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Yearling buck dispersal.

Last Father's Day my two little girls made me a card that said, "We love you, Daddy! We have the best time hunting with you! Since the girls are only five and eight years old, our hunting consists of setting up in a Game Tracker pop-up ground blind. Needless to say, many times the girls are so noisy I have little hope of getting a shot.

Nevertheless, I have experienced the joy--the same joy many hunters feel when they take their kids along--of success with my kids. The excitement after seeing daddy take a deer is something neither the girls nor I will ever forget.

Upon reading my Father's Day card, I couldn't help but wonder about their future, will they continue to feel the excitement of the hunt? When will they want to venture out by themselves? Only time will tell, of course, but one thing is for sure--one day my little girls will be leaving the nest and making their own way.

JUST LIKE CHILDREN, deer must at some point leave the nest (their maternal home range) and make their own way. Biologists refer to this process as dispersal.

One of the most intriguing aspects of deer management is dispersal of young deer. Years ago, biologists believed that competition among mature bucks for breeding rights was the primary reason why yearling bucks left their maternal home ranges. Thus, hunters simply would have to accept the "fact" that 50 to 90 percent of all yearling bucks would leave their property. Even today, many biologists still believe this.

In 1992, however, researchers Stefan Holzenbein and Dr. Larry Marchinton suggested that closely related females (mainly the mothers) were the primary reason why yearling bucks left their maternal home ranges. The aggressiveness of female deer has been widely reported, and some biologists believe that does actually will out-compete bucks for prime habitat.

In their study, Holzenbein and Marchinton found that if a hunter took a buck's mother or dam before natural dispersion took place, the newly "orphaned" buck was less likely than normal to disperse far from his mother's home range, and he had a much higher potential for surviving over the long term. In other words, killing the mother left one less doe around to kick the young buck out of his home range. He also stood a better chance of survival than normal since he didn't have to venture into unfamiliar territory. Additionally, since the yearling buck was already familiar with his birth area, he didn't have to venture out and find a new, unfamiliar home range. As a result of this research, many hunters--and especially those participating in quality deer management (QDM)--incorporated the harvest of adult does as a way of keeping yearling bucks on their property.

JUST WHEN WE THOUGHT we had a good handle on the reasons why yearling bucks disperse, deer researchers Chris Rosenberry and Jonathon Shaw found that, in Maryland, competition and social position among yearling bucks was the primary influence on dispersal. In fact, both researchers found maternal aggression had little to no effect on dispersal. Additionally, they found no differences in dispersal rates among orphaned and non-orphaned yearling bucks. Interestingly, higher-ranking yearling bucks dispersed more frequently and farther than lower-ranking yearling bucks. Maybe that's because they were, as the saying goes, "feeling their oats?"

The researchers also compared the dispersal rates of yearling bucks before and after the implementation of QDM. They found that, under a traditional deer management plan in which any buck was fair game, 70 percent of all yearling bucks dispersed. Once QDM or a rule that limited hunters to shooting bucks with a minimum inside spread of 15 inches was implemented, only 55 percent of all yearlings dispersed. These data are another "at-a-boy" for those who promote antler restrictions and QDM.

Shaw found the median dispersal distance was 3.7 miles with a range of 1.2 to 36 miles. The yearling buck that traveled 36 miles left his natal home range on October 2. By October 5 he was 6.2 miles away. He then swam the Chester River, which is about one mile wide, and was then killed by a hunter on October 19. Within a little over two weeks this buck had traveled an incredible 36 miles! The greatest dispersal distance recorded in the literature for a yearling buck was over 127 miles from his maternal home range,

When do yearling bucks actually leave or disperse? As in other dispersal studies, Rosenberry and Shaw found that 24 percent dispersed during the spring (May-June), which is peak fawning time, while 76 percent of bucks left during the fall (September-November), which is peak rutting time.

FOR THREE YEARS, deer researchers from the Pennsylvania Game Commission (PGC) and Cooperative Fish and Wildlife Research Unit at Penn State University also have been studying the dispersal rates of yearling bucks. After implementing statewide antler restrictions in 2002, researchers looked at two study areas: Armstrong and Centre Counties. Armstrong County, which is farmed extensively with isolated woodlots (51 percent wooded), has a high deer density and ideal deer habitat. Centre County has both a wooded (66 percent forest) and agriculture landscape located in the ridge and valley region. It has a moderate deer density and good habitat.

The researchers found that 70 percent of all yearling bucks dispersed from their maternal home ranges in Armstrong County, while only 45 percent dispersed in Centre County. Although the dispersal rates between the counties differed, they were consistent within each county for the two years of the study.

Researchers correlate the dispersal rates with the amount of forest cover--that is, the less forest cover (Armstrong County) the greater the dispersal rate, and the greater the forest cover (Centre County) the less the dispersal rate. Dispersal distances also correlated to forest cover. In Armstrong County, yearling bucks migrated a median distance of 6.5 miles from their mothers' home ranges, while in Centre County, they dispersed an average of 4.8 miles. In analyzing data from 11 other studies on nonmigratory populations of whitetails, the researchers found similar correlations between forest cover and dispersal of yearling bucks.

Does this mean that if your area is fairly open, like Armstrong County, and you plant a bunch of trees, you can increase the percentage of yearling bucks that remain on your property? Maybe so. And planting trees adds untold value to the aesthetics of your property and the critters that inhabit your little piece of heaven.

CJ'S SUMMARY: Whatever the mechanism that governs the dispersal of yearling males-(1) number of mature bucks in the herd, (2) maternal or aggressive does, (3) a hierarchy ranking among yearling bucks, (4) or the amount of forest cover--one thing is for sure: deer are complex. Perhaps both biologists and hunters are guilty at times of misinterpreting the facts. Not only does new research reveal new insight, but we must remember that the facts that apply to one area might be irrelevant in another.

Whatever the reasons for dispersal, the fact is that aggressively harvesting adult does is the foundation for quality deer management. Shooting adult does may keep yearling bucks on your property for social reasons among the deer, but it also could help you maintain a better buck population simply because it ensures better habitat. Eliminating does leads to the production of more forbs, weeds, buds, twigs, saplings, acorns, and agricultural crops. Not only might the resulting excellent forage keep some bucks at home, but it will attract and hold bucks dispersing from your neighbor's property--which only makes your little slice of heaven a little more heavenly.

Once a buck has established his post-dispersal home range, he most likely will live his entire life in that area. Thus, passing up and protecting yearling bucks simply makes good management sense because those bucks will develop into really decent 2.5-year-old or older bucks.
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Title Annotation:Hunting Whitetails
Author:Winand, C.J.
Date:Dec 1, 2004
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