption can alter herd genetics, the exact long-term consequences, if any, are still unknown.

On the other hand, I believe that older does are more inclined to remain on their established home ranges, even when they are socially isolated.

Management Implications

Unfortunately, lack of funding, as well as social and political pressures, often prevent sustained controlled hunting necessary to achieve negative deer population growth. As a result, large-scale controlled hunts are often one-time events that educate remaining animals, making future population management via hunting even more difficult.

Given these potential problems, Williams and his group recommend that managers concentrate their efforts on hunter behavior, rather than deer behavior, where controlled hunting is employed annually. “Minimally,” they say, “managers need to conduct thorough interviews with hunters, use shooting proficiency tests, and educate hunters when to best harvest an animal given its proximity to others.”

Since similar training tactics have been used in the past with minimal success, the Connecticut researchers suggest even more drastic measures might be necessary to increase hunter proficiency, such as restricting the amount of ammunition per hunter. For example, limiting each hunter to two or three rounds of ammunition per valid tag during controlled hunts would force them to take “clean-shot opportunities.” Theoretically, this would educate fewer deer and, in the long-run, increase the harvest.

Regardless of the specific strategy used, Williams and his coworkers emphasize the following: “Managers need to take into account the impact of density reduction of post-harvest [deer] behaviors when formulating management plans.”

— John J. Ozoga is one of North America’s most respected deer research biologists. He holds bachelor and master of science degrees in wildlife management from Michigan State University. He worked at the Cusino Wildlife Research Station for more than 33 years, where he wrote or co-wrote more than 80 technical papers, including some of the most comprehensive scientific studies on white-tailed deer ecology, physiology, reproduction, nutrition, behavior and population dynamics. Ozoga retired and became Deer & Deer Hunting’s freelance research editor in 1994.

LITERATURE CITED

Comer, C.E., J.C. Kilgo, G.J. D’Angelo, T.C. Glenn and K. V. Miller. 2005. “Fine-scale Genetic Structure and Social Organization in Female White-tailed Deer.” Journal of Wildlife Management 69:332-344.

Ozoga, J.J. 2007. “Is It Possible to Kill Too Many Does?” Deer & Deer Hunting 30 (6):28-36

Ozoga, J.J. and L.J. Verme. 1984. “Effect of Family Bond Deprivation on Reproductive Performance in Female White-tailed Deer.” Journal of Wildlife Management 48:1326-1334.

Root, B.G., E.K. Fritzell and N.F. Giessman. 1988. “Effects of Intensive Hunting on White-tailed Deer Movement.” Wildlife Society Bulletin 16:145-151.

Williams, S.C., A.J. DeNicola and I. M. Ortega. 2008. “Behavioral Responses of White-tailed Deer Subjected to Lethal Management.” Canadian Journal of Zoology 86:1358-1366.

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