By Rod Luke

Since 2001 Dr. Nancy Mathews has dedicated much of her professional and recreational time to understanding the travel and dispersal patterns of the whitetail deer. Dr. Mathews is a Biologist for the University of Wisconsin , in charge of gathering facts about how deer move and disperse across the landscape. The primary goal of this research is to aid the states efforts in understanding how Chronic Wasting Disease (CWD) is being spread. Another similar research study is being done almost one thousand miles away by Dr. Eric Long, a Biologist for the University of Pennsylvania . Both Biologists are studying hundreds of wild deer equipped with radio tracking devises. After reading their research, I’m convinced that their data can help deer hunters make informed decisions with regard to quality herd management.

I was given the opportunity to interview Dr. Mathews and Dr. Long in an effort to better understand their research. My goal during this interview was to gain information that would help us as deer hunters. What I found, was some very interesting information that dispelled some long believed myths and an even better understanding of what I’ve witnessed in the woods over the last 30 years of hunting and studying whitetails.

Many of the facts found in the abstracts written by Dr. Mathews master’s student, Lesa Skuldt, offer hunters and herd managers useful insight into the world of the whitetail deer. For example, According to data obtained during this study, yearling bucks will “generally” disperse from their natal home range and travel between 4.9 and 5.7 miles before setting up their new adult home range. On the other hand 97 % of yearling female deer remain in their natal home range even as adults with only a 3% dispersal rate. It is believed that this is nature’s way of ensuring a fresh gene pool and limiting inbreeding.

The research revealed that yearling males disperse for one of two reasons. In the spring, when a young male is one year old, the mother attempts to force him out of the herd as she prepares to give birth to new fawns. If the yearling buck is still within his birth home range in the fall, older bucks in the herd will generally force him out as they instinctively compete for breeding rights. The young buck then heads off to find a new place to call home. Dr. Long’s research exposed another phenomenon in that while mature bucks would not tolerate resident yearling bucks born in their home range, they would tolerate bucks that had dispersed from another home range miles away.

Dr. Mathews provided the following details on the average deer home range size by age and gender and according to the time of year.

Jan-April May-July August-Sept Nov-December

Adult females .97 .67 .56 .59

yearling females .84 .70 .74 .72

fawns 1.45

adult bucks 2.35 1.71 .97 1.55

yearling bucks 2.28 1.32 .72 1.99

fawns 1.13

ALL DATA IN SQ KM (1 square mile = 2.59 square kilometers)

Dr Long, provided the follow details from his study.

I’m wrapping up a large study of juvenile buck dispersal in Pennsylvania . From 2002 - 2004, we radio-collared over 400 fawn bucks and tracked their movements as yearlings. Similar to Dr. Matthews study, we found that many of our bucks dispersed long distances when they were about 1 - 1.5 years old. Average movements were about 4 miles, but some deer dispersed over 25 miles from where we tracked them as fawns to where they established their adult ranges. Two deer even dispersed across the Allegheny River in Western PA , which is about 400 yards wide and big enough for barge traffic. Because does tend not to move long distances, this dispersal is thought to be nature’s way of ensuring fresh genes get into the population each generation. (It doesn’t help a buck to stay in the same place his whole life if all the females are close relatives of his.)

We found that about 50 - 75% of yearling bucks dispersed in Pennsylvania , and the remainder established adult ranges that overlapped the range in which they were born. Dispersal occurred during two peak seasons. The first was in the spring (May - June), when bucks’ mothers were giving birth to their next set of fawns. For bucks that did not disperse in spring, many dispersed in the fall (late Sept to early Nov), immediately preceding the rut. Spring dispersal was most likely cued by maternal aggression (the mother essentially kicks her son out of the area), and fall dispersal most likely relates to breeding season competition among bucks.

When asked how hunting pressure influenced dispersal and home range patterns Dr Long reported the following.

One interesting thing that we found in our study is that hunting practices influenced dispersal patterns. We did our study during a time when new, statewide antler point restrictions increased the number of 2.5 year old bucks in our state’s population. Indirect evidence from our study tended to agree with observations that orphaned bucks were less likely to disperse in spring.

However, we found that fall dispersal increased as the number of yearling and older bucks in PA increased. So, we found that the overall number of young bucks that disperse in a given year didn’t change predictably from one year to the next, but we saw a higher percentage of that dispersal occur in the fall as the number of older bucks in our study areas increased. For instance, in one study area, in 2002, 75% of all dispersal occurred in the spring and 25% occurred in the fall. By the end of the study, 25% occurred in the spring, and 75% occurred in the fall. Greater fall dispersal is probably related to increased breeding season competition in the fall.

Dr Mathews report reflected these statistics.

Our pilot study looking at movements over 6 days (12 hr blocks), spaced 2 days before the 9 day hunt, 2 opening days, and 2 days 2 weeks after 9 day hunt) revealed that deer stayed in their home ranges during this time period. Several deer moved out of their established home range but came back within 12 hrs. We did not assess hunter pressure during the study and have no way to relate movements to hunter effort. The larger study reveled no correlation between home range sizes and the number of deer harvested in close proximity to the deer. This suggests that we can not detect behavioral changes that were correlated with the number of deer harvested in close proximity to our radio collared deer.

How does habitat influence dispersal and deer movement?

Dr Long,

We found that deer dispersed farther distances in habitats with less forest cover. For example, compared to Illinois , where there is very little forest cover, deer in forested regions of Pennsylvania dispersed much shorted distances, on average. This finding has important implications for the spread of diseases like CWD. For instance, if dispersing deer carry CWD from one population to the next, and managers decide to enact Eradication Zones to curb the spread of disease, I would recommend larger zones in less forested regions.

As you know, deer don’t behave identically everywhere they roam, and I’m sure our results in PA won’t directly mirror the results from Wisconsin .

How did an increase in mature bucks influence dispersal?

Dr Long,

One of the things that we found in our study is that increased density of older bucks does seem to increase fall dispersal of yearling (1.5-year-old) bucks (though not necessarily overall dispersal rate). Fall competition among bucks, though, definitely seems to be one of the cues that cause yearling bucks to leave their natal range. However, we still have very little idea what causes a dispersing buck to pick where he will stop. It does not seem that a dispersing buck travels around until he finds an area without older bucks present. In fact, often we found that two of our radio-collared bucks would essentially trade ranges. So, new yearling bucks will settle in the same areas that other yearling bucks have just left. In this way, older bucks seem to cue dispersal of younger resident bucks, but they do not necessarily prohibit the colonization of new bucks. For this reason, I would not recommend that older bucks be harvested simply to create room for incoming younger bucks. In many areas with abundant deer populations, reduction of overall deer density through increased harvest of adult does would serve the purposes of QDM much better.

A few things to keep in mind when considering dispersal of yearling bucks. First, this is not a bad thing. Dispersal is natural behavior for deer. When I tell a landowner that a buck that we caught on his land is now 10 miles away, he will often ask me what he did wrong. Bad food? Bad cover? Bad population management? Dispersal of deer from your land does not imply any of these things. Dispersal is something that bucks do, and no dispersal would result in inbreeding. Yes, many bucks born on your land will likely reach adulthood miles away, but if you have habitat that supports deer (i.e., good food and cover), new bucks will be coming onto your land.

So then the bucks I hunt on my land were actually born miles away?

Dr Long,

This is true: many of the bucks you are hunting were born miles away. However, keep in mind the timing of dispersal. Bucks most often disperse when they are 1 or 1.5 years old, before the hunting season in which they will have their first set of antlers. So, what you really need to hope for is that neighboring hunters are not shooting button bucks. If a button buck survives fall/winter hunting seasons, then he will likely disperse the following spring or early fall. Older bucks rarely disperse. If you see a yearling buck (1.5-years-old) where you hunt, and he does not get shot, he will most likely be in the same area the following year. In our study in PA, we found that about 80% of antlered bucks (yearling and older) that survived hunting season survived through the off-season and were in the same area the following year. So, if a landowner wants older bucks on his land, he does, to an extent, need to rely on his neighbors not to shoot button bucks, but it is his responsibility to pass young antlered bucks.

Did terrain and weather effect dispersal direction?

Dr Long,

We did our research in two areas in Pennsylvania . The one study area was in western PA, where there are a lot of hills scattered throughout the landscape. The other study area was in central PA, in the Ridge and Valley region of the state, where there are long, parallel ridges separated by valleys. In western PA, dispersal direction was perfectly random. Equal numbers of deer dispersed north, east, south, and west. In fact, since dispersal is a way to avoid inbreeding, random dispersal direction is the best way to achieve that. For instance, if deer always dispersed only north or south, then the son of a dispersing deer would have a greater chance of returning to his father’s natal range, and getting right back into the same gene pool. Random dispersal direction, though, reduces the probability of a young buck dispersing to the same range from which his father had previously dispersed.

In central PA, though, we found that the ridges seemed to direct the dispersal movements of deer. Ridges in our study area ran northeast-southwest, and deer in this area tended to disperse along the ridges, rather than cross them. Some dispersing deer did cross the ridges, but most of the deer choose to use the ridges as dispersal guides, and most deer dispersed northeast or southwest. While this may increase the possibility of inbreeding, there were enough deer to disperse across the ridges (bringing fresh genes in) that we do not think that this directed dispersal will cause enough inbreeding to do any damage to the herd genetics.

Although we did not directly measure wind and temperature while we were observing dispersal, it seems as if the influences of these things on dispersal were small. Landscape features like ridges seemed to have the biggest influence on dispersal direction.

Were you able to identify anything that would influence where a yearling buck would stop to set up his new home range?

Dr Long,

Once a buck leaves his natal range, it is very difficult to predict where he will stop, and we weren’t able to find any relationship between stopping location and number of bucks and does in that area. Interestingly, though, we did find that many of our dispersing bucks would travel 5 or 6 miles, until they hit their first major road, and then they would stop. And by major road, I don’t mean divided highways; many bucks would never cross a two-lane state route, and they would use these roads to define one side of their home-range. Obviously, some bucks did cross these roads (as the number of road-killed deer demonstrates), but I was surprised by the large number of bucks that traveled until they hit a road and then stopped.

In your study did the fall “rut” cause the bucks’ home ranges to expand?

Dr Mathews,

Our Wisconsin study has followed about 35 yearling and adult bucks for over a year (more than that for less than a year). We have defined home ranges by season and have found that bucks in our area do not use larger home ranges during the rut. This surprised us. Their home ranges are quite well defined during each season and the only season during which they use a larger area is during the winter. Their home ranges are generally less than a square mile in our area.

We are continuing to trap this winter to increase our sample sizes to further assess seasonal movements. We have not analyzed our data on a 24 hr clock at this time. However, during the rut, we do see more movements within their established home ranges. Rarely will they leave these areas, and when they do, it is for a very short time

(Less than 12 hrs).

After reading the research and interviewing Dr Mathews and Dr Long, I think it’s important to point out a key factor in these studies. The test subjects for both studies were done on moderate (60%) forest density tracts of land. In areas with less forest density, you may find your deer have larger seasonal home ranges. Another point of interest is that mature bucks stick within their home range during the rut. (Less than one square mile) This may indicate that if we are only seeing a mature buck during the “rut”, we may want to change our tactics to put the squeeze on his home range and tighten the noose around his core areas to increase our odds of success.

Another part of the study that caught my eye was the fact that female deer live out their lives in their natal home range and seldom disperse. This would suggest that over harvesting does could adversely affect your herd for years into the future. So caution should be used when determining how many does should be harvested on your land every year. It’s always a good idea to speak to a local Biologist or your DNR to help assess your properties specific needs.

In the future, Dr Mathews and Dr Long are planning to incorporate GPS technology into their studies as the cost of this technology becomes more affordable. This technology will be used to give a more exact course of travel over a one year period. These new GPS collars take a snap-shot reading every hour for one year. With a remote control the collars will detach from the deer and the research team simply goes in and retrieves the collar. The data is down loaded into a computer and will give the exact travel location of the test subject during the year the collar was in place. The information researches will gain from these GPS collars should prove very useful to their studies and provide deer hunters with an even better understanding of deer movement and better ways to manage our deer populations.

For additional information on Dr Mathews research, log onto http://www.colorsoluble.com/chronicwasting/researchpersonnel.htm