Deer Options Enterprise
White-Tailed Deer Biology and Ecology
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the Buck Stop?
WITH THE LATE DAYS of September passing into the first cool days of October, many of us have been busy preparing for the upcoming deer seasons, scouting our favorite spots, and even spotlighting to check out the deer population where we hunt.
Preseason scouting can provide information on the quantity and quality of bucks in an area. Oftentimes, though, after weeks or sometimes months of hunters becoming familiar with "their" buck, come mid-October, the buck disappears. He's gone from his usual hangout; there's no fresh sign, where just a short time earlier the buck was a regular visitor. Now the questions begin: Where did it go? Is it dead or alive?
The abrupt disappearance of a buck in the fall may be the result of dispersal. Dispersal, or movement away from the area where the buck was born, is common in Pennsylvania. Results from our ongoing buck study indicate between 45 and 75 percent of all yearling bucks will disperse. Although some dispersal occurs in the spring, when bucks are 11 to 12 months old, most dispersal occurs in the fall, during October and November, prior to the peak of the breeding season, when the bucks are 16 to 17 months old.
Mixing it Up
Dispersal results in substantial mixing within the deer population. Comparing capture locations of 8- to 10-month-old bucks (button bucks) in Armstrong County (Figure 1) with the locations where those same bucks were later in the fall, (Figure 2) illustrates how bucks spread out across the landscape.
If one considers the movements of this sample of marked bucks and multiplies them by all the bucks in Pennsylvania, the magnitude of movement within our deer population becomes clear. A lot of young bucks are on the move, leaving familiar haunts and traveling into unfamiliar areas.
Sometimes this lack of familiarity has dire consequences. Last year, dispersal for one buck ended abruptly when it fell off a cliff to its death. For those bucks surviving dispersal, habitat plays an important role in where they stop.
Habitat & Dispersal
Once a buck begins to disperse, where will it stop? No single factor is likely to explain why a buck ends dispersal where it does, but habitat and man-made obstacles certainly influence dispersal movements. For instance, dispersal movements often end when a buck nears a large river. This has been seen in Armstrong County where bucks encountered the Allegheny and Kiskiminetas rivers and established their new, adult range on the near side, choosing not to cross. We have seen similar patterns involving major roads, as many bucks have ended dispersal and established home ranges directly adjoining highways.
On the other hand, what are barriers to many deer barely slow the movements of others, as the travels of two particularly adventurous deer illustrate. Buck 49 in Centre County crossed five mountain ridges and many roads before establishing his adult range 20 miles away from where he was caught.
In Armstrong County, Buck 1080 swam across the Allegheny River, which is about 300 to 400 yards wide, and crossed two major highways before setting up his adult range 25 miles from his natal range.
Population density does not appear to influence deer dispersal. In a recent analysis, we investigated the effects forest cover and population density have on dispersal. Using data from Armstrong and Centre counties and from other deer populations across the U.S., we learned deer population density has little effect on the percent of young bucks that disperse or how far they disperse.
Forest cover, on the other hand, did influence dispersal distance. As percent of forest cover decreased, dispersal distance increased. In Armstrong County, which is less forested than Centre County, bucks dispersed about five miles, while bucks in Centre County dispersed four. The relationship between less forest and longer dispersal distance was consistent across other studies as well.
Buck Age & Movements
Dispersal may make hunting a particular buck difficult. A hunter may have done all of his homework, scouting the movement patterns of a buck, only to have it disperse miles away prior to or during hunting season.
Fortunately for hunters, movement patterns of older bucks are more predictable. Based on initial research results from the buck study, most dispersal occurs when bucks are 11 to 17 months old. Adult bucks, those that have survived at least two hunting seasons, are likely to be found in the same general area the following year. So, if during your preseason scouting, you come across a big buck, he's not as likely to head off somewhere else before hunting season. Of course, that older buck is by no means an easy animal to hunt, but the risk of losing it to dispersal is much less.
Dispersal of yearling bucks has important effects on deer population dynamics and is influenced by habitat more than deer population density. Dispersal may also impact deer hunters' efforts. First, disappearance of a buck in the fall may not indicate death of a buck; rather, the buck may have dispersed, in some cases 20 to 25 miles away. Second, for every buck that disperses from one's hunting area, there is a chance a buck from somebody else's hunting area will move in. Finally, following implementation of antler restrictions, the chance to pursue an older buck has increased. Along with the greater chance to pursue an older buck comes the advantage of knowing an older buck is not as likely to pick up some autumn evening and move far away.
- By Dr. Christopher S. Rosenberry & Eric S. Long
Pennsylvania Game Commission