Deer Behavior: Buck Dispersal

Buck dispersal is not only an interesting deer behavior; it can have a huge impact on the success or failure of your deer management program. Buck dispersal is defined as the permanent abandonment of a buck’s initial, natal home range for a new home range that is geographically separate.

Deer management effectiveness cannot be maximized without knowing the dispersal behavior of the deer in your area. Buck dispersal also affects the scale of management. Dispersal is the longest movement any deer will make in its lifetime therefore is an important contributor to gene flow across the landscape and can impact the spread of disease. As a result, it is important to know the dispersal rates for your deer herd.

A Dispersal Timeline
In south Texas, newborn buck fawns often hit the ground in July. They spend their first few weeks alone and only interact with their mother, two to three times a day while nursing. When not nursing, they are almost constantly bedded and not moving. Researchers believe this isolated behavior reduces the likelihood coyotes will discover the fawns, their primary threat to life.

Once a buck fawn is a month or so old, he is large enough and fast enough to begin traveling with the doe. He will stay near her side and will begin bedding next to her for the first time in his young life. Buck fawns continue to travel with the doe, essentially assuming her home range, for the remainder of the first year of their life.

In the highly productive Midwest, many buck fawns disperse around their first birthday, at only 12 months old. In south Texas however, telemetry research has shown that most bucks do not disperse until they are yearlings, between the ages of 16 to 18 months old.

Why Yearling Bucks?
Yearling bucks are more likely to disperse than any other deer sex or age class, because they are lowest on the dominance “totem pole.” They are subordinate to all other antlered bucks and to adult does as well. As a result, they are often forced out of their mother’s home range.

Surprisingly, it is often the buck’s mother who forces the buck to disperse! A telemetry study done by Drs. Stefan Holzenbein and Larry Marchinton in Virginia shed new light on this phenomenon. Radio collars were placed on 34 buck fawns to track their movements and death rates for two years. The mothers of 15 fawns were also caught and released 20 miles away. This was done to orphan 15 of the 34 bucks fawns (to simulate harvesting of does). The remaining 19 buck fawns were left with their mothers.
The scientists discovered that 9 percent of the orphaned bucks dispersed to new areas. However, over 85 percent of bucks left with their mothers dispersed. Most of this movement happened during either the summer fawning season or later that fall during the rut. The scientists concluded the mothers themselves forced these bucks to disperse! They suggested this occurred to reduce inbreeding.

The scientists also found that orphaned bucks lived longer. Only 55 percent of orphaned bucks died during the study while over 90 percent of bucks left when their mothers died. Starvation or predators caused most deaths.

The scientists felt orphaned bucks lived longer because they were able to stay home. Non-orphaned bucks were forced into unfamiliar areas (usually two to six miles away) where more deaths took place. These bucks did not know the escape routes and best places to find food and as a result, mortality was higher.

A South Texas Study on Buck Dispersal
During the years 1998 through 2000, Masters student Evan McCoy used radio telemetry to track the movements of 49 radio collared yearling bucks. All of these bucks were captured as part of the ongoing South Texas Buck Capture Project, based at the Caesar Kleberg Wildlife Research Institute at Texas A&M University-Kingsville. Twenty-two of these yearling bucks were captured during October 1998 on the 85,000-acre Callaghan Ranch. The remaining 27 bucks were captured during October 1999 on the Laureles Division of the 825,000-acre King Ranch.

McCoy tracked all of these bucks on a weekly basis to determine survival, home range and core area size, and most importantly, to determine when dispersal occurred. During the timeframe of Evan’s study, 68 percent (15 of 22) of the yearling bucks on the Callaghan Ranch dispersed an average of 2.7 miles (range = 1.2 to 4.5 miles) from the center of their home range as a fawn. On the King Ranch, 44 percent (12 of 27) of the yearling bucks dispersed an average of 5.1 miles (range = 1.3 to 9.3 miles) from their fawn home range.

McCoy determined that the average dispersal date for yearling bucks on the Callaghan Ranch was December 2nd (range = 5 Nov thru 2 Jan), approximately three weeks before the rut peak on December 24th. Only one collared buck on the Callaghan Ranch died during the study when it became entangled in a fence, so the mortality rate was only 4.5 percent. Average home range size for the Callaghan Ranch yearling bucks that dispersed was 1,036 acres versus only 726 acres for yearlings that did not disperse.

On the King Ranch, the average dispersal date was November 21st (range = 26 Oct thru 30 Dec), also roughly three weeks before the rut peak on December 16th. Five collared bucks died of natural causes during the study on King Ranch, resulting in a 22 percent mortality rate. A car hit one of these bucks nearly 10 miles from the capture location. This buck was obviously a disperser and died as a result. One buck died as a result of becoming entangled in a fence. Cause of death could not be determined for the other three bucks.

Five additional collared bucks were harvested on the King Ranch as the result of a concurrent selective harvest study in conjunction with the Texas Parks and Wildlife Department. Average home range size for the King Ranch yearling bucks that dispersed was 1,598 acres versus 1,297 acres for yearlings that did not disperse. Non-hunting mortality was higher for the yearling bucks that dispersed versus those that did not disperse.

Yearling Antler Size May Affect Dispersal Rate
On the King Ranch, four of the 27 yearling bucks captured and radio collared were spike antlered. None of these four yearling bucks dispersed during the time that McCoy tracked their movements. On the other hand, 12 of the 23 fork-antlered bucks (52 percent) dispersed. As a result, McCoy concluded that yearling bucks with forked antlers were more likely to abandon their initial home range and disperse to a new home range on the King Ranch.

McCoy theorized the larger antlered yearling bucks that dispersed did so because they reached sexual maturity earlier than the spike-antlered yearlings. As a result of being sexually mature, these fork-antlered bucks may have been “triggered” to disperse in an effort to search for females. Or, competition with other bucks for breeding privileges may have been the driving force to disperse. Another theory is these sexually mature yearling bucks wished to avoid inbreeding, so they dispersed outside their mother’s home range.

The good news is that the above is not always the case because yearling antler size did not seem to affect dispersal rates on the Callaghan Ranch. On this ranch, 16 of the yearling bucks were spike antlered, of which 11 (69 percent) dispersed. Only six yearling bucks were fork antlered, of which four (67 percent) dispersed.

Results of our on-going South Texas Buck Capture Project clearly show that yearling antler size is a good predictor of future antler size. Spikes, on average, will remain inferior-antlered bucks their entire lives when compared to fork-antlered yearling bucks. Obviously, the fact the larger antlered yearling bucks (those with forked antlers) were more likely to disperse is bad news for landowners and managers on small, low-fenced properties. This means that your neighbors may benefit more from your management program than yourself because your best yearling bucks are the most likely to disperse across the fence! Worse, the survival rates for the non-dispersers is higher meaning that the spike-antlered bucks that “stay home” will likely survive better as a result.

What Can Be Done?
The best ways to combat this dispersal is to plant food plots, erect a high fence around the boundary, or remove does from your herd.

Planting food plots will…..

The new high fence will obviously greatly reduce the chances your best yearling bucks will disperse off of your property.

Another option for small property landowners is to apply the results of the Virginia study to their property. As I pointed out above, the researchers in this study showed that buck fawns were much less likely to disperse if their mothers were removed. These orphaned bucks that stayed home also survived much better than the buck fawns that dispersed. Therefore, landowners could decrease the likelihood of their best bucks dispersing by purposely orphaning them when they were fawns. As a result of the orphaning, they are also likely improving the buck fawn’s chances of surviving.

If you elect to selectively remove does through harvest, I recommend waiting until December or January so that the orphaned fawns are at least four months old.

Posted by Dr. Mickey W. Hellickson